Q. I've heard that polyurethane spray-foam insulation may contain penta-BDE, a chemical that is called a "toxic flame retardant" by the EPA and has been banned in some states. How much of a risk does this chemical cause for the installer and the homeowner, and are there alternatives?

A.Mason Knowles, a former director of the Spray Polyurethane Foam Alliance and an industry consultant, responds: Penta-BDE (pentabromodiphenyl ether) is one of a family of brominated fire retardants that also includes deca-BDE and octa-BDE. Penta-BDE was once commonly used in the flexible-foam industry for car seats, furniture, and plastic circuit boards. However, its short shelf life made it ill-suited for SPF systems, which may not be sprayed until several months after they’ve been blended. According to the manufacturers I’ve spoken with, penta-BDE has seldom — if ever — been used in residential spray foam.

A concern with penta-BDE is that it accumulates in body fat; it first gained attention when dramatically elevated levels of the chemical were found in the breast milk of nursing mothers. According to the Agency for Toxic Substances and Disease Registry, nothing definite is known about the health effects of penta-BDE on humans, though studies with lab animals suggest it may affect the liver, the thyroid, and neurobehavioral development. Even though it’s not specifically identified as a carcinogen, penta-BDE is no longer manufactured in the U.S., and some states and countries have passed measures regulating its use or banning it altogether, as a precautionary measure.

While deca-BDE and a few other brominated fire retardants are still being manufactured, they’re gradually being phased out in favor of phosphorus-based flame retardants, which don’t form dioxins or furans when they’re burned. Probably the two retardants most commonly used in polyurethane spray foams are Tris(2-chloro-1-methylethyl)phosphate (TCPP/TMCP), which contains both chlorine and phosphorus, and halogen-free resorcinol-bis(diphenyl phosphate), or RDP. Because manufacturers are allowed to substitute one retardant for another in their formulas without having to retest, it’s difficult to know exactly which manufacturer uses which flame retardant, but outside of normal precautions for workers who handle the bulk materials, I haven’t heard of any health issues concerning these types of retardants.