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...

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