Specific extinction

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. 

Considering the fact that pigments exist as crystals dispersed in the application media, these studies are only of theoretical value. However, it has been shown that the maximum specific extinction of Pigment Red 112 is independent of whether it is measured in solution or in crystalline form. The study compared transmission spectra of the dissolved pigment with the solid-state spectra of crystals in a transparent film. 

The direct absorbance methods require only a protein-specific extinction coefficient to deliver an accurate protein concentration. These methods typically require minutes to perform and require only a spectrophotometer and a good quantitative... 

Hubert Tschamler They were derived either from mean values observed for model compounds of known structure or from the properties of solvent extracts of coals. In the latter case an accurate value for %H i can be derived by measuring proton spin resonance in solution and this, combined with the optical densities observed in the infrared spectra, gives the specific extinction coefficients. (See J. F. M. Oth, E. de Ruiter and H. Tschamler, Brennstoff-Chem. 42, 378 (1961) also Ref. 7). 

The ultraviolet spectra of coals, examined as suspensions in potassium bromide, show an absorption band at 2650 A that becomes more pronounced with increasing rank of the coal. This band has been assigned to aromatic nuclei, and on the basis of data obtained from comparison between the specific extinction coefficients of coal and those of standard condensed aromatic compounds, it has been concluded that the concentration of aromatic systems in coal is lower than had previously been believed. 

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). 

Mulholland, G. and Croarkin, C., Specific extinction coefficient of flame generated smoke. Fire and Materials 2000, 24, 227-230. 

The term absorptivity is synonymous with extinction coefficient, absorbancy index, and specific extinction (Browning 1967). 

Owing to the UV absorbance of ferulic acid, steryl ferulates (SFs) can be analyzed from oils and total lipid extracts using UV-spectropho-tometric methods. These methods are robust and easy to perform, and provide a good estimate of the total content of SFs in a sample. The absorption maximum varies between different solvents, being 314nm, 327 nm, and 328 nm in heptane, isopropanol, and methanol, respectively (Evershed et ah, 1988 Seetharamaiah and Prabhakar, 1989 Bucci et ah, 2003). Further, the specific extinction coefficients for quantification of SFs are 358.9 cm in hexane (314nm, 25 °C) and 19,500 L mol cm (328 nm) (Evershed et ah, 1988 Seetharamaiah and Prabhakar, 1989). 

When concentration is expressed in g/100 ml, k is described as the specific absorbance and given the symbol A cm or A(l%, 1 cm), defined as The absorbance of a 1% w/v solution in a cell of 1 cm path-length . It is usually written in the shortened form Ai and is widely used in analytical chemistry. It was formerly known as the specific extinction coefficient , symbol or E (1%, 1 cm). American convention recognises the constant k as absorptivity (a, litre/g/cm) defined as the absorbance of a 1 g/litre solution in a cell of 1 cm path-length . These terms for absorptivity can be readily inter-converted, as follows... 

Spantin, 943 Sparine, 931 Sparteine, 972 in sport, 99 Spasmaverine, 332 Spasmoban, 535 Spasmocyclon, 496 Spasmolysin, 943 Spasmolytine, 320 Spasmonal, 332 Spasuret, 619 Specific absorbance, 223 Specific extinction coefficient, 223 Specilline G, 390 SpectraBAN 4, 847 Spectrobid, 369... 

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. 

Absorption. The possible color of the last mentioned emulsion needs further explanation. Up till now, we have implicitly assumed that light is only scattered, not absorbed. If absorption occurs, we should use the complex refractive index h = n — in, where ri determines the adsorption (i = yj — 1). The relations now become more complicated, n is related to the specific extinction y according to y Ann /X. The absorbency as determined... 

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. 

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