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There are several pieces of equipment that are key in the field of fire science. This page will give a description of some of them. This information is mostly taken from Drysdale, D. (1998) An Introduction to Fire Dynamics, second ed. John Wiley and Sons, New York.

The cone calorimeter, also known as the oxygen consumption calorimeter, is based on the realization that the heat release rate of almost all hydrocarbon fuels is the same, when it is normalized by the amount of oxygen consumed. This is a rather surprising result, but it's true: almost all hydrocarbon fuels release 13.1 kJ / gram O2 (±5%) consumed assuming complete combustion. This assumption is not always met, but the main form of incomplete combustion products is carbon monoxide, and the change in energy release due to formation of carbon monoxide rather than dioxide can be calculated, using the methods described in the thermodynamics section (link to thermo section). However, this is a fairly small correction to the method, since a "high" concentration of CO in air (enough to incapacitate a person after 30 minutes of exposure) is only 0.1% by volume. Therefore, in its simplest form, a detector which can measure the amount of oxygen in the outlet flow is sufficient to give an estimate of the heat release rate from the fire. Note that, if there is no CO2 or H2O detector, the gas must be dried and the CO2 must be removed with a chemical sorbent. This is because the amount of CO2 and H2O in the exhaust is unknown - each must be either removed or measured in any form of this measurement. Note also that house fires are generally not hot enough to form significant amounts of nitrogen oxides (NOx), so nitrogen acts purely as an inert diluent in these systems.

A diagram of a cone calorimeter is shown below. The burning item is often placed on a scale to measure the mass burning rate as well.

300 cfm of air at 298 K flows into a cone calorimeter where a large upholstered recliner is burning. The pressure is atmospheric throughout. The outlet gas flow is dried, cooled to 298 K, and the CO2 is removed, at which point there is a minimum flow rate of 268 cfm and a simultaneous minimum oxygen concentration of 11.7%. Find the maximum heat released from the burning recliner.

By assumption, in the inlet air, there is 21% O₂ and 79% N₂ (X_O2,in=0.21, X_N2,in=0.79).

2) Find the outlet mass flow rate of oxygen, assuming that the nitrogen mass flow rate does not change (i.e. the nitrogen is inert).

3) Find the maximum heat released during combustion, , from the mass of oxygen consumed, using the heat released per O₂ consumed, E = 13.1 kJ/gm.

This calculation can be made more accurate by measuring the inlet and outlet concentrations of CO, CO₂, and H₂O.

Cone calorimeters are used in a wide range of sizes. The smallest are bench-scale devices easily used in any lab. One of the largest is the cone calorimeter planned for the new Fire Research Laboratory being built by the U.S. Bureau of Alcohol, Tobacco, and Firearms. It will be large enough that a two-story house can be built and burned inside it!

For more information on cone calorimeters, see several of the articles in Babrauskas, V., and Grayson, S. J. eds. (1992) Heat Release in Fires, Elsevier Science Publishing, New York.

The Pensky-Martens apparatus is used for measuring the flash point and fire point of liquid fuels. Flash point is defined as the temperature at which a flammable mixture is formed above a pool of liquid fuel. At the flash point, the fuel vapors will combust, but the combustion will not generate enough heat to create a sustained fire above the liquid fuel. The Pensky-Martens apparatus essentially allows a direct measurement of the lower flammability temperature calculated in the thermodynamics section (link). Flash point is usually given for a closed cup, but can also be given for an open cup where the fuel is exposed to open air. The fire point is the temperature at which the fuel vapors above an open cup of fuel are flammable, but also contains enough energy to heat the surface of the fuel, vaporizing more fuel and leading to a sustained pool fire. The fire point is always a higher temperature than the flash point for a given fuel.

Considering that the flash point is too cool to cause a sustained pool fire, one might wonder why it is important. The key to this question is to consider a flash in a closed container. The container holds a flammable mixture of fuel and air. As mentioned in thermodynamics, the pressure increase due to combustion in a closed chamber is generally a factor of 10 - an atmospheric mixture will suddenly be pressurized to 10 atmospheres. In all likelihood, a simple liquid container (like a gasoline can or a tanker truck) will not be designed to sustain such an overpressurization, and it will burst violently, potentially doing damage to whatever is nearby.

The Pensky-Martens apparatus is simply a small cup, usually with an airtight cover, holding liquid fuel. The cup and cover are designed to sustain the kind of overpressurization mentioned above without bursting. The temperature of the fuel is slowly increased, and a small pilot flame is periodically inserted into the atmosphere above the liquid for a brief period. The lowest temperature at which the pilot flame ignites the fuel-air mixture is the flashpoint.

The Pensky-Martens apparatus can also be used in an open cup form. As shown in the figure below, the concentration of fuel vapor above the surface of the liquid decreases monotonically with height, so it is important that the height of the pilot flame be closely controlled. The open cup apparatus can be used to find both an open cup flash point, which is generally greater than the closed cup flash point, and a fire point, when the pilot flame ignites a self-sustaining flame above the fuel. Because the chamber is open, there is no problem of overpressurization in this case, so the open cup flashpoint is perhaps less important than the closed cup flashpoint.

If a reference lists a flashpoint, it is almost certainly the closed cup flashpoint. However, if in doubt, it is good to clarify the test used to get a particular temperature. Assuming that a number is the closed cup flashpoint is not a conservative assumption, because the open cup flashpoint is higher than the closed. For example, the closed cup flashpoint of n-decane is 44 ºC, the open cup flashpoint is 52 ºC, and the fire point is 61.5 ºC.

For further information on the Pensky Martens apparatus, see Drysdale, D. (1998) An Introduction to Fire Dynamics, John Wiley and Sons, New York, p. 202-207.

The apparatus used to measure flammability limits was developed at the U.S. Bureau of Mines in the late 1940's and early 1950's. A schematic of the basic setup is shown below. A mixture of air and fuel vapor is injected in a vertical tube 150 cm long with a 5 cm inside diameter, and the circulation pump is activated briefly to assure good mixing. The cover plate at the base of the tube is opened to provide pressure relief, and a spark source is used to ignite the mixture at the bottom of the tube. The mixture is flammable if the flame propagates upward at least 75 cm. The tube inside diameter is 5 cm because that is the smallest diameter at which quenching effects from heat transfer to the tube walls were seen to be insignificant

For more information on the Bureau of Mines apparatus, see Coward, H. F., and Jones, G. W. (1952) 'Limits of Flammability of Gases and Vapors'. US Bureau of Mines Bulletin 503.