Cone calorimeter measurements

FIGURE 10.6 Characteristics of char formed during the cone calorimeter measurement of IFR-PP without BSil (on the left) and with BSil (on the right). (Reproduced from Marosi, Gy. et al., Polym. Degrad. Stab., 82, 379, 2003. With permission.)... 

Compounds of SWCNTs and MWCNTs in LDPE BPD 8063 were melt blended in a Brabender mixing chamber according to the formulations indicated in Tables 7.5 and 7.6. The corresponding cone calorimeter measurements are shown... 

Cone calorimetry is another most eflfective bench-scale method for studying the flammability properties of materials. The cone calorimeter measures fire-relevant properties such as HRR, mass loss rate (MLR) and smoke yield, among others. 

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. 

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... 

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 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... 

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. 

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. 

Mass Loss Rate as a Function of External Heat Flux. The technique for the measurement of mass loss rate as a function of heat flux was developed in 1976 at FMRC using the Small-Scale Flammability Apparatus (8 ). Several other flammability apparatuses are now available for such measurements, such as OSU Heat Release Rate Apparatus (13) and NIST Cone Calorimeter (1 4). 

Table 5 Ignition-time measured in the ASTM E 1354 cone calorimeter and thermal response parameter values derived from the data... 

FIGURE 6.25 Experimental setup for measuring heat gradient in an intumescent coating for a cone calorimeter experiment at the beginning of the experiment (a) and at the steady state (b). 

To further explore the influence of silica material properties (morphology, surface area, silanol concentration, and surface treatment) on the silica flame-retardant properties, various types of silicas (silica gel, fumed silicas, and fused silica) were investigated.50 51 Material properties of the various silicas are summarized in Table 8.6. These different types of silicas were added to polypropylene and polyethylene oxide to determine their flame-retardant effectiveness and mechanisms. Polypropylene was chosen as a non-char-forming thermoplastic, and polyethylene oxide was chosen as a polar slightly char-forming thermoplastic. Flammability properties were measured in the cone calorimeter and the mass loss rate was measured in the radiative gasification device in nitrogen to exclude any gas phase oxidation reactions. 

The quality of char formed for metal hydroxide/MMT combinations seems of prime importance to maximize the barrier effect. Incorporation of silica in combination with MH and MMT by partial substitution of MMT has been investigated by Ferry et al.,64 Laoutid et al.70 to improve the cohesion of charred and expanded structure. Even though silica generated cracks in the char and reduces its resistance, as measured by indentation, tire behavior, as studied by cone calorimeter was improved. 

The time to ignition as a function of incident radiant heat flux can also be measured in the ISO ignit-ability test apparatus. This apparatus and its use are described in ISO 5657. Bench-scale heat release calorimeters such as the Cone Calorimeter (Section 14.3.3.2.1) and the Fire Propagation Apparatus (Section 14.3.3.2.3) can also be used to obtain this kind of data. 

The latter is measured in a small container under high pressure and in pure oxygen, conditions that are not representative of real fires. The conditions in bench-scale calorimeters such as the cone calorimeter resemble those in real fires much more closely. For some fuels, in particular gases, both values are nearly identical. However, for charring solids such as wood, AHc is significantly lower and equal to the heat of combustion of the volatiles during flaming combustion. 

Most Cone Calorimeters include instrumentation for measuring light extinction in the exhaust duct, using a laser light source, described in ASTM E 1354 and ISO 5660-2 (Section 14.3.5.3.2). Instrumentation to measure concentrations of soot, carbon dioxide, carbon monoxide, and other gases are commonly added. Some laboratories have used a modified version of the standard apparatus to conduct studies in vitiated or oxygen enriched atmospheres.43 50... 

The standard Cone Calorimeter (Section 14.3.3.2.1) described in ASTM E 1354 includes a smoke photometer to measure light extinction in the exhaust duct. The system is based on a laser light source. The same system is also standardized internationally, although it is described in a separate document from the main Cone Calorimeter standard (ISO 5660-2). Smoke measurements are reported in terms of the average specific extinction area (ASTM E 1354 and ISO 5660-2) and the smoke production rate and total smoke production for the period prior to ignition and the flaming period (ISO 5660-2). 

The Intermediate-Scale Calorimeter (ICAL), described in ASTM E 1623, is essentially a scaled-up version of the Cone Calorimeter. The apparatus consists of a vertical gas-fired radiant panel with a height of approximately 1.33m and width of approximately 1.54m. The standard test specimen measures lxlm, and is positioned parallel to the radiant panel. The heat flux to the specimen is preset in the range of 10-60kW/m2 by adjusting the distance to the panel. The products of pyrolysis from the specimen are ignited with hot wires located near the top and bottom of the specimen. The specimen is placed on a load cell to measure mass loss during testing. Panel and specimen are positioned beneath the ISO 9705 hood and exhaust duct. 

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