Back to Basics - What is the L-Rating

The L-Rating is a measure of air leakage through an installed firestop system. The L-Rating measures the rate of airflow that passes through the firestop system. The L-Rating is listed in units of CFM (Cubic Feet per Minute) per device module or CFM per square foot, with achievable ratings listed at ambient and 400F. CFM per device module is intended to be applied to fixed device type firestop solutions, with CFM per Sq. Ft. intended for sealant or other soft seal-type firestop solutions, which have openings ranging from several inches to several feet in size. 

The L-Rating is measured at ambient, to replicate cold smoke is measured at elevated temperatures (400F) to be more indicative of hot smoke. Intumescent materials may begin to expand at elevated temperatures, and polymer jacket cabling may start to swell, so the L-Rating is typically lower at elevated temperatures.  

Unlike F & T-Ratings, the L-Rating is an optional test, and not every listing includes an L-Rating.

By STI Engineering Services