How long must the fire door and fire shutter assembly rating be for enclosures of shafts, interior exit stairways, and interior exit ramps?

The rating for fire doors and fire shutter assemblies that are installed in enclosures of shafts, interior exit stairways, and interior exit ramps is typically set at 1-1/2 hours. This requirement is rooted in fire safety codes, which aim to provide adequate time for occupants to evacuate a building safely in the event of a fire. The 1-1/2 hour rating allows for delay of fire spread and offers a reasonable timeframe for emergency response teams to address the situation without the immediate danger of fire breaching these critical areas.

Other ratings, such as 1 hour or 2 hours, do not specifically align with the safety requirements set forth in fire codes for these particular assemblies. A 1-hour rating may not provide sufficient time for safe evacuation, while a 2-hour rating, although it offers more protection, is not the standard for these specific assemblies in the mentioned contexts. Thus, the 1-1/2 hour requirement serves as a balanced approach to ensuring safety while not exceeding the necessary protection level.