How does FM categorize fire resistance?

• A. By color
• B. By installation method
• C. By weight
• D. By combustibility and spread of roof systems

Answer: (D)

FM’s approach to fire resistance focuses on how combustible the roof materials are and how readily fire can spread across the roof system. This reflects the practical need to know how a roof will perform under fire exposure: can it ignite easily, and will flames or embers travel across the surface to threaten other parts of the building? Materials that are noncombustible or of limited combustibility resist ignition and slow flame spread, providing better fire resistance. In contrast, more combustible assemblies can ignite quickly and permit faster spread, increasing risk and potential damage. Color, installation method, or weight don’t describe fire performance in FM’s categorization, so they aren’t used to define fire resistance.