CHALLENGES IN PREENGINEERED METAL ROOF DECKS OF POLYISO FOAM

BY JOHN NOVAK

At 1341 hours on Wednesday, July 7, 2004, Toms River (NJ) Fire Companies Nos. 1 and 2 were dispatched to a possible structural fire at the First United Methodist Church at 129 Chestnut Street. Fire Company No. 2 Chief Anthony Cirz responded from approximately a mile away. On arrival, he reported smoke showing from the roof of a noncombustible building under construction (photos 1, 2). The building was part of the church’s expansion project and was to be used as a multipurpose room and gymnasium. The structure measures 75 feet 2150 feet and is 37 feet high. The exterior shell construction was almost complete. However, interior construction had just started with the installation of metal studs for partitions and work on the sprinkler system. The roof structure was a sloping A-frame-style roof consisting of steel decking on top of a steel framework covered by roofing material (photo 3).


(1) First-arriving firefighters operate on the roof of the church under construction. The minimal smoke is not a true indication of the fire traveling in the one-inch air space beneath their feet. (Photos by author.)

null


(2)

null


(3) Roof-supporting structure: Lightweight steel trusses run parallel to the ridge.

null

First-arriving firefighters operate on the roof of the church under construction. The minimal smoke is not a true indication of the fire traveling in the one-inch air space beneath their feet. (Photos by author.)

After communicating the size-up, Cirz requested a general alarm based on the time of day; fire conditions; and the hot, humid weather. From the beginning, this greater alarm augmented the first-alarm companies with two additional ladder companies and two additional engine companies. Cirz, working within the incident command system, assigned Fire Company No. 1 Chief John Mount to the operations sector and Assistant Chief Gary Dye to the roof division. Dye reported that the fire was between the roof deck, the insulation, and the top layer of roofing material. He also observed that the fire seemed to be confined to the east side roof. Based on the smoke conditions, it appeared that the fire was under the northern half of the roof on the east side.

Firefighters used a thermal imaging camera (TIC) inside the building to verify the fire’s location above the metal roof deck. The image observed through the TIC showed the extent of the fire spread was greater than that observed when looking at the roof from the exterior. In light of this information, the plan of operations was to contain the fire to the one-quarter of the roof already involved. As a township fire inspector, I responded on the general alarm and was assigned as the staging and rehab sector. This gave me a good view of the operation along with operational input, with the incident commander (IC), into the decision-making process.


(4) Members complete a trench cut to remove roofing material to isolate the fire area. Removing roof material is difficult because the preengineered roof panels are screwed through the plywood and insulation into the metal roof deck.

null


(5) Firefighters continue to use power saws, hand tools, and brute force to remove the material. As plywood and insulation are removed, pockets of fire are continually found.

null

The roof sector used a variation of a trench cut to isolate the fire from the remaining uninvolved roof structure. Using power saws, firefighters cut a swath three feet wide from the ridge to the eave and removed the roofing material and insulation (photo 4). Members, however, left the metal roof deck intact so that the stability of the roof system would not be compromised. Simultaneously, the operations officer had the interior division deploy a deck gun to the structure’s interior to cool the underside of the roof deck in an attempt to reduce the fire’s spread and severity. Once the fire was contained, firefighters had to remove the roofing material and insulation to extinguish pockets of fire (photo 5).


(6) The fork truck was an invaluable tool. Pockets of fire were found with each panel removed by the machine. To remove all this material by hand would have been an insurmountable task

.


(7)

null

The hot July weather took its toll on firefighters. Incident command requested two additional mutual-aid companies and two additional engine companies from Dover Township. Firefighters were rotated in and out in short shifts to conduct the labor-intensive roof operations. Firefighters were able to commandeer an on-site fork truck being used to move construction materials around the site. It proved to be invaluable. The firefighter operating the machine used the forks to rip off large sections of roofing material and insulation. This saved command much time and effort. Even with the fork truck operating, it still took approximately three hours to complete the overhaul (photos 6, 7).

FIRE INVESTIGATION

After fire operations were completed, I was assigned to conduct the fire investigation for the Fire Prevention Bureau. The cause of the fire was clear-cut. Contractors on-site said they were welding 3/4-inch round stock onto the upper and lower chords of the trusses for added support. This reinforcing operation seemed strange, since the building’s shell and roof structure were already complete.


(8) Trusses that received reinforcing with 3/4-inch round stock. Heat from weld fillets conducted into the polyiso foam insulation on the other side of the roof deck.

null


(9)

null

On Friday, July 9, I went over the construction plans on file in the Building Department. Consulting with the building subcode official, I found nothing in the plans that required the welding of 3/4-inch round stock onto the existing trusses. On further investigation, the construction company’s vice president told me that the architect submitted a change order after the roof system was completed. The change order called for installing a curtain wall to support a large projection screen at the north end of the building. Trusses would support the curtain wall in this area. However, according to the contractor, the trusses were undersized to carry this new load. The truss manufacturer’s engineer submitted documentation that called for the welding of 3/4-inch sections of round stock 8 feet, 6 inches and 12 feet, 6 inches along the top and bottom chords of specific trusses. Two-inch-long weld fillets at specific intervals were to hold this round stock in place (photos 8, 9). The investigation concluded that the fire was caused by heat conduction through the metal roof deck into the combustible insulation.

INSULATED ROOF PANEL ASSEMBLIES

The problem with this truss fix was that the trusses supported a sloped metal deck roof. Laid on top of the metal deck roof were pre-engineered insulation panels made of four-inch-thick polyisocyanurate (polyiso) foam with an air space using one-inch 2 two-inch spacer strips covered with 5/8-inch plywood as a nailing surface for asphalt shingles (photo 10). This roofing assembly comes in four-foot 2 eight-foot sections and is patented under the name ACFoamTCrossVent™. The manufacturer states: “… the product is designed for use over sloped unventilated roof decks …. The primary purpose of CrossVent is to provide a thermally efficient insulation with uniform cross venting that promotes air circulation required by many shingle manufacturers … allows heat to dissipate while providing a nailable surface and efficient insulation in a one-step labor-saving process.”


