RollingSphereMethod-Lightni

The rolling sphere method is used to determine a building’s ‘zone of protection.’ NFPA 780 states, “to apply the method, an imaginary sphere is rolled over the surface. All surface contact points are deemed to require protection, while the unaffected surfaces and volumes are deemed to be protected.” A sphere with a radius of 45 m (150 ft) is suitable for typical buildings. While the rolling sphere method may show sides of tall buildings should be protected, NFPA finds, “unless there are specific reasons for side protection, as would be the case of a structure containing explosives, …the cost of side protection would not normally be justified.” Photo courtesy Lightning Safety Alliance

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