A firestopping classification having a minimum F rating of ? must be used on a two-hour rated firewall to resist the passage of flames.

• A. 60
• B. 120
• C. 240
• D. 360

Answer: (B)

Firestop systems in penetrations must be rated to match the fire’s duration that a barrier is designed to resist. A firewall rated for two hours can hold back flames for that period, so the firestop used in any openings through it must have an F rating of at least 120 minutes. The F rating is the time a firestop assembly can prevent flame passage during a fire test. Therefore, 120 minutes is the minimum you’d need to preserve the firewall’s two-hour integrity. A lower rating like 60 minutes wouldn’t meet the required duration, while higher ratings such as 240 or 360 minutes are acceptable but not necessary when aiming for the minimum.