You are designing a firestop system for a boiler room that will have conduits coming from the service provider maintenance hole into the building. Which test rating will address the firestops…

The F rating measures a firestop system's ability to prevent flame and hot gas passage through a penetration, not its resistance to water-related breakdown.

The L rating quantifies the volume of air leakage through a firestop assembly at ambient and elevated temperatures, which is unrelated to water damage resistance.

The T rating measures the temperature rise on the unexposed side of a firestop system to evaluate heat transfer, not the system's ability to withstand water damage.

The W rating tests whether a firestop system can withstand water exposure - such as condensation, flooding, or pipe leaks common in boiler rooms - without losing its ability to resist fire. A firestop assembly installed near a service provider maintenance hole in a boiler room is at high risk of water contact, making the W rating the relevant performance criterion. Without a W rating, a system may physically degrade from water exposure before a fire event even occurs, rendering it ineffective.