Lightning risk assessment

Complete probabilistic method

The assessment method described in NF EN 62305-2, IEC 62305-2 and NF C 17-102 standards is the most complete reference involving high number of parameters.

The basic method of this assessment lays in comparing the risk of a structure to a “tolerable”risk. If the level of risk on the structure is lower than the tolerable one, the structure is considered as “self-protected”, then if the risk is higher, the structure needs protection.

4 types of risks may be defined within lightning risk assessment according to NF EN 62305-2 standard :

R1 : Risk of human life casualty

R2 : Risk of public service loss

R3 : Risk of cultural legacy loss

R4 : Risk of economic values loss

Each type of risk is compared to a tolerable risk.

Risk 1 (main identified risk) is the sum of the included risks.

There are 4 levels of protection. Level 1 is the most severe.

simplified probabilistic method

UTE C 17-108 guide provides a simplified method of risk assessment. The method is called simplified because it includes only a limited number of parameters compared to the so-called complete method in EN 62305-2 standard. The other parameters were arbitrarily predetermined.

It is for this reason that this method only applies to structures :

  • where the fire risk is low or normal.
  • where the fire risk is high but the risk of panic is low.
  • which do not contain any product or explosive atmosphere.
  • which are safe for the environment.

The methodology for choosing the level of protection is then exactly the same as for the full method, i.e the level of protection is gradually increased until a lower tolerable risk is reached.


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