Improving smoldering test for upholstered furniture

In the United States, fires in which upholstered furniture is the first item ignited account for about 6,700 home fires annually and result in 480 deaths, according to the National Fire Protection Association. These fires can be started from an open-flame source, such as a candle, or from a smoldering source, such as a lit cigarette or incense.

In the smoldering test, two foam pieces about two-inches thick are covered with fabric and placed in a wooden frame to replicate a small-scale version of seat and back cushions. It mimics a scenario where furniture foam sits on a non-air-permeable substrate (e.g. the wooden frame). A cigarette (certified to burn consistently) is placed in the frame's crevice. To pass the test, the lit cigarette should not cause sustained smoldering of the fabric or the underlying foam.

Household furniture typically includes open wooden frames and springs, which enhance air flow through foam and increase the propensity for smoldering. The researchers changed the frame design to allow for air flow by including wire mesh to separate the foam pieces from the wooden frame. Their design better represented real furniture and provided a more realistic simulation of smoldering. In the process, they also identified foams that could be used for better smoldering consistency.

"Our goal is to help regulators develop a more realistic smoldering test. Our results show that the current test can severely underestimate smoldering propensity in real furniture," said AU Assistant Professor and NIST researcher Mauro Zammarano. "We recommend that regulators who administer the test consider creating gaps in the frame design to increase air flow."

The finding of the improved smoldering test came about as AU Chemistry Assistant Professor Doug Fox, Zammarano and their colleagues work to design non-toxic "green" flame retardants. The team focuses on molecular chemistry research using ingredients from natural materials such as cellulose. Cellulose, the most abundant polymer on Earth, is an effective reinforcing fiber for polymer composites, but it is extremely flammable. Fox's team modifies cellulose, often with phosphates or silicon-containing compounds. Modified cellulose acts as a flame retardant and a reinforcing phase, so that when blended with plastics, the fire resistance of the composite increases without weakening, as is often the case with other flame retardants.

Effective flame retardants in furniture delay time for ignition and the spread of flames, and the researchers envision a future where industry embraces green flame retardants. Currently, there are few options for affordable flame retardants that are effective, and the ones available are increasingly unpopular because of potential toxicity issues. In recent years, scientific studies have linked exposure to flame retardant chemicals in furniture with negative health effects in people. Because of the concerns, last year lawmakers in California voted for a change to the state's nearly 40-year-old flammability standards. Lawmakers ended the requirement for an open-flame test for filling materials in upholstered furniture. (The open-flame test, unlike the smoldering test, often required the use of flame retardants to pass.)

California's regulations are key because many foam manufacturers follow them for the entire U.S market rather than make separate products for California. The end of the open-flame test, however, hasn't meant all manufacturers have ended the use of flame retardants, which is why Fox's group pushes on to create a green solution.

"While manufacturers are no longer required to use flame retardants, some in the furniture industry still place them in foam due to concerns over potential lawsuits, possible reinstatement of open flame tests, or to satisfy the needs of European or commercial products, which still require a level of flammability reduction," Fox said.

The role of flame retardants in fire safety is seen in recent, high-profile fires. The 2003 Rhode Island nightclub fire that killed 100 people started when pyrotechnics ignited soundproofing material. When NIST scientists conducted an experiment using pyrotechnics to ignite soundproofing material containing flame retardants, the soundproofing material did not catch fire. In the airline crash of Asiana flight 214 in July 2013 in San Francisco, people survived in part because flame retardants delayed the time it took for the plane to catch on fire, providing people minutes, not seconds, to escape, Fox added.

While Fox and his team focus on creating green flame retardants used in furniture, the research could have wider industry applications. In addition to furniture, flame retardants are used in products that must meet flammability standards, including electronics, insulation and textiles.