Because the L rating test is optional within the UL 1479 test standard,
code users must not simply assume that a firestop system tested to
the UL standard will comply and must verify that the firestop system
being used has actually been tested and received an L rating. The
code specifies that the amount of leakage permitted cannot exceed
5.0 cubic feet per minute (cfm) per square foot of opening for each
penetration, or a total leakage rate of 50 cfm for any 100 square
feet of wall or floor area. Having the L rating requirement within
the code provides a specific means to evaluate the capabilities of
the system and eliminates the subjective requirements that smoke
barriers needed to “limit,” “restrict” or “resist” the passage of smoke.
A specified performance level reduces the inconsistent application
of the requirements and helps code users know exactly what level
of performance is required.
It is important to point out that penetration systems must be evaluated
for their L rating at “both the ambient temperature and elevated
temperature tests.” While it is permissible for an intumescent F-
or T-rated firestop system to leave a gap between the penetrant
and firestop material when it is initially installed (due to the fact the
intumescent will expand to close the gap when the temperature at the
penetration increases), an L-rated system must provide an effective
seal both at its original installation and when or if it is exposed to
the increased temperatures of a fire. Because the purpose of the
L rating is to stop the spread of smoke, the code recognizes that
smoke could be located away from the fire in a place where the
temperature has not elevated to the point that it would cause an
intumescent material to expand and fill any gaps that would allow
for the passage of smoke. It is because of this need to stop cold
smoke that the code requires the L-rated system to be evaluated at
both ambient temperatures and an elevated temperature of 400oF.