Fire protection is serious business. Fire, smoke, and toxic fumes take a terrible toll in lives and property every year. Every major building code is meant to reduce the threat of fire.
Fire protection encompasses three broad areas: prevention, containment, and suppression. The distinction between containment and suppression is that between passive and active protection systems. Passive systems protect by virtue of their inherent properties, while active systems rely on external energy sources such as electricity, water pressure, or human intervention.
Firestops are an integral part of any fully implemented containment system. Containment is the principal strategy embodied in all building codes.
In building codes, safety and environmental issues have been handled as overlays or amendments, while fire safety is the fabric that binds the code requirements together.
Important sections of the codes deal with safe and acceptable methods of using energy sources or handling and storing dangerous materials. These sections focus on preventing fire through misuse of resources. For example, electrical codes specify the size of conductor, type of insulation, method of installation, location of disconnecting means, and overcurrent protection for various applications, in order to eliminate unsafe wiring practices that may result in fire. Other sections of building codes deal with furnaces, fireplaces, ducts, flues, kitchens, etc.
The codes also recognize that accidental and arson fires cannot be entirely prevented. Fire-rated walls, floors, partitions, shafts, columns, drop-ceilings, and related assemblies are required to limit the size and spread of fires. Some areas require sprinklers or other active systems to extinguish fires.
Fire-rated barriers provide the basic, passive protection necessary for fire safety. By definition, passive protection is independent of any outside agency or energy source.
Active systems, such as sprinklers, CO2 extinguishers, or gas suppression systems, rely at the very least on the availability of a water, CO2, or gas supply, and often also require electricity for pumps, valves, and detectors. Active systems frequently control or suppress fires before human firefighters can respond, but failure of the supporting utilities can make an active system inoperative. That’s why an active system can never be considered as an alternative to the passive fire barriers required by the codes.
Firestops are an integral part of every passive protection system. Passive fire barriers create isolated compartments, which effectively contain a fire, preventing it from spreading to adjacent areas. Openings in fire-rated barriers permit access to the area and admit utilities: electricity, water, heat, etc. Provision must be made to preserve the integrity of the barriers when openings are required. Fire-rated doors and windows must be installed to protect the normal access openings, while fire-rated penetration seals (“firestops”) are required to seal openings for building utilities.
A firestop must satisfy a number of requirements. First, it must be able to meet the same fire resistance rating as the barrier in which it will be used. Second, it must accommodate the penetrating items, including any requirements for motion, thermal expansion, or other functions. Third, it should function as a smoke barrier.
Fourth, it must be reasonably easy to penetrate again to accommodate building service modifications. Finally, it must be reasonably inexpensive.
F-ratings and T-ratings
Current test standards for firestop systems, ASTME814, UL1479, and CAN4-S115M, generate multiple ratings for each system design. The test specimen is subjected to a standard fire exposure, followed by a standard hose stream test. During the fire exposure, thermocouples measure temperatures on the test wall or floor, on the field of the firestop material, and on the penetrating item 1 inch away from the surface of the firestop. Based on evaluation of test data and observations, the laboratory assigns ratings as follows:
* An F (for fire exposure) rating, in full hours, indicates that the test assembly withstood the standard fire exposure without penetration of flame of spontaneous ignition on the unexposed side, for the indicated period. And, except in Canada, it also indicates that there was no passage of water to the unexposed side during the hose stream test.
* An H (for hose stream) rating, in Canada only, indicates separately that the assembly passed the hose stream test.
* A T (for temperature) rating, in full or fractional hours, indicates that no temperature on the unexposed side increased over ambient by more than 325 degrees F (180 degrees C) for the indicated period. Measurements include the penetrating item as well as the firestop seal itself. The T-rating can be rated as “0,” but can never exceed the F-rating.
The F (and H) ratings demonstrate the effective ability of the seal to prevent the spread of fire by breaching the rated barrier. F-ratings should always equal or exceed the required rating for the barrier being penetrated.
The T-rating was incorporated into the test procedure to aid in hazard assessment. Low T-ratings are nearly always associated with massive or thermally conductive penetrating items able to carry heat from the exposed to the unexposed side.
Under some conditions, high temperatures on the unexposed side could presumably result in self-ignition of adjacent combustible materials. This is clearly a function of the penetrating item rather than the seal design, and where such a hazard might exist, the engineer can recommend provisions to prevent close proximity of combustibles.
The obligation to specify and/or install “Qualified” firestops may not be your only concern. Did you specify the innerduct and cable jackets to be installed (by type and manufacturer)?
If so, your responsibility may not end when you “light-off” a system and leave the premises.
Authority Having Jurisdiction. The term used in model building codes to refer to the specific individual, agency, or department responsible for local code enforcement. In practical terms, this is the building inspector.
Classification. The method used by UL to rate application-oriented products like firestop materials, where the final configuration is different in each installation. Firestop materials are “UL Classified,” never “listed” or “approved.”
Assembly. A wall, floor, or other partition, with or without such things as receptacles, outlet boxes, recessed lighting fixtures, or penetrations. The details of the assembly must be spelled out in any approval.
System. The assembly, the penetrating item(s), and the firestop materials together all constitute the system. The system is the only basis for classification.
Penetrating Items. The specific cables, conduit, pipe, ductwork, etc. that pass through the opening in the assembly, and that are to be protected by the firestop.
Intumescence. The formation of a high-volume, insulating char upon exposure to fire or elevated temperatures, the key property of an important class of firestop materials. To be useful, the expansion should be at least 30 percent, with most commercial materials running 100 percent or more. The resulting char should be strong enough to resist the turbulence of a severe fire, and insulate well enough to protect the underlying surface.
O’CONNOR is product manager at Nelson Firestop Products, Tulsa, Okla. He can be reached at (800) 331-7325.