OSU 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. 

Rate of heat release measurements have been attempted since the late 1950 s. A prominent example of instrument design for the direct measurement of the sensible enthalpy of combustion products is the Ohio State University (OSU) calorimeter. This has been standardized by ASTM and a test method employing this technique (ASTM-E-906) is part of a FAA specification for evaluation of large interior surface materials. 

Heat release equipment can be used to measure various parameters on the same instrument, in a manner generally relevant to real fires. The two most frequently rate of heat release (RHR) calorimeters used are the Ohio State University (OSU calorimeter) [4] and the NBS cone (Cone calorimeter)[5]. 

The OSU calorimeter [4] has long been used for simultaneously measuring heat and smoke release. It can also be used to measure release of combustion products. It is the basis of standard tests at both ASTM, the American Society for Testing and Materials (ASTM E906-1983), and FAA, the Federal Aviation Administration [6,7]. 

The Cone RHR calorimeter [5] is a more modern instrument, designed to meet the same objectives as the OSU calorimeter. It is now being considered for standardization by ASTM [8] and by the International Organization for Standardization (ISO). It is a very versatile instrument, which allows simultaneous determinations to be made of release of heat, smoke and other combustion products, and of sample mass loss and soot mass formation. The Cone RHR calorimeter can, thus, measure the same properties as the OSU RHR calorimeter, plus a number of other ones based on sample and soot mass. 

This parameter, the smoke parameter, is based on continuous mass loss measurements, since the specific extinction area is a function of the mass loss rate. A normal OSU calorimeter cannot, thus, be used to measure smoke parameter. An alternative approach is to determine similar properties, based on the same concept, but using variables which can be measured in isolation from the sample mass. The product of the specific extinction area by the mass loss rate per unit area is the rate of smoke release. A smoke factor (SmkFct) can thus be defined as the product of the total smoke released (time integral of the rate of smoke release) by the maximum rate of heat release [19], In order to test the validity of this magnitude, it is important to verify its correlation with the smoke parameter measured in the Cone calorimeter. 

One of the difficulties inherent in adiabatic calorimetry is that it will, almost inevitably, result in low results, because of heat losses. This is not an intrinsic deficiency of the OSU calorimeter unit, since it can easily be modified to incorporate other methods of heat measurement. However, the traditional detection device used (and recommended in the standards) is the use of a thermopile. 

The horizontal exposure method is not very adequate for the OSU RHR calorimeter, because the heat reflected from the aluminum foil onto the sample is much lower than the heat generated by the glow bars. Since the OSU calorimeter is based on the adiabaticity of the measurements, any heat losses will represent inaccurate results. The reflection on the aluminum foil is also uneven. Moreover, the use of higher radiant energy causes problems with the mechanical functioning of the instrument (bending and buckling of the back plate). 

National Bureau of Standards Cone Calorimeter. There are three main differences between the Cone and the OSU calorimeters. The Cone calorimeter has ... 

Tables VII-IX present heat release data for the same materials as in Tables IV-VI. The Tables also present the same smoke data as measured with the OSU calorimeter, plus smoke parameter information (SmkPar in MW/kg).

The principal interest are, of course, real fires. Since Cone calorimeter results correlate well with those from full scale fires, it is essential, thus, to check whether OSU calorimeter results correlate well with Cone calorimeter results. There are several aspects of this, but the present paper will focus mainly on measurement of smoke. 

Linear correlations were thus attempted for peak rate of heat release, total heat released after 15 min. and smoke factor between both calorimeters. Furthermore, linear correlations were also attempted between OSU calorimeter smoke factors and Cone calorimeter smoke parameters and between Cone calorimeter smoke factors and Cone calorimeter smoke parameters. Figures 1-3 show some of the results. 

Previous work had shown that the Cone and OSU calorimeter results were not identical, but was unclear as to whether the results were correlatable [23]. This work gives definitive proof of correlation between the OSU calorimeter and the Cone calorimeter RHR tests. 

This work does not give definitive proof, however, that the results from the OSU calorimeter correlate well with those from full scale fire tests. It is likely that this will happen, but the product of two good correlations cannot be guaranteed to give another good correlation. Thus, correlation between OSU calorimeter and full scale fires still remains to be firmly established. 

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.

Results from the NBS Cone Calorimeter have been shown to correlate with those from real fires. Moreover, it measures properties very relevant to fire hazard, in particular heat release, the most important of them. The OSU Calorimeter will measure many of the same properties. Furthermore, the results generated by both instruments have similar significance because of the good correlation between them. Smoke measurements are only relevant to fire... 

The NBS Cone calorimeter has been shown to be more versatile than the OSU calorimeter and to allow simultaneous measurements of a large variety of the properties required for a full assessment of fire hazard in real fires. Furthermore, it can be used to calculate combined properties, including those involving mass loss, which are much more useful as indicators of fire hazard than any individual one. 

Other test methods can also be used to assess ignitability, together with other properties. Some important ones are the cone calorimeter (ASTM E 1354,71 Figure 21.7, which has the assessment of heat and smoke release as its primary purpose) the OSU calorimeter (ASTM E 906,38 Figure 21.8, which also... 

The recent development of rate of heat release tests in a form that can be routinely used by test houses represents a major step forward. Probably the best known instrument is the cone calorimeter (ISO 5660-1), which determines the rate of heat release using the oxygen consumption technique. The OSU calorimeter (ASTM E906) uses a direct heat measuring system and is used in regulations by the FAA. 

ASTM E906 [99] defines the OSU calorimeter. The apparatus consists of an insulated box containing a vertical specimen, a parallel electric radiant heater, and a pilot ignition device. Air at a controlled rate flows through the box, and the inlet and outlet temperatures arc recorded. ASTM E906 also records the temperature of the box wall to compensate for the nonadiabatic characteristics of the apparatus. The box is calibrated using a preset gas flame. The vertical specimen size is 150 mm square, and the incident heat flux has a maximum value of 100 kW, m. Tests with a horizontal specimen, 110 x 150mm, which involve the use of aluminum foil to reflect heat onto the specimen, are apparently... 

Using factorial analysis, samples of the mohair/silk (MS) fabric were variously treated with a selection of flame retardants, back-coating formulations and adhesive, mounted on a typical aramid honeycomb board specimen, and each composite was tested using cone calorimetry at the preferred heat flux of 50 kW (shown to be equivalent to the 35 kW m flux used in the OSU calorimeter). 1 An optimum combination of flame retardant, back-coating and adhesive at specific application levels was found to yield the lowest heat release values, and this system was applied to each of the above six fabrics. Testing in both the OSU at 35 kW m heat flux and at 50 kW m" in the cone calorimeter gave the results for peak heat release in Table 4.5 below. From this it is seen that all fabrics have PHRR values < 65 kW m" and that OSU and cone calorimeter results are equivalent. 

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