Explosives and Blasting

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING

PARTHA DAS SHARMA’S TECHNICAL DIARY ON EXPLOSIVES AND BLASTING PARTHA DAS SHARMA (B.Tech-Hons.) In Mining Engineering (E.mail - [email protected]) Website: http://miningandblasting.wordpress.com/

1 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING INTRODUCTION TO EXPLOSIVES AND ACESSORIES Definition of Explosives : Explosives is a chemical compound or mixture, when exploded by action of heat, impact, gives large volume of gases in a very short time at high temperature & pressure. Classification : All commercial Explosives are broadly divided in two categories. 1) Low Explosives 2) High Explosives Low Explosives : The chemical reaction in low Explosives is called deflagration which is a rapid process of combustion without accompanying any shock wave but gives a heaving effect. Example : Gum Powder Chemical Composition : Sodium Nitrate - 72% Sulpher - 12% Coal - 16% High Explosives : Reaction in High Explosives is characterised by an associated shock wave initiated by a detonator, basically contains. Oxidisers - Such as Ammonium Nitrate Fuel Oil Sensitizers : Methyle Amino Nitrate, Per chlorate Salt Physical Sensitizer : Entrapped Air Bubbles Explosive Characteristics : Various important Explosives Characteristics are • • • • • • •

Velocity of Detonation (VOD) Weight Strength Fume Characteristics Thermal Stability Sensitivity Density Water Resistance

Velocity of Detonation : It is the speed at which detonation wave travels through the media, it depends upon Explosive type. VOD is measured by, some electronic means or by Dautriche test. Average VOD varies form 2500 M/S - 5800 M/Sec. Weight Strength : Weight strength is the energy generated by an Explosive relative to that produced by an equal weight of 94 AN 6 FO (94%) Fuel Oil. Bulk Strength : It is the energy released per unit volume of Explosive as compared to ANFO. Bulk strength can be calculated from weight strength using the equation Relative Wt. Strength x Density Relative Bulk Strength = -------------------------------------Density of ANFO Water Resistance : Explosives differ widely in resistance to water and moisture penetration. Some Explosives deteriorate rapidly under wet conditions, but others are designed to withstand water for long periods. When blasting is to be done under wet conditions, a water resistant Explosive is preferable. 2 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING Sensitivity : An Explosives is required to be insensitive to normal handling, shock and friction, but must remain sufficiently sensitive to be satisfactorily detonated, and capable of propagating satisfactorily, cartridge to cartridge, even over gaps such as may occur in practice. Fume Characteristics : Explosives, when used under stipulated ventilation conditions, should liberate a minimum of harmful gases in the products of detonation. Density : The density is important when selecting an Explosive for a particular use. With a high density Explosive the energy of the shot is concentrated a desirable feature in tunneling and mining operations in hard ground. On the other hand when the output of lump coal from a mine is important, it is advisable to use a low density Explosive, which distributes the energy along the shothole. Thermal Stability : Explosives compositions should be such as to be stable under all normal conditions of usage. The DGMS stipulates that no blast hole shall be charges if the temperature in the borehole exceeds 80oC when blasting in hot ground. Sometimes Explosives have to be used in sub zero conditions in which some explosives become insensitive. Explosives compositions of M/s. Solar Explosives Ltd. are designed to be stable and safe, under all conditions of use. When blasting in hot ground, precautions as stipulated by the DGMS should be adhered to. Properties of NG & AN : Nitro Glycerine (NG) - it is a liquid, insoluble in water, highly sensitive to stock, friction and heat. In all Explosives of N.G. based oniroglycol is mixed for lowering the freezing point, used for hardest rocks and metals and for shooting oil wells. Ammonium Nitrate (AN) : It is a weak Explosives base. Difficult to initiate, so a sensitizer like NG or TNT is used. It is Oxygen positive, Hygroscopic, soluble in water. Tendency to form hard cakes. A SPECIAL EXPLOSIVES FOR CONTOUR BLASTING It is known as pipe charges or Gruit charge. Consist of a plastic pipe (PVC) of dia 11mm & of length 460mm, containing Explosives within it at concentration 0.11 Kg/m & 1.24 Kg/m respectively. Rate of detonation 4000 m/Sec. These are used in presplitting, smooth blasting and when blasting close to buildings. Advantages being saving in handling & charging time, over charging is eliminated, less over break, less cracking & less vibration. BULK EMULSION : Emulsion technology comes in the following categories : • Repumpable Emulsion • Site Mix Emulsion with support Plant • Augered Heavy ANFO • Pumped Doped Emulsion To deliver the product down the borehole, company is offering initially repumpable type and Pumped Doped Emulsion. For this company has designed special pump, truck capable of pumping Bulk Emulsion after mixing with density control agent on site. TECHNOLOGY DETAILS : The system, which we are offering now, is named as Repumpable Bulk Doped Emulsion, Solar BE 101. For this system the emulsion of oxidiser and fuels is prepared at location, where this facilities are available. The emulsion can be stored in ambient conditions and is non-explosive. This non-explosive emulsion matrix after doping with Prilled Ammonium Nitrate is mixed with gassing agents are charged into bore hole by pump truck. The mixture becomes sensitive only after the same is delivered in to the blast hole and the gassing reaction completed in above 15 minutes.



BLASTING ACCESSORIES : Various important blasting accessories are as under : 1. Safety Fuse 2. Plastic Ignitor Cord. 3. Detonators. • Plain Detonators • Electric Detonators • Instantaneous Electric Detonators • Long delay Detonators • Short Delay Detonators • Non Electric Detonators 4. Cord Relay 5. Detonating Cord 6. Magnadet 7. Anodet 8. Ohm Meter 9. Exploder Safety Fuse : A cord of special black powder wrapped in envelope made up of various layers of textile yarn & water proofing material. Used for directly igniting low Explosive of initiating high Explosive through plain detonator. Burning rate 100-130 sec/m. Plastic Ignitor Cord : Used for ignition of several fuses in quick succession in any desire sequence. It is 1.8-2.5 mm dia fuse, which gives intense flame at uniform rate. Rates 3.3 S/M of 33 S/M. slower one contains a core of a cu wire coated with plastic incendiary composition and an iron wire added for strength, with plastic covering. PLAIN DETONATORS : Used for initiating high explosives but are them selves ignited by safety fuse consist of 6mm dia Al. Tube partly filled with detonating charges. Modern detonators have a base charge of PETN (Penta Erithetetrol Tetra Nitrate) with a priming charge of A.S.A. (Lead Azide, Lead Styphnate and Al. Powder) strength depends upon amount of base charge. No.6 & No.8, No.6=0.22gm. of PETN & 35mm long. No.8=0.45gm. PETN & 48 mm long both contains 0.2 gm ASA. 4 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING ELECTRIC DETONATORS : These are fired electrically. INSTANTTANEOUS ELECTRIC DETONATORS : Comprises of Cu of Al. Tube of 7mm dia and a little longer than the plain detonator so as to accommodate the fuse head and the neopren plug. Copper Detonators are for gassy coal mine where highly incendiary Al. is prohibited. Explosive charges are ignited by an electric fuse head of Nickel-Chromium-Iron alloy bridge wire soldered to the ends brass foils separated by an insulating piece of card board. Fuse Head Composition : Potassium Chlorate, Nitro Cellulose, Charcoal (See Sketch)

ELECTRIC DELAY DETONATORES : Special use in shaft sinking tunneling, drifting where successive rounds are better fired in a certain sequence with adequate time interval in between rounds so that each round breaks into clear free face. In delay detonators a time lag is deliberately introduced between the firing of the fuse head and the explosion of the detonator. LONG DELAY DETONATORS : These are also known as half second delay detonators having nominal delay interval of around 300 to 500 ms for each. These are widely used for tunneling work and generally from 1 to 10 Nos. are available. SHORT DELAY : Short Delay electric detonators are same as long delay in construction and strength and above nominal delay interval of 25 ms. for each delay. Delay composition of long delay detonator comprise of antimony and KMNO while it is Red Lead & Silicon for short delay. NON ELECTRIC DETONATORS : Earlier mentioned plain detonator also fall under this but due to its restricted use it is explained under separate heading. Non-electric delay detonator basically consist of a length of plastic single tube to which is fitted a powerful delay detonators. The single tube is made of a special plastic material. The outer dia being 3 mm and inner dia 1.0 mm. Its inner surface is lightly coated with a mixture of reactive powders which provide the energy transmitting medium with in the tubing on initation by a detonator cord or by a detonator a shock wave propagates along inside the tube at 5 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING a velocity of about 2000 M/sec. without bursting the tubing and therefore having no effect on any Explosives through which is passes. The resulting flame front ignites the top of the delay element with in the detonator tube. These are available in long delay and short delay series. CORD RELAY : These devices permit short delay to be introduced into trunk lines of detonating cords. A cord relay consists of two delay detonators mounted inside a resilient plastic shell. They are bi-directional in operation, Cord Relays are available in the 15 Ms, 17 Ms, 25 Ms, 50 Ms, 75 Ms, 100 Ms, delay time. The shorter delay intervals are generally required for small (65-90mm) dia blast holes drilled on close spacing whereas the longer intervals are suited to larger blast holes drilled on wider spacing. Cord Relays are designed for use with detonating cords, which have core loads of 10 gm/M. No special connecting tool is needed. DETONATING FUSE : It serves the same purpose as detonators and directly initiates the high Explosives while them needing a detonator for initiation. Useful in simultaneous multiple shot firing minimising the use of several detonators. Advantageous in blasting long hole. It comprises of PETN (Pentaerythrol Tetranitrate) train enclosed in a tape wrapped in textile yarn and whole thing covered by plastic. Finished dia 5 mm for the D.F., which contain 10 gm PETN meter (See Sketch).

OHM METER : Used for testing the continuity and resistance of blasting circuits. These are of two types. i) Powered by low voltage hand operated generator. ii) 1.5v dry battery type. EXPLODER : Used for firing shots electrically, these are of two types: i) Generator type :Magneto of dynamo (for large capacity) operated by a quick twist of strong down ward push of handle. ii) Condenser discharge type :- Can be battery of dynamo powered.


Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING Blasting: In terms of processing, blasting is the critical first step in the rock-fragmentation process. Maximum profitability depends largely on good blasting. Consider that drilling and blasting are the first operations performed in any hard-rock quarry operation. Therefore, the results of these operations will affect more down-line activities, such as loading, hauling and crushing, than any other processing operation. Blasting should always be viewed in the "global" sense. One should examine not only the effect of changes on the drilling and blasting program, but also how the change will affect the productivity and economics of other down-line cost centers. Blasting should also be viewed in the "local" sense. No other quarry operation has more capacity to cause community dissent than blasting. All quarry operations should have in place a proper public-relations program designed to communicate to the community that proper safety precautions and procedures are in place with regard to its blasting program. To understand the principles of rock blasting, it is necessary to start with the rock fragmentation process that follows the detonation of the explosives in a drill hole. The explosion is a very rapid combustion, in which the energy contained in the explosives is released in the form of heat and gas pressure. The transformation acts on the rock in three consecutive stages.

Compression: a pressure wave propagates through the rock at a velocity of 2,500–6,000 m/sec, depending on rock type and type of explosives. This pressure wave creates microfractures which promote rock fracturing. Reflection: during the next stage, the pressure wave bounces back from the free surface, which is normally the bench wall or natural fissures in the rock. The compression wave is now transformed into tension and shear waves, increasing the fracturing process. Gas pressure: large volumes of gas are released, entering and expanding the cracks under high pressure. Where the distance between the blasthole and the free face has been correctly Fragmentation In the 1990s increasing emphasis was placed on the role of fragmentation at the operation. In particular the effect of fragmentation on crushing, load and haul, and run-of-mine leach pad efficiency has received considerable attention. Better predictive techniques have been developed, and computer-aided methods for determining the fragmentation distributions in actual blasts are now available. Fragmentation studies can lead to improved profits at many operations. For example, studies at one operation showed that the same production could be obtained with one less excavator in good digging, when compared to poor digging conditions. This is a result with both capital- and operating-cost implications. 7 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING For maximum success it is essential that the mine or quarry carefully design its blasts to achieve the desired results. These designs must be accurately implemented in the field. The blasts must be shot in a safe manner, with the area properly barricaded and all persons removed a safe distance away. Environmental affects such as ground vibration, airblast and fume production must also be controlled. Explosives The past 15 years or so have seen new explosive formulations reach the marketplace, and reductions in the use of some products that have been in use for longer periods. The principal newcomers have been the emulsions, and emulsionANFO blends usually called Heavy ANFO, that denotes its greater density than ANFO dry mixes. Emulsions The formulation of an emulsion is very similar to that of blasting slurries (water gels). However, the cross-linking agent used to stiffen the slurry is replaced by an emulsifying agent. This water-in-oil emulsifying agent suspends minute droplets of the ammonium nitrate (or a combination of AN with either calcium nitrate or sodium nitrate) oxidizer within the fuel. This yields a very intimate oxidizer and fuel mix that leads to high detonation velocities. Emulsions may be bulk loaded, or used in packaged form. Packaged products are usually employed in small hole diameters. They are mechanically sensitized using microballoons to introduce sufficient air into the mix and control the density. Bulk emulsions are used in larger diameters and may be mechanically or chemically sensitized, with chemical sensitization being less costly. Bulk-loaded product fully fills the cross sectional area of the hole and delivers maximum energy to the surrounding rock. This is a characteristic of all bulk-loaded products unless they are intentionally decoupled as is often the case in presplitting. Packaged emulsion will usually result in some decoupling with a reduction in borehole pressures. This generally is not a great problem in small diameter blastholes. Ammonium Nitrate Fuel Oil (ANFO) ANFO remains one of the most commonly used products in quarry blasting. It is a combination of ammonium nitrate (oxidizer) and number-two fuel oil (fuel). Number-one fuel oil may be used in cold-weather applications. Blasting grade AN prills are made by spraying molten AN into a prilling tower. Droplets fall under carefully controlled cooling conditions. The AN solidifies while falling, taking on an approximately spherical shape of relatively uniform size. Prilling tower conditions must be such that will produce a "porous" prill that will absorb the proper amount of fuel oil (6 percent by weight). For those with overseas operations especially it will be important to confirm that a porous prill is being produced. High density prills will not properly absorb the fuel oil and blasting performance will suffer, unless these have been crushed to about -20 mesh. Blasting-grade AN prills are typically +6, -14 mesh in size. This uniformity in the size of the prills results in a poor packing density, with considerable interstitial voids present. Hence a product which typically bulk loads in a density range of 0.80 to 0.85 gm/cc. Some packaged ANFO products use a blend of sizes, where a portion of the prill is crushed, leading to densities of about 1.05 gm/cc. This product can be loaded in wet holes provided it is contained in a suitably waterproof bag. ANFO has virtually no water resistance. Many people are of the impression that it takes several hours before water attack seriously affects ANFO. The reality, however, is that degradation of the product is immediate. Even if holes will be detonated 2 or 3 hours after loading, performance will have been seriously affected. Therefore, whenever ANFO is to be loaded into wet holes, the blastholes should first be pumped and a plastic liner placed in the hole. The ANFO is loaded inside the liner. Care should be taken to obtain a liner that has a high integrity. Even a few pinholes are enough to allow water to attack ANFO. For hole diameters less than 5 in., using plastic liners is generally difficult. Therefore, small diameter waterproof products such as emulsions or slurries are generally used for small diameter, wet holes. 8 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING One way to increase the energy output in ANFO is to add aluminum. The reaction of ammonium nitrate with aluminum releases more energy per unit of weight. The aluminum must be of a suitable size to be reactive, but not so fine as to constitute an explosion hazard. This generally means a size range of -20, +150 mesh. The upper limit on aluminum addition is usually about 15 percent. As more Al is added to the mix increasing percentages of the energy are trapped in a solid product of detonation. Beyond 15 percent Al by weight there is little additional energy output for the aluminum added. Heavy ANFO Another way to increase the energy output of ANFO is to add emulsion to it. The emulsion fills the voids between the prills, the density increases and there is more energy output per unit of blasthole volume. This class of explosives are known as Heavy ANFO. They provide a cost effective way to increase the energy output of ANFO. Heavy ANFO may be produced solely for the purpose of increasing the energy output. However, at higher emulsion percentages by weight these products become waterproof. Such formulations can be bulk loaded into wet holes. Experiment has shown that the performance of Heavy ANFO becomes sluggish as more emulsion is added unless the emulsion has been sensitized by gassing or microballoons. It appears that in hard-rock performance will suffer when there is more than 30 percent of unsensitized emulsion in the mix. In softer formations greater percentages of unsensitized product can usually be employed because suitable fragmentation of the rock depends to a greater degree on heave energy. The degree of non-ideal detonation introduced by the lack of sensitization means that a greater degree of the total energy is released as heave energy. A waterproof product is typically produced at 50 percent emulsion addition. However, to obtain a product that can be pumped reliably it is common to use a waterproof Heavy ANFO containing 60 to 70 percent emulsion. Such products should always be made with a sensitized emulsion, or performance will suffer. When waterproof heavy ANFO blend is loaded into wet holes it should always be loaded from the bottom up. This is achieved using a bulk truck with a hose that can extend to the bottom of the blasthole. The product is pumped through the hose. The hose is retracted as loading proceeds, but is always kept in the explosive. The water rises on top of the advancing column of more dense explosive. Mixing does not occur if the loading is carefully performed. When Heavy ANFO is augured into wet holes it spatters on impact with the water, and prill goes into the solution. Water is mixed into the explosive column. Bridging may occur with portions of the explosive column separated by a water gap. Since the gap sensitivity of these products is not large this may lead to the failure of a portion of the explosive column to detonate unless it happens to be primed on both sides of the water gap. Heavy ANFO is also produced as a packaged product. In this case it is sensitized using microballons, which improves the shelf life. Package products can be used where there are insufficient wet holes to warrant bulk loading, or in small tonnage operations. It is also used as a toe load in holes that have only a few feet of water in the bottom of the hole, and can be used in small-diameter packaged formulations. Dynamite There is still a considerable amount of dynamite sold annually in the U.S. However, pits and quarries have almost completely moved from the use of dynamites to small diameter, cap-sensitive emulsions and slurries for appropriate applications. Dynamites are explosive substances that depend upon nitroglycerin or nitrostarch for sensitiveness. These products are usually cap sensitive with a detonation velocity dependent upon the diameter and density. Dynamites are used as decoupled charges in presplitting. They are also used sometimes to prime ANFO in small diameters. For this latter application a product with high detonation velocity should be chosen because it will have the 9 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING higher detonation pressures (a function of the square of the detonation velocity) that are important for efficient priming of ANFO.

