Fire resistance

Ever since cellulose insulation was first marketed in the late 1940s, sellers of competing products have raised questions about the safety of the material. Cellulose insulation, as an organic mate­rial, will burn without special processing. Unlike two competing insulation materials, fiberglass and rock wool, which are naturally fire resistant, cellulose’s fire resistance is achieved by adding chem­icals.

According to Dan Lea, executive director of СІМА, the common fire retardants in cellulose insulation are borax, boric acid, and ammonium sulfate. Public concerns may be due more to misinfor­mation than fact. For example, boric acid is commonly used as an eyewash. The salts of borax are used in laundry products but have a toxicity level even lower than that of boric acid. Ammonium sul­fate is used as a food preservative and a soil fertilizer.

The CPSC does not believe cellulose insulation is a hazardous product. Fire statistics do not support the hazard claim, and knowl­edgeable fire officials who have studied the matter agree. Extensive evidence indicates that cellulose is a positive factor in residential building fire safety, mainly due to the material charac­teristics of cellulose. Once the surface of a cellulose insulation lay­er is charred, it no longer flames, and the charred material actually becomes a barrier against rapid combustion deeper in the insula­tion. Smoldering combustion may continue, but its progress through the insulation will be very slow due to the dense fiber structure of cellulose and its fire-retardant characteristics.6

The most recent findings were released in test results made avail­able in February 2000. Independent laboratory tests, commissioned by СІМА and conducted according to the ASTM E119 protocol by Omega Point Laboratories of Elmendorf, Texas, have shown that cel­lulose insulation can increase the fire resistance of walls by up to 77 percent compared with uninsulated walls. Cellulose can now be used in a 1-hour fire-wall assembly that meets the new International Building Code and International Residential Code. Walls for the test were constructed with both V2" and 5/8" type X gypsum wallboard. The insulation was standard off-the-shelf cellulose installed by a local contractor.7 This is an increase in fire resistance as compared with earlier tests sponsored by the cellulose industry and the min­eral fiber insulation industry. These stated that cellulose produced a 22 to 55 percent increase in fire resistance.6

The biggest long-term performance concern with cellulose insu­lation is the possible loss of fire-retardant chemicals. There are oth­er reports that claim cellulose insulation may be safe initially but that over time the fire retardants bake out, leech out, settle out, break down, sublime, evaporate, or somehow disappear. Because borates are water soluble, they can leach out if the insulation gets wet. Some people claim that the chemicals gradually disappear even if the material does not get wet, although these claims have not been substantiated independently. According to Dan Lea of СІМА, there is a shift within the industry toward ammonium sul­fate fire retardants, which actually improve in fire-retardant per­formance over time. A concern with ammonium sulfate, however, is the corrosion of metals in contact with the insulation, particularly with wet-spray applications.

According to СІМА, the Forest Products Laboratory of the University of California at Berkeley performed an extensive litera­ture search and reviewed all relevant published studies on cellu­lose insulation chemical permanency. The study concluded that “the only substantive report that indicated an aging effect is that recently reported by the California Bureau of Home Furnishings and Thermal Insulation.” CBHF said of its study: “The results are inconclusive and variable, and certainly cannot be used to condemn this material.” Numerous other studies, including tests by scien­tists and technicians at Oak Ridge National Laboratory, Tennessee Technological University, Allied Signal Corp., U. S. Borax Corp., Underwriters Laboratories, and the United States Testing Company, found no sign of “disappearing fire retardants.”6

The competitive nature of the insulation business has generated a great amount of literature in support of, or in defense of, the material characteristics and performance of each product. Since an independent test is not within the scope of this book, one must weigh all the information in order to arrive at a general consensus as to the actual fire-resistance characteristics of cellulose insulation.

For example, the North American Insulation Manufacturers Association (NAIMA) claimed in one report that “independent tests confirm [the] potential fire hazards of cellulose insulation.” In defense of cellulose insulation, СІМА states that “all six cellulose products tested exceeded the requirements of the only material standard that references the test method used in the study.” According to СІМА, the NAIMA tests “actually proved the safety of cellulose insulation.”6

Even when a fire is classified as “insulation related,” the insula­tion is seldom the first material to ignite. Heat-producing devices and electrical short circuits were major factors in insulated-related fires. In the vast majority of cases, a heat-producing device, such as a recessed lighting fixture, is covered by the insulation. Heat builds up and is conducted through wiring or metal brackets to a wood structural member. This indicates that it is usually the wood or electrical insulation that ignites first.