The set of tests from Underwriters Laboratories determines a system's ability to prevent the spread of fire through penetrated barriers.
By Chris DeMarco, CFPS, Specified Technologies Inc.
When the subject of firestopping comes up in a conversation, most people in the structured cabling industry conjure up thoughts of red caulk smeared all over neatly installed cables. In some cases the thoughts and memories are of a hassle rather than of satisfaction with a job well done. In reality, firestopping is almost always a simple process when it is thought out ahead of time rather than after a cable installation is complete. Taking time to plan for firestopping allows cabling design and installation professionals to create openings that are easily sealed.
As illustrated on the left, an unsealed penetration allows fire to propagate quickly from room to room unchecked. A rated and properly installed firestopping system, as illustrated on the right, will prevent the passage of fire, smoke and heated gases for a period of time equal to the rating of the fire-barrier floor or wall.
The textbook definition of firestopping is the process of installing third-party tested and listed materials into openings in fire-rated barriers to restore hourly fire-resistance ratings. A wall or floor may have such a fire-resistance rating, and when an opening is created for cable, conduit or any other service element, that barrier's fire-resistance rating is compromised. A properly firestopped opening restores the barrier's ability to resist the passage of fire. A barrier with an unsealed opening, regardless of how small or where located, no longer has a fire-resistance rating.
Firestopping is an important component of a building's multi-component life-safety system. Understanding more about firestopping allows us to understand the role it plays in such an important building system. Concerning fire protection, the three essential elements are prevention, suppression and containment.
The concept of prevention is simple. Remove or limit fire hazards to prevent (or minimize the probability of) fire. Suppression is actively extinguishing a fire. Sprinklers, fire extinguishers and clean-agent suppression systems are examples of active suppression systems. Containment, more accurately referred to as compartmentation, is using passive building materials to prevent the spread of fire. Strategically locating fire-rated barriers is a method of localizing the fire to the point of origin so occupants can safely exit the building and firefighting personnel can safely enter to extinguish the fire. Importantly, these barriers can also restrict or eliminate the progression of fire so that the building's active suppression systems (e.g. sprinklers), working in combination with the passive elements, can trigger and extinguish the fire. Firestopping fits into this category.
The definition of compartmentation is the practice of partitioning building space into smaller compartments by constructing barrier walls and floors that contain a fire for a specific period of time. Generally the amount of time is expressed in hours. For example, a 1-hour fire-barrier wall can restrict passage of fire for 1 hour.
A through-penetration is defined as the service element (such as a conduit or cable) that breaches a fire-rated barrier. In the nearby illustration, the red object represents conduit breaching a fire-rated compartment. Leaving the opening around the conduit unprotected, the fire has a path to quickly propagate into the adjoining space. Therefore, the fire-resistance rating of the barrier is compromised.
A properly installed firestopping system, also depicted in the illustration, seals the opening around the conduit and restores the fire-resistance rating of the barrier. The fire is now contained to the compartment of origin.
As previously mentioned, for many people the notion of firestopping means red caulk around conduit or cable. It is true that many firestopping caulks are red in color. But a complete firestop system is made up of more than just caulk. It starts with the fire-rated barrier itself, the floor or wall. There is an opening in the floor or wall through which the penetrating items are routed. The firestop material is installed in the opening in a manner dictated by an Underwriters Laboratories (UL) Classified firestop system in order to achieve a rating. The complete assemblage of elements (the barrier, penetrant, and firestop product) achieves the rating, not an individual product. A product by itself has no fire rating.
In order to fully understand firestopping one must be familiar with the two types of penetrations that occur through fire-rated barriers. For the sake of this explanation, we will use the example of gypsum-board walls although the concept would be the same regardless of barrier type. In a through-penetration, the service element penetrates both membranes of a gypsum-wall assembly. When the service element penetrates only one membrane of the gypsum wall assembly, it is considered a membrane penetration. Common examples of membrane penetrations are outlet boxes or cable drops that serve a single wall jack.
This illustration depicting gypsum-board walls shows a through penetration on the left, where both parts of the membrane are penetrated, and a membrane penetration on the right, where one membrane is penetrated. Examples of membrane penetrations seen every day in cabling systems include an outlet box or a cable drop that serves a single wall jack.