Explosives and blast-initiation accessories Some of the explosive described above are cap sensitive. This means the product can be efficiently detonated by a blasting cap or delay detonator of adequate strength, or by compatible detonating cord. Small-diameter emulsions and slurries are typically cap sensitive. The manufacturer should be consulted as to the proper accessories to use. The sensitivity of some products may vary with temperature. Greater priming strength can be required when the product is to be detonated at low temperature. Bulk-loaded explosives used in hole diameters greater than 5 in. almost always require heavier priming than a detonator alone can provide. It is well-established that initiation of the bulk explosive is temperature- and pressure-dependent. Those primers yielding high detonation pressure initiate the explosive more efficiently. Thus formulations with high velocity of detonation (VOD) generally give the best results. For this reason the cast pentolite primers were developed. These generate 2.2 to 2.8 million psi detonation pressure, depending on the formulation. Various designs to provide an effective primer economically have been developed. Cast primers are often 1.0 lb. in weight. However, primers of greater weight are also produced. These may be useful in difficult applications or with an explosive having a higher minimum primer weight. The weight per primer used in the blastholes should be 4 to 6 times the minimum primer weight. Cast primers typically have a length to diameter ration of 3:1 to 4:1. The primer should have a sufficient diameter to act on an adequate cross sectional area of the explosive charge thereby insuring efficient initiation. It must be long enough to allow the VOD in the primer to build up, providing maximum pressure off the end of the primer. Therefore, there is a trade off between length and diameter to provide effective initiation with a primer of reasonable dimensions and cost. Cast primers are made with a single tunnel through which detonating cord can pass or with a tunnel through the primer and a cap well. The cap well accepts a down-the-hole delay detonator for in-hole delay applications Slider primers are used for multiple priming on a single detonating cord downline. This is often used when deck loading is employed. These primers are made with a tunnel affixed to the outside of the cast primer. Detonating cord passes through the tunnel. The pigtail on the end of the delay detonator is also passed through the tunnel. Upon initiation the delay is initiated from the contact between the detonating cord and the delay pigtail. Only certain types of downlines (usually of low grain count) can be used and this information should be obtained from the manufacturer.


Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING In some cases a stick of dynamite is used to initiate the hole. The approach is most common when priming ANFO in small diameters. The majority of dynamites do not generate the kind of pressures a cast primer provides. However, a few gelatin products detonate at very high VOD and do give high detonation pressure. When priming ANFO with dynamite this type should be used. Detonators and initiation systems Detonators are used to initiate the blast. These may be electronic, electric or non-electric. For modern-day blasting, delay detonators are virtually always used. Delay detonators are available for use in the hole, and also for connecting into the surface tie-in. A delay detonator is similar to an instantaneous cap except that a delay element is included between the initiation charge that is activated by the in-coming energy, and the base charge. The delay compound burns at an accurately know rate and provides the desired delay time. Down-the-hole delays are used alone to provide the proper firing rotation or in combination with surface delays. In the former case different delay times are used in the appropriate blastholes to provide the desired sequence of detonating holes. When used together with surface delays a constant down-the-hole delay time is often used. The in-hole delay is of sufficient duration to allow several rows of surface connections and downlines to be activated in advance of blasthole detonations. This approach avoids cutoffs and misfires that reduce blast performance and introduce subsequent safety concerns. When down-the-hole delays are used it is often possible to use longer surface delays without fear of cutoffs. In orebodies where hot holes are possible (such as reactive sulfides) down-the-hole detonators must be used very carefully, because these are the most sensitive element to heat in the blasthole. Holes over a certain temperature are often not loaded. Top priming just before shooting is often indicated. Avoiding the use of these detonators is also an approach taken by mines where this is a severe problem. Down-the-hole delays are often made with shock tube lead lines. These may be long lead where the shock tube extends all the way to the collar, or short lead where the shock tube is an 18- to 24-in. pigtail. These latter units are used with detonating cord downlines. The detonating cord must be compatible with the delay system used. Surface delays provide good flexibility in blast tie-in to provide for the desired sequence of detonating holes. Delay units are made that can be spliced into detonating cord trunklines used to connect the blastholes together. Systems are also available with long shock-tube leads, eliminating the need for the more noisy detonating cord. This is especially useful for quarries because these pits are often sited in close proximity to residential and commercial areas. However, the latter systems cannot be made redundant in the same manner as those that employ detonating cord, so shock-tube systems must be connected together with particular care. Detonating cord Detonating cord contains a core load of high explosive (usually PETN). It detonates at about 22,000 ft. per second. Detonating cord is made with various weights of PETN per ft. of cord. This is usually expressed as the grains per ft.. There are 7,000 grains in one pound. Detonating cord is used as downlines in the blasthole to transfer initiation energy to primers and down-the-hole delays. It is also used for surface trunklines to connect blastholes together. It is easy to connect up, but has the disadvantage of generating substantial airblast. Therefore, it is usually used on surface when operating in remote locations. Shock tube, electric and electronic blasting systems are more commonly used when operating in proximity to built up areas. Shock-tube systems The shock-tube system is a plastic tube with a thin explosive coating on the inside of the tube. Upon detonation this material continuously detonates at a low velocity of approximately 6,500 fps. Thus, the plastic tubes are not consumed 11 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING and the noise level is low. It is, therefore, good to use as lead-in line to initiate a non-electric blast in populated areas. It is also used to connect holes together when used as part of a long lead-surface delay system. It is used in the blasthole as a long lead down-the-hole (DTH) delay system to replace detonating cord downlines, or as a pigtail on DTH delays used in conjunction with detonating cord. Shock tube systems, unlike some detonating cords, will not set off a primer and must always be used with a DTH initiator and compatible primer. Electric detonators Fewer blasts in surface mines and quarries are initiated with electric systems today than once was the case. However, this practice is certainly still followed by many, especially in quarrying. Construction of electrical caps and delays is similar to non-electric components, except that the energy to ignite the ignition compound is provided electrically. This does have the advantage of minimizing noise on surface, but has the disadvantage of being more susceptible to stray radio frequency and currents, lightening, etc. The instantaneous electric blasting cap is sometimes called an E.B. cap. Like the non-electric blasting cap it is a thin metal shell containing various sensitive ignition powders and primary initiating high explosives sealed in a waterproof assembly. The electric cap is completely sealed with water-resistant plugs with only two insulated "leg wires" emerging. Inside the cap the leg wires are joined by a short piece of fine resistance wire called a "bridge wire." The bridge wire may be imbedded either directly into an ignition mixture or in an electric match. In either case, when an ample electric current passes through this bridge wire it heats it to incandescence. This ignites the ignition mixture and initiates the primer and base charges in the cap. Thus, the electric blasting cap converts a relatively small amount of electrical energy into a primary-initiating explosion capable of detonating cap-sensitive high explosives with which it is in intimate contact. Delay electric caps are similar to instantaneous caps in construction and action, except that between the ignition charge and the primer charge there is a column of powder called a "delay charge" which serves as a time fuse. Delay E.B. caps are of two general types: millisecond, and long-period delay. A wide choice of delay intervals are available running from about 8 milliseconds (a millisecond is one-thousandth of a second) through to about 12 seconds. Most quarries use millisecond delays because of the improved breakage and reduced vibration they provide. Many underground operations use the long-periods, although many have switched over to milliseconds. Scores of different hook-ups may be made. Determination of electrical resistances and other details pertinent to firing electrically are discussed in manufacturers' literature available to guide mine and quarry operators. Success requires that the operator precisely follow directions of the manufacturer who produced the electrical devices they utilize. Such directions give the exact procedure required to properly: 1. Select and lay out the blasting circuit. 2. Connect wires and protect splices. 3. Test the circuit. 4. Apply the required electrical energy. 5. Protect the circuit from extraneous electricity. Electronic blasting systems Both the shock-tube system and electric detonators rely on a pyrotechnic delay element to attain their delay timing. These pyrotechnic delays are subject to timing inaccuracies called "scatter." Scatter can be caused by variations in the pyrotechnic composition, age and temperature. Deviation from the detonators nominal firing time can cause out-of12 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING sequence firing. This will result in high vibrations, airblast and poor blast performance. Recognizing the accuracy issue and the safety concerns with both the electric system (stray current) and shock tube (cannot be tested) the industry has moved towards a more advanced initiation technology called electronic-blasting systems. Electronic-blasting systems are unique as they have eliminated the pyrotechnic delay element and replaced it with a high-accuracy timing "chip." These systems now deliver 1/10th of a millisecond timing accuracy with delays up to 20,000 milliseconds. The systems are available in both programmable and fixed times. Programmable systems allow the blast engineer to design blasts specific to the site conditions. Electronic systems also bring with them many safety advantages such as being fully testable with self-diagnostics, able to operate in areas of extraneous current and greater blast control through accurate timing. Field tests have proven that the use of electronic-blasting systems with proper blast designs have reduced vibration levels, airblasts and significantly improved blast performance. Summary The following summarizes the advantages of using delay detonators in production blasting. • • • • • •

Improved fragmentation due to the greater freedom for the material to relieve. Greater flexibility in firing sequences and burden to spacing relationships due to the ability to orient the blast through the tie-in. Greater ability to control blast vibration and airblast. More predictable blast movement and flyrock control. Reduced backbreak behind the last row of holes. Minimized cut-offs.

For extensive information about explosive and initiation produces provided by many domestic and overseas manufacturers the reader is referred to the Explosives Product Guide included in the Membership Directory and Desk Reference published each year by the International Society of Explosive Engineers. Blast-design factors There are a number of factors to be considered when designing a blast. These include: • • • • • • • • • • •

Material type to be blasted and the blast pattern and hole loading to use in the given rock. Degree of fragmentation desired. The geological structure and the attitude of the tie-in lines relative to the structure. The type and performance of the explosive charge. The type of initiation system and the duration of millisecond delays and accuracy needed. For a given pattern, the ratio of burden to spacing as defined by the tie-in or the layout. Subgrade drilling needed to fully break to the pit floor. Crest and toe locations (or average backbreak from the last row if the fact is not dug out). Upper bench elevations to determine hole depths. Blast size required to maintain quarry or mine production. Blasting ground vibration and airblast, and the design requirements to maintain acceptable levels.

Blasthole layout Once a suitable pattern and loading have been determined it is important that the holes be accurately laid out in the field and drilled in the proper location. Irregular blasthole locations lead to less acceptable blasting results, unless the 13 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING improperly drilled holes are redrilled. Burden and spacing dimensions vary and the tie-in is more difficult on irregular patterns. Some portions of the blast will be overshot, while other areas will experience hard toe and coarser fragmentation. It is especially important that the front row holes be properly located. If there is too much burden (especially at the toe) fragmentation will suffer and the remainder of the blast will not properly relieve. Hard toes are likely to be in evidence. When there is too little burden, the high-pressure explosion gases cannot be contained. Rapid gas venting through the face will occur. Greater flyrock throw and airblast can be expected. There will be hard toes and blocky fragmentation. Mines that have a survey department can measure toe and crest locations on the bench and plot these on the blast plan map, upon which drill pattern is designed. Thus, the front row locations can be more accurately determined. Quarries, where on-going surveying capability is less common can obtain a better idea of the face profile using a hand level and tape. Standing at the crest of the bench a point on the pit floor can be sighted and the angle measured with the hand level. Using simple trigonometry for the right triangle, the base length can be calculated since the bench height is known. This base length is the total horizontal distance from the crest of the bench to the point measured on the pit floor. A 100-ft. tape is used to measure the distance from the point on the pit floor back to the toe of the bench. The difference between the total base length and this distance is the crest to toe offset. The blastholes can then be set back from the crest a suitable distance to yield an acceptable toe burden (or one can identify areas where an overburdened toe is likely to occur). In areas where safety working around the high wall is a concern the operation should consider laser profiling and bore tracking the blast to confirm the face conditions and profile. Laser equipment and or services are available to help acquire this information. Blasthole loading It is important that holes be loaded correctly in accordance with the design. Improperly loaded holes can lead to poor fragmentation and/or excessive flyrock and noise. The hole depths must be correct. Operators must decide how short holes can be before redrilling is required. In very hard rock a blasthole that is one or two ft. short can result in hard toe. In softer rock more variance is acceptable, but is seldom more than four or five ft. Modern-day bulk trucks have more sophisticated measuring and control systems. The operator can set the weight to be loaded in the blasthole and the truck shuts off automatically. However, this does not eliminate the need to bob the blasting tape in the hole during loading. The truck-control systems cannot tell about voids or cavities in the hole, nor about control-system malfunctions. Thus to avoid over or under loading, and to obtain the correct column rise, it is still important to tape the hole during loading. Accurate loading is especially important regarding the column rise and corresponding stemming height. The explosive column must rise high enough in the given rock type to fully break to the surface of the upper bench. Good breakage is related to the depth of burial of the top of the charge. Too great a depth of burial and the top of the blast will be poorly fragmented. On the other hand, if the explosive column rises too high in the hole the depth of burial is low, gases vent rapidly to the surface, and there is more flyrock and noise. Also, the radius of the crater of fully broken material formed around the hole decreases and there may be hard areas between holes. Front-row stemming height Stemming heights on the front row may need to be increased. Since the bench-face angle is less than 90 degrees the burden on the front row holes is continuously decreasing between the toe and collar of the hole. Depending on where the front row blasthole must be drilled to maintain a suitable toe distance the burden may become too small to contain the explosion gases at the normal column rise. To avoid gas venting to the face causing flyrock, noise and loss of performance, stemming on front-row holes may need to be increased. 14 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING A simple measurement can be made in the field to determine the stemming height on the front row, using a telescoping surveyors rod and a 100-ft blasting tape. The rod is placed at the collar of the hole and extended over the face to the length of the desired minimum burden. A weighted tape is passed along the rod, through the ring at the top of the surveyor's pole and then drops vertically until it strikes the face. The total length is read from the tape. The burden distance is subtracted from the total, giving the vertical distance. This is the stemming height. For example, if 6-1/2 in. holes at the quarry require a 12-ft. minimum burden and the total taped length is 29 ft., the vertical distance is: 29-12 = 17 ft. This is the stemming height required to maintain minimum burden on the charge. Failure to make appropriate adjustments to front row stemming may well lead to hazardous flyrock. Blast tie-ins and burden to spacing relationships Drilled and loaded blast patterns may be tied-in to create different burden to spacing relationships. Commonly used designs are: 1. Square pattern tied en-echelon or across two free faces. Known as a V-1 tie-in. This is a non-staggered pattern. Tie-in is on the diagonal of the square and is oriented at 45 degrees to the free face. The effective burden is 0.707 times the drilled burden. The ratio of the effective spacing on the tie-in to the effective burden is 2:1. 2. Staggered square pattern tied on the diagonal of the parallelogram. This is known as the V-2 tie-in. The orientation is 34 degrees to the face. The effective burden is 0.56 times the drilled burden. The ratio of effective spacing to effective burden is 3:1. 3. Staggered equilateral pattern tied-in on the V-2 configuration. The angle to the free face is 30 degrees. The effective burden across the tie-in is 0.50 times the drilled spacing. The ratio of effective spacing to effective burden is 3-5:1. 4. Row on row tie-in. In this case successive rows detonate in progression. There is no burden reduction and the effective burden and spacing are the same as the drilled dimensions. The rows detonate parallel to the face rather than at an angle. Generally in open pits and quarries the tie-ins described above are preferred. Millisecond delay timing The duration of millisecond delay times must also be considered. Field experiments have shown that 1 to 1-1/2 ms-perft. of effective burden is the minimum that can be considered if any relief is to be obtained for holes firing on successive delay periods. For good relief, it is typically found that 2 to 2-1/2 ms-per-ft. of effective burden are required. In some cases where maximum relief is desired 5 to 6 ms-per-ft. may be appropriate. When delay times are long care must be taken to avoid cutoffs and misfires depending upon the type of initiation system being used. A down-the-hole delay of sufficient duration to allow much of the surface tie-in lines and blasthole downlines to be consumed before blastholes begin detonating is the usual procedure taken to avoid these problems. PRINCIPLE IN THE USE OF EXPLOSIVES Open up a New Excavation Apart form mining, rock excavation is frequently necessary during the construction of Roads, Railways, Canals, etc. In opening up a new excavation, the holes are normally drilled with jackhammers and subsequently charged with gelatins. A drilling pattern suitable for initial cut, 3M deep is shown in sketch.



