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The Cone Calorimeter Method

The Cone Calorimeter Method The cone calorimeter method for determining the rate of heat release (HRR) is described in ASTM E-1354 and ISO 5660.

ASTM International. Standard test method for heat and visible smoke release rates for materials and products using an oxygen consumption calorimeter. ASTM E 1354. ASTM International, West Conshohocken, PA.

International Organization for Standardization. Reaction to fire tests - Heat release, smoke production and mass loss rate. Part 1: Rate of heat release from building products (Cone calorimeter method) (ISO 5660-1:2002), Part 2. Smoke production rate (dynamic measurement) (ISO 5660-2:2002), and Part 3: Guidance on measurement (ISO/TR 5660-3:2003). ISO, Geneva.

In the cone calorimeter test, a 100-mm square specimen is exposed to a constant external heating flux. ASTM E1354 limits the thickness to 50 mm. The flux level of up to 100 kW/m2 is specified by the user. We generally use heat flux levels of either 35 kW/m2 or 50 kW/m2 to test wood products. In studies including multiple heat flux levels, heat fluxes included 20 (or 25), 35, 50 and 65 kW/m2. There are no tests in this FPL database at fluxes above 65 kW/m2. A spark igniter provides the piloted ignition source.

The Cone Calorimeter Method The primary result from the cone calorimeter test is a heat release rate (HRR) (or rate of heat release, or (RHR)) curve over the duration of the test. The HRR due to combustion is determined using the oxygen consumption methodology. The methodology is derived from the observation that the net heat of combustion is directly related to the amount of oxygen required for combustion. Thus, the oxygen concentration and the exhaust gas flow are measured in the test. A typical curve for wood has an initial increase to a peak heat release rate then a drop to a steady-state heat release rate, followed by a second peak as the final portion of the specimen is consumed. For reporting purposes, the heat release curve is often reduced to single numbers. These are the initial peak HRR and averages of the HRR over set periods of time (60, 180 and 300 seconds) after ignition of the specimen is observed. Units for heat release rate are kW/m2. The data is adjusted for the initial exposed surface area of the sample. The total heat release (THR, in MJ/m2) is the cumulative heat release (area under the heat release curve) through the duration of the test.

In addition, the mass loss of the burning specimen is recorded. From the heat release and mass loss, the effective heat of combustion (EHOC) (heat release per unit mass loss) is calculated. The average effective heat of combustion (AEHOC) is computed from the total heat release divided by the total mass loss. The obscuration of a laser beam in the exhaust duct is recorded as a measure of the visible smoke development from the burning specimen. The average specific extinction area (ASEA) is computed from the smoke obscuration data. Ignitability is determined by observing the time for sustained ignition of the specimen.

The standards allow for both vertical and horizontal orientation of the test specimen. In addition to the standard specimen holder, there is the option to use a retainer frame and grid with the specimen holder. The specimen is wrapped in aluminum foil so its sides and bottom are covered with the shiny side of the foil against the specimen and placed in the holder on top of a layer of low density refractory fiber blanket. We have examined the influence of the backing board on the test results. In general, we test in the horizontal orientation with the conical radiant electric heater located 25 millimeters above the specimen and use the retainer frame without the metal grid over the test specimen. The electric spark igniter is placed 13 millimeters above the test specimen until sustained ignition of the test specimen is observed.

The Cone Calorimeter Method HRR is a critical factor in the spread of flames over a surface and in the overall growth of a compartment fire. It is an option for an evaluation of the degree of combustibility of different materials.

Fire-retardant treatments for wood products are designed to reduce their flammability. In the United States, the regulatory test for flammability of building products is the 7.32 m (25-ft) tunnel test (ASTM E 84). In the E 84 test, the flame spread index (FSI) is reported. See the web site of the American Wood Council for a listing of FSI for domestic wood products (DCA 1 - Flame Spread Performance of Wood Products). To assist us in our use of the cone calorimeter, we have developed models that provide predictions of the E84 flame spread index from the cone calorimeter data.