NEED FOR PROVIDING EFFECTIVE LIGHTNING
PROTECTION FOR SAFETY OF BUILDING STRUCTURE
Everyone is aware of common news item of loss of lives and damages during monsoon Season due to a bolt of lightning thus it is the need of the hour to provide adequate safety to various installations (factories, offices, residential and public buildings, etc.) from the strike of lighting. In this article, a brief regarding lightning protection is highlighted.
LIGHTNING
A transient, high-current electric discharge whose path is generally measured on kilometer. Lightning occurs when some region of the atmosphere attains an electric charge sufficiently larger than the electric field associated with the charge cause the electrical breakdown of the air.
Lightning strikes can be a major risk to live stock and human lives. Persons and equipment. within a building thus needs to be protected from a direct lightning strike; circumstances may arise where the effects of lighting are transmitted into or within the building structure by various means, placing equipment and possibly persons at risk. communications and electronic equipment are practically susceptible to building/structure damage from lighting and such structure damage may occur at energy levels well below those needed to cause injury to persons.
EFFECTS OF LIGHTNING
by the interception of lightning on exterior metal work or other exposed conductors. This is characterized by the full impulse energy being transmitted by the conductor. This can be associated with extremely high voltages.
by the interception of lightning on other structures or services connected to the structure, for example the electricity distribution system or telephone lines to the site. Such an impulse is at a substantially lower energy level than for a direct strike.
by a lightning strike to the ground inducing a transient in conductors in the ground or the building structure or again in the electricity or telephone services to the site. This impulse involves relatively low energy and is thought to occur less frequently than above.
THE NEED FOR PROTECTION:
Data collected by the expensive equipment installed at the building structure gather more importance significance around monsoon when heavy rains lash the catchment areas. It is also known that maximum lightning occurs during the same period. The sensitive electronics within building structure can be very easily damaged in the event a direct lighting strikes and as per studies conducted around the world, 99%of the lightning strikes have strength of 3000 amp and above.
The effect of the direct strike described above would be sometimes very obvious, especially when sensors and cable are accessible and can be examined. At other times, lightning damages to building structure has to be deducted from symptoms such as electrical leakage from conductors to ground, excessive electrical noise, and inconsistent readings.
A typical strike that destroys an instrument can also leave pinhole punctures in cable jackets. Even when the sensor is not destroyed, the pinholes in the cable jackets will allow the entry of water, creating numerous other problems including instability through increased electrical noise. commonly routed cables can be building structure damaged due to arcing between adjacent cable such as in trenches or common bore holes.
And most importantly we have to ensure that LIFE & LVE STOCKS are adequately protected from lightning strikes.
What Indian standard Says
As per IS 2309 1989 Clause 8.1 shows following point for needs of protection
Where Large number of people congregate.
Where essential public services are concern.
Where area in which lightning, strokes are prevalent.
Where they are very tall or isolated structures.
How to PROTECT against DIRECT Lightning Strikes
The most effective way to provide protection against direct lightning strike would be to provide the lightning current a predetermined path to the safety of the earthing system.
This can be achieved by providing appropriate type and technology of lightning arrestors (LA). The traditional method is by using lightning rods of 1-3m made of either copper or GI with 3-5 spikes at the top of the structure. The more advanced and currently popular LA is based on the principle of ‘Early Streamer Remission (ESE).
In the ESE type of lightning arrestor, a streamer is sent in to the air to meet, 60m above the tip of the LA, the downward leader of the lightning strike and directing the strike to safety. As compared the conventional type of LA doesn’t meet the downward lightning after a considerable delay and therefore the impact is very much closer to the structure /equipment being protected.
How to PROTECT against DIRECT Lightning Strikes
| Description | ESE type LA | Conventional ROD type LA |
| Working Principal | Active device seeks for the lightning & engages it 25 to 60 meter above the tip of the LA. This ensures the impact is much above the structure and no currents get into the stray infrastructure. | Based on spike or finial, wait for the lightning to strike on its tip. The tip may align with the upward leader around 24 meters above the tip. In this case there could be stray currents getting into the structure. |
| Probability On strike | Only one device is sufficient to give a zonal protection up to 214 meters | To provide adequate protection several
Spikes are required to be installed. |
| Diameter | In general, the spike provides protection in a cone of 45 deg around the LA. These LA needs to be mounted at 20-meter diameter if tip of LA is 10 mtr above the structure being protected. | |
| Level Of protection | Only one system install at a height of 2 meter above the structure gives protection of 98% from lightning less than 10 KA | A grid is required to be formed a top the building to provide the protection and a passive device with the height of 1.2 meter gives a protection of 40% form lightning less than 10 KA., which may be hazardous to electronics components |
| Installation | Only one down conductor from top to bottom is required for effective drain path. | Several down conductors due to the presence of several LAs. |
| Effectiveness | Designed to perform effectively with 99% reliability | Non-reliable |
Conclusion
The importance of the protection of live stock and sensitive high value electronics assets within the building structures is maximum during monsoon, also there is a likelihood of personnel around the building structure in the case of any emergencies which are likely during the time of heavy rains lashing the region which needs to be adequately protected. considering the importance of the assets, life and live stocks in the proximity, protection against lightning is conclusive. Based on the comparison of the available technology and the value of assets to be protected it is strongly recommended to use advanced ESE type Lightning Arrestors.
We thus feel the need of providing effective Lightning Protection to all the building especially where the masses gather like schools, colleges, temples, stadiums, Highrise Buildings and also recommended that this should be made mandatory by law so as to avoid casualty and other damages due to LIGNTNING