A cavity of the requisites width is first created by drilling and blasting holes 1.5-1.7 meters deep in parallel rows. The holes in the two middle rows are inclined so as to form a wedge. These inclined holes are blasted first, followed by other holes fired in sequence. The resulting excavation is 1.5 meters deep and can be deepened further.



Ring Sumpers Inner Easers Quter Easers Trimmers

No. of Holes Per Ring

Charge Per Hole (Kg)

Total Charge Per Ring (Kg)

5 8 12 16 41

1.40 1.12 0.98 0.98

7.00 8.96 11.76 15.68 43.40

Volume of Rock-88m3 Charge Ratio 2m3 per Kg BENCHING Bench blasting is normally carried out by blasting a large number of parallel holes in each round. Considering the blasting mechanics, with a compression- reflection-gas pressure stage in consecutive order for each charge, it is of vital importance to have a proper delay between each row, and even between individual holes in each row. A proper delay will reduce rock throw, improve fragmentation, and limit ground vibrations. The blast should be planned so that the rock from the first row of holes has moved about one third of the burden, when the next row is blasted. The horizontal distance between the hole and the free face is the burden, and the parallel distance between holes in a row is the spacing. The ratio between spacing and burden will have great impact on the blasting result, and 1.25 can be considered as an average ratio. The optimum burden depends upon a number of parameters, such as rock type, required fragmentation, type of explosives, hole deviation, and hole inclination. Nevertheless, as large drill holes can accommodate more explosives, there is a distinct relationship between burden and hole diameter. As the bottom part of the blast is the constricted and critical part for successful blasting, it is used as a basis for deciding all other parameters. Stemming of the top part of the hole is used to ensure that the energy of explosives is properly utilised. It will also reduce and control the fly rock ejected from the blast.



OPTIMUM BLAST DESIGN : TECHNO ECONOMIC CONSIDERATIONS The measure of effectiveness of drilling and blasting operations is not in terms of blasting cost alone, but rather by its contribution of the efficiency and economy of total excavation system. Savings accrued through excessive reduction in the cost of drilling and blasting may well be lost by increased loading., handling and crushing costs. An optimum blast, with improved fragmentation, accounts for increased cost of drilling and blasting, while the cost of loading, handling and crushing are lowered.



CONCEPT OF OPTIMUM BLASTING The concept developed by Mackenzie describes the total blasting cost as :Ct= Cd+CB+cl+Cc P Where Ct = Total blasting cost per tonne of finished product. Cd = Cost of drilling Cb = Cost of blasting Cl = Cost of loading Ch = Cost of Hauling Cc = Cost of Crushing P = Total tones of production

Fig. is representation of what Mackenzie believed was the relationship between blasting cost and drilling cost Beginning from to the point to the left of OPTIMUM, he found that it was possible to reduce TOTAL cost by 19 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING increasing BLASTING COST. He found that better fragmentation produced increased shovel loading efficiency, reduced maintenance repair cost for shovels and dumpers and increased crusher output. Mackenzie achieved a superior "degree of fragmentation" primarily by using more energetic of high strength Explosives. He found higher BLASTING COST produced a very significant reduction in TOTAL COST. IMPORTANCE OF DEGREE OF PERFORMANCE Fragmentation levels required depend on the type of the excavating and hauling equipment. Fragmentation coarser than optimum results in decrease in the loading efficiency and increase in the downtime of loading equipment with added cost of maintenance. On the other hand, to achieve fragmentation finer than optimum, cost of drilling and blasting may rise disproportionately, which may not be offset by the additional advantage in loading. The blast design should, therefore, be aimed at optimum fragmentation to economise the overall cost of mining. Once the optimum fragmentation requirements for a particular mining equipment is decided, the question arises as to determine which would need secondary breaking. As has already been mentioned above, any attempt to produce "Zero Boulder Blast" would severely affect the drilling and blasting cost. The optimum ratio of percentage of oversize boulders against the volume of rock of 1-2%. Blast Economics : Efficient explosives application is the least expensive method of fragmenting and casting rock. Blast casting the over burden off coal dramatize the economic advantages of using explosive energy to increase production rate and enlarge over all operating profit margins. Fig below graphically illustrate the economic advantages of changing the blast design to an over burden casting configuration. In this case, the burden and spacing dimensions were reducing, which caused the drilling costs to rise marginally. In addition, higher energy explosives where added to increase the energy factor, which is required for higher fragmentation and higher through achieved in case of over burden casting. Despite the increase in drilling and explosives cost. a major reduction in total operating cost was observed due to increase in production and sooner access to the coal. Moreover, reduction in operating maintenance cost due to less running of stripping and hauling equipment because of less material to handle.


Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING Blast Hole Diameter : The optimum blast hole diameter is governed by factors such as type of Explosives, Rock mass properties, degree of fragmentation desired and height of bench. An optimum blast hole diameter is that which accommodates that much quantity of Explosives charge which not only breaks away several fold great rock mass but also displaces ti to convenient distance for efficient handling by shovel. However, in recent years, there is a discernible trend towards larger diameter because of lower drilling cost, and more dependable yield of energy, which assures good fragmentation. But at the same time, if diameter is too large the corresponding large blast hole array may result in poor fragmentation, especially in the case of highly fissured of jointed strata. Technical Considerations in Selecting Optimum Diameter for Blast Hole Drilling (a) Influence of hole size on fragmentation : Many a mining engineers are firmly of the view that an increase in hole diameter automatically means poorer fragmentation. Nothing could be further from truth. The Taconite iron ore mines of Minnesota, USA exhibits the classical example, where over the years, the operations have progressed from 190 to 380 mm diameter holes with continual improvement in fragmentation. There has been instances of operations that have had to reduce hole size because the blasting was producing too many fines. The phenomenon may be better understood by assuming that the larger the hole diameter, the larger the drill pattern, the larger the fragments. But suppose the hole diameter is increased, but not the drill pattern would not the fragmentation be improved? (b) Energy Utilization Factors : Following example shows energy comparison (measured in million ft-lbs per foot) for various Explosives diameter, which is indicative of the fact that with decrease in hole diameter measured energy also decreases. 1.

Measured energy of ANFO in a 1 inch hole = 4.8 million ft-lbs/ft. Measured energy of ANFO in a 8 inch hole = 19.2 million ft-lbs/ft. 19.2 - 4.8 ----------- x 100 = 300% 4.8 Measured energy of " Gelaprime A of 3½ inch diameter in a 4 inch hole = 6.9 million ft-lbs/ft Measured energy of " Gelaprime A of 3½ inch diameter in a 4 inch hole = 6.9 million ft-lbs/ft

% more energy utilization = 2.

% more energy utilization =

35.9 - 6.9 ----------- x 100 = 420% 6.9

(c) Production requirements Application of large diameter drills with high rate of penetration becomes indispensable to meet high production requirements. The same production could be achieved with smaller diameter holes but the number of drill machines required would be abnormally high. SELECTION OF OPTIMUM BURDEN & SPACING The most critical among geometric parameters of blasting is the burden, which has the greatest influence on fragmentation. For any particular geological setting, there is an optimum burden for which the volume of wellfragmented and loosened rock is maximum.


Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING If burden is too large, shock wave remains incapable of extending radial cracking upto the free face and heave energy is unable to provide adequate displacement. Gasses are bottled up within the blast holes for period of time, which results in rapid decay of effective borehde pressure. On the other hand, if the burden is too low, fracturing by shock increases and breakage by heave energy decreases and much of heave energy is lost as air blast. Thus, the optimum fragmentation burden is that which allows the gasses to losses virtually all of their energies by the time they escape into the atmosphere without producing any air blast, with minimum objectionable side effects, like toe, air blast, ground vibrations etc. Optimum Burden B = 37.8 (Pe/Pr) 1/3 x d Pe = Density of Explosive Pr = Density of rock d = Dia of Hole (mm) For lime stone quarry B = 0.024 x d + 0.85 other formula

KD B = -------12 K = 20 - 35 B = Burden in feet D = Dia in Inches CMRI equation (Pal Roy 93)

B=

Where

De 5.93 L ½ H x ------- x ------- + 0.37 ----Dh RQD C B S H De Dh RQD

= Burden (M) = Spacing (M) = Bench Height (M) = Dia of Explosives (MM) = Dia of Hole (MM) = Rock quality designation = 100 (0.1λ + 1) e -0.1 x λ λ = No. of bedding per meter L = Loading density Kglm C = charge factor Kg/M3 Thumb Rule B = 20 - 30 times dia of hole. Spacing Spacing must be large enough to prevent excessive overlap and over break zones behind adjacent holes but just small enough to give a relatively even distribution of Explosives energy in the rock to be broken. An interesting conclusion of the study conducted by the Department of Mining Engineering, Banaras Hindu University was that, at Burdens smaller than optimum fragmentation burden, the fragmentation was finer even at S/B value of 5.0 compared to the results obtained at optimum and greater than optimum fragmentation burden with smaller S/B values of even 1.0. For Lime Stone S = 0.9 B + 0.91 22 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING Sub - Drilling Effective sub drilling of about 8.d or 0.3 x B has been found to be satisfactory. In dipping faces, sub drilling of 10.d to 12.d may be necessary in front row because of the excessive toe burden. Sub drilling beyond 12.d rarely succeeds in pulling heavy toe. Instead it tends to make the situation worse. Optimum Ratio of Toe Burden ------------------------------------- = 40 Hole Dia Stemming The gaseous energy of an Explosives column will be utilised only if stemming is proper. It should be around 0.7 x Burden. Depth of Hole It mainly depends upon the size of machinery, but for better blast results depth D = 2.1 - 2.25 B (B is Burden) Delay Initiation Sequences In multi row blasting, various delay initiation sequences are possible. They are : 1. Instantaneous 2. Row Delay 3. V, V1, V2 pattern

Delay Initiators commonly used are : 1. 2. 3. 4. 5.

Electric delay detonators (ms) in conjunction with detonating cord down lines and/or Trunk lines. Delay detonators are tied to down lines of individual holes or to trunk line. Cord Relays (Detonating Relays) in conjunction with detonating cord trunklines and down lines. Down-the-hole non-electric delay initation system such as NONEL/ Raydet with of without additional surface delays. Use of electric delay detonators in conjunction with sequential blasting machine. Combination of 3 and 4.

The success of blasts using electric delay detonators largely depends on its accuracy, quality and satisfactory functioning of these detonators. Only II delay periods (0-10) are available in short delay detonators (ms) which greatly restricts the blast size, especially if one plans to use v or vi patterns or is required to provide a delay interval higher than their nominal values, thus warranting a need to skip one or two delay numbers.


Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING In cord relays, the blasting engineer has a very simple and versatile tool, which helps him carry out big blasts using large number of rows and yet ensuring adequate delay interval provided for. The probability of a misfire in a blast using cord relays is rather remote, because, while blasting, with detonating relays, additional surface detonation paths are always provided for the blast holes thus ensuring trouble free blasts. the pros and cons of the various initiation sequences mentioned earlier are discussed below. 1.

2.

3.

Instantaneous Blasts : Figure shows a multirow blast where are no delays in the surface hookup. All boreholes detonate more or less simultaneously. Except the first row, the back rows cannot effectively breakout and move in a forwardly direction. They crater up towards the only free face available, viz. bench surface. Such blasts results in poor fragmentation, tight muck piles, excessive fly rock and ground vibration/air blast. This method is not recommended. Row Delay : Most blasters prefer this method for ease of tying-in. In this method, individual rows in a blast are delayed in a sequence, (figure) so that the front row fires first and then the back rows in a sequence, thus creating free face for the individual rows. Though lot of forward movement of broken rock is achieved in this method. The muck pile is generally very loose and scattered. Simultaneous detonation of all holes in a row, results in high charge weights per delay resulting in excessive ground vibrations and often back break is considerable because of simultaneous detonation of all charges in the back row. This result in uneven walls and slope stability problems, modified row delay is shown in figure, which reduces, side-tear. Staggered hole patterns give marginally better fragmentation as compared to in-line patterns figure.

V, V1, V2 Patterns : These Pattern are far superior, to row delays. These result in superior fragmentation due to reduce hole burdens and increased spacing at the time of hole initiation and also due to inflight collision of broken rock during its movement. For example, in square pattern where holes are drilled S = B initiation in a 'V' sequence results in holes getting effectively staggered and also the effective spacing (se) to effective burden (Be) ration viz Se/Be is equal to 2 and Be reduces to a value equal to approximately 0.7B. In this sequence, though fragmentation is superior, forward dis-placement of rock is slightly restricted resulting in heaping up at the centre of the face. This can be overcome by using patterns such as modified square V of square/staggered V1/V2. The delayed action of holes in the back row reduces over break ensuring increased wall stability. The best available pattern is one where the holes are drilled (staggered) on a equilateral triangle pattern. This in a drilled spacing to burden ration of approximately 1.16. It has been observed that an effective spacing (Se) to Burden (Be), ratio of about 3.5" is achieved with holes drilled on an equilateral triangle grid and fired using a V1 initiation sequence.


Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING Drilling (staggered) equilateral triangular pattern require more operator skill and supervision as compared to inline patterns. Clear marking of the hole positions in advance by a responsible person would help the drillers immensely. Fig. gives various delay patterns discussed above.

