Which of the following rating classifications indicates the amount of time a firestop can resist the passage of air/smoke?

The L rating is specifically designed to indicate the amount of time a firestop system can resist the passage of air and smoke. This classification is essential in establishing how effectively a firestop can help maintain the integrity of fire-rated barriers by limiting air and smoke movement through openings that could compromise safety during a fire event.

The L rating focuses on the system's performance related to air leakage, which is critical for maintaining a safe environment by controlling smoke spread, reducing toxicity, and improving the overall effectiveness of firestop systems in fire protection. Understanding this classification is vital for anyone involved in the installation and inspection of firestop systems.

On the other hand, the other ratings, such as the F rating, generally indicate the effectiveness of firestop systems in preventing the passage of flames and heat, while the W rating pertains to water resistance. The R rating can relate to additional performance criteria beyond just smoke and air leakage. However, when it comes explicitly to measuring how well a system can resist the passage of air and smoke, the L rating is the right classification to reference.