Tragedy sparks innovation in fire-rated barriers
Rebuilding the Pentagon after 9/11 included thinking ‘square’ for firestopping sleeve technology.
Rebuilding the Pentagon after 9/11 included thinking ‘square’ for firestopping sleevetechnology.
According to the old saying, “necessity is the mother of invention.” If that’s true, then perhaps tragedy is its father.
The collapsing World Trade Center towers and the devastation at the Pentagon following the 9/11 terrorist attacks will be forever etched in our memories. But the tragic events of that day also became the seed for a new technology that we believe has greatly improved the process of penetrating fire-rated barriers with electrical and datacom cables.
An engineer developing fire protection products relies on tests that demonstrate the efficacy of the design, yet secretly hopes that it will never have to do its intended job. Just prior to 9/11, a major renovation of the Pentagon had begun. The first section (Wedge 1) had just been completed when the hijacked jet roared into the junction of Wedge 1 and Wedge 2. We received a call the next day indicating that the fire protection features had performed as expected. I was also asked to be ready to come down and do a walk-through to inspect the structure and advise as to what would need to be replaced or what could be considered functionally intact. About ten days later, I donned a protective suit and breathing apparatus and toured the devastation.
One point that the episode drove home was that fire could happen at any time and for any reason. The Pentagon needed a method of firestopping that would be effective during the reconstruction process, and for any time after that.
Integrity put to the test
Pipe and conduit penetrations through fire barriers are relatively straightforward: Make a hole, run the pipe or conduit, and seal the opening with firestop sealant. The job is done and the penetrant will, for all intents and purposes, be permanently installed. But data and communications cabling is another story. Frequent changes are typical and permanent sealing isn’t an option. Thus, these types of penetrations put fire barriers to the ultimate test.
Featuring a square sleeve rather than a traditional round sleeve, the EZ-Path firestop technology is designed to provide maximum resistance to fire, whether empty or filled with cabling.
In the Pentagon, wire basket trays carried cables over and along corridors. The trays terminated at the walls and the cables were routed through 4-inch EMT (electrical metallic tubing) sleeves, which were installed in typical fashion: An over-size square hole was being cut in the walls and four sleeves were being installed stacked two over two. The opening in the wall would have to be repaired as best as possible after the fact.
Firewalls constructed with gypsum board must be properly built and maintained. Based upon my testing experience, I felt that the Pentagon’s traditional sleeve installation method could marginalize the walls performance. I was struck by the fact that, yes, this may be typical of how it is generally done-but there must be a better way!
The three and a half hour drive back to New Jersey gave me the time to consider the problem and to begin to work on a solution. I began to consider all the problems related to running cables through fire barriers to see if one design could address most, if not all, of them.
Here is what I identified:
1. The need to minimize damage to the barrier. This, to me, was a big issue. The wall will be stronger and more fire resistant if you can minimize the size of the opening. At the Pentagon, round sleeves were the problem. The stacked 4-inch round sleeves required an opening approximately 12 × 12-inches. Once the sleeves were in place, it was difficult to properly restore the wall between them. How could we reduce the opening size and minimize damage to the wall?
2. More cable in a smaller opening. Part of the solution to minimizing damage to the barrier was to figure out how more cable could fit in a smaller area. Could we design a sleeve that would be more efficient in terms of cable loading, thus requiring less wall space?
3. Tray width constraint. The trays being used in the Pentagon were 12 × 2-inch wire basket trays. But cable trays come in a wide variety of widths. Could we develop a modular design that could be ganged to allow sleeve capacity to match tray capacity?
4. The need for effective firestopping at all times. The usual life cycle of a sleeve is, of course, installed empty and remains unfirestopped until some percentage of cables are added. Over time, cables are added here and there, and they eventually displace firestopping almost completely. More typically, in most structures, the firestopping will simply be removed and discarded after one or two cable changes. In my opinion, this common practice is unacceptable, and even more so for a facility as critical as the Pentagon. How could we assure that the firestops would be effective as soon as the sleeves were installed, and would remain effective throughout the life of the structure?
5. Smoke leakage. This is an inherent problem with cable bundles. Datacom cables typically transit the walls in dense bundles. While firestop products, such as putty, can effectively seal around the bundle, the interstitial space between the cables is never sealed. The fact that cables must be added or removed frequently only compounds the problem. Could we provide a more reliable and predictable level of smoke leakage protection?