FLYROCK PROBLEMS IN OPENPIT BLASTING Flyrock in open pit blasting usually means the unexpected/undesired outward projection of rock mass from blasting. Flyrock should be differentiated from 'throw' which now a days can be fairly controlled to produce a desired shape of the muck-pile for efficient loading. The Flyrock generated as such often poses a serious problem to the users of Explosives, as not only the mine equipment are at risk, but also the personal safety and adjacent property are endangered. Cause / Formation of Flyrock Many factors could contribute to the occurrence of undesired fly rock, like : i) Front Row Burden : Flyrock can be ejected from front row blast holes where insufficient burden exists either at the collar or at the toe. Reduced collar burden often occurs with vertical drilling in an inclined face to take care of the desired toe burden; on the other hand sufficient toe burden; could occur where the face has been under-cut or where excessive blast-hole deviation has occurred in angle drilling (see figure)



ii) Stemming Depth/Stemming Material : The collar region is usually fractured before hand due to back-break from previous blast or due to sub-grade blasting from the bench above. As the stemming depth decreases, a larger proportion of explosion gases become available for premature ejection of this pre-fractured rock. The stemming material acts to confine the explosion gases to perform the useful work before venting. With inefficient stemming material the gases stream-up the blast-hole prematurely resulting in fly rock formation. iii) Initiation Sequence : Progressive relief of burden in forward direction through use of inter-row delays is essential for optimum fragmentation and muck-pile looseness. However if the inter-row delay intervals are not adequately designed then the rear rows of holes may crater upward in absence of forward displacement; this will create substantial fly rock. Similar phenomena can happen when blast-holes are initiated out of sequence (back row initiated before front row). iv) Blast Pattern/Blast Shape : When Explosives charge column is overburdened, vertical crate ring can take place causing fly rock. Also when the borehole depth to burden ratio is around unity, forward displacement is inhibited due to higher stiffness length may have to be reduced to accommodate the necessary quantity of charge in the hole, leading to the fly rock from the collar region. If the shape of the blasting round is such that length to width ratio fir the bench is less than 1.5, the rock on both sides of the blast area has a constraining of drag effect on forward displacement thus resulting in fly rock from rear rows. v) Major Geological Faults : Where Explosives charges intersect or are in close proximity to the major geological faults or planes of weakness, the high pressure explosion gases preferentially stream out along these weakness plans. The concentrations of gas pressure energy in these areas lead to fly rock formation. Range of Fly Rock One of the most extensive study of the distance that fly rock is thrown by uncovered Explosives has been conducted by Lundborg. His work based on the observations that the throw distance and eject velocity is proportional to the specific charge or powder factor. Large specific charges produce greater throw distances. 26 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING Since most production blasting involves holes of 100mm. to 250mm. in diameter, the maximum throw can be 500 to 1000m. As an example for a specific charge of 0.56 Kg/m3 and for hole diameter 113mm, 150mm and 250mm the maximum throw of fly rocks will be 250m, 750m and 1020m respectively. For a specific charge of 0-75 Kg/m3 for hole diameter of 32mm (secondary blasting) the maximum throw will be 246 m. Control of Flyrock It should be possible to control the fly rock formation to acceptable levels with an appropriate blast design followed by adequate supervision during charging. the major parameters associated with controlling fly rock include. i) Blast-Hole Location/Charge Configuration : To avoid the irregularities on the front row burden it is important to ensure that the holes are correctly collared with respect to the back-break/inclination of the face and also that digging alongside the initiation face well controlled. Regarding the charge configurations it is often misunderstood to assume that under charging the front row holes solves all problems associated with fly rock. Inadequate forward displacement of the front row burden arising out of the under charging of these holes result in fly rock from vertical catering of the rear holes. It is therefore important that the charging of the front holes should be critically determine with some tolerance for forward throw to avoid harmful fly rock from the back. When the blast hold diameter is increased say from 100 mm to 200 mm, the linear packing density of fully coupled Explosives increases by the square of the ratio of the diameters. In such cases change in the explosives charge distribution particularly in the collar portion is a must to take care of the increased available gas volume with increased packing density. Where permanent the bedding planes are encountered, deck charging should be used to reduce the concentration of charge located directly adjacent to these planes of weakness. ii) Stemming Medium : Where fly rock posses a serious problem, the stemming length should not be less than the hole burden. Also an effective stemming material like crushed angular rock should be used to prevent premature venting of explosion gases through the stemming column. the fine drill cuttings commonly used in most of the opencast operations have been found to be a poor stemming medium as far as the fly rock control is concerned. iii) Initiation Pattern/Sequence : The forward fly rock could be fairly controlled to the commonly used 'inline open loop' pattern. The maximum inter-row delay interval consistent with the absence of cut off helped in minimising the fly rock formation. As a thumb rule an inter-row delay of 4-8ms/m of burden could be used for this purpose. Adequate care should be taken while connecting the delay devices in the holes/rows and the initiation sequence properly checked before firing to avoid initiation pf blast holes out of sequence. iv) Blast Pattern/Shape : Experience has shown that blasts designed on a face length to width ratio in the range of 3 to 4 produces minimum fly rock. In most of our opencast mines as the face length available is limited; it may be useful to restrict to a maximum of 4 rows for large diameter holes. v) Protection Cover : Protective covering of blast with blasting mats, scrap conveyor belting of truck tyres etc. can be used when there is a serious need to drastically reduce or even eliminate the incidence of fly rock. However as this poses a constraint on the overall rock movement, chances of fly rock due to cratering of rear charges could be there if the blast is not properly designed. Fly rock also result from secondary blasting by pop shooting. This can happen if the charge is too heavy of if the blast hole is incorrectly positioned in the burden. The blast hole should be directed as locate the charge in the centre of the boulder. The correct powder factor should also be determined and adhered to in routine secondary blasting. Using the guidelines given above, it is hoped that the quarry managers should be able to control the fly rock to acceptable levels from both primary and secondary blasting thereby avoiding expensive losses. 27 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING GROUND VIBRATION DUE TO BLASTING : Optimum Blasting for Indian Geomining Conditions, Suggestive Standards & Guidelines : Ground vibrations is considered as one of the most undesirable side effects of rock residential buildings in the vicinity of mining operations and thus may lead to conformation and hamper normal production of the mine. Presently huge amount of explosive usage in mining sectors coupled with urban sprawls encroaching the area of mining operation, has called for much better control of blast produced ground vibrations due to greater public environmental consciousness. Broadly, ground vibrations may be controlled by using the following safety measures. (a) (b) (c) (d) (e)

Use Delay Detonators Optimization of the firing time by trials Proper Blast Design Lower Charge Per Delay Direction of Initiation

USBM PREDICTOR EQUATION : This equation considers cylindrical Explosives geometry for long cylindrical charges in which any linear dimension should be scaled with square root of the charge weight. the equation is of the form : USBM : V = K (D/Q½)-B Where, V is the peak particle velocity, D is the distance of the measuring transducer and Q is the maximum charge weight per delay. K and B are site constants to be determined by regression analysis. Control Measures : (a) Use long stemming column in blast holes (b) Use electric detonators rather than detonating fuse as trunk line (c) Use 150 mm thick cover of stand of drill cuttings (d) Avoid blasting in cloudy weather (e) Carry out blasting at mid day (f) Avoid blasting when strong winds are blowing towards the residences Known methods and techniques to reduce Ground Vibrations : The following methods and Techniques have been successful in reducing ground vibration and resulting annoyance complaints : 1. Reduce weight of Explosives per delay. this is perhaps the greatest factor affecting the amplitude of particle velocity. Any decrease in amount of explosives through smaller hole diameter, reduced bench height and or decking will reduce the probability of damage. 2. Reduce explosives confinement by : a. Reducing burden and spacing. b. Reducing buffers in front of face holes. c. Reducing stemming, but not to the degree enhancing Air Blast and/or Rock Fly. d. Reducing sub-drilling. e. Reducing Hole depth. f. Using a blast design that produces maximum relief: this means using large delays between holes or rows of holes. Optimum delay intervals can be determined and substantiated with the use of high-speed motion picture photography. g. Allowing at least one free face to blast. 3. Whenever possible, the progression of detonating holes or a row of holes through millisecond delay intervals should progress away from the structure. 4. Use larger delays, where geological conditions in conjunction with initially system permit. 5. Where possible, keep the total lapsed time of the entire blast below 1-second duration. 6. Use electric millisecond detonators with sequential blasting machines or an initiating system with an adequate number of delay intervals preferably, with down the hole delays causing bottom charge and deck charge blast separated by delays. 28 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING 7. It has been using pre-splitting the production blast and by using air decking the ground vibration is reduced considerably. Threshold Value: (Ground Vibration) DGMS vide the circular No. 7 Dt. 29.8.97 have specified permissible standards of peak particle velocity (in millimeter per second) depending type of structure and dominant excitatory frequency. Permissible peak particle velocity at the foundation level of structure in mining areas is: Type of Structure Building structure not belonging to owner 1.Demostic House structure kucha brick &cement 2. Industrial building RCC& Framed Structure 3.Objects of historical importance and sensitive structure Building belonging to owners with limited span to life 1.Domastic houses structure Kucha bricks & cement 2.Industrial Building RCC & framed structure

PPV in mm/sec at a foundation level of Structure at a frequency. <8Hz 8-25 Hz >25Hz

5

10

15

10

25

25

2

5

10

10

15

25

15

25

50

Drilling and Blasting for Tunneling In Rocks : Tunneling in rocks is currently performed mainly by blasting, as this method only is capable of providing sufficiently high effectiveness and economics in the construction of tunnel in tough rocks. Tunneling by tunnel borers is considered to be less effective especially as regards the construction of tunnels of large cross sectional areas. Drifting /Tunnel Driving Methods in Rocks : The shot holes in a stone drift or tunnel are arranged in a particular form or pattern. The drifting pattern, holes are generally divided into three groups, e.g. Cut holes, Easer and Trimmers. Cut holes : Shot holes in this group are generally longer (approx. 15 cm) than the shot holes of other group. These holes are fired first to created free face for the shots of easers. Since these holes first make the opening in the face, they are prime responsible for the depth of pull. Easers : The shot holes of this group are placed in the drift around the cut holes in two or more rings depending on the cross - sectional area. These holes ease the burden between the succeeding shot holes to enlarge the excavation area of the drift. Trimmers : The shot holes of this group are place around the easer which are fired at the last to make the final shape of the drift. The following type of cuts commonly use in Drifting / Tunneling : a) Cone / Pyramid / Diamond cut : Four or Six cut holes are driven at the middle of the face which converge at the end to form either a Cone or a Pyramid or diamond shape. Maximum concentration of charge is at the apex of these cut holes, which are fired first to create a free face for the rest of the shot, which are fired next with the help of delays. b) Wedge Cut : Horizontal cut holes are driven in inclined at an angle less than 45 degree to the face towards the centre. Like Cone / Pyramid cut maximum concentration of charge at the apex of these cut holes, which are fired first to create a free face for the rest of the shot, which are fired next with the help of delays. 29 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING c) Parallel holes cut (Burn Cut, Cylinder Cut, Coromant Cut ) : A cluster of parallel shot holes are drilled at perpendicular to the face to blast out a cavity in the centre of the heading. Some of the holes are heavily charge with explosives while others are kept empty to provided free face for reflection of shock waves. There is specific geometrical relationship between the diameter of empty hole and spacing between the centres of empty hole and charged holes in a given rock, which gives the essential condition of free breakage. d) Drag Cut / Draw Cut : These type of cut is most suitable for the laminated rocks for "controlled blasting " in drivage of smaller cross-sectional area to brake the rock along the cleavage planes.

Despite their limitations stated above, burn cuts offer the advantages: The advance per round does not depend upon the working space available for drilling blast holes at acute angles to the face. (With a wedge cut, the width the 30 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING Tunnel restricts the apical angle and, hence, the advance per round, specially in tunnels with small cross-sectional areas). Design of Burn Cut holes - The overriding principle of all burn cut designs is as follows: Burden on loaded holes are selected so the volume of the rock broken by any hole cannot be greater than what would occupy the void space created by either the burn hole or subsequent holes firing. In this calculation one must also consider the fact that when rock web breaks between holes, it will occupy a larger space. In other words, the swell factor of the blasted rock must be considered. One of the parameters for good advance of the blasted round is the diameter of the large empty hole. The larger the diameter, the deeper the round may be drilled, and a greater advance can be expected. One of the most common causes of short advance is too small an empty hole in relation to the hole depth. An advance of approximately 95% can be expected for a hole depth of 4 m, and one empty hole with 102 mm diameter. If several empty holes are used, a fictitious diameter has to be calculated. The fictitious diameter of the opening may be calculated in accordance with the formula D = d √n, where D = fictitious empty large hole diameter; d = diameter of empty large holes; n = number of holes.

In order to calculate the burden in the first square, the diameter of the large hole is used in the case of one large hole, and the fictitious diameter in the case of several large holes. The distance between the blasthole and the large empty hole should not be greater than 1.5 times the diameter of the larger hole for the opening to be clean blasted. If the distance is longer, there is merely breakage, and when the distance is shorter, there is a great risk that the blasthole and empty hole will meet. So the position of the blastholes in the 1st square is expressed as: a =1.5d, where a = C- C distance between the large hole and the blasthole, d = diameter of the large hole. In the case of several large holes, the relation is expressed as: a =1.5D Where a = C- C distance between the centre point of the large holes and the blasthole, D = fictitious diameter. Therefore, side of the 1st square w1 = a√2. Position of blastholes in the 2nd square of the cut located at a distance of B1 from one of the sides of the 1st square, in such a way that B1 = w1 and C-C distance between the centre point of the large holes and the blasthole in the 2nd square is 1.5w1. Therefore, side of the 2nd square w2 = 1.5w1√2. Similarly, blastholes in the 3rd square of the cut located at a distance of B2 from side of 2nd square, in such a way that B2 = w2 and C-C distance between the centre point of the large holes and the blasthole 3rd square is 1.5w2. Therefore, side of the 3rd square w3 = 1.5w2√2. Similar calculation be followed for 4th square as well. The holes closest to the empty holes must be charged carefully. Too low a charge concentration in the hole may not break the rock, while too high a charge concentrate of ion may throw the rock against the opposite wall of the large hole with such high a velocity that the broken rock will be recompacted there, and not blown out through the large hole. Full advance is then not obtained. Generally, in average blastability rock, for 34 to 37 mm dia. blastholes in the 31 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING 1st square are charged at a charge concentration of 0.5kg/m; for 2nd square blastholes charge concentration of 0.75kg/m; for 3rd square blastholes charge concentration of 1.15kg/m and for 4th square blastholes charge concentration of 1.25kg/m should be used.

Organisation of blast hole drilling: 1. Making of blast hole: It should be made as accurately as possible, particularly the line holes. This can be effected by template, or marking use of spray paint as convenient. A very efficient procedure of pointing holes on the working face with a light projector with an optical attachment consisting of metallic casing, lenses and a frame that receives a metallic plate carrying the location of the blast holes. Each hole is represented on the plate as an orifice 1mm in dia. The projector is placed at a distance from the working face equal to 1.5-3 times the height of the working. Source of the light is a lamp of 1000W. The apparatus is located using two marks. Spotted on the face is an advance light spot projected through the plate on the face correspond to the holes to be drilled. 2.

Charging and shooting of blast holes: To reduce the charging time it is possible to employ composite explosive charges consisting of several cartridges placed whether in paper shell or PVC pipes. The use of composite charge, which is 5-10 times the carting length, shortens the charging time by 50-60%.

3.

Parallel wiring is generally used for firing shots from an electric power mains and series for a blasting machine. In case of NONEL use of D-cord and electrical instantaneous detonators is fired with exploder.

4.

Periphery holes: To control over break, effective decoupling is required. It can be done by, (i) By using 25mm dia. Cartridge in 38mm dia. Hole. (ii) By using comparative weaker explosive (iii) By keeping air gap between two explosives cartridges by using hollow bamboo spacer of 150mm long.


Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING Typical charges for primary blasting (source-CMRI bulletin): Calculation of optimum charge and some design parameters is the pre-requisite to the primary blasting. The charge ratio and charge per hole would depend on many geologic and rock parameters. However, as an initial approximation, the chart given can be used which may subsequently be changed subject to the performance of the blast. Table: Estimation of various charges for different Hole Dia., Cart. Dia. and Hole depths. Dia. of hole (mm)

Dia. of cart. (mm)

32

25

38

32

63

50

100

83

150

125

200

175

250

200

Depth of hole (m)

Burden (m)

Spacing (m)

1.0 1.5 2.0 2.5 3.0 2.0 2.5 3.0 3.5 4.0 5.0 6.0 5.0 6.0 8.0 10.0 6.0 8.0 10.0 12.0 8.0 10.0 12.0 15.0 10.0 12.0 15.0 20.0

0.6 0.8 1.0 1.1 1.2 1.0 1.2 1.4 1.5 1.6 2.4 2.4 2.0 2.4 3.0 3.5 2.5 3.5 4.0 4.5 3.6 4.2 4.5 5.0 4.5 5.0 5.5 6.0

0.7 1.0 1.2 1.3 1.3 1.2 1.4 1.6 1.6 2.0 2.4 2.8 2.4 2.6 3.5 4.2 3.0 4.2 4.8 5.0 4.5 5.0 5.4 6.0 5.4 6.4 6.5 7.0

Vol. of rock/hole (cu.m) 0.42 1.20 2.40 3.57 4.68 2.4 4.2 6.72 8.40 12.80 24.00 40.32 24.00 37.44 84.00 147.0 45.0 117.6 192.0 270.0 129.6 210.0 291.6 450.0 243.0 360.0 536.25 840.0

Charge/hole(k g) 0.13 0.39 0.65 0.91 1.17 0.75 1.20 1.80 2.25 5.00 8.00 13.00 13.90 19.46 41.70 69.50 31.25 68.75 100.0 125.0 91.63 141.6 183.26 253.23 187.5 262.5 350.0 512.5

Charge ratio (cu.m/kg) 3.23 3.08 3.69 3.92 4.00 3.20 3.50 3.73 3.73 2.56 3.00 3.10 1.72 1.92 2.01 2.12 1.44 1.71 1.92 2.62 1.41 1.48 1.59 1.74 1.30 1.37 1.53 1.64

Loading density of explosives (source: CMRI bulletin): Loading density of explosives means the weight (in kg) of explosive charge per meter of borehole. It is thus different for different hole dia. and explosives due to varying densities. Hole Diameter (mm) 100 150 165 250 310 320 350

Slurry / Emulsion (Kg)/m 7-9 20-22 24-26 55-60 85-87 90-95 110-112

ANFO (Kg)/m 8 16 18-20 40-45 65-68 70-74 84-86 33

-----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING Secondary Blasting (Source CMRI bulletin): Secondary blasting is used to break oversize boulders, which appear in a primary blast. It is achieved by either ‘Pop shooting ‘or ‘Plaster Shooting’. Pop shooting: In this boulder blasting technique, the explosives charge is placed in a drill hole, and confined with clay to the collar. The hole length may be slightly more than half of the thickness of boulders. For larger boulders, several holes may be drilled keeping approximate spacing of 0.6m. For small boulders, the hole may be drilled at the centre of the boulder. A pop shooting generally creates fly rocks and thus it is advisable to keep a min. distance of nearly 200m from nearest structures. Plaster shooting: Plaster shooting (mud shooting) is a commercially used method for boulder blasting. In this method, a thin layer of mud is placed on the boulder and explosives cartridge is firmly placed in to the mud. The charge is then covered hemi spherically with some handful of mud to make a wave shaper. The average charge ratio 1.0-1.5kg of explosive for every cubic meter of boulder size. Plaster shooting creates much noise, which may lead to human psychological effect and may be heard with in a periphery of 1km. Coal blasting Underground: Thumb rules for u/g coal blasting: A) Cut face blasting: 1. No. of holes 2. Depth of hole 3. Charge per hole 4. Stemming 5. Explosive

For each 1 square meter area = 1 hole 15cm less than cut length 40% of hole length 60% of hole length P1 type for degree 1 mines P3 type for degree 2/3 mines

B) Solid blasting (wedge cut pattern): 1. No. of holes a)For normal conditions,0.7 sq.mt = 1 hole b)Tougher conditions, 0.5 sq.mt = 1 hole 2. Maximum depth of cut holes 0.7 x height of gallery 3. Depth of other holes = 0.8 x cut hole length 4. Charge per hole = 40% of hole length 5. Stemming = 60% of hole length 6. Explosive = P-5 type Belgex Coal-V 7. Max. Possible pull = 0.8 x cut hole length Points of Remember : 'Concepts of Blasting' 1. 'Freedom to Move : Insitu Coal needs free passage to move out during blasting, i.e. Free face to be created either by (a) CCM - Cut face blasting (b) Creating wedge opening by drilling and blasting a few additional holes preferably at centre of face. 2.

