LIGHTNING PROTECTION RISK ASSESSMENT
Contents 1.0 1.1
2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10
3.0
INTRODUCTION ............................................................................................. 2 SCOPE ............................................................................................................................................. 2
LIGHTNING RISK ASSESSMENT STUDY ........................... ............ ............................. ......................... ........... 2 LIGHTING STRIKE DENSITY (NG) ................................................................................................... 2 DANGER FOR PEOPLE (H) ............................................................................................................. 2 OCCUPANCY COEFFICIENT (LF1) .............................................. ..................... ............................................... ............................................... .............................. ..... 2 RELATIVE LOCATION OF SITE (CD) ............................................................................................... 3 FIRE RISK (RF) ................................................................................................................................ 3 ASSOCIATED SERVICES (LF2) ....................................................................................................... 3 ELECTRICAL LINES (AI) .................................................................................................................. 3 LIGHTNING PROTECTION LEVEL (PD) ............................................... ...................... ............................................... ............................................ ...................... 4 SURGE ARRESTORS (PI) ................................................................................................................ 4 TOLERABLE RISKS (RT) ................................................................................................................. 4
CALCULATIONS ........................... ............. ............................ .......................... ........................... ............................. ......................... ........... 6
LIGHTNING PROTECTION RISK ASSESSMENT
1.0
INTRODUCTION
1.1
Scope This Document covers the Lightning Protection Risk Assessment Study.
2.0
LIGHTNING RISK ASSESSMENT STUDY Lightning Risk assessment Study is actually the measure of risk of a lightning strike and probability of damages. It assesses the lightening risks to the facility according to international standards requirements. These calculations are according to IEC Standard 62305-2. All these calculations are based on lightning strike density in that particular area ( provided by OMV i.e. Ng = 8), Danger for people, Occupation coefficient of structure, Relative location of site, Fire Risk, Associated services, Electrical Lines, Lightning Protection Level, Surge Arrestor and dimensions of installation. Brief introduction of all are given below.
2.1
Lighting Strike Density (Ng) It is the measure of lightning strikes per kilometre square per year in the particular area. Higher the lighting strike density, higher the probability of lightning strike which needs higher level of lightning protection level.
2.2
Danger for People (h) It is the factor of presence of people and panic in the building in case of a lightning strike.
2.3
No particular danger
1
Low panic level(<=2 floors, < 100 persons
2
Medium risk of panic (< 1000 persons)
5
Difficult to evacuate (disabled people, hospitals)
5
High risk of panic (> 1000 persons)
10
Hazard for surroundings or environment
20
Contamination of surroundings or environment
50
Occupancy Coefficient (Lf1) It is the risk reduction factor with respect to the occupancy of the building / installation. For example, loss due to lighting strike is higher in hospital as compared to a store / warehouse. Structure unoccupied
0.1
Structure normally occupied
0.01
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LIGHTNING PROTECTION RISK ASSESSMENT
2.4
Relative Location of Site (Cd) It is the risk reduction factor with respect to the location and surrounding of the building / installation. For example, chance of lighting strike is minimized if the building is near to a high tower.
2.5
Structure surrounded by higher objects or trees
0.25
Structure surrounded by similar or lower objects
0.5
Isolated structure-No other objects nearby
1
Isolated structure on top of a hill or a hillock
2
Fire Risk (rf) It is the risk reduction factor with respect to the flammability of the material present in the building / installation. For example, in case of lighting strike, loss will be very high at a gas station as compare to the cement store. Explosion
2.6
1
High
0.1
Ordinary
0.01
Low
0.001
Associated Services (Lf2) It is the risk reduction factor with respect to the services associated with the building. For example, a lightning strike at a power station will result a power break down which replicates the loss and disturbance. No
0
Gas, water
0.1
TV, Communication, Electricity, Radio
2.7
0.01
Electrical Lines (Ai) Presence of electrical lines increased the chance of lightning strike. For example, if lightning strike on the overhead line, line will transport this to installation. No
14400
Aerial
6600
Underground
0
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LIGHTNING PROTECTION RISK ASSESSMENT
2.8
Lightning Protection Level (Pd) Lightning protection level defines the kilo ampere rating of the lightning protection system, minimum distance between the lightning arrestors and density of protective mesh. None
2.9
1
Protection Level IV
0.2
Protection Level III
0.1
Protection Level II
0.05
Protection Level I
0.02
Surge Arrestors (Pi) These are the protective devices which blocks the surge from entering the installation premises. Normally installed at the incomer supply (main distribution box). These are used if the system is connected with over head lines. None
2.10
1
Necessary - I imp >= 12.5 kA
0.03
Necessary - I imp = 75/(m x n)
0.02
Necessary - I imp = 100/(m x n)
0.01
Tolerable Risks (RT) As a result of lightning protection risk assessment study, risk to human life, services and cultural heritage will be obtained in figures which must be lesser than tolerable risk (specified in codes and standards). The outcome of the study will then be used as a guide to select the level of lightning protection level to contain the risk with in tolerable limits. Tolerable Risk denoted by RT, is the maximum value of the risk which can be tolerated for the structure to be protected. As per IEC 62305-2, tolerable risks are as follows. Sr.
Type of Loss
1
RT1
Loss of human life
2
RT2
Loss of service to public
3
RT3
Loss of cultural Heritage
Sheet 4 of 6
Tolerable Risk 10Risk of 1 in 100,000 10Risk of 1 in 1,000 10Risk of 1 in 1,000
LIGHTNING PROTECTION RISK ASSESSMENT
As per IEC 62305-2, these risks can be calculated from given formulas. Tolerable Risk = Rd1 + Ri1 = (Nd x Pd x h x rf x Lf1) + (Ni x Pi x h x rf x Lf1) RT1
= ((Ng x Ad x Cd x 0.000001) x Pd x h x rf x Lf1) + ((Ng x Cd x Ai x 0.000001) x Pi x h x rf x Lf1) =Rd2 + Ri2 =(Nd x Pd x rf x Lf2) + (Ni x Pi x rf x Lf2)
RT2
=((Ng x Ad x Cd x 0.000001) x Pd x rf x Lf2) + ((Ng x Cd x Ai x 0.000001) x Pi x rf x Lf2) =Rd3 + Ri3 =(Nd x Pd x rf x 0.1) + (Ni x Pi x rf x 0.1)
RT3
=((Ng x Ad x Cd x 0.000001) x Pd x rf x 0.1) + ((Ng x Cd x Ai x 0.000001) x Pi x rf x 0.1)
Where, Ai
=
Electrical Lines
Ad
=
Collection area for flashes to an isolated structure
Cd
=
Relative Location of Site
‘h
=
Danger for People
Lf1
=
Occupancy Coefficient
Lf2 Pi
= =
Associated Services Surge Arrestors
Pd
=
Lightning Protection Level
Ng
=
Lighting Strike Density
rf
=
Fire Risk
Sheet 5 of 6
LIGHTNING PROTECTION RISK ASSESSMENT
3.0
CALCULATIONS Excel Sheet
Sheet 6 of 6
