The Rigors of Firestop Tests

Posted on 5/23/2018 9:02:15 AM By Sharron Halpert

We have talked a lot about firestop and how it is tested, but we have not really discussed the various ratings they can achieve.  I’m not talking about the hourly ratings, but rather something different.  Firestop assemblies can be tested to the following ratings F, T, L and W.  Some are code required and some are optional.  Some, like the L rating we will discuss today, are required in some cases and optional in others.  Today’s blog will go over the L ratings, what it is, when it is required and how to be sure you meet this requirement.  We will get into the others shortly, but if you can’t wait to learn what they are, you can go HERE.

Let’s dig into these L-ratings. They are defined as“the amount of air (or cold smoke) that can leak through a penetration and the number indicates the amount of air in cubic feet per minute. L-ratings are tested with a differential pressure of 0.30 inches water column (75 Pa) at 75 oF and at 400 oF.”  Similar to the test for movement criteria that we talked about in THIS POST  for the joint assemblies.  This test is conducted before the assembly is placed on the furnace for the burn test.  This is true of both rated joint assemblies as well as to rated through penetrations.

The L rating is a requirement that can be found in the 2015 IBC and several previous code cycles as well. It specifically states: “714.4.4 Penetrations in smoke barriers shall be protected by an approved through penetration firestop system installed and tested in accordance with the requirements of UL 1479 for air leakage.The L rating of the system measure at 0.03 inch of water in both the ambient temperature and elevated temperature tests shall not exceed:

1) 5.0cfm per square foot of penetration opening for each through penetration system; or

2) a total cumulative leakage of 500 cfm for any 100 sq ft of wall area or floor area”

Reference for 714.4.4 HERE.

This means that if you are a firestop installer or inspector, you need to know where the smoke barriers are in the building. Then you need to ensure that the firestop details that are submitted will meet this requirement, which means they need to have an L rating listed. If you are an architect responsible for reviewing firestop submittals you need to ensure that the smoke barrier walls have all the firestop details they need and that needs to include L ratings. It also means that if you are a manufacturer this L rating will be a requirement for your firestop details. 

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When you are looking at the firestop submittals, the image above is from a UL listed detail that does not have an L rating.  Below is a system that has an L rating.  Please note it says see Item 1B.  This means likely means that something particular needs to be done in order to achieve this L rating. This is potentially one more step for the installer and the inspector to follow through on during their scope of work.

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The article started by saying that L ratings could be a code requirement in some cases and we discussed this, but we did not discuss the cases where they may not be required by codes but rather by the architect’s specifications.  A few examples could be in hospitals, data centers and even condominiums and apartments.

An architect may specify L ratings in these types of occupancies for very different reasons. Let’s take apartments and condominiums for our first example.  The biggest complaints are noise and smells that make their way from one unit to another. L ratings can help reduce both of these complaints.  Hospitals have this concern with what they call nosocomial infection. The basic idea is that you go into the hospital with a broken arm and you leave with a cast and the germy bug you have ever had.  Properly firestop buildings can reduce the rate of nosocomial infection and this happens by reducing the air leakage. Data centers are a concern because when you look at all the plastics that are in a data center, lets take PVC for an example.  When that burns you get airborne particles of polyvinylchloride. When the chlorine combines with the water in the atmosphere you suddenly have airborne hydrochloric acid that gets into the electronics and renders them useless.   The more airflow is reduced the less damage from smoke migration.

Hopefully, this helps you understand the importance of this little know firestop rating. If you have any questions about this code requirement, you are welcome to reach out to the author.  Additional resources are the international Firestop Council ( the International Code Council ( or Underwriters Laboratories ( as well as the individual firestop manufacturers.

Thanks for your time and keep learning about this industry, you never know when it could save your life.

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