Lightning is one of the common weather phenomena. At any instance, lightning strikes the earth around 100 times per second. This only accounts Cloud to Ground lightning strokes which is one of the common form of lightning. As per the data by Indian Institute of Tropical Meteorology (IITM), there were almost 41000 Cloud to ground lightning strikes recorded all over India on April 16, 2019. Over the past decade, lightning strike accounted for approximately 2000 deaths every year throughout India. Significantly, this numbers are increasing day by day due to changes in atmospheric cycle of an Earth resulted by industrialization, Global warming etc.
For an industry, Lightning strike may cause damage to 3M – Man (Human), Material and Machines. Neglecting effects of lightning may create electrocution to people, damage to Building structure and stoppage of process/production and thereafter revenue of an industry. The purpose of lightning protection system (LPS) is to protect buildings (Industrial, Commercial and Residential etc.) from direct lightning strikes and its consequence effects. For any building, Special directives by National building Code (NBC) must be implemented to protect building from direct lightning. As per IS 62305 – Part 2, Risk assessment study to be done for the building and lightning protection level to be decided.
Risk assessment study considers following criteria to decide probability of occurring lightning on the building and its consequence effects,
- Use of Structure (House, Factory, School, Hospital etc.)
- Type of construction
- Material / process vulnerable to fire
- Degree of isolation of building from nearby structures
- Location of Building (To decide lightning strike density – No. of Thunderstorm/Km3 / Year)
IS 2309: 2010 defines acceptable limit for probable no. of lightning strikes on building per year (P) is 1 in 100000. After completion of Risk assessment study,
- If P ≥ 1, LPS should be considered for building.
- If P < 1, implementation of LPS is not necessary.
For special case, if consequence effect of lightning is very negligible and slightly damage the building, it may be economical to not opt for protection and go for the risk.
To design lightning protection system, Designer should have proper understanding of building, its Usage, density of lightning strike and consequence effect. Proper consultation should be done by Designer with Architect, Public Utilities, Fire/Safety officer, Radio installer and contractor to ensure effective design and installation of Lightning protection system.
We @ VMS, design lightning protection system considering criteria provided by IEC 62305 (IS 2309) and guidelines by National Building code-2016. Faradays’ cage method, Angle protection method and Rolling sphere method is being suggested to valued customer for protection of an Industrial building against direct Lightning strike. As per the guidelines by NBC-2016, Radio-active system / Dissipation system / Early Streamer Emission type Lightning Protection System is not accepted and not recommended by VMS as well.
-Tushar Sharma Design Engineer