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Risk Assessment for Effective Risk Management as per IS/IEC 62305-2

May 25,2016

Published in IEEME Journal, December 2015
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Lightning is one of the biggest threats to mankind and animals apart from property loss. When there is a threat, risk will be there always, which needs to be mitigated. Otherwise there will be damages which results in losses.

Due to the enormous increase of the high rise buildings, the risk has only increased to manifold. To address the issue, BIS – Bureau of Indian Standards has recently adopted IEC 62305 as Indian Standard, which means it is IS/IEC 62305 from now on and replaces IS 2309 Code of practice for the protection of buildings and allied structures against lightning.

IS/IEC 62305 – Protection against lightning has 4 parts

IS/IEC 62305-1: Basic Principles

IS/IEC 62305-2: Risk Assessment

IS/IEC 62305-3: Protection of structures & Life Hazards.

IS/IEC 62305-4: Protection of electrical & electronic systems within structure.

The relation between these 4 parts is best explained in the figure below:

LPS – Lightning Protection System

SPM – Surge Protection Measures

Lightning threat is mainly due to 4 sources of damages

Source S1: Lightning striking the structure

Source S2: Lightning striking near the structure

Source S3: Lightning striking a service

Source S4: Lightning striking near the service.

To mitigate the risks, the damages need to be ascertained. There are basically 3 types of damages.

  1. Injury/death to the living beings
  2. Physical damage to the structure
  3. Failure of electrical & electronic equipment

The above damages have to be controlled within ‘TOLERABLE LEVELS’ to minimise 4 types of losses.

  1. Loss of Human life
  2. Loss of essential public services (wherever applicable)
  3. Loss of cultural damage (wherever applicable)
  4. Economic loss.

The relation between SOURCES/DAMAGES & LOSSES is explained below.

Lightning protection systemAs this tree structure involves lot of complex formulae with many variables & relation between them in other formulae. Risk assessment software is available as per IEC 62305-3 which is a simple menu driven software prompting questions about the building which needs protection. It takes into account the number of thunder storm days as per metrological dept data or the flash density which can be input directly.

Lightning risk assessment calculatorNormally lightning protection is either over designed or inadequately designed most of the times which goes as per the experience of Electrical Consultant/Architect/Contractor. This problem is addressed precisely in IS/IEC 62305 by a simple technique. Tolerable risk levels are defined for each type of loss. Then, risk has to be calculated for the building that needs protection. If the calculated risk is above the tolerable level, then the most economical protection technique can be employed to bring the calculated risk level below the tolerable level.

To reduce the losses due to lightning protection measures may be required. Whether they are needed & to what extent can be determined by using Risk assessment software. A snap shot of the software is given below.

Inadequate protection the structural Increase Protection Levels!!

lightning protection system for building

In the figure above, the calculated risk for the building, which is under study, is more than the tolerable limit for 2 factors: loss of domain & Economic loss (displayed in RED colour). Loss of public service & loss of cultural heritage is not applicable for industries. To bring the above risks within the tolerable levels, one or any combination of following protection techniques need to be employed.

  • Lightning protection as per LPL 1 to 4
  • Co-ordinated SPD protection
  • Fire protection (manual or automatic)
  • Soil equi-potentialisation
  • Warning notices
  • Physical restriction
  • Electrical insulation

An important unique feature of this software is that, by having different permutations & combinations, most economical solution can be easily arrived within very little iterations. It means the just adequate protection for the typo of building is achieved without the risk of over design or under design.

In a broader perspective, Risk assessment using the software helps in 3 following key areas.

  1. Proof as per IS/IEC 62305-2 that, the calculated risk is below the tolerable risk levels & in case of any loss, insurance can be claimed.
  2. Menu driven step by step technique which does not need any expertise in any software language.
  3. Cheap & nest solution can be arrived easily for the building under consideration which gives the best Cost vs. Performance ratio.

This software is based on the current edition of IS/IEC 62305-2.

Published in IEEME Journal, December 2015
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