Specific roofing material, including metal roofs, doesn't increase the probability of a lightning strike but can decrease the threats created by a lightning strike, such as fire.
What is Lightning?
Lightning occurs when charged particles in one area discharge electricity to another area with oppositely charged particles. This discharge can occur cloud to cloud, cloud to ground or within a cloud. A single strike can carry millions of volts of electricity.
Probability of Lightning Strikes
Metal does conduct electricity, but metal roofs don't attract lightning or increase the probability of a lightning strike. Four factors affect the probability of a lightning strike:
- Topography: a structure located on a mountain or hill has a higher probability of a strike than one in a field.
- Structure size and height: a tall structure or one that covers a great deal of ground has a higher probability of a strike a short or small building.
- Relative location in relation to taller structures: a small, short building near a taller structure has a lower probability of strike than the taller structure.
- Severity and frequency of thunderstorms in the structure's vicinity.
Roofing material can affect the threats created by a lightning strike. Electrically conductive, noncombustible materials such as metal roofs reduce the threat of fire and explosion.
Effect of a Strike on a Metal Roof
If hit by lightning, a metal roof safely disperses the electricity through the building. Although it can conduct the electricity, this does not make it safe to touch a metal roof or metal windows during a storm.
The safest place during lightning is inside a fully enclosed building in an interior room. The second safest place is in a vehicle with a solid metal roof and metal sides with the windows closed. In both locations, avoid touching any conductive path to the outside. This may include telephones, plumbing, electrical appliances, wires, TV cables, metal doors or metal window frames.
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