Cut Face Blasting : Holes need to be shorter by 15 cm from cut depth because explosives energy released during blasting hits in a crater shape and the point of concentrated energy is 15 cm beyond the end of cartridges, where free face should be available for breakage of coal.

3.

Solid Blasting : (a) To create an initial cut, holes need to be drilled in inclined position so as to provide direction and force for coal to move outwardly, to create free face for other holes. (Lever action theory) (b) Wider the opening (i.e. Free face) easier it would be for other holes to perform better. It is advisable to give zero delay for 6 cut holes in the centre. (c) Considering Beam theory, hole length beyond 70% of seam height would not bring expected result. Rather long sockets will be left and explosive energy will be wasted and P.F. will be reduced.


Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING (d) Stemming less than 60% of hole length or un proper packing may not be able to sustain the volume / pressure of gases generated during blasting and explosive energy will be wasted in form of a blown out shot. (e) Cut holes should be charged more as compared to other holes. (f) Initiation sequence should be maintained so as that cut holes give way first, nearest hole next and farthest holes last.

Cut Face Blasting : A typical round of hole used in blasting an under cut face is shown below:

(Numbers show sequence of firing rounds) Depth of Hole 1.5 Meters No. of Holes Charge / Holes 300 g Total yield of Coal Yield per kg -

8 14 tones 6.00 tones

Off - The Solid : The technique of blasting off-the solid (BOS) has been found to be simpler, more economical and less hazardous that the conventional method of breaking coal with machine cutting and blasting. Mechanised methods using BOS with scraper loaders and side loaders have already proved successful. Several long wall mining faces employing BOS are also tired out. The hazards associated with blasting off the solid in gassy coalmines, are such that the usual permitted explosives of the category P1 and P3 are not considered safe. Solarcoal-5 belongs to P5 category and has been designed to meet the exacting safety requirements in blasting coal off-the solid. The delay detonators, required for use with this type of explosives, must be non-incentive. Typical rounds of shot holes wedge cut and fan cut patterns, and a schematic diagram indicating blasting pattern and initiation sequence in long wall faces are shown on the following pages. For effective blasting off-the solid, full face firing in a heading is necessary both form safety as well as productivity point of view indigenously available Schaffer type 350 and Rhino 25 shot exploders are designed to meet this requirement of BOS.



Recommended Pattern for Seam Height 2.6 m Face Size 4.6 x 2.6 Total Holes = 15 Type of Number Depth of Holes Holes

Explosive / hole

Delay Number

Cut Holes 6 1.7 m (5.6) 3 555 Z Other 6 1.6 m (5') 3 555 I Holes 3 1.6 m (5') 3 555 II Total Explosives per Expected Pull Expected Coal Powder Factor Round (Insitu) T/Kg. 8.32 Kg. 1.27 m (4') 19.74 M. T. 2.37 Remark 1.* 2-4 holes to be increased if encouraged with shale /stone bend. 2. ** Full packaging with sand clay cartridges gives 10% better results.

Stemming 60-65% 60% 60% Detonator Factor 1.31


Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING Table : Types of Permitted Explosives for different degrees of gassiness. Degree of Gassiness of Coal seam I

II

III

Classification of Gassiness

< 0.1% of gas in the general body of air and rate of emission of such gas is less than 1 cu. m/t of coal production > 0.1% of gas in the general body of air and rate of emission of such gas is greater than but less than 10 cu. m/t of coal production Rate of emission of the gas is greater than 10 cu. m/t pf coal production

Type of Permitted Explosives P1 / P3 / P5

P3 / P5

P3 / P5

DGMS (India) Stipulations on Maximum Permissible Charge in a Short Hole, Delay Interval Etc. 1.

Explosives: Types of Explosives

P1 P3 P5 P5 2.

3.

Degree of gassiness / Type of Application

Degree 1 mines, Cut face Degree I, II & III mines, Cut face Degree I-‘BOS’, Degree II &III-‘BOS’

Max Permissible charge per Shot hole (gms) 800 1000 1000 565

Delay Detonator : (a) While using non-incentive delay detonators in ‘BOS’ application, the maximum delay period between the first and last shot in a degree I and II Gassy coal seams will not exceed 150 ms. (b)

While using non-incentive delay detonators in ‘BOS’ application the maximum delay period between the 1st & last shot in Degree III gassy coal seams will not exceed 100 ms.

(c)

The delay period between 2 consecutive shots with different delay numbers will not exceed 60 ms.

Distance between 2 adjacent shots with different delay numbers will not come closer than 0.6 m at the explosives charges ends.

OTHER APPLICATIONS OF EXPLOSIVES Explosives are also used for a variety of other applications some of which are listed below : 1. Agriculture. 2. Breaking blast furnace hearths / salamander blasting. 3. Cutting dimensional stones. 4. Demolitions. 5. Metal breaking. 6. Metal forming. 7. Salvaging scraps and wrecks. 8. Seismic prospecting. 9. Presplitting, smooth wall blasting etc. 10. Underwater blasting. 11. Roads & railway Construction. 37 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING CODE OF GOOD PRACTICE IN SHOTFIRING 1. While storing transporting of handling explosives, do not smoke or have in your possession matches, naked light or apparatus of any kind capable of producing flame or spark. 2. Do not keep explosives and detonators in the same container or magazine. Explosives and detonators must be transported separately to the blasting site. 3. Do not use tools made of iron or steel for opening cases or for making holes in primer cartridges. Use implements of hard wood, brass or other non-sparking material. 4. Do not break an explosives cartridge. 5. Check the condition of shot holes with a scraper/stemming rod before inserting cartridges. 6. Do not force a detonator into a cartridge. 7. Do not try to soften hardened explosives by heating over fire or by rolling cartridges on the ground. 8. Do not fire a blast until you have made sure that all surplus explosives have been removed, and all persons, vehicles and equipment are at a safe distance. 9. Post guards with red flags around the site to prevent persons approaching the danger area inadvertently while the shots are being fired. 10. Keep primed cartridges separately and away from other explosives until they are loaded into the holes. Firing Electrically : 1. Test the exploder before use. 2. Stop all blasting work during an electrical storm and clears the working area of all men. 3. While straightening the lead wires, do not hold the electric detonator by the tube. Grip the wires about 10cm from the detonator with one hand and smooth them out with the other. This will avoid any pull on the fuse head. 4. While charging and stemming, take care to avoid damaging the insulation of the lead wires of the electric detonator, which may cause misfires. 5. Twin-core cables have top conductors and care should be taken to make sure that the stands of one conductor are mot in contract with those of the other. It is good practice to have the exposed ends of the conductors staggered in relation to each other. 6. While making connections, the bare ends of the conductors should be twisted together tightly for a length of about 3 cm. The conductors should be thoroughly cleaned since greasy of dirty wires give a poor connection and may cause misfires. 7. To ensure good insulation and avoid short circuits in wet conditions use insulating tape. 7. The key of the exploder should always be in the possession of the shot fire. 8. All connections should be made by the shot fire himself; this work should be not entrusted to any other person. 9. Before returning to the blast site, remove the exploder key, disconnect the cable form the exploder and short circuit the cable by twisting together the bare ends of the two conductors. 10. Keep the exploder in a dry place. 12. Do not leave bare conductors on wet ground. 13. Take precautions against stray currents while blasting near electrically operated machines or high voltage power lines. MISFIRES IN BLASTING There are many circumstances under which a misfire can occur and there are official regulations covering the treatment of misfires. These should be strictly adhered to and nothing in this chapter should be construed as altering or amending such regulations. All misfires should be treated with greatest care and all operations dealing with them should be entrusted only to experienced conscientious and careful men. No person should be allowed to approach a misfire until either it has exploded or a sage period has elapsed. This period should be at least 30 minutes with safety use initiation and at least 5 minutes with electric shot firing. 1. Misfires with Safety Fuse Initiation : In safety fuse firing faulty cutting of safety fuse, loose crimping, use of non-waterproof fuse in watery conditions can lead to misfires. 38 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING 2. Misfires with Electric Shot Firing : In electric shot firing faulty connections, detonators left-off unconnected, lead wires becoming bare during stemming internally shot-circuited cable / damage in the insulation, inadequate firing current due to failure of the exploder to reach the rated output or the number of detonators being greater that that can be fired by the exploder, current leakage and other factors can cause misfires. 3. Misfires with Detonating Fuse : While firing with detonating fuse incorrect method of limiting the detonating fuse, loop cross-over, approach of a different branch of detonating fuse, improper joints and branch-line failure, use of detonators with too long a delay interval, wrong sequencing of shots and improper handling / use if delay detonator-relays could lead to cut-offs of detonating fuse. 4. Misfire with Exploders : A large number of misfires are generally caused by the use of faulty exploders and use of wrong type of exploder for a given purpose; Maintenance of exploders is very essential to obtain the output. Following are the causes of misfires with exploders : a. Inadequate exploder capacity b. Faulty exploder-defective generator/conductor c. Poor contact in rotating crank type exploders d. Exhausted cells e. Faulty indicator Wherever possible, it is sager to fire the explosives using a fresh primer than to attempt to dislodge it and recover the cartridges from the debris. However, before deciding on the repriming of the explosives, consideration should be given to the possibility of excessive cracks in rocks, which may occur because of the relief of the burden of the misfired hole, by adjacent shots. BLASTING IN LOW TEMPERATURE AREAS In the event of explosives becoming frozen, cartridges may he safety thawed either by placing them in the sun of, if necessary, by heating in a suitably designed vessel. Such a vessel should consist of two zinc sheet containers with a space between them in which water at a maximum temperature of 71O C is poured. The outer vessel and the cover should be lagged with non-conducting material to prevent heat loss. The frozen cartridges are placed in the inner vessel where they should be left until thawing is complete. Do not attempt to soften cartridges by heating them over an open fire or by any other improper means. Under no circumstances should Explosives in frozen condition be used for blasting. BLASTING IN HOT HOLES CMRI carried out substantial experiments to obtain a general guideline of blasting in hot holes to make use of huge amount of coal which would otherwise be lost or un recovered, The following stepwise approach may be followed for the successful operation : Step-1 : Select the number of holes properly so that the total blasting operation should not exceed 2 h from charging of first hole. Step-2 : Measures the temperature of the holes Step-3 : Use water at least 12 h before blasting to flush hot holes till the temperature comes down below 80oC Step-4 : Record the temperature of holes at a regular interval of time. Step-5 : Use a mixture of Bentonite, Sodium Silicate and Water in holes which do not retain water to seal microfractures and cracks. Guar gum up 5 percent may be also be used for the same purpose. Step-6 : Check before charging whether the detonating cord is detached from the main reel or not. If not, then detach it immediately before charging operation starts. Step-7 : Stemming operation should be done after charging all holes.



ROCK DENSITIES INSITU AND AFTER BLASTING Material Basalt Coal-Anthracite Coal-Bituminous Diabase Diorite Dolomite Gneiss Granfte Gypsum Hematite Limestone Limonite Magnesite Magnetite Marble Mica-Schist Porphyry Quartzite Salt-Rock Sandstone Shale Silica Sand State Tale Trap Rock

Specific Gravity (g/cc) 2.8 - 3.0 1.3 - 1.8 1.2 - 1.5 2.6 - 3.0 2.8 - 3.0 2.8 - 2.9 2.6 - 2.9 2.6 - 2.9 2.3 - 3.3 4.5- 5.3 2.4 -2.9 3.6 - 4.0 3.0 - 3.2 4.9 - 5.2 2.1 - 2.9 2.5 - 2.9 2.5 - 2.6 2.0 - 2.8 2.1 - 2.6 2.0 - 2.8 2.4 - 2.8 2.2 - 2.8 2.5 - 2.8 2.6 - 2.8 2.6 - 3.0

Solid Tonne/ cu.m 3.02 1.61 1.37 2.78 2.97 2.87 2.87 2.72 2.78 4.86 2.64 3.77 3.21 5.00 2.51 2.72 2.57 2.57 2.33 2.42 2.57 2.57 2.72 2.64 2.78

Broken Tonne/ cu.m. 2.00 1.04 0.88 1.85 1.94 1.85 1.85 1.78 1.85 3.21 1.68 2.50 2.00 3.28 1.60 1.78 1.68 1.68 1.52 1.52 1.68 1.68 1.78 1.78 1.85

GAS AND SHOCK ENERGIES OF SOME COMMERICAL EXPLOSIVES Source : CMRI Bulletin

Name of Explosives Pentolite (50% TNT + 50% PETN) TNT Pentolite OCG Emulsion ANFO Heavy ANFO

Ebl (Cal/g) 490

Esh (Cal/g) 234

Total Energy (Cal/g) 724

505 475 495 460 500 470

215 469 408 370 340 360

720 944 903 830 840 830

DGMS (India) CIRCULARS 1. Use of L.O.X. in opencast Coal Mines : Recently, there was an incident of fire with the use of L.O.X. under the following circumstances. Blasting was done with L.O.X. in the overburden of the opencast workings if a coalmine. Old developed coal pillars were being quarried. One of the shot holes in the overburden punctured into the underground working and as such it could not be stemmed properly before blasting. L.O.X. cartridges in the inadequately stemmed hole were thus 40 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING blasted without sufficient confinement. In all probability, a part of the charge which had not blasted, communication down below and configurated to set the coal debris lying belowground in the gallery on fire. In order to avert such situations, you are advised that L.O.X. shall not be used for blasting in overburden within 15 m of u\g workings in the coal seam immediately below or in the vicinity. (Cir. Tech. 11/1979) 2. Adequacy of Ventilation while using Explosives in underground Metalliferous Mines : During trials conducted for assessment of fume characteristics of new explosives formulations both from I.D.L. and I.E.L. for use in underground Metalliferous Mines, it has been observed that unless ventilation is of High Standard, Carbon Monoxide and or Nitrous fumes formed by blasting of practically all types of explosives above the threshold/ceiling limits internationally accepted for the these noxious gases are met with for some time after the blast and thus injurious to the health of the work persons in the vicinity. In view of this it is advised that while using any explosive, be it NG-Based, AN Based or slurry, in underground Metalliferous Mines the following precautions regarding ventilation should be observed :1)

Adequate arrangements should be made to circulate such quantity of air upto the site of blasting as to ensure, after every round of blast, dilution of Carbon Monoxide and Oxides of Nitrogen in the blasting fumes to less than 50 parts per million and 5 parts per million respectively within a period of 5 minutes.

2)

For drivages more than 50m long a suitable auxiliary ventilators should be provided to ensure at least 150m3/min ventilation air current within 4.5m of these faces. In addition, in view of the difficulty of sampling and analyzing for CO and nitrous fumes as well as paucity of suitable detector tubes for these gases no person should be allowed to re-enter the place where blasting has been carried out unless the fumes are cleared and unless a period of at least 15 minutes has elapsed from the time of blasting.

3)

Accidents due to inhalation of nitrous fumes :- The effect of inhalation of nitrous fumes on workers employed belowground does not appear to have received adequate attention nor the dangers associated duly recoganised. Instances have come to light recently where some belowground workers who were so affected died shortly after. In all such cases, death was apparently taken to be due to bronchopneumonia where as in actual, it was due to Broncho spasm due to inhalation of noxious fumes. Had the patients been treated for the later viz., noxious fumes by provision of oxygen etc., it is likely that their lives could have been saved. It is also to be recoganised that the effect of inhalation nitrous fumes on different individuals may be different, depending upon the concentration of the noxious fumes in the general body of air, degree of exposure and the constitution of the individual. Thus, in some extreme, cases, even a week later. It is because of this time lag and similarly of symptoms that such deaths are being recorded as natural deaths instead of recognising them as natural deaths instead of recognizing them as occupational hazards. An extract on this topic form ILO publication Occupational Health & Safety is reproduced below in this connection for information : "There is some doubt concerning the toxic actions of nitric oxide, but it is certain that nitrogen dioxide, with its associated dinitrogen tetdioxide, is a powerful lung irritant and it is probable that the hazard form 'nitrous fumes' is due mainly to this component. Exposure to high concentrations in the region of 100 - 500 ppm may lead to sudden death from bronchospasm and respiratory failure. A more typical death arises from delayed pulmonary oedema, the initial signs on exposure being no more than moderate irritation of the eyes and respiratory tract. A third type of death may ensure several weeks after exposure and may be associated with inflammatory changes termed broncholities fibrosa obliterans and thought to be due to an auto-immune response or with bronchitis, pneumonia or other lung infections."


Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING In drawing the above to your notice, I am to request you to bring the same to the attention of all concerned, more particularly to the Mine \ Hospital Doctors to the above occupational hazard and of the dire necessity of treating such patients more for inhalation of noxious fumes rather than for bronchitis. (Cir. Tech.7/1981) In Coal shall be charged with water ampoules or with most sand of at least 0.6m in length at the bottom of the hole. 9. Shelter- No person including shot firer shall take shelter within 100 meters of the quarry openings, and such shelter shall be of an approved design. 10. Administrative control : The opencast working over underground part of working shall be under the administrative and technical direction and control of the Manager and Agent. 4.

Danger Associated with use of ANFO in pyrite bearing ores : In the United States of America Ammonium Nitrate Fuel Oil (AN-FO) explosives were accidents occurred. It was thought that the accidents were caused by misfired charges of AN-FO. The actual ore from the vicinity of the accidents and the ingredients used to prepare the AN-FO charges onsite were examined. A thorough investigation into the matter revealed the following : "Ammonium Nitrate-Fuel Oil (AN-FO) mixtures are used as blasting agents in mining pyrite-bearing ores. The temperature of these ores can increased by the continuous, though are times, oxidation weathering of the pyrite and the reaction becomes self-sustained at 120 ±10O C. The Bureau of Mines has conducted an investigation determine the reactivity of mixtures of AN-FO with pyrite containing ferrous sulphate. The results of tests in a heated vessel simulating a hot borehole demonstrate that small amounts of ferrous sulphate, a major product of pyrite weathering, initiate a self-sustained exothermic reaction with AN-FO at 80OC. Five percent by weight of urea was found sufficient prevent a reaction among the three ingredients, at least within the limits of the test, which reached 180OC.Smaller amounts of urea and of potassium oxalate slowed down the reaction and delayed its onset to higher temp but did not prevent it. For fuller details about the investigations a reference may be made to USBM investigation report No. 8373 of 1979. The purpose of bringing the above to your notice is that in case the mining activities under your control fall within the parameters indicated above, you may take appropriate action. (Cir. Tech. 4/1980)

5.

Quality and condition of explosives provided for use in mines – Attention is invited to Reg.159 of CMR1957 and Reg. 153 of MMR 1961 which require that the explosives provided for use by the owner, Agent or Manager shall be of good quality and as far as can be known in good condition. It has come to the notice to this Directorate that suitable checks and controls have not been provided at every mine magazine to comply with the said requirement. Needless to mention that use of explosives, which are not in good condition lead to, hazards, which can be easily avoided. I trust you would in consultation with the manufacturer/suppliers of explosives take immediate steps to institute suitable checks and controls to comply with the aforesaid statutory requirement. (Cir. Tech. 5/1985)

6.

Storage of explosive beyond its shelf life : It understand that following the general shortage of explosives sometime last year, a number magazine had build up large buffer stocks to tide over shortfall in supply. This has, however, resulted in a situation when old stock of explosive had been kept in storage beyond its shelf life in some places. This is, therefore, to caution you that old stock of explosive should not be used in mines beyond its shelf life. Further you are advised to take immediate action to destroy such old stock in the manner given in DGMS Circular No. 57 of 1964. 42 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING (Cir. Tech. 5/1985) 7.

Safe destruction of Blasting Explosives – Instructions issued by the office of the Chief Inspector of Mines for destruction of high and other explosives are reproduced below: Instructions for the destruction of Blasting Explosives : (1) Gunpowder : Gunpowder should be thrown into water preferably hot water which dissolve out the saltpeter and renders the explosive harmless. An alternative methods is to lay it out in a train and fire this from one end by means of a piece of safety fuse, but if more than one train is laid, care should be taken to lay the second at such a distance form the site of the first as to run no risk of its being fired by the heated soil, as many serious accidents have occurred in this way. (2)

Nitrate of Ammonium Explosives : These should be scattered on damp soil. These are so bygroscopic that even on a dry summer day a short exposure to the air renders them harmless, but it is generally easy to find a ditch damp enough to take immediate effect. If not generously applied these explosives make excellent manure.

(3)

Nitro Compounds, Gelignite, Gelatin and other similar Explosives : Not more than 50 pounds of explosives should be destroyed at a time. A clear space of ground about 100 yards all round should be selected, and a line of shavings or dry straw or grass laid down. On this the cartridges should be placed in a continuous line not more than two abreast with the cartridges wrappers and any other available paper below them. Paraffin or other similar oil, should then be poured over the shavings, straw or grass and cartridges for combustion. The line of shavings, straw or grass should be prolonged some distance beyond the explosives (say 20ft) and lit with a short length of safety fuse and the operator should then retire quickly to a safe distance. The ground on which the destruction is to take place should be clear of dry grass and inflammable substances. The direction of the fire should be at about an angle of 45 degrees to the direction of the wind and the fire should be ignited form the weather end.

(4)

Dynamites : Even in small cartridges and small quantities dynamites burn very easily to detonations. The degree of confinement caused by the cartridges wrappers is often sufficient to caused explosion. Dynamite should never be brunt in larger quantities than 5ibs. at a time and the wrappers must be opened and up rolled. The site on which the destruction is to take place should be so chosen, and the fire initiated by means of safety fuse of such a length that no risk is run by personal or property in the event of the changing to explosion.

(5)

Safety fuse : This should be destroyed by burning in lengths in the open under precautions.

(6)

Detonators : Detonators should be disposed off by being taken to deep river, or to the sea, and then thrown into the deep water by twos and threes, or they may be thoroughly soaked in miner oil for 48 hours and then be destroyed one at a time, under suitable precautions, by burning. (Cr. 57/1964)

(7)

Approval of mechanically propelled vehicle for transport of explosives under Reg.164A (2) (a) of CMR 1957 : By virtue of powers conferred upon me under Reg. 164A (2) (a) of the Coal Mines Regulations 1957, I hereby approve all mechanically propelled vehicles which are duly licensed under Rule 76 of the Explosives Rules 1983 for transport of explosives in mines subject to the conditions stipulated in the licence.

(8)

Pilferage of Explosives : Employment of trustworthy persons and checks : The owners, Agents and Managers should instruct and impress on their subordinate staff responsible fir handling and using explosives (particularly detonators and high explosives) the necessity of exercising strictest vigilance to prevent leakage of explosives. 1. Only such persons should be appointed as magazine incharges, shot fires and explosives carriers, who have been found to be trustworthy 43 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING 2. The number of shot fires and explosives carries should be kept to a minimum. 3. Senior officials should frequently have surprises checks on the amount of explosives with carriers and shot fires at different times during the shift. (9)

Pilferage of Explosives through authorised persons : It has noted that pilferage of explosives has taken place form some of the mines through authorised persons, mainly shot fires explosives usually find their way to undesirable persons and used for anti social activities. To stop this pilferage it is necessary to check the antecedents of shot fires and to keep a watch on them. Managements are requested to furnish DGMS with a list of the shot fires in service at their respective mines on 1st January every year with the following details: 1. Name in Full : 2. Father's Name : 3. Residential Address : 4. Home Address : 5. Number and kind of certificate he holds for firing shots : A copy of the list should be sent to the Superintendent of Police having jurisdiction in the area, which the mine is situated. Managements are also advised to enforce strict check or kind of personal search by the attendance clerks at the mine entrance at the time the unspent balance is brought to the surface by shot fires.

10.

Pilferage of Explosives : Attention is invited to circulars 13/1956 and 9/1957 regarding pilferage of explosives through authorised persons in mines. It has been reported by the Superintendent of Police, Dhanbad that pilferage of explosives on a large scale is taking face form some of mine magazines and that explosives are going to the hands of undesirable persons. In order to stop such an undesirable practice it is essential that explosives are issued to the shot fires very carefully after, ascertaining their actual needs. It is equally necessary that the magazine clerk and the shot fires be kept under constant watch to ensure that there is no misuse of explosives. The quantity of explosives actually used by the shot firer should be checked by a senior officer of the rank of an Assistant Manager. The magazine incharge should be asked to maintain a proper account of the quantity of explosives issued from the magazine and the number of shots fired. (Cir. 44/1963)

CMR 168 / MMR 162 1.

Stemming Material : the stemming material most commonly used in this country is clay, a plastic mixture being formed into plugs which are than allowed to dry out in the sun. The plugs thus attain a consistency similar to that of unbrunt brick and are often so hard that very forceful treatment is required in the shot holes to break them down. Such plugs are completely unsuitable as stemming material. The stemming material should be compact but not hard. The use of mixture containing 70% fine sand, 30% clay and a small percentage of calcium chloride to keep it in a plastic condition is recommended for the purpose. (Cir. 49/1959)

2.

Forcing down of Explosives Cartridges : Forcing a cartridges of explosives down a shot-hole is always fraught with danger particularly when it is stuck up. Instruction exists in the Regulations when the shot hole is of insufficient size [Reg.168 (9) of CMR 1957 and Reg. 192(9) of MMR 1961]. It is equally dangerous when attempts are made to press or force a cartridges stuck up in a shot-hole of bigger size either due to some obstruction in the shot-hole or the cartridge having fallen diagonally. In drawing attention to the danger associated with such practice, it is required that at no stage should attempts be made to push any cartridges down when it gets stuck up either because of insufficient diameter, obstruction in the shothole or any other reason. 44 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING Such shot hole should be dealt with the manner laid down in the regulations for misfired shots. (Cir. Tech. 1/1975) 3.

Shots in shafts and tunnels to be Fired Electricity in Coal Mines : In exercise of the powers conferred on the regional inspector of Mines under Red.168(14) of the coal mines regulations 1957 and in exercise of the provisions of Reg.202 of CMR 1957, the DGMS has specified that every shot to be fired in a shaft or tunnel shall be fired electrically. A similar requirement has been made under Reg.162 (14) of MMR 1961 also. (Cir.Legis.6 & 7/1991)

4.

Shots to be fired in shafts, tunnels and workings belowground electrically in Metalliferous Mines : In exercise of powers conferred on the Regional inspector of mine, under Reg.162 (14) of the Metalliferous Mines Regulations 1961 and in exercise of the provisions of Reg.193, the DGMS has specified that shot to be fired in a shaft, tunnel or working belowground in a Metalliferous Mine shall be fired electrically of ten meters form the place of firing. In either case the techniques of blasting and/or muffling should be got approved form the concerned Director of Mines Safety. (Cir. Tech. 8/1982)

5.

Simultaneous Blasting with Fuse in opencast working : It has been seen that, in many opencast mines a number of shot firers/blasters are engaged side by side for simultaneous blasting operations. As shots fired by all such shot firers/blasters are likely to go off together, it is difficult to count them for ascertaining whether there has been any misfire or not. If in case there is slight time stagger in blasting operations some of the shot firers/blasters may be injured by missiles thrown off by other blasting in the neighborhood, as they may not be able to take proper shelter in time. (Cir. 1/1967) It is therefore advisable that, where a number of shot firers/blasters are employed in proximity to each other (i.e. 300 meters) only one shot firer/blaster are time may fire shots, and the interval between two shot firers/blasters firing shots should not be less than 30 mines.

6.

Blasting in quarries beyond day light hours : Precautions exist to prevent danger form projectiles due to blasting operations carried out in opencast workings within the dangers zone of 300 meters. However, when such operations are carried out beyond daylight hours, it may not be possible to ensure that all persons in the danger zone had taken shelter. There is also the possibility of some inadvertent entry into the danger zone by workers or even outsiders, possibility of persons remaining unprotected in the danger zone therefore cannot be ruled out and hence additional precautions are required. It is therefore felt that shots, if fired after day light hours, should be muffled so that flying fragments form blasting cannot project beyond a distance of ten meters from the place of blasting. The above may be noted for strict compliance in all blasting operations. (Cir. Tech. 8/1976)

7.

Danger Zone in opencast Mines : Reg. 164 of the MMR 1961, as amended by notification no. 1093 dated the 20th September, 1974 specifies that in opencast workings a blaster shall not charge on fire a shot unless sufficient warning be efficient signals or other means approved by the manager is given over the entire area falling within a radius of 300 meters from the place of firing (referred to as the danger zone) and the blaster has ensured that all persons within the danger zone have taken proper shelter. During the last four years six accidents, including one fatal, have occurred in different opencast mines in which persons beyond the aforesaid danger zone of 300 meters have been hit by projectiles from the place of firing. The maximum distance at which a person was struck was about 362 meters. Expect at one mine, where the depth of shot holes was 5 meters, jack hammer holes, about 1.5 meters deep, were fired at the other mines, where accidents took place 45 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING The above accidents amply demonstrate that the minimum distance specified in the regulation, is not adequate in all circumstances. May, I, Therefore, request you, in the interest of safety, to treat all places within a radius of 400 meters of the place of firing as the danger zone. Necessary action is being taken to suitably amend the regulations. (Cir. Tech. 15/1977) Extracts from Indian Coal Mines Regulations, 1957 Standard of Ventilation : Reg. 130 (2) For the purpose of securing adequate ventilation as aforesaid, the owner, agent and manager shall ensure: (i) In every ventilation district, not less than six cubic meters per minute of air per person employed, in the district on the largest shift or not less that 2.5 cubic meters per minute of air daily tones output, whichever is larger, passes along the last ventilation connection in the district which means the in by most gallery in the district along which the air passes; (ii)

At every place in the mine where persons are required to work or pass, the air does not contain less than 19 percent of oxygen and more than 0.5 percent of Carbon Dioxide or any Noxious gas in quantity likely to affect the health of any person; (iii) The percentage of inflammable gas does not exceed 0.75 in the general body of the return air of any ventilating district and 1.25 in any place in the mine; (iv)

The wet bulb temperature in any working place does not exceed 33.5 degree centigrade, and where the wet bulb temperature exceeds 30.5 degree centigrade arrangements are made to ventilate the same with a current of air moving at a speed of not less than one meter per second.

CMR 173 Use of double copper coated steel tube delay detonators : Double copper coated steel tube coal delay detonators manufactured by M/s. IDL Chemicals ltd., have been provisionally approved for use in gassy seams of first degree. Although these detonators are provisionally approved for use in gassy seams of first degree, yet it is obligatory on the part of individual Mine Managements to obtain an exemption from the provisions of Reg. 173(b) of the CMR 1957 for the use if detonators other than copper tube detonators. You are, therefore, advised to obtain such exemption before using steel tube detonators of approved type. It is apprehended that using of steel tube detonators may constitute hazard in their handling and use. Adequate steps shall therefore be taken during storage of these detonators to obviate the risk of rusting. A competent person should examine these detonators before the same are issued for use. If any signs of rusting are noticed, the matter shall be reported to this Directorate and the concerned Director of Mines Safety. (Cir. Tech. 6/1981) CMR 175 1.

Testing for inflammable gas before blasting : In particular, the shorfirer should test carefully for inflammable gas the mouth of shot-hole (s). (Cir.1/1940)

2.

Use of clay plug at the back of a shot-hole : Wherever permitted explosives are used, plug of stemming shall be placed at the back of every shot-hole before it is changed. This provides an added precaution against the danger arising form the presence of a crack at the back of the holes, as such cracks are mot easy to detect. Of course, any hole in which a break has been found should not be charged as required by Reg. 175 (4) of CMR 1957.


Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING CMR Reg. 136 A TABLE : VELOCITIES OF VENTILATION Degree of Gassiness 1 [First, Second or Third Degree]

1

2

[First, Second]

Place where velocity of air is to be measured 2 Immediate out bye ventilation connection form the face. (i)

3 30

4.5 meters from any face whether working or discontinued on the in take side of the brattice or partition. 7.5 meters out bye of the discharge end of an air pipe. At the maximum span of 60 a long wall face.

30

4.5 meters from any face whether working or discontinued on the intake side of the brattice or partition. (ii) 7.5 meters out bye of the discharge end of an air pipe. (iii) At the maximum span of a long wall face.

