Weather & Climate

Lightning Hazard

Lightning is perhaps one of the most beautiful, and at the same time, one of the most frightening phenomena in nature. While it is terrifying, and could be fatal when it happens at close quarters, its beauty from a distance is often breath-taking.

Thomas-François Dalibard (1709-1778), a French scientist, in May 1772 established that lightning contains electricity, based on an experiment originally suggested by the famous American polymath Benjamin Franklin. The experiment consisted of raising a metal wire into the cloud and seeing whether it is electrified. While Dalibard used a 40-foot steel rod, Franklin used a kite to raise one end of a wire to such heights, and both were able to extract sparks from the lower end of the wire.

Air is normally electrically neutral and a bad conductor of electricity. However, inside a cumulonimbus, electrical charges tend to separate and accumulate in different regions of the cloud with positive charges generally moving upwards and negative charges moving towards the bottom. These charged accumulations eventually lead to such high potential differences within the cloud, between clouds, and between cloud and surface of the earth below that ions that are always present in the air are accelerated to high speeds. Such fast ions collide with air molecules and ionise them. This leads to a ‘cascade’ of ions that travel quickly through the air, conducting current.

Eventually these form a conducting path between the charge collections, helping the charges to flow freely through air, constituting an electric current. Such currents are so huge that the air in its path gets suddenly heated to a very high temperature, often 30 to 40 thousand degrees. This may seem enormous, but insignificant when we remember that the temperature at the surface of the Sun is 6,000 degrees! This heat produces the light we see in lightning and the sound we call thunder, which is due to the sudden expansion of the heated air.

The data from the National Crime Records Bureau show that more than 2,000 people in India lose their lives annually from lightning. Of this, around 70 are from Kerala, which is one of the highly lightning-prone areas in India. Other than Kerala and much of the Western coastal areas, highly lightning prone areas in India are in the northeast, including Assam, West Bengal and Odisha.

Studies by Dr. S. Murali Das, Centre for Earth Science Studies, Thiruvananthapuram have shown that thunderstorms in Kerala are mainly formed when the sea breeze reaches the Western Ghats and the humid air rises, causing it to cool and form clouds. Hence, most parts of Kerala are lightning-prone, though the highest incidents of lightning strike are reported from the district of Kollam, followed by Kannur. The least lightning-prone area in Kerala is the area to the West of the Palghat gap, a wide gap in the Ghats that provides a passage between Kerala and the rest of India.

Safety measures during lightning activity depend on where you are located. First, being in an open area is highly risky. Hence, if one is located in a football ground or lake when a thunderstorm approaches, you need to rush to a safe building. In case you are far from a safe building, the best thing to do is to crouch with your feet close together and your head bent. The idea is to keep as low as possible and the points of contact with the ground as close together as possible. If you are in an open area, never stand near a tree, as lightning may strike it and from there affect you by a side flash or from the lightning current that flows through the ground, which creates a step voltage between two points on the ground. Also, you should keep away from metallic objects including posts, towers, wire fences, etc. Fishing or boating is best avoided when lightning activity commences.

Contrary to popular belief, automobiles with metallic bodies are very safe. Therefore, it is perfectly safe to continue driving your car, if it has a fully metallic body when there is a thunderstorm. All buildings with lightning protection systems installed are safe. Buildings made of reinforced cement concrete are relatively safe as they have steel rods embedded in the concrete. If lightning strikes the electric current will pass mainly through the steel. But just being inside such buildings cannot make one completely safe, although it saves one from the possibility of direct strikes. Lightning can strike power and telephone, data cables or water pipes which could then carry the electric current into the buildings. Hence, to be safe from such sources, one has to keep away from device that use power, such as television, refrigerators, air conditioners, electric heaters, etc. It is also not safe to use water taps during lightning.

Adequate precautions can thus easily ensure safety from lightning.

Post a Comment

Your email address will not be published. Required fields are marked *

*