A properly designed and tested firestop system will be evaluated in accordance with the Underwriters Laboratories Inc. standard UL 1479, entitled Fire Tests of Through-Penetration Firestops. ASTM International has a similar standard, ASTM E814, entitled Standard Test Method for Fire Tests of Penetration Firestop Systems. This standard may be used at laboratories other than UL. Current building codes refer to both UL 1479 and ASTM E814. The two standards are almost identical in terms of test requirements, though there are some minor differences. In Canada, the referenced UL standard is CAN ULC S115 entitled Fire Tests of Firestop Systems. Its requirements are very similar to those of the other two standards. It is important to recognize these standards as building codes require the use of firestop systems tested to these standards.
UL 1479 exposes the test specimen to a standardized time-temperature curve, which assures all systems are tested to the same rigorous requirements in order to provide a benchmark. The time-temperature curve, which is shown in the nearby illustration, has been developed from studies of typical building fires and burn temperatures of normal building contents such as carpeting and office furniture.
This figure illustrates the critical nature of testing to UL 1479. At five minutes, the furnace temperature is 1,000 deg. Fahrenheit (538 deg. Celsius); at 1 hour the temperature reaches 1,700 deg. F (927 deg. C); at 2 hours the temperature reaches 1,850 deg. F (1,010 deg. C); at 3 hours the temperature reaches 1,925 deg. F (1,052 deg. C); and at four hours the temperature reaches 2,000 deg. F (1,093 deg. C). Consider how critical these high temperatures are, especially since aluminum cable conductors typically melt at 1,200 deg. F and many plastics will ignite at temperatures significantly below 1,000 deg.
Successfully passing tests to UL 1479 provides a firestop system with an F rating and a T rating. The F rating can be considered a flame rating. It indicates the time period, measured in hours, which a firestop system has successfully prevented the passage of a fire. A 2-hour F rating means the firestop system prevented fire spread for 2 hours. Typically, the test sponsor predetermines the duration of the fire exposure and the test specimen is removed from the furnace at that point.
The T rating is a measure of the thermal conductivity of a firestop system and can be considered a temperature rating. This is the time required for various points on the unexposed side of the test assembly to rise 325 degrees over the starting (ambient) temperature. The T rating is intended to provide engineering information relative to how hot penetrants might become in a fire exposure. Certain types of cables, cable trays or steel conduits may not be capable of achieving T ratings equal to the F rating because of the heat conducted through the penetrant itself. A large conduit, for example, might have only a 15-minute T rating. Physics cannot be denied; metals simply get hot!
The following paragraphs will describe the process of UL testing on gypsum-wall and concrete-floor-slab assemblies. A properly installed firestop system consisting of firestop sealants and devices seals the openings on each assembly and restores the fire-resistance rating of the barrier.
Thermocouples are placed on the unexposed (or non-fire-side) of the test assembly. Locations are as required by the test Standard including the following locations: 1) the firestop material, 2) the penetrant (if present), 3) the barrier, and 4) the sleeves (if present). Thermocouples measure heat rise through the firestop system and the data is used to evaluate the T rating. Multiple thermocouples may also be used in each of these locations in order to obtain a good understanding of the temperature rise and its effect on the surrounding construction and firestop system. Thermocouples may also be included at any critical location. Temperature measurements are made throughout the test process, even if the limiting temperature has already been achieved.
The test assembly is anchored to the test furnace, typically the top of the furnace for floors and the side of the furnace for walls. The furnace is computer-controlled to ensure it accurately follows the time-temperature curve. When the fire exposure test is completed and the test assembly is removed from the furnace, the combustible material on the fire side (such as plastic pipes or conduits, cable jacketing and insulation, etc.) has been consumed. Non-combustible materials (such as steel conduit and cable conductors) are glowing with heat. But if the firestop material has performed as designed and expected, fire has been stopped from passing through the assembly and everything on the unexposed side is in rather pristine condition.
During the testing process, firestop devices used on plastic conduit, for example, choke off the pipe through a process called intumescence–a chemical reaction in which heat applied to the firestop material causes it to expand quickly and in doing so, closes off the opening and prevents the fire from spreading. Intumescent products are very common in the industry and are particularly well-suited to plastic-jacketed cables, plastic conduits, innerduct and other combustible materials. Intumescent products are frequently used on non-combustible materials as well.