45

(ii) (iii)

Third Degree

Velocity of air

(i)

15 60

25 75

CMR 161. Cartridges : (1) No explosives, other than a fuse or a detonator, shall be issued for use in a mine, or taken into or used in any part of a mine unless it is in the form or a cartridge. Cartridge shall be used only in the form in which they are received. (2)

The preparation of cartridges form loose gun power, the drying of gunpowder and the reconstruction of damp cartridges shall be d\carried out by a competent person and only in a place approved by the Licensing Authority and in accordance with the rules made under the Indian Explosives Act, 1884.

*1.

Bulk Explosives : As per clause (1) of Reg. 161 explosives for use in mines have to be in cartridge from only. But these days bulk explosives are used in large opencast mines for which exemption has to be sought. Further, in deep hole blasting the primary charge is often non sensitive necessitating use of a booster. Thus more than one type of explosives is used in the same shot hole fir which relaxation has to be obtained from the provisions of Reg. 168 (5). Use of explosives form two different manufactures in the same blast should be avoided.

*2.

Sleeping Holes : In opencast mines using large quantity of explosives, it sometimes becomes necessary to allow the holes to sleep for which special exemption has to be obtained.

CMR 168 Drilling, charging, Stemming and Firing of Shot-Holes : (1) No drill shall be used for boring a shot-hole unless it allows a clearance of at least 0.3 centimeters over the diameter of the cartridge of Explosives, which it is intend to use. (2) No shot hole shall be charged before it is thoroughly cleaned. 47 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING (3) Before any shot hole is charged, the direction of the hole shall, where practicable, be distinctly marked on the roof or other convenient place. (4) No detonator shall be inserted into a priming cartridge until immediately before it is to be used; so however that in case of wet workings, priming cartridge may be prepared at the nearest convenient dry place; and such primed cartridges shall be carried to the working place in a securely closed case or container, Detonators once inserted into a priming cartridge, shall not be taken out. (5) The change in any shot hole shall consist of one or more complete cartridges of the same diameter and the same type of Explosives. (6) The shot-firer shall, to the best of his judgment, ensure that no charge in a shot hole is overcharged or under charged, having regard to the task to be performed. (7) No shot shall be fired by use less than 1.2 meters in length (8) Every shot hole shall be stemmed with sufficient and suitable non-inflammable stemming so as to prevent the shot the blowing out. Only sand loosely filled in or soft clay lightly pressed home, or a compact mixture of sand and clay, or water, shall be used as stemming. In no case shall coal dust be used for purpose of stemming. (9) In charging or stemming a shot hole, no metallic tool, scraper or rod shall be used; and no explosives shall be forcibly pressed into a hole insufficient size. (10) No shot shall be fired except in a property drilled, charged and stemmed shot hole. (11) Blasting galantine or other high explosives shall be lighted in order to set fire to fuses. CMR 170. *1.

Danger zone in opencast mines : The need for increasing the Danger Zone from 300 m to 500 m, or even more has been highlighted by the DGMS in (Cir. Tech. 8/1982). In permissions, the Directorate now gives danger zone as 500 m.

*2.

Controlled blasting near built up areas : When the entire area of 500 m from the site of blasting cannot be got vacated, the shots have to be fired by controlled blasting technique with action detonators/detonating relays or be muffled in a manner such that flying fragments do not project beyond a distance of ten meters from the place of blasting. For controlled blasting and for muffled blasting approval has to be obtained from the regional inspector.

*3.

Accidents due to blown though shots : The over man incharge of the district, who carries a hand plan, has to forewarn the shot firer in writing to take necessary precautions when the face being blasted approaches within 10 meters of any other face/working/roadway [DGMS Cir.Tech.16/1982]. The other face/workings/roadway has to be kept fenced while charging/blasting [DGMS Cir.Tech.6/1983]. Apart from the shot firer, the mining sider of the district should also see that all persons in the vicinity of shot firing, including those in direct line of the approaching galleries, are withdrawn and all approaches suitable fenced [DGMS Cir.Tech.1/1977]. Precautions have also to be taken against dangers form projectiles through long exploratory boreholes, viz., withdrawal of persons form the other end and fencing etc. [DGMS Cir.Tech.15/1982].

CMR 172 : Conditions requiring use of permitted Explosives: (1) Notwithstanding anything contained in the regulations, to or more shots shall not be charged or fired in the same place simultaneously below ground if the Explosive used is not Permitted Explosive, except in: (a) A stone –drift, if it does not contain dry coal dust: or (b) A shaft, which is in the course of being sunk. (2)

In gassy seams of second or third degree no explosives other than permitted sheathed explosives or other explosives equally safe or any device or apparatus for breaking coal approved by the chief Inspector shall use while in gassy seams of the first degrees permitted sheathed explosives or any device for breaking coal approved by Chief Inspector in writing may be used:


Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING Provided that the Chief Inspector may, by an order in writing and subject to conditions as he may specify therein, permit in gassy seam of the first degree the use of any explosive other than permitted explosive CMR 173. Precautions in the use of permitted explosivesIn any mine in which use of permitted explosive is required : (a) No shot shall fired in coal mines unless: (i) The coal has been undercut, over cut or side cut ; and (ii) The length of the shot hole is atleast 15 centimeters less than the depth of the cut (b) No detonator shall be used, unless it is an electric detonator with copper tube (c) Where more shots than one are charged for firing, the shots shall be fired simultaneously: and (d) The aggregate charge in any shot to be fired in coal shall not exceed such permissible maximum charge, as the Chief Inspector may, by a notification in the official gazette, lay down for the kind of permitted explosives used. Solid Blasting : Solid blasting is permitted in gassy seams of first and second degree only. Aspects considered are standard of ventilation, availability of methanometers, arrangements for treatment of coal dust including permanent source of water supply and provision of stone dust barriers, training of staff, possibility of emission of gas due to presence of fault, dyke or other geological disturbances, any history of blowers etc. However, special conditions such as horizon mining (where the heading machines cannot be used due to special circumstances), solid blasting may be permitted if in coal laterals or in chimneys atleast 300-600 cu. m. per minute of air, depending upon the dimensions of the drivage and rate of emission of gas can be ensured at the face. Some of the precautions required may be as fallows: Total delay interval between first and last shot in a round should not exceed 100 mile seconds (0.1 second); proper arrangements shall be made for treatment of coal dust at and within 90 meters of the site of blasting; 5 stone dust barriers shall be provided; blasting operations shall be supervised by an assistant manager; advance bore holes, atleast 1.5 meters longer than drill holes shall be made to detect geological disturbances. Local methane detector (LMD) in working order and set to give an alarm when gas exceeds 0.5% shall be provided; no solid blasting can be done when a geological disturbance has been detected or methane exceeds 0.5%. CMR 175 - Additional precautions in gassy mine –In any gassy seam the following additional precautions shall be taken – (1) If in a ventilating district, presence of inflammable gas is detected in any place, no shot hole shall be charged, stemmed or fired in that place or in any place situated on its return side till such place has been cleared of gas and declared safe. (2) Immediately before charging a shot-hole or a round of shot-holes, and again before firing the shots, the shot-firer shall carefully test for inflammable gas at all places within a radius of 18 meters of the place of firing. (3) No shot hole shall be charged if any break is found therein or if inflammable gas is found issuing there from. (4) If after charging a shot hole, inflammable gas is found in any place within the prescribed radius, no shot shall be fired until the place has been cleared of gas and declared safe. (5) No delay action detonator shall be used, except with the previous permission in writing of the Chief Inspector and subject to such conditions as he may specify therein. CMR 176. Inspections after shot firing : After a shot has been fired the shot-firer shall not enter or allow any other person to enter the place until the atmosphere in the area is free from dust, smoke or fumes. He shall, before any other person enters the place, make a careful examination and with his assistants, if any, make the place safe. No other person shall enter the place, and where guards have been posted they shall not be withdrawn, until the examination has been made and the place has 49 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING been declared safe in all respects. In the case of opencast workings, after shots have been fired, an all-clear signal shall be given except in the case of a misfire. CMR 177. Misfires : (1) The number of shots which explode shall, unless shots are fired electrically, be counted by shot firer and any other competent person authorised for the purpose, and unless it is certain that all the shots have been exploded, no person shall be re-entered or be permitted to re-enter the place until 30 minutes after the firing of shots:

(2)

(3) (4) (5)

(6)

(7)

(8)

(9)

Provided that the shots are fired electrically, this interval may be reduced to not less than 5 minutes after the source of electricity has been disconnected from the cable. In the event of a misfire, the entrance or entrances to the working place shall be fenced so as to prevent inadvertent access, and no work other than that of locating or relieving the misfired hole shall be done therein until the misfire has been located and relieved. In opencast workings, it shall be sufficient to mark the place of the misfire with a red flag. In the event of a misfire, a second charge shall not be placed in the same hole. If the misfire contains a detonator, the leads or fuse there of shall be attached by a string to the shot-firing cable or some distinctive marker. Except where the misfire is due to a faulty cable or a faulty connection and the shot is to be fired as soon as practicable after the defect is remedied, another shot shall be fired in a relieving hole which shall be so placed and drilled in such a direction that at no point shall it be nearer than 30 centimeters from the misfired hole. The new hole shall be bored in the presence of shot-firer, preferably the same person who fired the shot. After a relieving shot has been fired, a careful search cartridge or detonators, if any, shall be made in the presence of the shot-firer, amongst the material brought down by the shot. Provided that, in case of workings below -ground if such cartridge or detonator is not recovered, the tubs into which the material is loaded shall be marked and further search made on the surface. As far as possible, the search for the detonators and cartridges and the loading of any coal, stone or debris that may contain detonator, shall be carried out without the aid of tools. If the misfired hole is not dislodged by a relieving shot, the procedure laid down in sub regulation (5) and (6) above shall be repeated. A misfired hole which cannot be dealt with in the manner so prescribed, shall be securely plugged with a wooden plug and no person other than a shot-firer, an official or a person authorised for the person shall remove or attempt to remove any such plug. When a misfired shot is not found or when a misfired shot is not relieved, the shot-firer shall before leaving the mine, give information of the failure to such shot-firer or officials as may relieve or take over charge from him. He shall also record, in a bound paged book kept for the purpose, a report on every misfire, whether suspected, and whether the shot hole is relieved or not relieved. It shall be the responsibility of the relieving shot firer or official also to sign the report and to record in the said book the action taken for relieving the misfired shot-hole. The shot-firer of the next shift shall locate and blast the misfire hole, but if after a thorough examination of the place, the place where the misfire was reported to have occurred, he is satisfied that no misfire has actually occurred, he may permit drilling in the place.

CMR 180 - General precautions regarding explosives. (1)

No person, whilst handling explosives or engaged or assisting in the preparation of charges or in the charging of holes, shall smoke or carry or use a light other than an enclosed light, electric torch or lamp: Provided that, nothing in this sub-regulation shall be deemed to prohibit the use of an open light for lighting fuses. (1)

No person shall take any light other than an electric torch or an enclosed electric lamp into any explosive magazine or store or premises. 50 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING (a) The owner, agent or manager shall take adequate steps to prevent pilferage of explosives during its storage, transport and use in the mine. (b) No person shall have explosives in his possession except as provided for in these regulations or keep explosives in a dwelling house. (2) Any person finding any explosives in or about a mine shall deposit the same in the magazine or stores or premises. Every such occurrence shall be reported to the manager in writing. PRECAUTIONS FOR USE OF SLURRY EXPLOSIVES IN OPENCAST MINE 1. 2. 3. 4.

5. 6. 7.

8. 9. 10. 11. 12. 13. 14. 15. 16.

Slurry explosives of only one manufacture shall be used in one blast hole and as far as possible in one blast. All boulders formed as a result of earlier blast, which cannot be handled by excavator/shovel etc., shall be blasted or removed from the mine before next deep hole blast in the mine. (a) Slurry Explosives shall be used in order of their date of manufacture. (b) Explosives manufactured earlier than six month shall not be used. (a) Smoking, naked lights or open flame shall not be allowed in the vicinity of the explosives. (b) No person when charging or handling the slurry explosives shall allow smoking, naked light or fire within 10m. of shot holes or the explosives. Broken and discarded empty bag of slurry explosives can be cleaned up and properly disposed off daily in a safe manner, such as by burning in an isolated place or burying. The slurry explosives when transported in vehicles shall be carried in an Explosives Van approved by the Chief Controller of Explosives (a) The Explosives Vans used for the transport of slurry explosives shall be in safe operating condition and should be driven by competent licensed drives. (b) The vans shall be kept in isolated locations while loaded. (c) The vans shall be well locked except during times of placement and removal of stocks of slurry explosives. (d) No smoking and no open flames shall be permitted in our near the vans containing explosives. (e) The area surrounding the vans (when used of emporary) storage not less than 10m., in all directions shall be kept free of rubbish, dry leaves of other materials of combustible nature. (f) Normally not more than day's requirement of slurry explosives shall be permitted to be temporarily stored in the vans at any one time. All detonators and priming cartridges shall be kept in secure receptacles at a safe distance from the detonating fuse and the Explosives until actually required for use. The cases of slurry explosives shall not be opened unless the holes are ready for charging in every respect. The holes shall be charged and fired as soon as possible after the explosives is transported to the blasting. All normal precautions for charging as laid down. Charging of explosives shall be such as to ensure continuity of the explosives column. Where deck charging is done, continuity shall be ensured for each check of explosives charge. Explosives cartridges shall not be split or performed. Adequate amount of cap sensitive explosives shall be used with non-cap sensitive charge to ensure complete detonation of the explosive charge. Before entering an area after blasting the blaster/shot firer and other personal shall make certain that the place is clear of dust and fumes and is safe in every respect. In case of misfires, precautions as laid down in the regulation 177 of the Coal Mines Regulations, 1957 shall be taken. The entire operations of transport of the explosives to the site of its use, and charging and blasting shall be placed under the overall charge of a competent person holding manager's certificate or such other qualifications as may be approved by the Director General of Mines Safety, and appointed in writing by the manager for the purpose.


Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING DGMS (India) CONDITIONS FOR USE FO BULK EXPLOSIVES U/R 161(1) AND 168(5) OF CMR 1957. 1. 2. 3.

4. 5. 6. 7.

8. 9. 10. 11. 12. 13. 14. 15.

The operations of making site mixed emulsion explosives charging and firing of shot holes shall be carried out under the super vision of Technical Officer of Manufacturer. General precautions and normal rules regarding handling and use of explosives shall be in a safe operating conditions and should be driven by competent licensed drivers. (a) Pump truck carrying constituents of emulsion explosives shall be in a safe operating conditions and should be driven by competent licenced drives. (b) The pump truck shall be kept in isolated location while loaded. (c) No smoking and no open flames shall be permitted within 60m. of the pump truck. (d) The area surrounding truck not less than 10m in all directions shall be kept free of rubbish, dry leaves or other materials or combustible nature. Only necessary minimum number of persons shall be allowed during charging and firing of shot holes. Due care shall be taken to ensure that the explosives is pumped only into proper-drilled shot holes and that there is no spilling of explosives. A proper record shall be kept of the quantity of explosives charged in every shot holes and that fired in a around of shots. (a) All detonators and priming cartridges shall be kept in secure receptables at a safe distance from the detonating fuse and the explosives until actually required for use. (b) Detonators/detonating, fuse shall not be carried in the same truck/van. The Explosives charges shall not be allowed to sleep over in bore holes unless express permission in writing to that effect has been obtained. The holes shall be charged and fired as soon as possible after the explosive is transported to the site of blasting. All normal precautions for charging and firing as laid down in the regulations shall be strictly observed. Charging of explosives shall be such as to ensure continuity of the explosives column. Where deck charging is done, continuity shall be ensured for each deck of explosive charge. Primer explosives cartridge shall not be split or deformed. Adequate amount of cap sensitive explosive shall be used with non-cap sensitive explosive charge to ensure complete detonation of the explosive charge. Before entering as area after blasting, the shot firer and other personal shall make certain that the place is clear of dust and safe in every respect. In case of misfires, precautions as laid down in the Reg. 177 of the CMR, 1957 shall be taken The entire operations of transport of the explosives to the site of its used charging and blasting shall be placed under the overall charge of a competent person holding Managers Certificates and appointed in writing by the Manager for the purpose. EXTRACT OF INDIAN EXPLOSIVE RULES 1983 THE STORAGE AND TRANSPORT OF EXPLOSIVES

