BY P.J. NORWOOD AND SEAN M. GRAY
The building industry is always looking to reduce costs and offer the homeowner a higher level of product satisfaction. Some define this as reduced cost or the use of materials that increase the home’s R-value or thermal resistance. Some materials are engineered to allow for greater unsupported spans to meet the desire of today’s consumers for an open floor plan. We have seen this trend in roof and floor structures, in exterior sheathing, and in windows. You name it, and a developer has looked into and designed a “better” product for today’s builders and consumers. One of the current buzzwords in the housing industry is “green”-i.e., offering increased energy efficiency/savings, decreased environmental impact by using natural resources (sunlight, rainwater, and wind), or new and improved building materials. Green design and materials also raise the price and value of the homes.
We all know that many of these products are not firefighter friendly. We can sit around the firehouse kitchen table and bash the industry, the developers, and the designers. However, we, too, are end users and want to decrease our home’s monthly operating costs. It is our responsibility to learn and understand these “new” materials and construction practices to both develop and apply the appropriate tactics. Some will say, “It’s lightweight construction; we are not going in.” Statements like this are damaging to the fire service as a whole and, quite frankly, not appropriate. We are called professional firefighters because the public depends on us to arrive and solve its problems. Of course, every scenario is different, and you should not base any tactical decision solely on the construction or materials used. Using our training, education, experience, and observation of the current situation while performing a good size-up is the only way to make solid fireground decisions.
Spray Polyurethane Foam Insulation
One “new” material that you need to be aware of is spray polyurethane foam (SPF). This foam product is sprayed on to coat surfaces between the joists and studs in walls and in ceilings to eliminate voids and increase energy efficiency (photo 1). This is very different from the traditional installation of attic insulation (photo 2). Builders are using this foam in homes regardless of the homes’ ages. You will find it anywhere from the newly built, lightweight construction to the newly remodeled, 40-year-old home. This foam is nothing new in commercial construction. Firefighters across the nation have encountered foam products used on commercial flat roofs and typically end up executing a step cut or skim cut when performing vertical ventilation because of the thickness of the roof.
|(1, 2) Photos courtesy of UL Firefighter Safety Research Institute.|
In a step cut or skim cut, the roof sheathing cut is layered. After cutting an inspection cut and discovering the makeup of the roof sheathing, a firefighter can determine if a step/skim cut is necessary. In many instances, firefighters may have to sink the rotary saw up to the blade guard or the chain saw to cut the top layer and foam insulation off. Once you have made the cuts, remove the insulation and top sheathing, cut the bottom layer of sheathing that is still attached to the joist, and remove it.
Use caution when performing these cuts. In many installations, the top layer may be a rubberized membrane, which has been known to offgas and ignite, chasing many members off the roof at fire operations. When faced with this type of a roof, a good tactic may be to stretch a precautionary hoseline to the roof for safety.
Photos 3 and 4 show examples of the skim or step cut. You can see where firefighters had to make multiple cuts to overcome the depth of the roof system. Although the foam pictured is not SPF, the same principles apply.
|(3) A commercial building roof system where members executed a skim cut. [Photos 3-4 courtesy of Colin Kelley, Clark County (NV) Fire Department.]|
|(4) Side view of the roofing material that companies may face during roof operations.|
In the residential attic spaces, rather than laying down insulation on the ceiling above the living space, the insulation is sprayed underneath the roofing materials, coating the underside of the roof decking and filling the voids between the rafters. This material’s manufacturer states that the SPF is a thermoset rather than a thermoplastic and that the product does not burn. However, other SPF manufacturers have concluded that when spray foam catches fire, it releases a number of dangerous chemicals. Safety guidelines published by Bayer Material Science, a spray foam manufacturer, warn that burning foam can release “isocyanates, carbon monoxide, carbon dioxide, nitrogen oxides, and hydrogen cyanide, among other compounds.”
