How Do You Stop Something Burning Without Making It Fireproof? Interrupt the Fire

Burning is a chain reaction in the gas above a material, in which highly reactive fragments are produced and go on to produce more, so combustion sustains itself once started. Additives interrupt that in several distinct ways. Some release compounds into the flame that mop up the reactive fragments and break the chain. Some decompose to release water or other gases that dilute the fuel and the oxygen. Some form a thick insulating char on the surface that keeps heat from the material beneath and keeps combustible vapours from escaping. Some absorb heat as they decompose, lowering the temperature. The aim throughout is to slow ignition and spread rather than to make anything genuinely incombustible.

Several chemical types are used and they behave quite differently:

• •Brominated compounds, effective at low loadings and heavily restricted now
• •Chlorinated compounds, similar in action and similarly problematic
• •Phosphorus compounds, which promote char formation
• •Aluminium and magnesium hydroxides, which release water on heating
• •Nitrogen compounds, frequently used alongside phosphorus ones
• •Intumescent coatings, which swell into a thick insulating foam

The brominated compounds used in enormous quantities from the 1970s proved to share properties with other persistent pollutants, being resistant to breakdown, soluble in fat and therefore accumulating in animal and human tissue, and capable of travelling long distances in air and water. They were found in wildlife far from any industry, in household dust at substantial concentrations, and in human blood and breast milk with levels rising over decades. Associations with effects on thyroid function and on neurological development in children were reported in a substantial body of research. Several were added to international agreements restricting persistent organic pollutants from 2009 onwards, and manufacturers moved to replacements that are in several cases not well characterised.

Regulations specify test methods, and how well those tests represent real fires determines whether the regulation achieves anything. A small flame test applies a burner for a fixed period and records whether the material ignites and how far flame spreads, which is cheap, reproducible and represents a cigarette or a match rather than a burning wastepaper basket. Larger tests burn a whole item in a room and measure the rate of heat release, which represents reality far better and costs enormously more. Smoke density and toxicity are measured separately and are frequently not required at all. Since most fire deaths are caused by smoke rather than by flame, a standard that ignores smoke can approve a material that is more dangerous in a real fire than the one it replaced.

Whether adding these compounds to upholstered furniture is worthwhile has been contested for two decades and is instructive. Regulations in the United States and Britain required furniture to resist ignition, which was met by loading foam with additives. Research then questioned whether that reduced deaths, on the grounds that the tests used a small flame while real fires involve larger ignition sources against which the treatment achieves little, and that the treated foam produces far more smoke and toxic gas when it does burn, which is what actually kills people in fires. Investigative reporting in 2012 documented lobbying by manufacturers to maintain the requirements. Several jurisdictions have since revised their standards towards barrier fabrics rather than chemical treatment.

Additives interrupt the chain reaction in the flame, dilute the fuel with released gases, form insulating char or absorb heat, which slows ignition and spread rather than preventing burning. Brominated compounds used since the 1970s persist, accumulate in tissue and were found worldwide, and several are now restricted internationally. Whether treating furniture reduces deaths is contested, since treated foam produces more toxic smoke.