Immediately following the fire-resistance evaluation, is the hose stream test. This is by far the most difficult segment of the test to pass. The hot assembly is blasted with a stream of cold water from a 2.5-inch-diameter hose discharged at high pressure. Not only does the assembly need to withstand the force of the water pressure, but also the internal forces developed by the rapid cooling. UL 1479 prescribes the pressure and duration of the hose-stream exposure, which depends on the hourly rating being tested. For example, in order to achieve a 2-hour fire rating the assembly must withstand a hose stream of 30 pounds per square inch (psi) for 0.9 seconds per exposed square-foot area. This may not sound like a very long time, but consider a 4-foot-by-4-foot exposed area. Calculating, the test assembly will be subject to a 30-psi stream of cold water for 14.4 seconds.
Criterion for passing the hose stream test is the firestop system preventing passage of water beyond the unexposed side. It is important to remember that a building fire is a dynamic event. As pressure levels change and heat becomes more intense, surrounding structures and elements can fail, thereby stressing the firestop. The thermal shock of applying a cold, high-pressure stream of water to a red-hot assembly is a good measure of system integrity.
For purposes of testing in Canada to CAN/ULC-S115, the ratings derived are slightly different, although very similar to F and T Ratings established by either UL 1479 or ASTM E814 tests. The exception is that unlike UL 1479 or ASTM E814, successfully passing a water hose stream test is not required, but rather optional. Thus, the ratings are the F, FT, FH and FTH Rating. The FH and FT Ratings are equivalent to UL 1479 and ASTM E814's F and T Ratings, respectively. The F Rating is simply a measure of the ability of the system to resist fire, but no hose stream test. The FTH Rating is a combination of all of the above.
UL 1479 testing raises the temperature of the system under test to 1,000 degrees Fahrenheit in 5 minutes and to 2,000 degrees Fahrenheit by 4 hours. Aluminum conductors typically melt at 1,200 degrees and many plastics will ignite at temperatures well below 1,000 degrees.
L and W ratings
The Standard UL 1479 includes test protocols that are conducted at the option of the test sponsor. Two such protocols are for evaluating the L rating and W rating. These protocols are not included in the ASTM E814 and re two subtle differences between the test standards.
The L rating is a measure of airflow through a firestop system. Airflow is used in the absence of a test method specific for measuring smoke passage; the passage of air is considered similar to the passage of smoke. A "smoke rating" simply does not exist.
To conduct the L rating test, the test specimen is installed onto a test chamber that surrounds the entire firestop system. Air pressure within the test chamber is adjusted so the pressure differential between the inside and outside of the chamber is a 0.30-inch water column, which equates to about 75 pascals. An air flow metering system is used to measure the amount of air passing through the firestop system. The test is conducted both at ambient temperature and at an elevated temperature of 400 deg. F (204.4 deg. C) to evaluate the firestop's ability to restrict the passage of both cold and hot air.
The L rating takes into account air flow through all areas of the firestop system. For example, when the system addresses grouped cables, this method registers air flow through the interstitial spaces of those grouped cables, not only the firestop product surrounding the cables.
The W rating is used to evaluate a system's ability to restrict water migration in applications that demand a higher degree of water resistance. Most commonly tested are Class 1 ratings in concrete floors. To evaluate a W rating, a test vessel is installed over the firestop system, sealed directly to the barrier, and filled to a 3-foot waterhead or equivalent pressure. The water is dyed so any migration through the firestop system is recognizable on a white indicating medium located below the firestop system.
The duration of water exposure is 72 hours. During this time the test specimen is evaluated by looking for evidence of water migration on the white indicating medium. After water exposure, the test specimen is conditioned and subjected to the fire-resistance and hose stream portion of the UL 1479 test. To achieve the W rating, the system must not only resist water migration, but also successfully resist the fire exposure and hose stream test.
To summarize, firestop systems, not individual firestop products, achieve ratings based on evaluation to the Standards UL 1479, ASTM E814 or CAN ULC S115. F and T ratings are mandatory results of these tests. UL 1479 offers optional test protocols for evaluating L and W ratings.
As with many materials and systems, a firestop system is only as effective as the manner in which it is installed. A good installation will be consistent with the characteristics described in the firestop system. Unfortunately a firestop system can be rendered ineffective if installed improperly. Installation practices considered improper include inappropriate mixing of products, using materials other than those tested as part of a firestop system, not following the parameters of a firestop system, and of course penetrations that are not protected at all or whose protection has been removed or reduced over time. Such a system has no integrity and presents a safety hazard rather than being an important component of a building's life-safety system.
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