You are designing a firestop system for a hospital with several floors that have isolation rooms. Air leakage control is important to ensure rooms are sealed and restrict the spread of disease…

The F rating evaluates a firestop system's ability to resist flame passage and maintain structural integrity under fire conditions, with no measurement of air leakage at ambient or elevated temperatures.

The L rating, evaluated under UL 1479 and ASTM E283, measures the volume of air that passes through a through-penetration firestop assembly at both ambient temperature (L-ambient) and elevated temperature (L-400). For hospital isolation rooms that rely on negative or positive pressure to contain airborne pathogens and prevent cross-contamination between spaces, specifying a firestop system with a verified L rating ensures that cable and conduit penetrations do not undermine the room's pressure boundary and infection control design.

The T rating measures the temperature rise on the unexposed side of a firestop assembly to assess thermal transfer performance, which is unrelated to air leakage or pressure containment.

The W rating assesses a firestop system's resistance to water penetration under hydrostatic pressure, and has no relevance to air leakage or room air pressure control.