CONE CALORIMETER

ASTM E1354-90 Cone calorimeter heat release and smoke... 

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. 

V. Babrauskas, Development of the Cone Calorimeter. A Bench-Scale EHR Apparatus Based on Occggen Consumption, NSBIR 82-2611, U.S. Dept, of Commerce, Gaithersburg, Md., 1982. 

The small scale fire tests were, the Scandinavian "box test", Nordtest NT-FIRE 004, the DIN 53436-test and a cone calorimeter test. The study covered six different wall lining materials. 

The cone calorimeter used in this study (5) is a somewhat enlarged version of the model used at the National Institute of Standards and Technology in the United States. This particular equipment takes samples of size 20 cm x 20 cm mounted in a horisontal position on top of a load cell. Above the sample there is a cone heater and a spark ignitor. Gas samples are taken in fan ventilated exhaust duct mounted above the cone heater. The radiation used has been 50 kW/m2 and free convection ventilation over the sample. 

In each experiment with the cone calorimeter one piece of sample. 20 cm x 20 cm. was tested. During the test period three pieces of each type of sample were tested. The results presented in Table IV are therefore the average integrated amount of gases generated during sets of three experiments. 

Keeping in mind the somewhat different approach for the production of fire effluents in the different methods used, one will find that the results presented in Table VII do not differ dramatically much from each other. The results for the cone calorimeter are however distinctly higher than the corresponding values for the other methods. 

A discussion of test methodology is beyond the scope of the present paper. However, the fact that established tests do not accurately reflect the behavior of materials in fires has been widely recognized (9), and the search for more meaningful techniques for the evaluation of engineering materials has continued to be a valid research objective. The development of the cone calorimeter, a bench-scale tool for the evaluation of fire properties of materials (10a) at NBS, is of particular significance in this context. 

Babrauskas, Vytenis. Development of the Cone Calorimeter—A Bench-scale Heat Release Rate Apparatus Based on Oxygen Consumption. U.S. Department of Commerce NBSIR 82-2611, 1982. 

This secondary effect of materials is illustrated by the difficulties encountered, in a recent study [54], when attempts were made to correlate CO concentrations measured in small scale and full scale fire tests. The same small scale equipment (typically the cone calorimeter rate of heat release test) could predict adequately a number of very important full scale fire properties, including ignitability, rate of heat release, amount of heat release and smoke obscuration. It could not, however, be used to... 

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/. 

The group also agreed to work with the Swedish proposal /12/ employing the Cone Calorimeter and the Room/Corner Test and explore whether it proves to be adequate in terms of technical relevance, costs, etc. 

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. 

An informal survey revealed that in the near future as many as 22 Cone Calorimeters will be installed in 10 European countries and 15 Romm/Corner Test facilities will be available in 8 countries. 

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 Cone calorimeter yields smoke results which have been shown to correlate with those from full scale fires [10, 15-18]. The concept of a combined heat and smoke release measurement variable for small scale tests has been put into mathematical terms for the cone calorimeter smoke parameter (SmkPar) [10]. It is the product of the maximum rate of heat release and the average specific extinction area (a measure of smoke obscuration). The correlation between this smoke parameter and the smoke obscuration in full scale tests has been found to be excellent [10]. The corresponding equation is ... 

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. 

The same hazard concept could, potentially, be used for full scale tests, multiplying the total heat released, per unit surface exposed, by the maximum smoke obscuration. This is the basis for the magnitude smoke hazard (Smoke Haz.), shown in Table II. It is of interest that smoke hazard results yield the same ranking as mass of soot formed. Cone calorimeter tests are being planned with the same materials used in the full scale tests to investigate the usefulness of this concept. 

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

The principle of oxygen consumption is an empirical finding that the rate of heat release is proportional to the decrease in oxygen concentration in the combustion atmosphere [20, 21]. Thus, cone calorimeter heat release measurements do not require adiabaticity of reactions. Therefore, the combustion process can be carried out more openly, and reactions seen with the naked eye. The Cone calorimeter contains a load cell and can, thus, measure any property on a per mass lost basis. This permits... 

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. 

It is of greater interest to this work, however, that the Cone calorimeter can also be used to measure combined... 

It has already been shown that the Cone calorimeter smoke parameter correlates well with the obscuration in full-scale fires (Equation 1). At least four other correlations have also been found for Cone data (a) peak specific extinction area results parallel those of furniture calorimeter work [12] (b) specific extinction area of simple fuels burnt in the cone calorimeter correlates well with the value at a much larger scale, at similar fuel burning rates [15] (c)maximum rate of heat release values predicted from Cone data tie in well with corresponding full scale room furniture fire results [16] and (d) a function based on total heat release and time to ignition accurately predicts the relative rankings of wall lining materials in terms of times to flashover in a full room [22]. 

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. 

A summary of the results of correlation models for smoke factor and smoke parameter is shown in Table X. For comparison purposes, correlation models for OSU and Cone calorimeter peak rates of heat release are also shown in Table X, together with one of the total heat release models. 

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. 

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... 

Smoke parameter (in the Cone calorimeter) and smoke factor (in both calorimeters) are combined properties of smoke obscuration and heat release which compensate for the incomplete burning of fire retardant samples and which should predict smoke hazard in real fires. 

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. 

The heat generated in a fire is due to various chemical reactions, the major contributors being those reactions where CO and COg are generated, and O2 is consumed, and is defined as the chemical heat release rate (3). Techniques are available to quantify chemical heat release rate using FMRC s Flammability Apparatus (2-6), Ohio State University (OSU) Heat Release Rate Apparatus (J 3) and the NIST Cone Calorimeter (J jO. Techniques are also available to quantify the convective heat release rate using the FMRC Flammability Apparatus (2, 3) and the OSU Heat Release Rate Apparatus (J 3) The radiative heat release rate is the difference between the chemical and convective heat release rates (2,3). In the study, FMRC techniques were used. 

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