Fire Risks Not Limited to Spray-Foam Insulation
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Spray foam is only one of a number of building products and methods which increase the risk of catastrophic fire loss (and potential loss of life). [Editor's note: After asking him to pen his series of 10 Riversong's Random Reflections on ou... As one who has been both a designer/builder and a volunteer firefighter for 30 years, as well as an instructor in sustainable design and construction, I can shed some light on the issue of fire safety in construction and remodeling. Dangers of truss and engineered lumber construction One common construction practice has been the use of light-frame floor and roof trusses. These have often been replaced, at least in floors and sometimes roof assemblies, with "engineered lumber" such as wood I-beams. In both cases, structural integrity depends on the synergy of all parts of the assembly, including chords, webs, struts & ties and their connectors (typically metal truss plates). With smaller elements, these engineered structural units fail much more quickly in a fire than either light wood frame or timber frame construction. In trusses, the metal gang nailing plates quickly overheat, char the wood they penetrate and fail. Even small-town fire departments often have to engage in pre-planning to note which buildings in their jurisdiction are made from truss or engineered lumber construction. An I-joist, like a truss, will also fail more quickly than a comparable 2x joist or rafter. We typically will not enter such a building for interior fire suppression and will avoid going onto the roof to ventilate the heat. This leaves only outside fire suppression and makes the building more vulnerable to fire and water damage as well as collapse. Ventilating a fire in progress A non-combustible roofing material may be sensible if using a woodstove for heat or if in a wildfire zone. But with interior-origin fires (which most are), a non-flammable roof such as metal or slate will contain the heat and fire longer and often result in more serious structural damage. One of the first things we firefighters do at a structure fire is to cut one or more holes in the roof to ventilate the super-heated air. Sometimes breaking windows is sufficient unless the fire is already in the attic. Early morning of April Fools Day, 2008, my department responded to a structure fire in our central village--a former home and barn used as a spa/salon and an antique store. The fire was triggered by a propane explosion, and the building was fully involved at our arrival. The building had been renovated so many times that we discovered (after the fact) a number of double walls and a double roof built up over an existing roof. Attempting to ventilate the roof did not work because of the secondary roof below. Outside attack hose streams were blocked by extra walls just inside the windows, and the fire chases created by the doubled interior partitions increased the rate of fire spread. Unintended consequences. Cellulose implicated in convenience store fire In August of 2006, our department was called to a convenience store under construction after the original one burnt down and a new model replacement (which was meant to be the prototype for all similar stores for this locally-owned Vermont chain) also burnt to the ground just two months earlier. It seems the same cellulose insulation contractor who had blown the suspended ceiling the day before the previous fire was at the site filling the ceiling again. This time, an employee noticed smoke coming from the hopper of the truck-mounted blowing machine, so he stopped the operation and emptied out the hopper. At the bottom, just above the overheated muffler from the compressor, was some charred cellulose. If properly treated with borates, cellulose is one of the most fire-proof insulations on the market. While it won't support combustion, it will char and smolder. Apparently, two months earlier and with the same blower, this contractor had put some smoldering cellulose into the ceiling. Overnight, it ignited some non-protected framing member, which spread the fire to the entire hollow ceiling and metal-clad roof. Almost as soon as the fire department arrived, the entire roof collapsed. Unintended consequences. I was the firefighter who collected samples of the charred cellulose from the second reconstruction and got it to the state fire inspector. The earlier fire was then determined to be caused by a faulty cellulose machine and that contractor went out of business. We provided water while a septic pumper sucked all the new cellulose out of the ceiling and saved the store from a third fire. While cellulose-related fires are an aberration (cellulose is so effective at fire prevention that it's been third-party certified as a fire stop), there are an infinite number of potential errors which can result in a fire during construction (two of the most common are oily rags auto-combusting and space heaters left unattended). Choose building materials with care--and think about unintended consequences The lesson is that care and consideration are required, both in choosing materials and methods and in maintaining a safe construction site environment. Some materials, such as plastic foams, can dramatically increase fire risk – both in application (ASTM E85, referenced in IRC R316, sets flammability standards and thickness limits, which are often less than code-minimum R-values) and during occupancy. If foam insulation is part of a structural panel system, then the structure can collapse once the melting point is reached or the required 15-minute ignition barrier is breached. Once burning, plastics accelerate fire spread, smoke development and building damage. Using non-flammable materials and avoiding fire chases (including the exterior chase created by a rainscreen cladding system) can help reduce both the likelihood of fire and the extent of fire damage. Make sure there are adequate fire stops in all enclosed soffits, attic kneewall areas, under first floor bathtubs and around chimneys. Install wood-burning appliances (and all combustion appliances) to factory specifications and according to applicable fire codes. Design in fire egress windows in all sleeping areas, and a safe route to the ground. Beware of wildfire zone issues and codes. Of course, install hard-wired smoke and CO alarms and make sure any exhaust flue exits the house above maximum snow level to avoid CO back-drafting. But, above all, think about potential unintended consequences. Every design and construction decision has the potential to increase or reduce the risk, intensity and extent of fire. About 4,000 people die every year from fire in the US, and the almost 400,000 annual residential fires create nearly $8 billion in losses. These are consequences best to anticipate and avoid. Editor's note: BuildingGreen's guide to insulation materials and practices helps readers navigate some of the material choices alluded to here. copyleft by Robert Riversong: may be reproduced only with attribution for non-commercial purposes Robert Riversong has been a pioneer in super-insulated and passive solar construction, an instructor in building science and hygro-thermal engineering, a philosopher, wilderness guide and rites-of-passage facilitator. He can be reached at HouseWright (at) Ponds-Edge (dot) net. Some of his work can be seen at BuildItSolar.com (an article on his modified Larsen Truss system), GreenHomeBuilding.com (more on the Larsen Truss), GreenBuildingAdvisor.com (a case study of a Vermont home), and Transition Vermont (photos).