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Without a designated path to reach ground, a lightning strike may choose to instead utilize any conductor available inside a house or building. 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 can 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 appliances - Televisions, VCRs, 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.

Adding a protection system doesn't prevent a strike, but gives it a better, safer path to ground. The air terminals, cables and ground rods work together to carry the immense currents away from the structure, preventing fire and most appliance damage: