Lightning strike is a natural phenomenon of sudden discharge of charges from highly concentrated cloud or any objects. Lightning cannot be avoided but the damages can be reduced by proper preventive measures.
IS/IEC 62305 part 2 explains about the damages due to lightning strikes, sources of such damages, Losses due to lightning and the corresponding risks. In this article, we shall explore about the risk management process as specified by IS/IEC 62305 part 2.
IS/IEC 62305 describes the risk components for each source of damage. When calculating the risk, the risk components of same category due to different sources should be grouped together.
The risk component also depends on the nature of the structure and its purpose. For highly sensitive areas like hospitals and storage of explosives, the lightning strikes near the structure or near the line connected to the structure may also result in loss of human life.
The summary of risk components associated with each type of loss is as follows.
Picture Source: IS/IEC 62305-2
IS/IEC 62305 part 2 explains the basic procedure for evaluating the risks associated with the
structure to be protected.
1) Identify the characteristics of the structure to be protected.
2) Identify all the losses (L1 to L4) for the structure due to lightning and the corresponding risks (R1 to R4).
3) Evaluate the risk (R1 to R4) by calculating the corresponding risk components for each type of risks.
4) Compare the values R1, R2 and R3 with the tolerable risk Rt for evaluating the need of protection.
5) Evaluate the cost effectiveness of protection by comparing the costs of total loss with and without protection measures. The risk R4 shall be used for evaluating the cost effectiveness.
The following procedures shall be followed to evaluate the each risk (R1 to R3).
• Identify the components (Rx) of the risk.
• Calculate the individual risk components.
• Calculate the total risk (R).
• Identify the tolerable risk (Rt) limit.
• Compare the calculated risk value (R) with the tolerable risk (Rt).
o If R ≤ Rt , then lightning protection is not necessary.
o If R > Rt, protection measures shall be adopted
Each risk component RA, RB, RC, RM, RU, RV, RW and RZ shall be expressed by the following general
RX = NX * PX * LX
NX - number of dangerous events per annum;
PX - probability of damage to a structure;
LX - consequent loss.
The number of dangerous events (NX) depends on the lightning ground flash density (NG) and the physical characteristics of the structure to be protected, lines connected to the structures to be protected and the type of soil.
The probability of damage (PX) depends on the characteristics of the structure to be protected, the connected lines and the protection measures provided.
The consequent loss (LX) depends on the purpose and contents of the structure, the type of service provided to public, the value of goods affected by the damage and the measures provided to limit the amount of loss.
For evaluating the risk associated with a structure, the following points have to be considered.
• The structure to be protected.
• Installations on the structure.
• Contents of the structure.
• Persons in the structure and in the zones up to 3m from outside the structure to be protected.
• Environment affected by damages to the structure.
The assessment of each risk components as per IS/IEC62305 part 2 is as follows.
Picture Source: IS/IEC 62305-2