The lightning threat to mankind is well known (even without considering economic losses) because, in a second, there are at least 8 lightning strikes around the world. There are 4 sources of lightning, which results in 3 types of damages and bring in 4 types of losses. Damages need to be minimized so that, losses can be reduced.
Nowadays, the risk due to lightning increases due to skyscraper.
Bureau of Indian Standards has adopted IEC 62305 as Indian Standard in December 2015, which means it is IS/IEC 62305 and replaces IS 2309 Code of practice for the protection of buildings and allied structures against lightning. India has adopted this IEC 62305 as Indian Standard only in 2015, whereas many countries have adopted it as their national standard, many years back.
- 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 the structure.
The relation between these 4 parts is best explained in the figure below:
- LPS – Lightning Protection System
- SPM – Surge Protection Measures
The 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.
3 types of damages are :
- Damage D1: Injury/death to the living beings
- Damage D2: Physical damage to the structure
- Damage D3: Failure of electrical & electronic equipment
The above damages have to be controlled within ‘TOLERABLE LEVELS’ so that 4 types of losses can be minimized.
- Loss L1: Loss of Human life
- Loss L2: Loss of essential public services (wherever applicable)
- Loss L3: Loss of cultural damage (wherever applicable)
- Loss L4: Economic loss.
The relation between Sources, Damages, and losses involves a lot of complex formulae which includes many variables. Jef has developed Risk Assessment Software which is based on IS/IEC 62305-2. As there is no third party available to validate this software, It has been validated by doing the risk based on the 4 worked out examples given in IS/IEC 62305-2 and the result is compared with the output given in IS/IEC 62305-2. This completes validation process. Number of thunderstorm days for about 158 cities in pan India, which is given in NBC 2016 is taken into account, as it is very difficult to get this details from the customer.
Prior to the availability of IS/IEC 62305, lightning protection was over-designed by Consultants because there was no tolerable risk to compare. Tolerable risk levels are defined for each type of loss. Then, risk has to be calculated for the building that needs protection. The only exception to this is Solid Explosive & hazardous area buildings. (pl. Refer another article on this subject). If the calculated risk is above the tolerable level, then economical protection technique can be employed to bring the calculated risk level below the tolerable level. This is the biggest advantage of this software, as iterations can be done to bring the cost of protection to the optimum level. What is more, if building steel is used as part of the Lightning protection system, you not only have the most economical solution, but also the most reliable system whose life is almost equal to the life of the building.
For non-hazardous buildings, Risk Assessment has to be carried out to know whether the building under consideration, needs protection or not. If protection is needed, the software can be used to find out the most economical protection technique, which may be a single solution or combination of different solutions.
For example, a small building surrounded by other taller buildings on all 4 sides, may not need any lightning protection system at all. But it definitely requires ring earthing or foundation earthing and SPDs- Surge protection Devices for Power & Data lines.
Software Result for the Typical Building with the dimension of (30 x 40 x 30 Meters)
Without any protection measures, Building Calculated value is greater than the tolerable value, Hence Lightning Protection Measures Required.
In the table above, the calculated risk for the building, which is under study, is more than the tolerable limit for 2 factors: loss of human life & Economic loss (displayed in Red color highlighted in Yellow.) To bring the above risks within the tolerable levels, one or any combination of following protection techniques need to be employed.
Mitigation Measures:- as per IS-IEC 62305-2
Installing an LPS of Class IV .According to Table B.2 this reduces the value of PB FROM 1 to 0,
Installing SPDs of LPL IV at the line entrance (lightning equipotential bonding) to protect both power and teleohone lines.According to Table B.7 this reduces the value of PEB (due to SPDs on connected lines ) from 1 to 0.05
Table B.2 - Probability PB that a flash to a structure will cause physical damage
Table B.7 - Value of the probability PEB as a function of LPL for which SPDs are designed
Results after Mitigation:-
As per the above calculation, the calculated value (R1 & R4) is brought to less than or equal to a tolerable value (RT) as per IS/IEC 62305
Hence it is recommended to implement Class – IV (Level – IV) Lightning protection measures & Level – IV Surge protection device (Type 1+2 SPD at Main Incomer & Type – 2 SPD at Sub-Distribution boards.)
(This is displayed in Green color, highlighted in Yellow.)
Lightning protection as per LPL 1 to 4
- • Co-ordinated SPD protection
- • Fire protection (manual or automatic)
- • Soil equi-potentialisation
- • Warning notices
- • Electrical insulation
In a broader perspective, Risk assessment using the software helps in 3 following key areas.
1. To claim insurance, in case of any loss, as the protection is done as per IS/IEC 62305, which is followed by CEA, CEIG & Insurance companies to provide compensation.
2. Maintenance Engineers can use this software effectively without the need to know any software language because it is a simple, menu-driven software.
3. Best Cost Vs Performance as iterations can be done to choose the most economical solutions.
To know more about the subject and Risk Assessment Software please write to us at email@example.com.