A lightning protection system is designed to control or force the lightning discharge on a specified path, thus eliminating the chance of fire or explosion within nonconductive parts of the house. This may include the phone, cable, or electrical lines, the water or gas pipes, or (in the case of a steel-framed building) the structure itself. Lightning usually will follow one or more of these paths to ground, sometimes jumping through the air via a side flash to reach a better-grounded conductor (watch animation above). As a result, lightning presents several hazards to any house or building:
Fire– Fire can start anywhere the exposed lightning channel contacts, penetrates or comes near flammable material (wood, paper, gas pipes, etc) in a building – including structural lumber or insulation inside walls and roofs. When lightning follows electrical wiring, it will often overheat or even vaporize the wires, creating a fire hazard anywhere along affected circuits.
Side flashes – Side flashes can jump across rooms, possibly injuring anyone who happens to be in the way. They can also ignite materials such as a gasoline in a garage.
Damage to building materials – The explosive shock wave created by a lightning discharge can blow out sections of walls, fragment concrete and plaster, and shatter nearby glass.
Damage to electrical appliances – Televisions, microwaves, phones, washers, lamps and just about anything plugged into an affected circuit may be damaged beyond repair. Electronic devices and computers are especially vulnerable.
Each year 32 million lightning strike truck the surface of earth. The consequences of so many lightning are thousands of homes and other properties are destroyed or damaged by lightning strikes. Unprotected homes risk to be damaged by fire, explosions or electrical surges. Personal injury can occur in an unprotected house which has been struck by the lightning. The effects of such a lighting strike can devastate a human both physically and emotionally.
A lightning protection system does not prevent a lightning strike, but provides a safe path on which the lightning current can safely be directed to the ground. The air terminals, cables and ground rods work together to prevent fire and other hazard which can damage the structure and appliances.
Franklin's Lightning Rod 