When lightning roars go indoors

April 26, 2012, 12:00 pm

Source – The Island

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By Prof. Chandima Gomes

Center of Excellence on Lightning Protection (CELP)

‘Universiti Putra Malaysia’

During the last few weeks lightning has become a hot topic in the country due to a sharp increase in the number of victims. The situation is going from bad to worse. As per the meteorological data analysis the thunderstorm weather may prevail over the next few weeks.

Lightning is a complicated way of transferring electric charges from cloud to earth. In a lightning strike a current as large as 30,000 amperes flows to earth. Many domestic appliances require a current of less than 15 amperes for their operation. In the event of a lightning strike the temperature around the area reaches to about 40,000 degrees celsius. We know that water boils at 100 degrees celsius and the temperature of the surface of the sun is about 6,000 degrees celsius.

When lightning strikes a human being he may be killed, badly injured or survive with few skin burns. When lightning strikes a building it may explode, catch fire or be left with few cracks on walls. However, most often when a building is struck by lightning, many of the electrical and electronic appliances therein will be destroyed. Equipment may also be damaged due to massive current pulses that may come through service lines such as electricity and telephone even if lightning strikes a nearby place.

Lightning kills about 50-60 people in Sri Lanka annually. The annual property damage may exceed close to billion rupees. The indirect effects of lightning such as out-of-operation time in the industrial, banking and other service sectors due to damaged equipment will be much higher. Therefore, the general public should pay extra attention to lightning protection.

People should not stay in open areas such as playgrounds, beaches, rivers, work sites etc. under thunderstorm conditions. They should also avoid higher elevations such as mountain tops and slopes, rooftops etc. One of the most important rules of lightning safety is to avoid seeking shelter under large trees during thunderstorm. When a tree struck by lightning, the current flowing along the tree trunk may injure or kill people in the vicinity. Taking shelter in huts or temporary structures of tin roofs on wooden poles is also dangerous. These huts can be grounded by steel rods, as a low cost solution, if staying inside such shelters under lightning environment is unavoidable due to societal reasons.

Avoid swimming

Also avoid taking a swim or bath in open waters, such as rivers, lakes and swimming pools. A nearby lightning may give rise to surface current which may temporarily paralyse the nearby people. Even if you are in two feet of water such paralysis may end your life as you may be drowned if no one will be there to rescue you.

If you happen to be outdoors during a thunderstorm with no easy access to a safe building, then the safety pose that you have to adopt is given in the pictures. Keep your feet close, squat down and close your ears by hands while keeping the head as low as possible.

Schools must suspend all outdoor activities under overcast conditions irrespective of the importance of the event. It should be noted that there are no lightning protection devices invented so far which can protect the living beings in open space. This advice should strictly be followed irrespective of the false claims of some vendors who sell lightning safety devices. School children must be given lightning safety training as a part of their curriculum.

When the lightning occurs, avoid using telephones or wired microphones. However, there is no additional lightning threat of using mobile phones, cordless phones or FM microphones. Nevertheless, it should be noted that the person who handles the electronics of the public addressing system is at a risk of getting a shock if the system has electric cables.

When lightning strikes a structure, the current is most likely to flow along metal parts such as railings, fences etc. Therefore, avoid touching or staying very close to such parts. It should also be noted that structures with metal roofs are very much likely to attract lightning. If the roof is fixed on a structure which is not properly earthed, the occupants will be at a great risk of getting side flashes.

Structural protection

In order to protect buildings against lightning, a structural protection system should be installed at the building. Such a system consists of a number of metal rods installed at the roof level and an array of copper tapes (called down conductors) that connect those metal rods to an earthing network. Designing a lightning protection system is a state-of art technique and it should be done according to either Sri Lankan Standards or recognised International Standards, under the guidance of an expert. Those who seek lightning protection should ensure that the lightning protection consultant visit the site before he designs the system. There are no temporary solutions to lightning related problems.

Domestic appliances can usually be protected from lightning currents by unplugging them from service lines during thunderstorm periods. However, such an act is not realistic in most of the industrial and service sectors as even a short period of out-of-operation will cost the company dear. Therefore in such cases, lightning surges should be prevented from entering the building. This is done by connecting the so-called “surge protection devices” to the power and communication lines. In the case of surge protection, both the quality of the product and the engineering of installation are equally important.

Safety measures for towers

If your home is located very close to a communication or any other metal tower, take extra protection and safety measures, as the ground potential rise due to frequent strikes on the tower, may harm the occupants, both human beings and four-legged animals due to step potential. The equipment in the nearby houses also have a high risk of being damaged due to induced voltages, ground potential rise and lightning currents coming through the neutral wire after being filtered by surge protective devices in the tower base station. The threat will aggravate if the tower and related transformer grounding systems are not properly maintained.

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