Specific extinction area

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. 

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]. 

For the specific extinction area correlation described in (a) those materials which did not burn completely in the full-scale were specifically excluded [12]. The small scale test always leads to complete consumption of the sample. Therefore, more smoke is being produced in the small scale test than in real fires for those materials usually associated with lower fire hazards. This is exactly the kind of issue that is being remedied by measurements of smoke parameter or smoke factor. 

Note rign = time to ignition, PHRR = peak of heat release rate, THR = total heat release, AMLR = average mass loss rate, ASEA = average specific extinction area. 

The smoke production rate can also be expressed per unit of specimen mass loss by dividing the RHS in Equation 14.14 by the mass loss rate. The result is referred to as the specific extinction area, because it has the units of area divided by mass. 

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). 

Cone calorimetry was used to measure the effectiveness of the additives on reducing the flammability of PE the parameters available include the heat release rate and especially its peak value, the peak heat release rate (PHRR) and time to peak heat release rate (tPHHR) total heat release (THR) time to ignition (tig) average mass loss rate (AMLR) and average specific extinction area (ASEA), a measure of smoke formation. A decrease in the PHRR, THR, AMLR, and ASEA are desired along with an increase in tig and tPHRR. The heat release rate (HRR) curves as a function of time for pure PE and its nanocomposites are shown in Figure 4A and cone data are summarized in Table II. 

Specific extinction area The measure of smoke obscuration averaged over the whole test period m 7kg... 

Smoke parameter The product of the average specific extinction area and the peak rate of heat release. This parameter indicates the amount of smoke generated MW/kg... 

Smoke production rate A product of the average mass loss rate and the average specific extinction area m 7s... 

Fire retardant fillers affect smoke formation. " Table 12.5 gives some data on the specific extinction area. The data show that, with the exceptions of A1(OH)3 and Mg(OH)2, fillers have a small effect on smoke suppression. 

Filler, wt% Polymer Specific extinction area, m kg Refs. 

The ASTM test requires to report smoke obscuration as the average specific extinction area (m /kg) for each specimen. The average specific extinction area (<7, m / kg) is calcnlated as the volume exhaust flow rate (V, mVs), measured at the location of the laser photometer, multiplied by the smoke extinction coefficient k, m ) and by the sampling time interval (At, s), divided by the specimen mass loss (Am, kg), and averaged for repeated tests. 

The ASTM procedure gives a range for average specific extinction areas for a nnmber of different materials, which is between 30 and 2200 m /kg. Among those materials were fire retardant treated ABS, polyethylene, PVC, polyisocyanurate, polynrethane, and gypsum board. 

Samples External heat flux (kW m ) Peak rate of heat release (kW m ) Specific extinction area (m kg- )... 

Table 2 Cone calorimeter data for modified bisphenol A vinyl ester (Mod-Bis-A Vinyl Ester), bisphenol A novolac vinyl ester (Bis-/Novolac Vinyl Ester) and methylenedianiline and benzyldimaine (BDMA) cured epoxy resins and their intercalated nanocomposites ( ) containing 6% dimethyl dioctadecylammonium-exchanged montmorillonite. Heat flux = 35 kW/m, HRR = heat release rate, MLR = mass loss rate. He = heat of combustion, SEA = specific extinction area [121]...

Figures 8 and 9 show graphs for the specific extinction area and effective heat of combustion, correspondingly, for PP and PP/MWCNT(3) nanocomposites. Calculated values of effective heat of combustion for PP and PP/MWNT demonstrate invariant shift of this parameter for these nanocomposites.

FIGURE 8 Specific extinction area versus time for PP and PP/MWCNT(3) nanocomposites obtained by cone calorimeter at the incident heat flux of 35 kW m l... 

In the present study the combustibility of polypropylene nanocomposite was evaluated by a cone calorimeter. The tests were performed at an incident heat flux of 35 kW/m using the cone heater [21]. Peak heat release rate (RHR), mass loss rate (MLR), specific extinction area (SEA) data, earbon monoxide and heat of eombustion data measured at 35 kW/m2, are presented in Figs. 11 and 12. 

The RHR plots for PP-MAPP-Cloisite 20A nanocomposite and PP at 35 kW/m heat flux shown in Figure indicate a 60% - decrease of peak of RHR (Fig. 11). Comparison of the Cone calorimeter data PP and PP-MAPP- 7% Cloisite 20A reveals that the specific heat of combustion (He), specific extinction area (SEA), a measure of smoke yield, and carbon monoxide yields are practically unchanged this suggests that the source of the improved flammability properties of these materials is due to differences in condensed-phase decomposition processes and not to a gas-phase effect. The primary parameter responsible for the lower RHR of the nanocomposites is the mass loss rate (MLR) during combustion, which is significantly reduced from the value observed for the pure PP (Fig. 12). It is supposed, that this effect is caused by ability to initiate the formation of char barrier on a surface of burning polymeric nanocomposites that drastically limits the heat and mass transfer in a burning zone. 

Unlike halogenated additives silica gel /K2CO3 does not significantly affect the specific heat of combustion when added to PP [227]. Furthermore, since the CO yield and the soot (mean specific extinction area) are not significantly increased by these additives, the use of this system may represent an improvement over halogenated and some phosphorus based additives, which commonly tend to increase CO yield and soot [227]. These data indicate that these additives most likely act primarily in the condensed phase not in the gas phase. The cone calorimeter results for PP are summarized in Table 5.5 along with data for the other polymers examined [227]. 

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