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Sunday, 15 March 2015





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Watch out for Inter Monsoon lightning hazards

Lightning activity over Sri Lanka shows peaks during two Inter-monsoon seasons, March-April and October-November. But since thunderstorms develop under any atmospheric conditions that are capable in developing convective clouds, we should be alert in launching precautionary steps to reduce lightning hazards during all seasons with special concern in Inter-monsoon seasons. Normally, in addition to the development of thunder clouds by convection, Sri Lanka is influenced by frequent cyclonic weather system during the second Inter-monsoon season resulting widespread thundershowers.

How lightning is reported in Sri Lanka

Information of lightning incidents in Sri Lanka witnesses for over 50 deaths of human beings and damage to property of billions of rupees worth every year.

Natural hazard

The electric current of a ground lightning flash (lightning between the clouds and the earth) is about 25,000 Amperes (25,000 A) on average. It can vary in the range 2000 - 200000A. The potential difference between a charged cloud and the earth is about 100 million Volts and the energy of a lightning flash is about 500 million Joules. Therefore, lightning is a natural hazard and it causes death and damage outdoors and indoors as well. Even though being inside a building is the best precaution against effects of lightning in thunderstorms still it may be risky if the building is not protected with Lightning Protection Systems.

During bad weather conditions with thunderstorms, lightning surges that induces in power and communication supply lines may reach the inside of a building in a number of ways mainly directly and as side flashes.

As mentioned earlier, lightning is a natural phenomenon and therefore it is difficult thing to stop it.

But it has been found that the lightning caused hazards could be reduced with a number of precautionary measures, which are introduced to pass the high current surge of a direct or indirect lightning current to the earth safely. Some of them are,

1) Install good earth for the electric circuit of buildings.

Use Power surge diverters

Supply lines of power and communication can be interrupted by a gadget called power diverter which is capable in directing high currents intruding a building along supply cables as a result of a lightning flash to the ground without allowing it to come into the interior parts of the building circuit.

3) Installing lightning conductors/arrester.

Direct hit of a lightning flash to a building is the most dangerous event when the lightning hazards are concerned. Lonely and tall buildings are the most vulnerable to lightning. Protection of buildings from direct hits of lightning has been discussed even in the time of the leading scientist, Benjamin Franklin in this field.

The lightning rod (LR) (or lightning arrester or conductor), which was first introduced by Franklin, is the widely used device for protection of buildings even these days. Continuous research in this field has been useful to apply modifications to the lightning rod to make it efficient in conducting lightning currents to the ground protecting the building and the property inside.

The LR usually consists of three parts namely, air terminal, down conductor and the ground terminal. The installation should be performed properly, according to the standards, to reach the necessary requirement of the characteristics of an efficient arrester.

The care has to be taken to have the ground resistance as low as possible and to avoid margins for sparks of the surge to close by parts of the building.

There is a very important point to remember. Precautionary steps such as installing lightning rods and power diverters should be planned and performed in time without waiting till a lightning flash strikes your house.

Lightning protection systems are a little costly. But compared with the cost of the life of a human or cost of electronic infrastructure installed in present day houses, the protection cost is comparatively small.

Eventhough our residences, office buildings, school buildings are not protected against hazards of lightning, the hazards can be mitigated through practices of precautionary steps in time. Some of them are briefely mentioned below.

If thunderstorms are forecast, find shelter in a safe place to avoid exposing yourself to the open air. If the time interval between lightning flash and hearing thunder becomes less than 15 seconds, move quickly to a protected location, as there is immediate danger of a lightning strike nearby.

Different kinds of conducting materials existing in the environment help in conducting the huge current of a lightning stroke, partly or fully, from place to place. Electric power supply cables, telephone cables and TV antenna cables are good examples. Therefore, in environments with thunderstorms,

(a). Keep electrical instruments disconnected from the main power supply.

(b). Television antennas should be disconnected from the television sets and the antenna socket should be placed close to the earth outside the house.

(c). As far as possible, avoid handling/touching electrical instruments like refrigerator, electric iron, metal frame, TV, and radio.

(d). Avoid touching or standing close to tall metal structures, wire fences and metal clothes lines.

(e). Limit the use of telephones when a thunderstorm is overhead. Best advice is not to touch the telephone in such instances.

In environments with thunderstorms

(i). Try to avoid loitering in open areas such as paddy fields, tea estates or play grounds. Specially avoid working in open air holding metal tools such as mammoty, knife and iron rods. If this cannot be avoided, crouch, singly, with feet together.

Footwear or a layer of any non-absorbing material, such as plastic sheet, will offer some protection against ground currents.

(ii). Do not seek shelter under or near isolated tall trees and in high grounds. If the vicinity of a tree cannot be avoided, seek a position just beyond the spread of the foliage.

(iii). By sitting down or lying down, reduce the effective height of the body.

(iv). If in an open boat, keep a low profile. Additional protection is gained by anchoring under relatively high objects such as jetties and bridges, provided that no direct contact is made with them.

(v) Avoid riding horses or bicycles, or riding in any open vehicle such as a tractor.

(vi). Avoid swimming or wading.

Life of a thundercloud is short as 30 minutes. As a result, fatal lightning occurs during a very short period like 20-20 minutes.

If we are careful to take necessary precautionary steps during that period it is obvious that the lightning hazards can be reduced. It should be stressed that the first lightning flash and the flash following a short break of activity cause most of severe damage to life.

First aid

Lightning hazards are not fatal always. The state of the damage depends on the path of the lighting discharge through the body and the intensity of the current. In case of lighting strikes to persons, first aid should be given to the diseased before taking him for medical treatment.

Body should be massaged to treat in case of temporary paralysis due to lightning strikes.

If respiration is disturbed, artificial respiration should be tried. This could be done by blowing air into the patient's body through his mouth. In many cases, massage and artificial respiration have to be given simultaneously.

The writer is Visiting lecturer, Post Graduate Institute of Science (PGIS), University of Peradeniya, and Retired Director of Meteorology)

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