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As per NFPA 780, how would you calculate lightning risk assesment for a building?

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Question added by Muhammad Qasim , Senior Electrical Engineer , Energy Associates (SMC Ptv.) Ltd.
Date Posted: 2016/08/16
Ahmad Khalil
by Ahmad Khalil , Middle East Project Supervisor , Pladis Group - FMC Ulker

First :

Nd = (Ng) * (Ae) * (C1)

where

Nd = lightning strike frequency

Ng = yearly average flash density in a region

Ae = equivalent collective area of the structure in km2 , or LW + 6H (L+W) + 9H2

C1 = environmental coefficient

Second :

Nc = (1.5x10-3) / C

where

C = (C2) * (C3) * (C4) * (C5)

C2 is the structural coefficient, from 0.5 to 3.0 and based on the contents of the structure (metal, nonmetallic or flammable) and the content of the roof (metal, nonmetallic or flammable)

C3 is a coefficient based on the value of the contents in the structure, their flammability and whether they are replaceable. This value can range from 0.50 to 4.00.

C4 is the coefficient of the occupancy of the structure. The choices for this value are unoccupied, normally occupied and difficult to evacuate or risk of panic. These values can range from 0.5 to 3.00.

C5 is the coefficient of the consequence of a lightning strike

Third

After the calculation of Nd & Nc if Nd is greater than Nc, then lighting protection is recommended. Otherwise, protection is optional. 

Mahmoud Zaher Tarakji
by Mahmoud Zaher Tarakji , مدير , أوال جاليري

....................sorry .............i am  not electric

Deleted user
by Deleted user

As per NFPA risk assessment calculator for a building, the lightning flash annual threat of occurence is calculated (Ng *A*C) and compared with tolerable lightning frequency. If the annual threat of occurence for lightning flash is more than the tolerable limit, then lightning protection method needs to be applied

In the above formula Ng is lightning flash density from map, A- area of collection, C - location factor

 

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