Firestopping Through-Wall Cable Penetrations

Firestopping of through-wall cable penetrations involves more than simply buying and installing one of the many products available on the market today. A firestopping system encompasses the fire-rated wall, the penetration itself, the cables, the cable tray or conduit that pass through the penetration, and one or more firestopping products. Recent advances in firestopping technology have resulted in systems that demonstrate improved results in standard tests, and that are not dependent on the actions of contractors to ensure performance over the long term.

Current methods and analysis

Cable tray is terminated at the wall and a conduit sleeve penetrates the wall to provide a path for cables and contains firestopping material. Alternatively, the entire cable tray passes through a wall opening, which is then filled with firestopping materials. Many of today's firestopping products employ intumescent materials that, when exposed to heat, expand to fill a void in the penetration. Commonly used materials include:

• Firestop mortar and caulk are semi-permanent products. Caulk is applied to the penetration a with hand-held caulk gun.
• Putty sticks are manually molded around cables, conduit, and pipes.
• Firestop blocks and pillows contain intumescent material and are typically stacked and otherwise fitted into large penetrations.

Although the products listed above are effective as firestop materials, their effectiveness can be compromised by the effects of moving, adding, or changing cables; failure to follow the UL Fire Resistance Directory; and the difficulty of proper inspection of the installation.

While some wall penetrations are permanent, it is far more likely that cables will be added and/or removed during the life of a building due to changes in cabling technology and/or number of workstations in a given space. Semi-permanent materials like caulk and mortar must be removed and replaced each time a cable is added or removed. While putty does not harden and crack, and thus can be reused, care must be taken following the cable change to ensure that the material is properly placed. Pillows are designed to be removed but they, too, must be reinstalled properly. Also, when installed in exposed locations, pillows are subject to tampering.

Certain materials, including caulks and putties, can be difficult to inspect following installation. An improper or incomplete installation may be masked by an outer surface that appears to be code-compliant but which conceals gaps, voids, and other potential hazards.

Testing and Performance

Firestopping systems are typically categorized by one or more of the following ratings, according to UL 1479 (ASTM E814).

Flame: The F rating (FH in Canada) is expressed in hours. This number indicates the specific length of time that a barrier can withstand fire before being consumed or before permitting the passage of flame through the opening.

Temperature: The T rating (FTH in Canada) is expressed in hours and indicates the length of time that the temperature on the non-fire side of the penetration does not exceed 325°F above the ambient temperature. This ensures that the temperature on the side of the wall away from the flame does not reach the flash point of any materials on that side of the wall.

Smoke: The L rating (U.S. and Canada) is the amount of air (and thus cold smoke) that can leak through a penetration, measured in cubic feet per minute. The test is administered at ambient temperature and at 400°F due to the actual performance of firestop materials at different temperatures.

Through-wall penetration firestop devices may also be tested to UL 2043 as to their suitability for use in air handling spaces (plenums). This test measures the rate of heat release and the optical smoke density of a burning sample.

Next-generation firestop technology

The newest development in firestopping is an integral system that combines intumescent firestopping material with a through-wall penetration device. This system reduces the size of the wall penetration when compared to the large opening required to allow a cable tray to pass through. This technology is also easier to install, maintains the fire rating of the wall without the need to add firestop material after the cable installation, is tamper-resistant, and is more convenient to inspect. Further, the through-wall penetration remains fully accessible to add or remove cables without disturbing the firestopping material.

These through-wall penetration systems are similar to fire-rated poke-through devices in that they contain a pathway for cables and integral intumescent material. Poke-through devices, which allow cabling to penetrate fire-rated floors, use integral intumescent material that expands when exposed to heat and seals the penetration. This same technology is now being applied to firestopping through-wall penetrations. Such a system consists of a cover that houses a block of intumescent material with an opening through which the cables pass. A length of conduit carries the cables through the penetration to a similar cover and block of intumescent material on the opposite side of the wall.

In a fire, when the temperature reaches approximately 375°F, the intumescent material begins to expand. Unrestrained, this material will expand to six to 12 times its initial volume; in an enclosed space, it creates a hard char that fills voids around the cables and blocks the path of the fire. One such through-wall penetration device from The Wiremold Company has achieved an F rating (flame) of four hours and a T rating (temperature) of up to four hours. It has also achieved an L rating for air leakage, indicating the ability to provide an effective smoke stop. Because the intumescent material is integral to the device and is not installed after cable installation, these ratings apply at all cable fill levels from zero to full capacity. This device also includes adjustable metal doors that create a solid barrier between rooms. It is classified by UL for use in air handling spaces (plenums).

Conclusions

The science of firestopping through-wall penetrations is evolving - and so are regulatory requirements. Current U.S. and Canadian building codes only require an F rating for through-wall penetrations. However, many specifiers and a growing number of local authorities are starting to require T and L ratings as well. These decision-makers also recognize that the effectiveness of firewalls can be compromised as firestopping materials are removed and replaced in the course of routine cabling moves, adds, and changes.

The most effective firestop system is one that both demonstrates a high level of performance as measured by UL testing, and contains integral firestopping material that is not affected in any way by the addition or reduction of cabling.