Firestopping: Start With the Basics

Bill Ronca

William (Bill) J. Ronca is a Business Development Manager for K-Flex USA. ( in Youngsville, North Carolina. He has also served as a Regional Sales Manager, Product Manager, and Technical Advisor for their insulation product lines. Mr. Ronca has 38 years of experience in the construction industry and is currently a member of ASHRAE, RETA, IIAR, SMACNA, and NADCA. He can be reached at

June 1, 2005

As a technical advisor for a manufacturer of closed-cell flexible foam insulation materials, I often hear the question, "Can I use firestopping materials with your products?" While the simple answer is yes, a basic understanding of what firestopping systems do and what they entail is necessary in order to provide the correct firestopping system for the construction conditions.

Building codes require firestopping wherever piping penetrates a fire-rated floor, ceiling or wall. Since most holes are drilled or cut oversized, firestopping is used to fill the gap, or "annular space" between the penetrating item and the edges of the floor, ceiling or wall. Providing the correct firestopping system maintains the integrity and fire rating of the construction.

Firestopping systems are usually tested on large-scale or small-scale fire-test furnaces following the ASTM E119 (UL 263) time-versus-temperature profile. In this test, there is an "exposed" side that is subjected to fire, and a non-fire or "unexposed" side. There are three components to a firestopping fire rating: F, T and L ratings. The F rating demonstrates the ability to prevent the passage of flame through the opening. The T rating indicates the ability of the firestop system to limit the temperature increase on the non-fire side of the floor, ceiling or wall. The most recent component, the L or leakage rating, is a measure of the system’s ability to prevent the passage of hot and potentially toxic gases. Firestopping fire ratings are expressed in terms of time, with ratings ranging from 15 minutes to four hours.

Firestopping approvals, such as those listed in the Underwriters Laboratories’ (UL) Fire Resistance Directory, Vols. 2A and 2B, are very specific to the floor, ceiling and wall construction, the size of the opening, the type, size and number of pipes penetrating the opening, and the size of the annular space and the spacing between pipes when there is more than one penetrating item. Firestopping ratings are also very specific to the type and thickness of insulation used on these pipes.

Elastomeric insulation products are acceptable for use in 294 firestopping designs listed in the UL Fire Resistance Directory. In the directory, elastomeric products are listed as "Tube Insulation-Plastics." Products acceptable for use must be UL-listed in Category QMFZ2 of the Plastics Recognized Components Directory. The UL-listed firestopping systems require the insulation composition to be "acrylonitrile butadiene rubber/polyvinyl chloride (AB/PVC)," which is synonymous with nitrile butadiene rubber/PVC composition of the most widely used elastomeric insulation products. This requirement currently would preclude the use of ethylene propylene diene monomer-based insulation materials.

Elastomeric products are listed for use in wall thicknesses up to 1 inch on copper, iron, steel, PVC and chlorinated polyvinyl chloride piping and polyethylene tubing for F ratings of up to three hours, T ratings to two hours, and L ratings to two hours. Pipe sizes up to 10 inches are listed. Some of the firestopping manufacturers with products approved for use in these designs include 3M, DAP, Hilti, Nelson, Passive Fire Protection Partners, Rectorseal, Royal, Specified Technologies, Tremco, USG and W.R. Grace.

There are numerous firestopping systems for protecting constructions containing uninsulated pipes. While this may seem like a simple solution when using insulation products that are not UL-listed, it is not necessarily the best solution. On hot piping systems, the worst effect may be a limited heat loss. On cold piping systems, the elimination of insulation may result in condensation and the potential for mold growth, especially in pipes passing through wall systems.

For insulation products that are not listed in any UL firestopping systems, it is recommended that a short length of elastomeric or fiberglass insulation be used for where the pipe passes through the opening. This allows for the selection of a firestopping design based on elastomeric or fiberglass insulation materials. The use of fiberglass is not recommended on any systems where condensation is a concern. It is also recommended that any non-listed firestopping system proposed for use be submitted to the authority having jurisdiction for approval prior to installation.

While my focus has been on Underwriters Laboratories, it should be recognized that there are several other testing laboratories that are accredited by the code agencies to test and maintain firestopping system listings: Southwest Research Institute, OmegaPoint Laboratories and Intertek/ETL (Warnock Hersey) are just a few.

The easiest way to navigate the firestopping maze is to obtain information from the firestopping material manufacturers. They provide information on their websites, on CDs and in hard copy that encompasses their approvals from all certified testing agencies. They are also an excellent source of information and recommendations for job-site conditions that do not quite comply with any listed firestopping systems.

Insulation products are only one component of an approved firestopping system, and do not have an hourly fire rating independent of the other components of the system. For more information on firestopping systems, consult the UL Fire Resistance Directory or the manufacturers of firestopping materials listed above.