How to reduce lightning hazards

K. R. ABHAYASINGHA

Most of us have a certain level of understanding of the lightning hazards that occur every year particularly in March, April, October and November. But it is an unfortunate thing to note the continuing incidents of death and property damage caused by lightning every year.

Being in a safe place is the most important precautionary step during a thunderstorm. The only or very common safe place for us is either the home or the office building.

Sometimes it may be the school building, church or the temple. Therefore, for our precautionary steps to be a reality, the building in which we expect to be in for the protection against lightning should have been provided with the protective measures for the purpose.

As in any other natural event, there are a number of concepts and understandings of lightning among us. But since Benjamin Franklin suggested first that lightning is produced by clouds which are charged with electrostatic charges, researchers have launched several types of studies on lightning and the environmental characteristics that are favourable for generating lightning and as a result now we know that lightning flash is as strong as (on average) 25,000 Amperes produced by a cloud with voltages in the order of one hundred million volts.

One can compare this with the power of the electricity supply in our houses and offices which is feeding about 15 Amperes with 240 volts.

The enormous energy of a lightning flash naturally flows to the ground through the most appropriate route or point to get neutralized. A lightning flash selects the best conductive and also the closest object in the location for this purpose. For this reason, it is obvious that the tallest structure in a location is the most vulnerable to lightning.

Also any metallic object, particularly those taller than the ground level, is selected by a descending lightning flash even when there are taller trees near and around it.

In the course of the technical development, man has introduced a number of metallic, conductive materials, gadgets, devices and objects, to the environment particularly in providing infrastructure like, electric power and communication.

Electrical overhead cables, telephone cables, TV antennas, CDM antennas etc. are very efficient attractors of lightning flashes. Although these objects are installed outside our houses and office buildings, they are connected to the buildings with conductive materials.

Therefore, it is obvious that the high currents reaching the objects outside in thunderstorms can easily travel to inside of the building in no time.

As a result of above characteristic of lightning surges, buildings with modern infrastructure facilities, are vulnerable to lightning during thunderstorms irrespective of the location of the building and hence such buildings incur more lightning hazards than a colonial house with no metallic connection with outside.

This fact has been misunderstood by many of us as an increase of lightning density in their respective areas.

Studies show that the domestic (indoor) lightning hazards, particularly property damage, are likely to increase along with the increasing trend of usage of modern technology in buildings.

But these hazards can be easily controlled through the installation of protective devices in buildings.

If the people are keen to introduce the available protective methods the managing of domestic lightning hazards is not a significant problem.

The lightning surges that flow to inside the buildings through conductive connections with the outside metallic structures, will ultimately flow to the earth in a very short time through any available, mostly conductive, material inside the buildings.

Domestic power circuits, reinforced iron bars inside concrete slabs and columns, electrical appliances, steel furniture, steel window or door frames and rods, nails and other metal parts fixed on walls, mercury paintings of mirrors etc. are some of materials supporting to approaching lightning currents in thunderstorms.

In such cases, the large electric currents associated with lightning may cause complete destruction, bursts, burns, scattering of objects and even death of inhabitants.

As discussed above, the probability is significant for our houses, offices, schools, churches, temples or any building to have indoor lightning hazards and it is our responsibility to plan of the steps to protect such buildings from lightning currents that can come from outside.

This is the best time for that purpose because the second peak lightning season, October-November inter monsoon, is very close.

Buildings can be affected by lightning directly or indirectly. Any building whether it has or has no any conductive connection with outside can be hit directly by lightning.

But the isolated buildings, those situated at high elevations, those with metal roofing and those situated in areas with high lightening density are the most vulnerable. Such buildings should be protected with a good, standard lightning arrester (lightning rod).

All buildings with any mode of connection with the outside through conductive materials must be protected with electronic instruments called Surge Diverters to stop the lightning surges from intruding the building. Surge Diverters divert the lightning surges to the ground.

If the buildings are not provided with surge diverters as protective measure, they are vulnerable to indirect effects of lightning when the buildings have connection with outside.

Since most of our houses and offices are powered by main electricity delivered through overhead lines, majority of indoor lightning hazards are carried to inside by the cables connecting the building with the nearest power post. Meantime other structures like TV antenna and CDM antenna which have connection with building are responsible to a minor portion of indoor lightning hazards.

The main helper in reducing the hazards caused by intruding lightning surges through conductive connection with outside is the earth rod of any building.

If the earth rod and the earth circuit which includes both the earth rod and the earth wire (usually green) are installed and maintained properly it could serve positively to provide protection during thunderstorms.

But it is unfortunate to mention that most of us do not have much care to install and maintain a good earth rod. There are a few, very common, reason for the earth rods and earth circuits to have deteriorated characteristics.

They are:

1. Decay of earth rods

2. Poor bonding between the earth wire and the earth rod

3. Corrosion of the earth rod and the un-insulated part of the earth wire

4. Disconnection of the earth wire

5. Dryness of soil around earth rod

The installation of the earth rod of the electrical circuit of any building has to be done properly according to the standard.

The resistance between the rod and soil (earth resistance) should be maintained at very low values as 10 ohms. The condition of an installed earth rod should be checked on a regular basis and the improvements should be attended if necessary.

Otherwise a house or a building with improperly maintained earth rod is very vulnerable in thunderstorms irrespective of the location or the area of its situation. If we are keen enough to understand the purpose of the earth rod of our houses or office, we could reduce the indoor lightning hazards significantly.

The writer is former Director of Meteorology.