Firestopping exposed wires and cables
An “almost perfect” firestopping system isn’t good enough when a fire starts in a building. There are several reasons for providing firestopping for wires and cables. It may be a requirement of the building code, or of an insurance carrier or a building owner that wants to minimize the risk associated with fire spreading from one part of the building to another.
By Tim Kuhlman, PE, RCDD, CH2M HILL, Portland, Ore.
When a fire occurs, you rely on the firestopping to mitigate the loss of people and property. Having a firestopping system that is “almost” perfect isn’t good enough when a fire starts in a building.
There are several reasons for providing firestopping for wires and cables. It may be a requirement of the building code, or of an insurance carrier or a building owner that wants to minimize the risk associated with fire spreading from one part of the building to another.
Under ideal conditions, a firestopping device is exposed to extreme conditions when a fire occurs, and it is required to function as it was designed. In simple terms, the device is designed to seal the opening in a fire-rated wall or floor to prevent a fire or smoke from spreading.
During a fire, the rated assembly and firestop device will be exposed to flames, high temperatures, and the water pressure of a fireman’s hose. In the case of firestopping for wiring and cables, exposed cabling will change in size as the insulation is burned off. As a result, bundles of cable will not form a rigid structure for the intumescent material to work against. Plastic conduits will melt or burn, and even thin-walled metal conduit will deform and melt.
The firestopping industry has developed a plethora of devices for firestopping wires and cables whether they are routed exposed or enclosed in a conduit, wireway, or cable tray. The list of firestopping materials includes sprays, caulking, putties, grouts, sleeves, grommets, plugs, wraps, plates, blankets, pillows, sheets, inserts, and a variety of other devices. There is a firestopping system or device for just about every annular space in a wall or floor that you can imagine.
Engineers and installers have imaginative ways of routing their cables through a building, and penetrating a rated wall is often not a primary concern for them. The firestopping industry has stepped up to the challenge to accommodate a variety of installation requirements with the intent of properly firestopping the penetrations. However, even a properly specified and installed firestopping device can result in something that is less than perfect for a building owner.
For any given rated wall or floor, there may be multiple methods to firestop the wires and cables passing through it. For the sake of argument, we will assume that the firestopping appliance selected and installed matches the fire rating of the wall or floor system. This may meet the requirements of the building code, but may fail in meeting the building owner’s operational needs or the building’s long-term fire protection requirements.
Labeling and warning signs
Identifying the rated walls and floors for a building begins in the design phase. The architect will define the rated walls and floors as part of his code analysis. The drawings are used to communicate the rated areas to the engineering design team and then to the contractor. This facilitates the engineers to select the proper firestopping device for their wiring methods and therefore instructs the contractor how to build it. At least this is ideally what should happen. In most cases, a list of Underwriters Laboratories (UL) listed systems for penetrating a rated wall assembly is provided in the specifications by the architect, and it is left up to the contractor to select the correct firestop device to use.
The International Building Code (IBC) 2009 does not require a rated wall or floor to be labeled with its fire or smoke rating. The key is to extend the communication of rated walls or floor types beyond the initial design and construction team. This information needs to be communicated to building operations and even to subsequent contractors that will be involved with the adds, moves, and changes during the building’s life. A good way to start is to provide labeling or warning signs on the rated walls or flooring identifying the fire rating (see Figure 1).
Labeling and signage is usually left to the very end of a project when the last of the finish paint work is completed and prior to inspection. The requirement to provide rated wall or floor warning signs should be dictated in the specifications or drawings provided to the contractor so that the labeling occurs during the initial building construction. This way, the labeling will benefit both the building owner and the installer who may not have access to the original construction documents.
A measure of common sense needs to be applied in determining where to place the warning labels. Choose areas where wall or floor penetrations are likely, such as in utility riser rooms or above the suspended ceiling. In buildings with rated floors where there are large open floor spaces, such as in office areas using modular furniture, it might be difficult to find a location to place the floor rating label. Since the cabling to the open areas has to run back to a set of electrical panels or a communications room, consider placing the warning labels in these areas. When placing labels on a rated wall above a suspended ceiling, consider how far a person can see while standing on a ladder with a limited field of view. A label just above the suspended ceiling at a spacing of two or three ceiling tiles widths should be viewable. In open corridors where there is no suspended ceiling, place the label in the area where other penetrations have already been made during the initial construction.
Mixing of manufacturer’s materials
The labeling for firestopping also should include a label identifying the specific firestopping device being used at each location. A common mistake in post-build installation of cabling occurs when firestopping material, such as putty, has been removed to add cabling and the firestopped penetration was repaired with putty from a different manufacturer. Do not mix manufacturer’s components and materials.
However, this can be difficult to avoid if you don’t know the manufacturer of the installed firestopping appliance. Each manufacturer tests its designed assemblies and receives a UL system number. The manufacturers do not test their products with other manufacturers’ components. Even mixing components such as putty and pillows can cause a firestopping device to fail. For the system to work properly, the materials need to react at a uniform rate. If a manufacturer’s materials are mixed, one material can react at a different rate than the other and, in turn, push the remaining firestopping out of the filled annular space before it can react to seal the opening.