During a wall burn test at the Underwriters Laboratories (UL) Fire Research Center in Northbrook, Illinois, as part of the current study of Residential Attic Fire Mitigation Tactics and Exterior Fire Spread Hazards on Fire Fighter Safety, we unintentionally stumbled across some problems that truck company members might encounter with SPF.
During the July 2, 2013, test burn, the firefighters participating in this UL test were surprised at what we saw. We, like many of you, need to see things firsthand to have a complete understanding of a phenomenon. Most of us couldn’t believe what we saw during the final soffit/wall burn.
After ignition of the wall assembly, the fire reached the attic quickly because of the failure of the vinyl soffit, but it then took a surprisingly long time for the fire to start burning any materials within the attic space. On further examination, we noticed that the foam itself was charring, not melting. The SPF was charring in a way very similar to volcanic lava. As it burned, it created a protective char layer. Again, similar to a lava field, there was an outer hardened crust, and in places where flames directly impinged on the foam, there was some minor flame production underneath that hardened crust. It appeared that the flame was produced from the burning gases that the melting (thermoset) of this foam produced. The material itself didn’t completely burn as we had anticipated. However, it created a large amount of thick black smoke that quickly turned to flame once it had reached the optimal temperature.
The purpose of this test was to build a wall assembly with an attic space (as seen in photos 5 and 6), then start an exterior fire at the bottom of the exterior wall, observe fire spread up the wall to the soffit vent, and observe the fire dynamics that were created inside the attic space. Many types of wall materials and attic insulation materials have been used throughout this testing process. On this day, SPF was used in the attic space as insulation, which is the focus for this article because of the observations we made and how they could impact truck company operations.
|(5, 6) A wall assembly set up for testing within the UL laboratory. (Photos courtesy of UL Firefighter Safety Research Institute.)|
During this test burn, the fire entered from the soffit vent; the end result was a giant slab of foam with wood joists and roofing materials attached to it. SPF held the entire roof system together. During the overhaul phase of the project, it was nearly impossible to disassemble. We tried removing all of the supporting wall and trusses that supported the roof assembly. The entire roof system stayed together. We tried striking the roof system in the middle with a sledgehammer; all that did was create a crack in the foam.
We didn’t want this 25-foot-high, three-sided structure to collapse inside of a confined laboratory space. So we decided to use a tractor to pull the walls out from under the roof assembly, keeping the walls upright. This proved challenging for a variety of reasons including the safety of the overhaul crew. After several attempts to pull the walls apart, we decided to cut the crossbeam away from one of the walls to create a lean-to collapse of the roof system. It finally fell as one piece into the interior of the walls. Once we got the roof assembly down and cut into it, cross sections looked like a roasted marshmallow (photos 7, 8).
|(7, 8) SPF in attic after exposure to fire. (Photos courtesy of John Shafer.)|
Impact on Fire Service
As with all “new” materials, we must look to determine what, if any, effect it will have on the fire service. We have to look at flame spread, smoke production, fire attack concerns, stability, added static loads, and many other concerns based on the different materials. With SPF, it is important to look toward the manufacturers to provide additional information. However, we must also be cautious with the information that comes from biased organizations. UL has proven to be nonbiased and has no agenda other than to save firefighter lives. The UL Firefighter Safety Research Institute will provide us with the information we need for progress in the fire service.
What does SPF mean to the fire service? SPF is sprayed on from below and inside the attic space to cover/insulate the entire roof system. When fire enters the attic space, the SPF chars and becomes a solid structure. We found amazing how intact the roof system was after it had been burning for more than 10 minutes.
Size-up. It may be nearly impossible to detect SPF during size-up. If foam is used in the attic space, companies may not see the traditional signs of an attic fire: smoke from the ridge vent, vent caps, or eaves. Companies may see smoke, but because of the toxic smoke that the SPF may emit, it will likely be black smoke rather than gray/brown laminar smoke.
Preplanning is essential to determine whether SPF is being used in your area. Preplanning is critical on new construction and remodeling, since SPF can be used in both applications. This highlights the need for our departments to work more closely with our city/county building departments so we are in the loop to be updated on all construction types and materials in use.
