Which statement correctly describes the minimum fire-resistance requirement for transformer vaults' walls and roofs?

Which statement correctly describes the minimum fire-resistance requirement for transformer vaults' walls and roofs?

• A. 2 hours
• B. 6 hours
• C. 3 hours
• D. 4 hours

Answer: (C)

Transformer vaults must be enclosed by fire-resistive construction to keep the high-energy equipment contained and prevent fire from spreading quickly. The minimum rating specified for the walls and the roof is three hours. That level of protection helps maintain the enclosure’s integrity during a fire, limits heat and flame exposure to surrounding materials, and buys time for firefighters to control the incident and for occupants to evacuate if needed. If a lower rating were used, like two hours, the enclosure could fail sooner and allow fire to escape; higher ratings like four or six hours aren’t required for standard transformer vaults, though they might be specified in special cases by local codes. The three-hour requirement is the standard baseline for walls and roofs.

Transformer vaults must be enclosed by fire-resistive construction to keep the high-energy equipment contained and prevent fire from spreading quickly. The minimum rating specified for the walls and the roof is three hours. That level of protection helps maintain the enclosure’s integrity during a fire, limits heat and flame exposure to surrounding materials, and buys time for firefighters to control the incident and for occupants to evacuate if needed. If a lower rating were used, like two hours, the enclosure could fail sooner and allow fire to escape; higher ratings like four or six hours aren’t required for standard transformer vaults, though they might be specified in special cases by local codes. The three-hour requirement is the standard baseline for walls and roofs.