(10) A section of roof panel. Sections come in four-foot x eight-foot panels. A panel consists of polyiso foam insulation with one-inch wood spacer covered by OSB or plywood. Roofing paper and shingles were added at the job site. Panels are patented under the name ACFoamT CrossVent�; they range in thickness from 2.5 inches to 6.5 inches and have a one- to two-inch vent space. This roof system has also been sold under the name Vent-Top ThermalCalT1.

null


(11) Field test of polyiso foam. The heat source for the test was a disposable lighter; the flame source was removed after approximately 20 seconds.

null

The physical properties of the material supplied by the manufacturer indicate that the foam has a flame spread rating of 25-50 with a smoke rating of 50-170 based on ASTM 84 10-minute testing. It should be noted that the manufacturer also states that flame spread values are not required for foam plastic roof insulation used in roof deck constructions that comply as an assembly with FM 4450 or UL 1256. During the investigation, I conducted a field test on the foam insulation and found that the material was able to support combustion once the ignition source was removed (photo 11).

In my research for this article, I found a technical perspective on polyisocyanurate foam written by Ray Corbin at http://www.roofingcontractor.com/. Corbin is director of the Better Understanding of Roofing Systems Institute (BURSI), an educational program sponsored by Johns Manville. Corbin, in response to the question “How does polyiso perform versus polystyrene in a fire test?” says the following:

    Polyiso is the only foam plastic insulation to have both FM and UL approval for direct-to-steel deck. FM Approval for Class 1 Roof Systems was granted to polyiso for passing FM 4450. UL classification was earned by passing ANSI/UL 1256. Polyiso insulation can withstand high temperatures and passes both FM 4450 and ANSI/UL 1256.

    Polystyrene is a thermoplastic material that softens at 165°F and melts between 200°F and 210°F, making it incapable of reaching the standard 30-minute fire exposure. The high temperatures reached in FM 4450 melt the polystyrene, which can then run through the joints in the steel deck, increasing the risk for fire to spread on the underside. Therefore, FM does not list any Class 1 Roof System Approvals for the use of polystyrene insulation in a direct-to-steel deck application.

Based on this information, it is my understanding that the polyiso foam does not melt and run in high heat conditions, as reflected in the UL and FM testing. This physical property allows this material to be used in the direct-to-steel deck installation, therefore meeting UL and FM testing. In a conventional built-up roof application, the roof deck, in many instances, is covered with a combination of hot asphalt, paper, insulation, and membrane layers. Under fire conditions, the heat from below causes the asphalt to run, vaporize, and drip through the seams in the roof deck; this, in turn, can spread the fire throughout the building. A detailed explanation of the hazards of metal roof deck fires can be found in Building Construction for the Fire Service, 3rd Edition, by Frank Brannigan ((National Fire Protection Association, 1992), starting on page 302.

POINTS TO CONSIDER

Building classifications. Fire officers should be aware that although a building is classified and constructed as noncombustible, there might be components that will support combustion. In this instance, the building in question was designed as a 2C, noncombustible building under the NJ Uniform Construction Code. At this fire, the IC told me that based on his observations, he thought the building was of ordinary construction. This was based on his observation of the sloped roof covered with standard shingles and the masonry walls. My own observations on arrival also led me to believe that the roof construction was of wood and that we were also dealing with an attic space. However, one look inside told a different story, as can be seen in photo 3.

The IC at this fire used the tactic of cooling the underside of the metal roof deck. This is a recommended tactic for fire involving a metal roof deck. Although this tactic helped slow the fire’s spread, the major problem was the air space between the foam insulation and the underside of the plywood. Once the fire had entered the air space, the cooling operation from underneath had a limited effect. Firefighters were forced to remove roofing material that was fastened with screw fasteners. This was a labor-intensive and time-consuming operation. It was important for the IC to realize the limitations of one of the tactics and implement an attack on the fire problem on a second front.

Building construction is a major part of the fire suppression equation. The construction industry is constantly inventing new products or developing new ideas. As consumers, we reap the benefits of this innovation in our own homes. However, anyone who has been around for a while knows that new products in the construction industry often pose new risks for firefighters. Firefighters and fire officers need to keep abreast of new materials and construction methods that are continually being introduced. Next time you’re driving by a construction site, stop and take a look around. Why not make this a habit? Don’t be afraid to ask questions; many of the guys on the job site are very knowledgeable and want to talk about their trade.

New construction materials, assemblies, and building practices may force us to modify existing tactics and operations. A case in point at this fire was that the majority of members operating on the roof had little experience with this type of roof system and anchoring with screw fasteners. Most members had experience only with wood roofs nailed to rafters. They did not expect to find it so difficult to remove the roof material. We need to be open to new ideas in suppression and tactics and to modifying tactics if necessary, but we must also stay grounded in what has proven to work. This can only be accomplished through education and training and understanding the basics.

JOHN NOVAK has been a firefighter with Toms River (NJ) Fire Company No. 2 for 28 years. He is a fire inspector in Dover Township and is the deputy director of the Dover Township Fire Academy. He is certified by the N.J. Division of Fire Safety and the N.J. Division of Community Affairs as a Uniform Construction Code Fire High Hazard Structure/Subcode Inspector and as a certified New Jersey Level 2 instructor. He has an associate’s degree in fire science from Ocean County College, New Jersey.

No posts to display