The Heat is On: Fire Fuels Research at FPL

Where there’s smoke, there’s fire — but where there’s wood, there’s always the chance of fire. Luckily, where wood and fire meet, there’s the Building and Fire Science work unit at the Forest Products Laboratory (FPL).

This CLT specimen survived almost 100 minutes of exposure in a standardized test reaching nearly 1000°C. The unexposed side of the specimen remained at less than 50°C for the entire test.

Throughout its existence, FPL has long been on the cutting edge of fire science. Fire prevention will continue to be a major area of study as wood expands into commercial and high-rise construction.

This unit is charged with researching how wood and fire interact, and help make wood products more fire resistant and in compliance with international fire safety standards. One way to accomplish this daunting task is through the use of flame-retardant treatments (FRTs) — but what exactly do these treatments do?

FPL Research General Engineer Mark Dietenberger, and Laura Hasburgh, a Fire Protection Engineer at FPL, know exactly how FRTs work. Their recently published document Wood Products Thermal Degradation and Fire in the Materials Science and Materials Engineering Reference Module for Elsevier takes an in-depth look at these treatments and explains how they work to keep wood from going up in flames.

Most FRTs delay ignition, reduce heat release, and reduce flame spread. Other possible mechanisms for fire retardancy include conducting heat away from the heat source, endothermic chemical reactions to absorb heat, or the releasing radicals that inhibit combustion. Some flame-retardant coatings can even swell to form an expanded low-density protective film for the material upon exposure to fire. These FRTs are known as intumescent formulations.

For interior applications, Dietenberger and Hasburgh note that water-soluble inorganic salts are the most common flame retardants. These chemicals are combined by researchers in specific ways to optimize a material’s fire performance and reduce individual aspects of a fire. Boric acid, for example, can be added to an FRT formulation to reduce smoldering or glowing.

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FRTs can reduce the heat release characteristics of wood. Above are heat release curves for untreated and FRT Douglas-fir plywood.

Although the FRTs decrease the flammability of a material, they can increase other dangers associated with fire, like the production of smoke or weaken a material’s structural integrity. Fire retardant-treated wood is often more brittle than untreated wood, and some FRTs can cause further losses in strength with continued exposure to elevated temperatures, for example, the roof of a burning building.

FRT research thus is a delicate balancing act, and researchers strive to create FRTs that allow wood to remain both strong and fire-free. Though the heat is on for the men and women from FPL’s Building and Fire Science unit, they have proven they are up to the challenge — continually pushing the limits of FRT with every experiment, and helping to make our wood, and us, safer.

For more information, please see the full article, Wood Products Thermal Degradation and Fire.

Throwback Thursday: Early Fire-Retardant Treatments

In the early days of developing fire-retardant treatments, researchers at the Forest Products Laboratory (FPL) investigated about 130 treatments. Combinations of chemicals were used to obtain the best performance for both fire resistance and other performance properties, such as corrosion, leaching, gluing, finishing, and cost.

Chemicals tested included ammonium sulfate, mono- and di-ammonium phosphates, ammonium chloride, zinc chloride, borax, and boric acid. The phosphates were identified as the most effective. These chemicals were used in the first generation of commercial fire-retardant-treated wood in the United States.

Fire retardant test at FPL, 1940s.

Fire retardant test at FPL, 1940s. (click to enlarge)

The 1940s test pictured above shows an attic section in which the rafters, roof boards, inside of the end wall, and the top ply of the flooring, were impregnated with a moderate degree of fire retardant and exposed to a 5.25-lb magnesium bomb. The treatment completely stopped the spread of fire on exposed surfaces, but the untreated subfloor was ignited by the excessive heat transmitted through the flooring.

(Excerpt from John Koning’s book Forest Products Laboratory 1910-2010: Celebrating a Century of Accomplishments.)