Firestopping CABLES by the Numbers

Six Steps to Firestopping Cables for Information Transport Systems

By Mike Tobias

Early in the morning on November 21, 1980, a fire erupted in a delicatessen at the MGM Grand Hotel and Casino in Las Vegas, Nevada. At the time, about 5000 people were in the 26-story resort. As smoke and fire spread throughout the building, 84 people were killed and 679 injured. The disaster is considered the second worst hotel fire in U.S. history. Its official cause was an improperly grounded electrical wire. Most fire damage occurred in the casino on the second floor and adjacent restaurant, although most deaths occurred from smoke inhalation in the upper rooms of the hotel. The tragedy jumpstarted concern in the information transport systems (ITS) industry about appropriate firestopping.” Then there was the World Trade Center disaster that hammered home at least to me, that SOMETHING NEEDED TO BE DONE.

According to the BICSI Telecommunications Dictionary, 2nd edition, firestopping is defined as “The process of installing listed fire-rated materials into penetrations of fire-rated barriers to reestablish the fire-resistance rating of the barrier.” The Dictionary further defines firestop system as “A specific construction consisting of the material(s) (firestop penetration seals) that fill the opening in the wall or floor assembly, and around and between any items that penetrate the wall or floor (e.g., cables, cable trays, conduit ducts, pipes), and any termination devices (e.g., electrical outlet boxes along with their means of support.”

As ITS designers and installers plan routes for the latest in high speed communications cables, they must routinely seal penetrations in fire-rated barriers. Many new systems by various manufacturers have been recently developed specifically for this task. These systems work in essentially the same way. The two key elements of a typical low voltage penetration system are the intumescent caulk or putty and the method of “ bounding” the intumescent.

Intumescent caulk and putty are the active material of a firestop system. They will expand to form a sort of insulation within the system to prevent passage of the smoke as well as the flame. All intumescents work about the same way. The key to a successful firestop system is the method selected for “bounding” the intumescent. As the term implies, bounding the intumescent can be done with sleeve systems, square or triangular metal boxes, or even chicken wire for bounding putty pillows in a large cable tray penetration. There are many new devises created especially for the ITS Installer on the market today. Seek out those manufacturers for training and guidance on system selection. Professionals in the ITS industry (designers, specifiers, installers, etc.) must know more than firestopping theory for very good reasons. If you are involved in the firestop selection or installation of a building that subsequently has a fire resulting in loss of life or property, you may be liable. You can avoid these issues by using a simple six-step system that I call firestopping by the numbers. Make this part of your standard operating procedure for selecting and installing all firestop systems.

Firestopping by the numbers is completely vendor-neutral. It works well with any tested systems on the market.

Step # 1
Establish the Hourly Rating of the Wall
Each sheet of 5/8” thick fire rated gypsum board is rated at a half-hour. A typical cinder block wall will usually be rated at two hours. If the cinder block wall is filled with concrete and reinforced with rebar, it could be rated for up to four hours. All barriers are tested in increments of time. Be sure to check the barrier for all applicable ratings such as fire (F), temperature (T), and air leakage (L):

F (hours)

  • Resists flames passing through the barrier.
  • Prevents ignition on the opposite side of the barrier.
  • Prevents developing an opening where water could pass through.

T (hours)

  • Meets criteria for F rating.
  • Limits temperature rise on unexposed surface.

L Optional rating (cubic feet per minute, per square foot area)

  • Ability to provide effective smoke stop.
  • Lower number, better L rating.

The L rating is a completely separate test from the typical burn. It is the first defense from loss of life to cold smoke. It would be a good thing if the firestop industry would spend more time on acquiring L ratings for their systems. A good L rating will save more lives in a fire and is at work even before the sprinklers are activated. This rating can save millions of dollars on smoke damaged high dollar equipment like computer networks and PBX systems.

Once the rating of the barrier is established, seek a tested through penetration system to match or exceed the barriers rating. Manufacturers will assist with this task.

Step # 2
Select and Acquire the Systems Listing
Have the selected firestop manufacturer furnish you a hard copy of the UL or other independent Testing Facility Listing. This document is the result of testing that had been performed using the system in the application it was designed for. It is very important that the Specifiers and Installers understand that there can be no deviations in the installation procedure spelled out in the text of the listing. The AHJ will quickly reject any system that is not properly installed and within the limitations established in the test burn. Pay close attention to the cable load limits, the fill procedure, and packing requirements if any. Place a hard copy of the listing in the job file for future reference. Have it on hand for the official inspection. Download the Material Safety Data Sheet (MSDS) for the intumescent material you will use to seal the system. Have the document faxed or emailed to you along with the specifications sheet for the job and the job drawings. Keep them, all in a file at the job site or in your office for easy retrieval when the AHJ ask for them. It is recommended that you keep this information on file in your office. You never know when a building you have worked in will catch fire. Be prepared to prove that you work was within specs.

Step # 3
Plan the Installation
After you have established the hourly rating and selected a tested system, pay close attention to the allowable % cable load usually found in section (2) referencing “cables”. There is usually a % defined for minimum and maximum allowed cable load. Do the math or seek out manufacturer’s cable load charts. If you are not sure of your calculations, seek the help of the manufacturer. Also carefully follow instructions on packing (mineral wool batt insulation) and sealing the ends with the required manufacturers firestop caulk or putty. You might consider the possibilities of adding cables at a later date and future proof the penetration. However, do not make a hole any larger than necessary as a large hole is much more difficult to seal than a series of smaller holes. Never mix or match components of a tested system.

Step # 4
Seek Pre-approval from the Authority Having Jurisdiction (AHJ)
This is a crucial, not-to-be-missed step. I know most of you are rolling your eyes, but just do it! At the outset of the job, learn the inspection schedule and proper authority. Seek out the inspector and submit your system’s information for pre-approval. This is a GOOD thing. First of all the AHJ will be pleasantly surprised by your request. It is not that often someone in our industry asks permission. Forgiveness is the usual request. Secondly, if you are convincing, the AHJ will pre-approve your selected system as well as tell his colleagues about your professionalism. Remember—it is not approved unless the AHJ says it is. If your selected firestop is accepted by the AHJ before you start the job, all you have to do now is install it within the limitations and guidelines provided by the listing. Find or make up an “AHJ Request for Consideration Form “. Submit it to the AHJ along with the listing, specs, MSDS, drawings and supporting documents.

Step # 5
Follow the Manufacturer’s Assembly Instructions
Cable load limitations are the most commonly violated portion of a through penetration system installed today. An overfilled sleeve system or extremely large whole Pay close attention to the limitations in the tested system and consult with the manufacturer when the situation requires a deviation. Many manufacturers can perform an engineering judgment to cover you if your deviation is minor or cosmetic and will not interfere with the function of the firestop. Never assume anything about firestop. Our industry has alienated many Inspectors in the field and most of them are out looking for low voltage people who are violating the fire barriers in their justiction. Inspectors today will require you to seal the entire barrier once caught in violation. Also – Never argue with an Inspector. It will bring you nothing but grief and may be a career move for you in the wrong direction. If an Inspector says he wants the system to be painted purple, you ask “what shade?” Then call the manufacturer to explain what happened and have them make recommendations to appease the AHJ.

Step # 6
Digitally Document Your Installed System
Label and alpha-numerically identify each penetration system with an indelible marker. This is necessary for you to be able to maintain the systems you have installed. This is the first step towards maintain the firestop you have installed. Many systems will come with documentation/warning labels to be filled out and adhered to an adjacent wall. Be sure to take a time-dated digital photo from a short distance away as well as a close up of the label. Submit these photos to your customer as their Firestop Certification. Keep a version (also time-dated) on your computer. It’s always possible that in the future, others may use your penetration system and overfill it or otherwise negate its value. Producing the photos may be necessary in the event an inspector calls to discuss a violation. The photos may also place you in a position for some residual work and can be used to justify the expense of proper methods. ITS Installers should get compensated when they have protected a buildings occupants and property. If you are proud of your firestopping efforts there is no hesitation by the building owners or tenants to pay you for your effort. Imagine that, getting paid to save lives and property!

Firestopping by the Numbers is the result of issues that have arisen over the years from hundreds of projects and meetings with architects, designers, engineers, inspectors, installers, and project managers. Firestopping an installation can seem complicated. Following these easy steps will help ensure a safe job, no matter which manufacturer you use.

About the Author: Mike Tobias is the Chief Executive Officer of Unique Firestop Products. He is a member of the BICSI Codes Committee and consults with BICSI on firestopping issues. He may be reached at

Unique Fire StopUnique Fire Stop products, Inc.
(251) 960-5018

Made in the USA

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