6. Construction variables. The Pentagon project would involve areas with totally new construction as well as areas where existing walls would need to be retrofitted. Where new walls were being built, the preferred cabling method was to install the trays as the walls were being built and before the areas were enclosed. Thus, the walls were studded but no gypsum board was in place. Could we develop sleeve mounting methods that would accommodate installing the pathways as the wall was being built or in the finished existing walls?
7. The Swiss Cheese Syndrome. Each new installer will not want to mix his cables with anyone else’s. Thus, a new hole may be punched through the walls every time new cables are run. Could we provide effective cable organization and separation so that cables could be segregated by use, application, or installer?
Engineered for rapid expansion when exposed to flame, intumescent material inside the EZ-Path quickly seals the cabling pathway, preventing passage of flames and smoke.
8. The difficulties of working above the ceiling grid. Wire basket trays fed the cables to the sleeves. A mechanic installing cables and then firestopping would need to work over the tray with awkward and limited access to the sleeves, making firestopping difficult. Every time cables are added, access would be required, meaning ceiling tiles and firestops would have to be removed from both sides of the barrier. How could we provide for future cable changes that would be less disruptive to the facility?
9. Firestopping expertise. This is not a task that the wiring contractor has easily and willingly embraced. Cabling mechanics make money for their companies when they are installing cables. Could we achieve all of the above and improve both the process and the economics for the datacom contractors?
Brainstorming and breakthrough
As I pondered these and other points on my trip home, I experienced a real breakthrough-the thought that a sleeve did not necessarily have to be round! The idea of a square sleeve made a lot of sense. With this idea in mind, the answers began to fall in place.
I brought back the concept, and our skilled engineering team took it and ran with it. The resulting product, in relatively short order, became the EZ-Path System. Here is why we believed the technology’s design resolved the issues identified above:
•It would minimize damage to the barrier while maximizing cable-loading capacity. The square profile allowed sleeves to be nested tightly against one and other. This, in itself, would dramatically reduce the required opening size. A square profile can accommodate cables more effectively than a round one. I reasoned that cables would nest better. Later, I calculated that loading efficiency improved from 50 to 60 percent to about 82 to 85 percent. This meant more cables in a smaller space. Since the Pentagon was using 12 × 2-inch tray, the sleeves would have to provide a similar loading area. Using the 12-inch tray width as a guideline, I divided the area into four segments. Thus, the approximate size of each device would be 3-inches wide. By making the device square, the overall size could be 3 × 3-inches. Thus, the 144-square-inch opening presently being used in the walls could be reduced to just 36 square inches by using four of the modular pathways while actually improving cable capacity by about 10 percent.
•Full time firestopping could be achieved by building the firestopping into the device. My thoughts were that this pathway product should be totally mechanical-no caulk or putty required. Foam plugs were a possibility, since you could remove them and stuff them back in after cable changes. But sooner or later, they would be discarded and the sleeve would end up completely filled with cables. So, I began to envision a device with an area reserved for the firestopping, where adding cables would not require removing or reducing the amount of firestopping materials contained in the sleeve. With a square device, I reasoned that it should be easy to devise a mechanism that would automatically open and close to accommodate changes to the cable bundle. This would allow frequent cable changes without the possibility of degrading the firestop’s performance over time. It would also mean a sleeve that is installed firestopped and remains protected throughout its life.
•It could meet the challenge of smoke sealing. Most people assume that putty-sealed cable penetrations are sealed airtight. But this could only be the case if each cable were individually spaced and literally potted in the sealing compound. While this is possible in the controlled environment of a laboratory test, it certainly is not possible in the real life environment that exists above the ceiling tiles. Cable bundles are inherently leaky because even a tight bundle has considerable open space within the bundle. This is particularly true in the case of a round bundle in the traditional round sleeve. We can illustrate this by considering a conduit that appears visually to be filled with cables. Using NEC computations for cross-sectional fill, you will find that the conduit is only 50 to 60 percent filled, depending on cable size. This means that a typical traditional conduit sleeve can have up to 50 percent unsealed space between the cables. Even a cable penetration that appears perfectly sealed can pump a considerable amount of smoke through the wall. In most facilities, more cables are installed over time, along with more sleeves. Some will be well sealed. Others will not be sealed as well or the seals will be removed as more cables are added. The net result is totally unpredictable smoke leakage.
•Sealing each cable is not a practical option. We needed to provide a mechanism for making cable changes that wouldn’t substantially impact the amount of leakage. An effective compromise was required. The improvements in cable-loading efficiency that I mentioned earlier would go a long way towards reducing leakage. But I reasoned that it would also be critical to find a way for the device to remain essentially closed at all times, even when additional cables were installed or later removed. Traditional methods using removable materials, such as putties and foam plugs, would not provide the level of reliability that I wanted, since these solutions would re-introduce the human factor. Conformable intumescent foam pads seemed like the best choice. By making the pads longer than the pathway, they would naturally arch inward toward the cables at all times. Being soft and conformable, adding cables would displace these foam arches but would remain in contact with the cables at all times. This would mean that the actual amount of space in and around the cables would remain minimal and predictable. In actuality, hermetic sealing is not practical and the codes recognize this. The model codes do, however, have a requirement for limiting the amount of unsealed openings in a barrier. Typical putty/sleeve systems are all over the map on that score because of variations in size, cable bundles, and the skill of the installing mechanics. Thus, compliance is never fully assured. Code officials in California, for example, asked that we evaluate the design in regards to this requirement. We were able to demonstrate that the design provided a predictable maximum leakage area so that it would be easier to calculate the maximum number of devices that could be installed in a given area. (UL testing eventually showed a 50 percent reduction in leakage when compared to a typical putty sealed penetration utilizing the same number of cables. Additional improvements in the design further reduced the leakage potential.)
•Accommodating installation in both new and existing construction seemed easy once the gangable, modular design was conceptualized. Wall plates could capture the ganged pathways and be used to either attach directly to the exposed studs or to sandwich the finished wall on both sides and hold the pathways in place. Simply reversing the plates would allow installation under either condition. Attaching the plates directly to the studs meant that the pathways could be installed before the wall facing, with no need to come back and address any firestopping requirements.
•Eliminating unneeded openings could be achieved by providing easier cable access as well as better cable management. Installers tend to run cables through the soft spots. In gypsum board, many installers would rather hammer a hole through the board than dig out firestopping materials. The self-adjusting cable throat would be that soft spot and encourage installers to use these portals again and again. A modular device lent itself well to compartmentalizing cables. In addition, a factory kit could provide wall labels that would further encourage better organization. Other facilities easily recognized and appreciated these efforts and asked if the pathways could be color-coded as well. Thus, rather than being an impediment to effective cable management, firestopping has become a solution that helps prevent unnecessary damage to fire barriers while dramatically improving the cable management process.
•Working above the ceiling grid could be made considerably easier by a design that adjusts automatically to the cable bundle. In my view, leaving a pulling line in place would do little good if you still had to pop the ceiling tiles on both sides of a wall to access the sleeve so that you could remove and then reinstall firestop materials with each cable change. Even a mechanical solution offered little advantage if it required gates to be adjusted or foam to be removed and perhaps trimmed and then reinstalled. The self-adjusting throat mechanism that I envisioned would let cables be pulled remotely, using a previously installed pulling line. While this would benefit any office environment, it has turned out to be of particular interest to health care facilities concerned with the potential spread of infectious disease.
•Meeting safety code requirements required us to also look at a number of other issues. The codes call for sleeves to be firestopped inside and out. Some products simply utilize a steel escutcheon or washer to seal around the pathway. Our feeling was that a firestop gasket was required to meet the actual intent of the code. And while the codes don’t specifically require sleeves to be grounded, there are requirements for the raceway systems feeding the sleeve to have a continuous ground. Thus, provisions would be made for this as well.
•Making the economics work for the facility owner and the contractor would be a key factor. Life Safety may be an important issue, but as I mentioned earlier, we all hope that there will never be a fire. The true benefit of the product that I was envisioning was that it would greatly improve cable installations from a fire safety standpoint and also enhance the cabling process. A good design could make penetrating barriers of any type an easier process. Providing a method for remotely adding cables without having to get above the ceiling on both sides of the walls would make the cable installer far more effective, and improve productivity by allowing contractors to focus on doing what they are being paid to do-install cables. The Life Safety benefits to this type of pathway should have even greater importance to the facility owner. Never having to firestop cable penetrations also translates into money saved when the pathway is initially installed, and continued savings with each subsequent cable change.
Reducing future risk
Necessity didn’t drive the development of the EZ-Path product, but tragedy certainly provided its impetus. Prior to 9/11, I think most Americans failed to realize that our military’s headquarters was really just a very big office building and as vulnerable to fire as any other structure.
My concern was only magnified after inspecting the very place where so many people died following the Pentagon terrorist attack. But I do find satisfaction in knowing that the ideas fostered by that visit will make cable penetrations safer and may, in turn, help to reduce the risk associated with fire in the future.
JIM STAHL, SR. is Executive Vice President/Director of Technical Services at Specified Technologies Inc. (STI; www.stifirestop.com).