New Technology, Old Problems: Heat Release Research an FPL Mainstay

The following post is adapted from the book Forest Products Laboratory 1910-2010, Celebrating A Century of Accomplishments.

As an early promoter of the use of heat release rate as a measure of relative flammability, John Brenden developed the original Forest Products Laboratory (FPL) apparatus to measure the heat released by a burning material in the 1960s. Heat release research was reliable and effective, and FPL continued to obtain new equipment as better technologies were developed to measure heat release rates.

The cone calorimeter replaced the apparatus from Ohio State University that was employed by FPL researchers in the 1980s.

In the 1980s, the original apparatus was replaced by one from Ohio State University, and 10 years later, was replaced by a cone calorimeter developed by the National Bureau of Standards. Today this organization is known as the National Institute for Standards and Technology. The cone calorimeter is used in investigations into fire-retardant treatments (FRT) for composite materials and fundamental research on the fire behavior of wood.

A cone calorimeter is a laboratory instrument that gathers data ranging from ignition time, to combustion products and, of course, heat release rate. It is used with small samples of flammable material. Its name reflects the conical shape of the radiant heater used in the device.

In addition to their use in evaluating the effectiveness of fire-retardant treatments, test methods for the rate of heat release were critical in the development of models to predict flame spread behavior of wood and times for flashover in the standard room-corner test.

Heat release graphs are still used by FPL researchers to determine the effectiveness of flame-retardant wood treatments.

Today, FPL researchers still use heat release rates to determine a material’s flammability. FPL Research General Engineer Mark Dietenberger, and Laura Hasburgh, a Fire Protection Engineer at FPL, feature an FRT heat release rate graph in their recently published document, Wood Products Thermal Degradation and Fire in the Materials Science and Materials Engineering Reference Module for Elsevier. More information can be viewed here.


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.


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.