Average 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 ... 

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 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. 

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... 

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. 

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

Heat flux, 35 kW/m. He, specific heat of combustion SEA, specific extinction area g , ignition time. Peak heat release rale, mass loss rate, and SEA data are reproducible to within 10%. The heat of combustion and the time to ignition data are reproducible to within 15%. The cone data reported are the average of three repheated samples. The samples are square plates 100 mm large and 8 mm thick. 

A typical heat release rate curve for a neat epoxy system and the respective layered silicate nanocomposite, is shown in Fig. 2.12. Both peak and average heat release rate, as well as mass loss rates, are all significantly improved through the incorporation of the nanopartieles. In addition, no increase in specific extinction area (soot), CO yields or heat of combustion is noticeable. However, the mechanism of improved flame retardation is still not clear and no general agreement exists as to whether the intercalated or exfoliated structure leads to a better outcome. The reduced mass loss rate occurs only after the sample surface is partially covered with char. The major benefits of the use of layered silicates as a flame retardation additive is that the filler is more environmentally-friendly compared to the commonly used flame retardants and often improves other properties of the material at the same time. However, whilst the layered silicate strategy is not sufficient to meet the strict requirements for most of its application in the electrical and transportation industry, the use of layered silicates for improved flammability performance may allow the removal of a significant portion of conventional flame retardants. 

Smoke. The smoke extinction area (SEA m /kg) is a global measure of the condensed phase (liquid and solid) products of flaming combustion having units of square meters of particulate scattering surface per kilogram of material burned. The SEA is measured in a fire calorimeter under well-ventilated conditions from optical extinction of the combustion gas stream (25). Table 15 lists the specific SEA for a variety of polymers averaged from the literature. Figure 22 is a plot... 

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