Vertical ventilation. When assigned vertical ventilation, you will not be able to tell from the topside if SPF is present. Because of the foam’s solid form, it may also be difficult to feel the rafters while cutting. Once you get the hole cut, it will be difficult to pull up the cut materials. A deep punch cut with a chain saw is the only way to get all the way through on the initial cut. You may complete a punch cut using a chain saw and inserting it straight down into the roof rather than at an angle. However, we need more testing on our tactics with these new materials. Our current skill sets may not be the best options on new materials such as SPF. Using a power saw also may not be the best option. We may have to resort to hand tools by peeling each layer back.
During this test, a 2 × 6 roof system was built, and the SPF was about five to six inches thick. Hand tools will be critical to pry and pull up the cut materials. The foam will come apart in small pieces, not in the preferred larger section. Go to the roof prepared with the appropriate tools (photo 9).
|(9) Even after fire exposure, SPF held the roof assembly together despite the three cuts made (arrows). (Photo courtesy of John Shafer.)|
Remember, your tool selection will be based on your size-up of the roof sheathing. Not all tools work on every type of sheathing. However, there are tools that should always go to the roof-e.g., the power saw, the hook, an ax, a portable radio, the roof ladder, and the thermal imaging camera (TIC).
One tactic not routinely performed on residential construction is the kerf or triangle inspection cut. Just as with commercial roof systems, we must know and understand what we are cutting before opening it up. We must also understand the amount of heat and smoke that is produced in the attic space. Using a kerf or triangle cut has benefits even in residential construction.
Overhaul. Overhaul will pose some challenges since the thermoset properties can allow hidden fire to burn underneath the hardened crust. We watched as the UL crew attempted to overhaul some small areas. It was difficult and time-consuming to break apart the foam with hand tools. Using a TIC and a pressurized water extinguisher filled with a foam-type solution could be the answer to finding and extinguishing this deep-seated fire under the outer crust. However, since the SPF is usually sprayed on the underside of the roof, overhaul of the attic floor or the top-floor ceiling space will be limited. This also has an added benefit for customer service. We all know the mess that is made when we begin overhauling an attic with blown-in insulation.
Beware: If making an opening in the ceiling to overhaul the fire, you are essentially creating a vent opening for a possible ventilation-limited fire. We need to apply our fire behavior knowledge and remember that firefighters have been injured and killed from an attic flashover.
SPF and all new modern building materials offer the fire service new challenges that we need to stay on top of within our districts. We must be proactive in our communities and perform building preplanning and work more closely with our building permit departments.
“New” doesn’t automatically translate into “bad” for the fire service. Rather, it is something that we must research, learn about, and adapt our tactics to if necessary. It doesn’t necessarily mean that we will be standing outside and allowing the building to burn.
Aggressive firefighting is still valid, but it must not be reckless. Company and command officers must make solid decisions based on training, education, practical application, and experience to ensure that the tactics meet the needs of the incident.
To further educate yourself on fire research-based tactics, go to http://ulfirefightersafety.com/training/.
P.J. NORWOOD is a deputy chief training officer for the East Haven (CT) Fire Department and has served four years with the Connecticut Army National Guard. He has authored Dispatch, Handling the Mayday (Fire Engineering, 2012); coauthored Tactical Perspectives of Ventilation and Mayday DVDs (2011, 2012); and was a key contributor to the Tactical Perspectives DVD series. He is a Fire Engineering University faculty member, co-creator of Fire Engineering’s weekly video blog “The Job,” and host of a Fire Engineering Blog Talk Radio show. He is certified to the instructor II, officer III, and paramedic levels.
SEAN M. GRAY started his fire service career in 1993 in Southern California and is a lieutenant with Cobb County (GA) Fire and Emergency Services. He has a bachelor’s degree in fire safety engineering from the University of Cincinnati. He has presented at FDIC and has been published in Fire Engineering. He is an advisory board member for the UL Firefighter Safety Research Institute and has served on the Exterior/Attic Fire UL Technical Panel.
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