The storage and transport of explosives is governed by the Explosives Rules, 1983. It is important that all users of Explosives are familiar with the rules, and ensure that they are not infringed. Storage Explosives can be stored only in a specially constructed magazine duly licence by the Chief Controller of Explosives, Government of India. A. Maintenance and Operation of Magazine : Certain important recommendations are given below : 1. Magazine should be kept scrupulously clean and overshoes should be provided for use inside. Dirty shoes must not be taken inside. 2. Persons entering the magazine should be searched for cigarettes/matches or other inflammable material. 3. Tools for opening explosives boxes must be of wood, brass, and copper of borzes; use of tools made of iron, steel or other sparking materials etc. 52 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING 4. Empty boxes, loose packing materials etc. should not be kept in the magazine. 5. Area surrounding the magazine should be kept free of 'inflammable' material; to avoid 'bush fires', undergrowth and vegetation should be trimmed regularly. 6. Magazine should be well ventilated; it is advisable to keep the magazines open for at least one hour everyday. 7. Strict records of 'receipt' and 'issue' of explosives should be maintained and stocks issued on a 'First in - First out' basis. 8. Cases should be stacked on trestles and a 15cm air space should be allowed between the cases and the walls for free circulation of air. Cases should not be stacked more than 3 m high and should be so arranged that their date of manufacture is always visible. Stocks should be physically checked periodically to ensure that they are in good conditions. 9. Magazines should be securely locked and well guarded at all times. 10. Magazine buildings should be kept in a good state of repair while undertaking repairs, explosives should be removed from the magazines to some other approved place of storage. 11. General rules governing conduct in the magazine such as use of overshoes, prohibiting smoking etc., should be posted outside. A copy of the licence and the lighting conductor test certificate should also be kept in the magazine. A warning sign for tespassers should be displayed outside. 12. The design of the magazine should be such that there is an internal volume of not less than 0.4 cu m per 100 per kg of explosives stored. B. Storage of Different Classes of Explosives : Under the Indian Explosives Rules, the various explosives and accessories are classified under separate under separate headings : Class 1 Gunpowder Class 2 Nitrate Mixtures Class 3 Nitro compounds Div.1 Blasting Gelatine, Special Gelatine, Opencast Gelatine, Belgex, etc. Div 2 Pentolite, Primers, Gun, Cotton, PETN, TNT Class 4 Chlorate Mixtures Class 5 Fulminate Class 6 Ammunition Div 1 Safety Fuse, Fog Signals, Igniter Cord Connectors, Electric Lighters, Safety Electric Fuses, Percussion Caps, Safety Cartridges for small arms. Div 2 Plastic Igniter Cord, 'Cordtex' detonating Fuse, Electric Fuses, Fuse Igniters. Div 3 Detonators, Delay Detonator Relays. Class 7 Fireworks Class 8 LOX Under the Indian Explosives Rules, the following can be stored together in the same magazine : Gunpowder Class 1 Nitrate Mixture Class 2 Nitro compounds Class 3 Chlorate Mixture Class 4 Safety Fuse Class 6 Div.1 Cordtex Det Fuses, Plastic Igniter Cord Class 6 Div.2 On no account must detonators be stored together with the above. Normally, detonators are stored in a separate building, but if the number of detonators does not exceed 44,000 it is permissible to store them in a propertyconstructed annex attached to the main magazine.



SOME LICENCES RELATING TO STORAGE / HANDLING / USE OF EXPLOSIVES (Extra from the Indian Explosives Rules, 1983, Schedule IV) Article No. 1 (a)

Form of Licence 20

1 (b)

20

1 (c)

20

1 (d)

38

1 (e) 2 (a)

39 21

2 (B)

21

3 (a)

22

3 (b)

22

4 (a)

24

5 (a)

23

5 (b)

23

5 (c)

23

6 7 8 9

27 28 26 25

11

Special

Purpose for which granted To manufacture Explosives other than Fire works, Gunpowder, ANFO at site and Liquid Oxygen Explosives. To manufacture Fire works and Gunpowder upto 200 kg. at a time. To manufacture Fire works and / or Gunpowder more than upto 200 kg. at a time. To manufacture ANFO Explosives at site

To manufacture Liquid Oxygen Explosives To possess for Sale Explosives not exceeding 2000 kg Class 1,2,3,4 & 7 together with Explosives of Class 6. To possess Sale Explosives exceeding 2000 kg of Class 1,2,3,4 & 7 and any quantity of Class 5, 6 and 8. To possess for use Explosives not exceeding 2000 kg of Class 1,2,3,4 & 7 together with Explosives of Class 6. To possess for use Explosives not exceeding 2000 kg of Class 1,2,3,4 & 7 and any quantity of Class 5, 6 and 8. To possess and sell from a shop Gunpowder and or small arms Nito-Compound not exceeding 25 kg or fireworks not exceeding 100 kg of Class 7 Division 2 Sub Division 2, 1000 kg of Class 7 Division 2 Sub-Division 1 of safety fuse not exceeding 10000 meters. To possess for own use Class 2 and / or Class 3 Explosives not exceeding 5 kg, electric ordinary detonators not exceeding 100 numbers and safety fuse not exceeding 200 meters. To possess for use small arms Nito-Compound not exceeding 5 kg in the State of Kerala To possess for use Gunpowder not exceeding 5 kg and safety fuse not exceeding 50 meters in the state of Bihar, Kerala and West Bengal To Importer Explosives To Export Explosives To Transport Explosives For Road Van To Manufacture Explosives not provided in Article 1.

Authority empower to grant Licence Chief Controller

Controller of Explosives Authorised by Chief Controller Chief Controller Controller of Explosives Authorised by Chief Controller Chief Controller Chief Controller Chief Controller Controller of Explosives Authorised by Chief Controller Chief Controller Controller of Explosives Authorised by Chief Controller

District Authority

District Authority District Authority

Chief Controller Chief Controller Controller of Explosives Controller Authorised by Chief Controller Chief Controller


Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING " DO'S AND DON'TS" Definitions 1. 2. 3. A.

The term "Explosives" as used herein includes any or all of the following: dynamite, black blasting powder, pellet powder, blasting caps, electric blasting caps and detonating fuse. The term "Electric Blasting Cap" as used herein includes both instantaneous electric blasting caps and all types of delay electric blasting caps. The term "Primer" as used herein means a cartridge of explosives in combination with a blasting cap or an electric blasting cap. When Transporting Explosives 1. 2.

3. 4. 5. 6. 7. 8. 9. B.

DO obey all laws and regulations. DO see that any vehicle used to transport explosives is in proper working condition and equipped with a tight wooden or non-sparking metal floor with sides and ends high enough to prevent the Explosives from falling off. The load in an open-bodied truck should be covered with a waterproof and fire-resistant tarpaulin, and the Explosives should not be allowed to contact any source of heat such as an exhaust pipe. Wiring should be fully insulated so as to prevent short-circuiting, and at least two fire extinguishers should be carried. The truck should be plainly marked so as to give adequate warning to the public of the nature of the cargo. DON'T permit metal, except approved metal truck v\bodies, to contact cases of explosives. Metal, flammable, or corrosive substances should not be transported with explosives. DON'T allow smoking or unauthorized or unnecessary persons in the vehicle. DO load and unload Explosives carefully. Never throw Explosives from the vehicle. DO see that other Explosives, including detonating fuse, are separated from blasting caps and/of electric blasting caps where it is permitted to transport them in the same vehicle. DON'T drive trucks containing explosives through cities, towns or villages, or park them near such places as restaurants, garages and filling stations, unless it cannot be avoided. DO request that explosives deliveries be made at the magazine or in some other location well removed from populated areas. DON'T fight fires after they have come in contact with explosives. Remove all personnel to a safe location and guard the area against intruders.

When storing Explosives 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

DO store explosives in accordance with laws and regulations. DO store explosives only in a magazine which is clean, dry, well ventilated, reasonably cool, properly located, substantially constructed, bullet and fire resistance and securely locked. DON’T store blasting caps or electric blasting caps in the same box, container or magazine with other explosives. DON’T store explosives, fuse, or fuse lighters in a wet or damp place, or near place, or near oil, gasoline, cleaning solution or solvents, or near radiators, steam pipes, exhaust pipes, stoves, or other sources of heat. DON’T store any sparking metal, or sparking metal tools in an explosives magazine. DON’T smoke or have matches, or have any source of fire or flame in or near explosives magazine. DON’T allow leaves, grass, brush, or debris to accumulate within 25 feet of an explosives magazine. DON’T shoot into explosives or allow the discharge or firearms in the vicinity of an explosives magazine. DO consult the manufacturer if nitroglycerin from deteriorated explosives has leaked onto the floor of a magazine. The floor should be desensitized by washing thoroughly with an agent approved for that purpose. DO locate explosives magazines in the most isolated places available. They should be separated from each other, and from inhabited buildings, highways, and railroads, by distances not less then those recommended in the American Table of Distances.


Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING C. When using Explosives 20. DON’T use sparking metal tools to open kegs or wooden cases of explosives. Metallic slitters may be used for opening fiberboard cases, provided that metallic slitter does not come in contact with the metallic fasteners of the case. 21. DON’T smoke or have matches, or any source of fire or flame, within 100 feet of an area in which explosives are being handed or used. 22. DON’T place explosives where they may be exposed to flame, excessive heat, sparks or impact. 23. DO replace or close the cover of explosives cases or packages after using. 24. DON’T carry explosives in the pockets of your clothing or elsewhere on your person. 25. DON’T insert anything but fuse in the open end of blasting caps. 26. DON’T strike, tamper with or attempt to remove or investigate the contents of blasting caps, or try to pull the wires out of an electric blasting cap. 27. DON’T allow children or unauthorized or unnecessary persons to be present where explosives being handled or used. 28. DON’T handle use, or be near explosives during the approach or progress of any electrical storm. All persons should retire to a place of safety. 29. DON’T use explosives or accessories equipment that are obviously deteriorated or damaged. 30. DON’T attempt to reclaim or to use fuse, bleating caps, electric blasting caps, or any explosives that have been water soaked, even if they have dried out. Consult the manufacturer. D. When Preparing The Primer 31. 32. 33.

E.

DON’T make up primer in a magazine, or near excessive quantities of explosives, or in excess in immediate needs. DON’T force a blasting caps or an electric blasting caps into dynamite. Insert the cap into a hole made in the dynamite with a punch suitable in the purpose. DO make up primes in accordance with proven and established methods. Make sure that the cap shell is completely encased in the dynamite or booster and so secured that in loading no tension will be placed on the wires or fuse at the point of entry into the cap.

When Drilling and Loading 34. 35. 36. 37. 38. 39. 40.

41. 42. 43. 44. 45.

DO comply with applicable regulations relative to drilling and loading. DO carefully examine the surface or face before drilling to determine the possible presence of unfired explosives. Never drill into explosives. DO check the borehole carefully with a wooden tamping pole or a measuring tape to determine its condition before loading. DO recognize the possibility of static electrical hazards from pneumatic loading and take adequate precautionary measures. If any doubt exists, consult your explosives supplier. DON’T stack surplus explosives near working areas during loading. DO cut from the spool the line of detonating fuse extending into a borehole before loading the remainder of the charge. DON’T load a borehole with explosives after springing (enlarging the holes with explosives) or upon complication of drilling without making certain that it is cool and that it does not contain any hot metal, burning or smoldering material. Temperature in excess of 150 F is dangerous. DON’T spring a borehole near another hole loaded with explosives. DON’T force explosives into a borehole or through obstruction in a borehole. Any such practice is particularly hazardous in dry holes and when the charge is primed. DON’T slit, drop, deform or abuse the primer. DON’T drop a large size, heavy cartridge directly on the primer. DO avoid placing any unnecessary part of the body aver the borehole during loading. DON’T load any borehole near electric power lines unless the firing line, including the blasting cap wires, is so short it cannot reach the power wires. 56 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING 46. DON’T connect blasting caps, or electric blasting caps, to detonating fuse except by methods recommended by the manufacturer. F.

When Tamping 47. 48.

49. 50.

DON’T tamp dynamite that has been removed from the cartridge. DON’T tamp with metallic devices of any kind, including the metal end of loading the metal end of loading poles. Use wooden tamping tools with no exposed metal non-sparking metal connectors for joint poles. Avoid violet tamping. Never tamp the primer. DO confine the explosives in the borehole with sani, earth, clay or other suitable incombustible stemming material. DON’T kink or injure fuse, or electric blasting cap wires, when tamping.

G. When Shooting Electrically 51. 52.

53. 54. 55. 56.

57. 58. 59.

DON’T uncoil the wires or use electric blasting caps during dust storms or near any other source of large charges of static electricity. DON’T uncoil the wires or use electric blasting caps in the vicinity in of radio frequency transmitters, except at safe distances. Consults the manufactures or the institute of makers of explosives pamphlet on “Radio Frequency Hazards.” DO keep the firing circuit completely insulated from the ground or other conductors such as bare wires, rails, pipes or other part of stray currents. DON’T have electric wire or cables of any kind near electric blasting caps or other explosives except at the time and for the purpose of firing the blast. DO test all the circuit blasting caps, either single or either connected in a series circuit, using only a blasting galvanometer specifically design for the purpose. DON’T use the same circuit either electric blasting caps made by more then one manufacturer, or electric blasting caps of different style or function even if made by the same manufacturer, unless such use is approved by the manufacturer. DON’T attempt to fire a single electric blasting cap or a circuit of electric blasting caps with less then the minimum current specified by the manufacturer. DO be sure that all the wire ends to be connected are bright and clean. DO keep the electric cap wires or leading wires short-circuited until ready to fire.

H. When Shooting With Fuse 60. 61. 62.

63. 64.

65. 66. I.

DO handle fuse carefully to avoid damaging the covering. In cold weather warm slightly before using the avoid cracking the waterproofing. DON’T use the short fuse. Know the burning speed of the fuse and make sure you time to reach the place of safety after lighting. Never use less then two feet. DON’T cut fuse until you are ready to insert it into a blasting cap. Cat of an inch or two to ensure a dry end. Cut fuse squarely across with sharp blade. Seat the fuse lightly against the cap charge and avoid twisting after it in a place. DON’T crimp blasting caps by any means except a cap crimper designed for the purpose. Make certain that the cap is securely crimped to the fuse. DO light fuse with a fuse lighter designed for the purpose. If a match is used the fuse should be slit at the end and the match head held in the slit against the powder core. Then scratch the match head with an abrasive surface to light fuse. DON’T light fuse until sufficient stemming has been placed over the explosive to prevent sparks or flying match heads from coming into correct with the explosive. DON’T hold explosives in the hands when lighting fuse.

Underground Work 67.

DO use permissible explosives only in the manner specified by the Director General of Mines Safety. 57 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING 68. DON’T take excessive quantities of explosives into a mine at any one time. 69. DON’T use black blasting powder or pellet powder with permissible explosives or dynamite in the same borehole in a coal mine. J.

Before and After Firing 70.

71. 72. 73.

DON’T fire a blast without a positive signal from the one in charge who has made certain that all surplus explosives are in a safe place, all persons and vehicles are at a sage distance or under sufficient cover and that adequate warning has been given. DON’T return to the area of any blast until the smoke and fumes from the blast have been dissipated. DON’T attempt to investigate a misfire too soon. Follow recognized rules and regulations or if no riles of regulations are in effect, wait at least one hour. DON’T drill, bore, or pick out a charge of explosives that has misfired. Misfires should be handled only by or under the direction of a competent and experienced person.

K. Explosives Disposal 74. 75. 76. 77.

DON’T abandon any explosives. DO dispose of or destroy explosives in strict accordance with approved methods. Consult the manufacturer or DGMS pamphlet measures on destroying explosives. DON’T leave explosives, empty cartridges, boxes, liners, or other materials used in the packing of explosives lying around where children or unauthorized persons or livestock can get at them. DON’T allow any wood, paper, or any other materials employed in packing explosives to be burned in a stove, a fireplace, or other confined space, or to be used for any purpose. Such materials should be destroyed by burning at an isolated location out of doors and no person should be nearer than 100 feet after the burning has started.

*********************************************************************************************

Author’s Bio-data: Partha Das Sharma is Graduate (B.Tech – Hons.) in Mining Engineering from IIT, Kharagpur, India (1979) and was associated with number of mining and explosives organizations, namely MOIL, BALCO, Century Cement, Anil Chemicals, VBC Industries, Mah. Explosives etc., before joining the present organization, Solar Group of Explosives Industries at Nagpur (India), few years ago. Author has presented number of technical papers in many of the seminars and journals on varied topics like Overburden side casting by blasting, Blast induced Ground Vibration and its control, Tunnel blasting, Drilling & blasting in metalliferous underground mines, Controlled blasting techniques, Development of Non-primary explosive detonators (NPED), Hot hole blasting, Signature hole blast analysis with Electronic detonator, Signature hole blast analysis for control of blast induced vibration etc. Currently, author has following useful blogs on Web:

• • • •

http://miningandblasting.wordpress.com/ http://saferenvironment.wordpress.com http://www.environmentengineering.blogspot.com www.coalandfuel.blogspot.com

Author can be contacted at E-mail: [email protected], [email protected], ---------------------------------------------------------------------------------------------------------Disclaimer: Views expressed in the article are solely of the author’s own and do not necessarily belong to any of the Company. *** 58 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

Explosives and Blasting

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