Flame calorimeter

The Ohio State University (OSU) calorimeter (12) differs from the Cone calorimeter ia that it is a tme adiabatic instmment which measures heat released dufing burning of polymers by measurement of the temperature of the exhaust gases. This test has been adopted by the Federal Aeronautics Administration (FAA) to test total and peak heat release of materials used ia the iateriors of commercial aircraft. The other principal heat release test ia use is the Factory Mutual flammabiHty apparatus (13,14). Unlike the Cone or OSU calorimeters this test allows the measurement of flame spread as weU as heat release and smoke. A unique feature is that it uses oxygen concentrations higher than ambient to simulate back radiation from the flames of a large-scale fire. 

Metal deck assembhes are tested by UL for under-deck fire hazard by usiag their steiaer tunnel (ASTM E84). The assembly, exposed to an under-deck gas flame, must not allow rapid propagation of the fire down the length of the tuimel. FM uses a calorimeter fire-test chamber to evaluate the hazard of an under-deck fire. The deck is exposed to a gas flame and the rate of heat release is measured and correlated to the rate of flame propagation. A different FM test assesses the damage to roof iasulations exposed to radiant heat. 

Heat-flux data obtained from calorimeters present in the fire-affected area revealed maximum heat fluxes of 160-300 kW/m. Figure 5.1 shows the calorimeter positions, the final contours of the flash fire, and heat-flux data from calorimeters positioned near or in the flames. No data are available on flame propagation during the vapor-bum tests. 

NOTE The moisture content of steam can be measured by means of a throttling calorimeter or by analysis of the sodium content in a sample of condensed steam, using perhaps a specific ion electrode or flame photometer. 

Some of the other properties of interest for fire hazard assessment cannot be measured with RHR calorimeters. They include flame spread, limiting oxygen index (LOI, or simply oxygen index, 01 both names have been used, but the author s preferred nomenclature is the one used here) and fire endurance. 

The number of small scale test methods, used for classification purposes, should be limited and based on ISO tests, presumably the Cone Calorimeter /10/ (see Fig. 8) and possibly the ISO Surface Spread of Flame test /11/. 

In addition the room-corridor scenario will also be investigated in full scale and attempts made to seek correlations with the Cone Calorimeter and the ISO spread of flame test. 

Once ignited they produced considerable amounts of heat and smoke. Flame retarded flexible PU foams became available in 1954-55, i.e. within a few years of flexible PU foams becoming available in commercial quantities(22). These FR PU foams contained trichloroethyl phosphate or brominated phosphate esters and resisted ignition from small flame sources. Unfortunately they may burn when subjected to a larger ignition source or when covered by a flammable fabric and may then produce as much heat and more smoke than the standard grade of PU foam(3). This was identified by UK room tests in the early 1970 s and has been confirmed more recently by furniture calorimeter tests at the NBS(21). 

Samples are normally exposed in a vertical orientation. If samples melt and drip, the heat can be redirected, by means of a system of aluminum foil mirrors, towards a horizontal sample. Many of the materials used for the series of experiments reported here melted excessively, away from the flame. Therefore, vertical burns were impossible for them, without distorting the data. All the materials investigated in the OSU RHR calorimeter, with the exception of the experimental flexible vinyl wire and cable compound, were, thus, exposed horizontally. 

Furthermore, it has been shown that the time period until ignition occurs, in the Cone calorimeter, is proportional to the inverse of the flame spread rate [16]. The Cone calorimeter can also be used to provide the mass loss rate information required for the simplified classification into categories of toxic hazard [1] quick toxic hazard assessment. Thus, the NBS Cone calorimeter is a very useful tool to overcome some of the disadvantages associated with measuring a single property at a time. 

Table XI presents the results of tests on the same materials in the NBS smoke chamber. It is immediately clear that these results do not correlate well with those measured on the RHR apparatuses. Furthermore, an attempt at a linear correlation between the flaming mode specific maximum optical density and the Cone calorimeter SmkPar at 20 kW/m2 yielded a correlation coefficient of ca. 1%, a coefficient of variation of 217% and statistically invalid correlations. A comparison between a Cone and OSU calorimeter correlation and one with the NBS smoke chamber is shown in Figure 4. This suggests that unrelated properties are being measured.

Table I. Results from the Surface Spread of Flame Test and the Cone Calorimeter... 

D. L. Ornellas, The Heat and Products of Detonation in a Calorimeter of CNO, HNO, CHNR CHNO, CHNOF, and CHNOSi Explosives, Combustion and Flame 23, 37-46 (1974). 

Fluorine flame calorimetry is a logical extension of oxygen flame calorimetry in which a gas is burned in excess of gaseous oxidant (214). The decision does not reach that of the oxygen flame calorimeter in which, for example, Affj(H20) was determined with a standard deviation of 0.01%. Combustions of H2, NH3 (8), and fluorinated hydrocarbons are typical applications, but the uncertain nonideality corrections of HF(g) prevent full realization of the inherent accuracy. 

Figure 7.10 shows the flame combustion calorimeter used by Rossini in 1931 to determine the enthalpy of formation of liquid water, from the direct reaction of hydrogen with oxygen [54,99] ... 

The experimental data and the calculations involved in the determination of a reaction enthalpy by isoperibol flame combustion calorimetry are in many aspects similar to those described for bomb combustion calorimetry (see section 7.1) It is necessary to obtain the adiabatic temperature rise, A Tad, from a temperaturetime curve such as that in figure 7.2, to determine the energy equivalent of the calorimeter in an separate experiment and to compute the enthalpy of the isothermal calorimetric process, AI/icp, by an analogous scheme to that used in the case of equations 7.17-7.19 and A /ibp. The corrections to the standard state are, however, much less important because the pressure inside the burner vessel is very close to 0.1 MPa. 

The calorimeter in figure 7.10 was electrically calibrated [54,99] by using the heater O. Flame calorimeters are, however, most frequently calibrated on the basis of the reaction of hydrogen with oxygen, which has been recommended for this purpose by IUPAC [39]. 

Figure 7.13 Combustion chamber and primary solution vessel of a fluorine flame calorimeter.

F. D. Rossini. Calibrations of Calorimeters for Reactions in a Flame at Constant Pressure. In Experimental Thermochemistry, vol. 1 F. D. Rossini, Ed. Interscience New York, 1956 chapter 4. 

Magnesium ribbon burns in air in a highly exothermic combustion reaction. (See equation (1).) A very bright flame accompanies the production of magnesium oxide, as shown in the photograph below. It is impractical and dangerous to use a coffee-cup calorimeter to determine the enthalpy change for this reaction. 

There remain to be considered the data of Thomsen3 15 who burned oxygen in hydrogen in a flame at constant pressure in a calorimeter at room temperature of Schuller and Wartha,1 who burned oxygen in hydrogen in a flame at constant pressure in an ice calorimeter and of... 

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