The firestopping device identification label should identify the following: the manufacturer, the UL system number, facility contact name, and the maximum capacity for a specific cable type (see Figure 2). If the label is to indicate the maximum cable capacity, then a specific cable type needs to be listed.
With some firestop devices, the T rating of the device may change depending on the size or type of cabling that is routed through it. A label may not be necessary for penetrations that will not see any adds, move, or changes, such as in feeder conduits to an electrical room. However, labels should be required for smaller cables that will most likely see a lot of changes over the life of the building. With the information on the label, the installer should be able to identify the system and get information on how to re-enter and re-seal the device.
A fire riser pipe that is firestopped at every rated floor and wall penetration may never need to be touched again for the life of the building—or at least until there is a major retrofit of the building. This is not the case for wire and cable. Through the life of a building, the tenant spaces will be reconfigured, equipment will be relocated, or additional power and communication circuits will be added as the amount of technology increases or changes in the building. The smaller the wire or cable that is run in a building, the more likely they are to change over time. This applies to lighting circuits, power receptacles, fire alarm cabling, security systems, communications cabling, and other technology-related cabling.
When selecting the firestopping device, ask yourself the following questions:
- Will multiple re-entries into the firestopping device be likely and required?
- Can the materials that make up the firestopping device tolerate multiple entries?
- Will the contractor, after the initial installation, understand how to disassemble and reassemble a firestopping device after adding more wire and cable?
- Will the contractor know when adding or removing a cable if he has jeopardized the integrity of a fire stopping device because he has added or removed too much cable?
- Will the person installing the cable be a licensed contractor? Will he or she know what a fire-rated wall is or how a firestopping device is designed to work? It is not uncommon for an unlicensed or inadequately trained facility employee or handyman to install some additional data or audio/visual cables.
- Are you selecting a firestopping system that will be installed per the UL system requirements at initial construction but will be easily compromised when a new cable is added?
Figure 3 illustrates three different types of firestop penetrations commonly seen for use with exposed cabling for a rated wall constructed of gypsum board. The specific limitations of each firestop system will depend on the manufacturer. System 1 is the least expensive of the three systems illustrated. It consists of a hole in a rated wall with cable passing through it. The annular space is filled with an intumescent putty. Variations of this system may use a coil of steel as a sleeve. This firestopping system has the least amount of capacity for cable, and it is also the most likely to be violated in high-traffic areas. After the initial install, each subsequent installer will be tempted to reuse the existing penetration. They are likely to remove the putty to feed through another cable or may even chip away at the wallboard to make the opening larger. An installer willing to cut corners on the cabling installation may even ignore the requirements posted in a firestopping label.
For this system to work properly, the annular space between the cable and the wallboard has to have enough intumescent putty or caulk to expand and seal the hole when exposed to a fire. The dimensional limits of the annular space are defined in the firestop UL system information. The cable has to be supported at both ends such that the cables are centered in the hole and over time the weight of the cable does not push it to the bottom of the opening. This can be difficult to maintain with cables that are supported on either side of the rate wall from support wires.
System 2 uses firestopping pillows to seal the annular space, which are convenient to remove and replace. System 2 has a higher initial cost than system 1, but the cost can vary depending on the size of the penetration allowed for the cable tray to pass through. The larger the space, the more pillows it will take to fill the void. The cable tray provides a rigid support structure for the cabling, which makes it easier to maintain a fixed annular space between the wallboard and the cable tray. However, this system also has drawbacks. Once removed, the pillows might not be replaced. I have seen cases where the pillows have fallen into the hollow space of the rated wall. In fact, normal building vibration can cause the pillows to vibrate out of place. Chicken wire can be used to keep the pillows in place, but this makes it more difficult when more cables need to be added. The cable tray can easily be overloaded, with cables beyond what the UL system allows. For data cables whose cable tray fill is allowed to go up to 50% calculated fill, the firestopping system may allow only for 30% calculated fill.
System 3 is an engineered device consisting of an intumescent material integrated into a sleeve. This system has a higher initial cost than system 2, but it is more likely to maintain its integrity with multiple re-entries. There are a few types of manufactured sleeves on the market. One manufacturer uses intumescent foam inserts at each end of the sleeve, while another uses an intumescent pad that resides inside the sleeve. The design using the pad has the advantage that it is permanently in place and is not removed when more cables are added through the device. As cables are added or deleted, the integrated pad adjusts to the number of cables routed through it. If the pad doesn’t have to be removed, it cannot be lost by the cable installer. The manufactured sleeves typically allow for 100% visual fill for cable capacity.
In working with smaller cables, I have found that 100% visual fill is approximately 40% to 50% calculated fill. Of course, this will vary depending on the size of the cables and how neatly they are bundled together.
