Bolts from the sky
Apart from human injuries and deaths, another matter of concern is the innumerable deaths of animals caused by lightning every year. On an average 71 people die and 112 people get injured every year in Kerala due to incidents of lightning.
Widespread the use of electronic gadgets, extension of the national power grid into rural areas and the mushrooming of communication towers have led to increasing equipment damage. The loss for year 2002 to telecom had been put at Rs. 2 crores. In general, mid lands of Kerala are more affected than the coastal plains and high lands.
Lightning ignites fires that may bring an entire building or house down to ashes. At a lower degree of damage, the lightning current may destroy electrical, electronic and communication equipment beyond repair. However, one of the most significant loses that lighting may cause as far as industries are concerned is the downtime.
The right protection
Damages can be avoided or at least minimised with a proper engineering knowledge in lightning protection, says Dr. Chandima Gomes, Director, South Asian Lightning Information and Resources Centre, Sri Lanka and Honorary Advisor, Lightning Awareness Cell, Regional Energy Centre, Kerala.
A lightning flash originates inside a cloud, several kilometres above the ground level. Except for ball lightning, which is rare, lightning is simply an electric spark between a cloud and ground, between two clouds or between two parts of a cloud.
Lightning may cause damages to a building and equipment in three ways, says Dr. Gomes. Maximum damage will result when a building attracts direct strike or attract a part of a lightning flash that hit another structure in the proximity (side flash).
The second mode of getting lightning currents into installation is through the service lines such as power, communication and cable TV. Once a lightning strikes a service line, fractions of the lightning current enter all the nearby buildings and may destroy all the equipments that are plugged into the system. This mode of intrusion of the lightning current cause less damages than a direct strike, yet service lines are subjected to lightning strikes much more frequently than buildings themselves.
The lightning current that flows from cloud to ground is a good emitter of electromagnetic radiations. Once a lightning hits a nearby object, even a building is exposed to a strong dose of electromagnetic radiation. When this radiation passes through electronic equipment such as computers, medical equipment, military installations, etc., the sophisticated parts of the equipment can be destroyed. This may happen even when the equipment is unplugged from service lines. However, the chances of ordinary electrical equipments getting damaged due to such radiation is very slim.
The lightning threats can be eliminated by three types of lightning protection systems.
A building protection system is meant to protect a building from direct lightning strikes and side flashes. An ordinary building protection system consists of one or several sharp pointed rods (or a mesh of metal strips/wires) installed at the roof of the building (called air termination), several metal stripes or metal wires from roof to base (down conductors) and one or several conducting rods buried in the ground (earth conductors).
The down conductor system connects the air termination to the earth conductors. When a downward channel comes from a cloud, the air termination sends an upward channel much faster than the other parts of the building thus the lightning is attracted to one of the rods.
Then the lightning current is safely passed into earth through the rest of the system. Thus, instead of repelling a lightning channel, a lightning protection system attracts that. As the lightning current is safely driven into earth the building will not be damaged.
Dr. Gomes says one of the new concepts developed in lightning protection proposes a device that can repel or neutralise a lightning leader so that the protected site comes to no harm. The protection of high-risk structures needs special designs in contrast to low-risk structures irrespective of the type of protection system selected.
Special devices (surge diverters or surge suppressors) prevent these current impulses from entering your building. A surge diverter is connected at the entrance of the service line to the installation. At high-level of protection they are connected at the power socket of each electrical or electronic equipment as well.
Under normal operation, the surge diverter does not interfere with the line signals. In the case of a lightning strike it provides a convenient path for the current to be diverted into the earth without letting it enter the building or affect the equipment. Surge suppressors, which have to be connected to protect power lines, communication lines and data lines, are different from one another.
Dr. Gomes says it is always much less costly to design and implement the lightning protection system at the construction stage of a building rather than doing so after the building is constructed. It is also advisable to get your entire lightning protection network from one company or consultant to avoid complexities that may arise afterwards, he says.
Lightning current, which may propagate through power cables, can easily jump across the open switches and enter the equipment. It is advisable to disconnect electrical households from power lines during thunderstorm periods. TV antenna cables should be disconnected. Fax machines and computers should be disconnected from the telephone network.
Sharp and pointed metallic objects attract lightning more than blunt and smooth objects do.
Thus, if the house is struck by lightning, theoretically, there is a chance that the needle would get a side flash from walls, power lines, etc.
A metal rod kept close to the wall or especially a power line or a metallic drainpipe may attract a side flash if the building is struck by lightning.
Such a side flash may cause fires and explosions.
Being a tall tree and having leaves with sharp edges and pointed ends, a coconut tree may be the object in a certain landscape that send the first channel to meet the descending channel from the cloud. In addition, being the most abundant tree, he says coconut trees will obviously have a high probability of getting lightning strikes.
With all these systems still nobody can guarantee 100 per protection from lightning. The company, Dr. Gomes says, which provides lightning protection, will give a certain level of protection (by a percentage) related to the system one buys.
Lightning protection system attracts a downward channel from the cloud.
Thus, there are no possibilities that it enhances the probability of lightning strikes to the neighbour.
It is understandable that tall buildings are more prone to lightning than short ones.
However, Dr. Gomes says there is no evidence to point out that tall buildings cause more lightning to come down due to their presence, unless they are extremely tall.