Flame quencher offers less toxic approach to fighting fire

A new fire-retardant coating suppresses flames without the toxic effects of some commercially used flame retardants. Torch a piece of furniture foam that’s been dipped in the coating and the flame smolders and snuffs out, new experiments show.

“The fire just can’t keep going,” says materials scientist Jaime Grunlan of Texas A&M University in College Station, who led the work. “It puts itself out.”

The new coating creates a blanket of heavy gas that starves the fire of oxygen, Grunlan says. Galina Laufer, a researcher in Grunlan’s lab, devised the coating by combining two polymers called PVS (polyvinyl sulfonic acid sodium salt) and chitosan, which is made from the shells of lobster, shrimp and other crustaceans. The researchers tested the coating on polyurethane foam, a highly flammable material commonly used in furniture.

After applying several layers of nanometer-thick coating, Laufer held a torch to the foam for 10 seconds. The fire smoldered and died, and the foam was only charred rather than a melted mess, Grunlan says. The fire degrades the coating, breaking and forming bonds to release ammonia, water and sulfur dioxide — all nonflammable gases. These gases are heavy and sit on the foam, starving the fire of oxygen, the team reports April 12 in ACS Macro Letters.

Rather than being mixed throughout foam like traditional flame retardants, the coating is intended for application on a product’s surface. As a result, it might be easier for furniture manufacturers to use. Adding a 10-layer coating (about 30 nanometers thick) adds only a bit more than 5 percent to the foam’s original weight, whereas traditional flame retardants add upwards of 20 percent, says Charles Wilkie, a specialist in fire-retardant materials at Marquette University in Milwaukee.

“It’s a very nice approach,” says Wilkie. “It’s practical and has real potential application.”

Wilkie would like to see how the foam holds up when the flame is applied for longer than 10 seconds, to more closely mimic a real fire.

New flame retardants are much needed, says environmental chemist Cynthia de Wit of Stockholm University. Many of the classic brominated flame retardants are now banned or being phased out in many countries because of concerns about the toxic effects of long-term exposure.

“There’s a cost-benefit question,” de Wit says. “Is it worth putting several pounds of chemicals in a sofa if that’s a health hazard? How do you rate the threat of fire compared with the long term threat to health?”