Do not substitute components. As noted earlier, firestopping products of different manufacturers cannot be mixed in a device. Likewise, if a device is designed to use a metal coil sleeve, it cannot be substituted with a piece of electrical conduit. In many cases a sleeve is split and is designed to expand or contract as the intumescent material around it reacts. A piece of metallic tubing is rigid and will not react the same. Do not use a material in a firestopping device unless it is specifically allowed in the firestop device application notes. Manufacturers vary in their UL system designs for the length of the sleeve that extends beyond wall surface of the penetration. What is acceptable for one manufacturer is not for another.
The National Electrical Code requires electrical continuity in non-current-carrying conductors such as metal raceways and cable trays. There is an exception for the bonding of metallic sleeves that provide protection to cabling. However, it is prudent to bond a sleeve if it is in close proximity to a grounded cable tray or raceway. Do not bond a firestopping sleeve to a raceway or cable tray unless the firestopping manufacturer specifically allows for this. This would be noted in the manufacturer’s UL system application notes. Even though the NEC has an exception for not bonding sleeves, the local inspector may still require the sleeve to be bonded. If you think this is a likely issue in your jurisdiction, select a firestopping sleeve device that can be bonded. Make sure you bond both ends of a metallic raceway, or you will have an antenna.
Industrial facilities bring their own set of challenges to firestopping. The complexity of the building construction, the size of the facility, adjacencies, and possible exposure to chemicals may result in needing a firestop UL system that cannot be found in a firestop manufacturer’s catalog. In these cases, the firestopping device may be engineered by a licensed engineer or architect and then submitted to the jurisdiction and insurer for approval. Third-party testing of the system may be required. Often, when alternative means and methods are being considered for a rated wall system, it is not for the evaluation of a single firestopping penetration. The approval process may look at the broader system, taking into consideration each type of utility penetrating the rated assembly and the overall fire protection plan for the building. It’s a good idea to interview local inspectors to determine what they are looking for.
The integrity of a fire-rated wall or floor assembly is at the mercy of the “small wire” installers. This is not to say a mechanical duct or some other utility can’t equally jeopardize a rated wall assembly if improperly installed. However, there are more likely to be changes in the exposed cabling routed in a building than other building systems. Therefore, the chance that cabling changes can jeopardize a rated wall or floor assembly is higher. We need to focus more effort in identifying the rated wall and floor assemblies and in the selection of the firestopping devices. The IBC doesn’t require the labeling of a rated wall or floor assembly, and most jurisdictions do not require an inspection of the rated assemblies past the initial construction of the building. I don’t believe there is a firestopping device that is foolproof, but consider the knowledge of the person installing the cable. The installer who re-enters a firestopping system can vary from a highly skilled craftsman to a cable-pulling day laborer.
Of all the systems installed in a building, a firestopping system is unique in that it must sit dormant until the one moment—during a fire—when it needs to function. Firestop penetrations are typically out of sight and can be easily overlooked. Yet maintaining the integrity of a building’s rated walls and floors is critical when a fire occurs. A firestopping system that is compromised cannot be trusted to contain the fire and smoke.
What is a reasonable approach to firestopping wires and cables? Start with labeling the rated wall and floor assemblies, focusing on areas where penetrations are likely to occur. Specify firestopping devices that make it easy for the cable installer not to compromise the rated wall or the firestop device. Devices that do not require an installer to remove or add caulk, inserts, or pillows are less likely to be compromised. In high-traffic areas provide enough penetration capacity to allow for added cable so new penetrations can be avoided. Label the firestop devices with their manufacturer and UL system number. Finally, the building owner must provide vigilant marshaling of all cabling installations in its building. Maintaining the integrity of the building rated walls and floors is critical when a fire occurs, and having a firestopping system that “almost” works is not good enough.
- Kuhlman has 22 years of experience in the design and construction of telecommunications infrastructure. He is a member of Consulting-Specifying Engineer's Editorial Advisory Board.
Annular space: The opening around the penetrating system.
F-rating: The time period that the through-penetration firestop system limits the spread of fire through the penetration when tested in accordance with ASTM E 814 or UL 1479.
Intumescent material: A material that swells and chars when exposed to flame.
T-rating: The time period that the penetration firestop system, including the penetrating item, limits the maximum temperature rise to 325 F above its initial temperate through the penetration on the non-fire side when tested in accordance with ASTM E 814 or UL 1479.
Through-penetration firestop system: An assemblage of specific materials or products that are designed, tested, and fire-resistance rated to resist for a prescribed period of time the spread of fire through penetrations. The F and T rating criteria for penetration firestop systems shall be in accordance with ASTM E 814 or UL 1479.
Source: 2009 International Building Code, Section 702.
International Building Code – 2009
3M UL System No. W-L-3015 Application Notes
3M UL System No. W-L-4037 Application Notes
3M UL System No. W-L-3289 Application Notes
Specified Technologies User Guide