Smoke chamber test

One particularly widely used test is the National Bureau of Standards (NBS) smoke chamber test. This provides a measure of the obscuration of visible light by smoke in units of specific optical density. The NBS smoke test can be run in either of two modes ... 

Table VII. NBS Smoke Chamber Tests EMI Coating and Corresponding Substrate...

Table XIII. Arapahoe Smoke Chamber Tests % of weight burned...

Consequently, rather than simulating a specific fire scenario, conditions in smoke chamber tests vary over time and are not well-defined. A relatively new tube furnace method greatly alleviates this problem and, for that reason, is gaining increased international acceptance. The method is described in ISO TS 19700. 

It is also a good smoke suppressant. The addition of 9% to polystyrene reduces the maximum smoke density in the NBS Smoke Chamber from 2556 to 375. In a test on an EPDM compound, a mixture of 75% magnesium hydroxide and 25% ATH produced significantly less smoke than ATH alone in Smouldering Mode NIST (ASTM 2843) smoke chamber testing. 

Figure 8.6 NBS smoke chamber test of CSM laminates with various resins (smouldering mode) (Forsdyke).

Table II. Smoke Generation in a Room Corner Burn Test and in the NBS Smoke Chamber...

It is noteworthy to restate that there was no correlation in the series of experiments shown in Table II between the maximum smoke density in the NBS smoke chamber, flaming mode, and the obscuration in the full scale tests. 

TSR 15). The data (Tables IV-VI) suggest that this instrument provides a satisfactory method for measuring heat release, even in the horizontal mode. Furthermore, it can differentiate between those materials which are prone to release much heat rapidly and those which perform much better in terms of heat release. The reliability of smoke data is, in principle, lower than that of heat data. In order to establish some criteria, the Tables include SmkFct values at 5 min (in MW/m2), which will be compared with SmkFct and SmkPar values for the same materials tested in the Cone and with values of specific maximum smoke density measured in the NBS smoke chamber. 

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.

The expected discrepancy between NBS smoke chamber results and those from a good smoke production test were compounded in this work by the fact that many of the materials used melt and drip. 

ISO 5659-1 1996 Plastics - Smoke generation - Part 1 Guidance on optical-density testing ISO 5659-2 1997 Plastics - Smoke generation - Part 2 Determination of optical density by a single-chamber test... 

The NBS smoke chamber is the most commonly used bench-scale test apparatus for measuring the optical density of smoke. The apparatus and test procedure are described in ASTM E 662. The method was developed at the NBS in the 1960s.69... 

The smoke chamber method described in ASTM E 662 is often supplemented with toxic gas analysis. A PTFE-lined stainless steel tube is used to take a gas sample from the geometric center of the chamber at a specified time. This time can be fixed, for example V/2 or 4 min into the test, or variable, for example immediately following the maximum specific optical density. Regulations and specifications that call for these measurements require the concentration of a predefined set of gases to be determined. The product is acceptable if the concentration of every gas is within specified limits. These limits have been established from experience based on data for products that are deemed to be acceptable or not acceptable. 

Static smoke chamber methods have major limitations in terms of being indicative of the fire hazard due to smoke toxicity of products and materials in actual fires. As combustion products accumulate in the chamber during a test, the burning behavior of the test specimen may have a significant effect on the level of vitiation (oxygen concentration) and temperature rise in the chamber. 

ISO 5659-2 Plastics—Smoke Generation—Part 2 Determination of Optical Density by a Single-Chamber Test. International Organization for Standardization, Geneva, Switzerland. 

FIGURE 17.5 Diagram of fire smoke toxicity test based on NBS smoke chamber. (From Hull, T.R. and Paul. K.T., Fire Saf. /., 42, 349, 2007. With permission.)... 

The range of toxicity test methods is bound to produce different fire conditions, and hence different toxic product yields. Four test methods (NBS Smoke Chamber, NF X 70-100, Fire Propagation Apparatus [FPA], and SSTF) have been compared, primarily from published data64 66 using the carbon monoxide yields and hydrocarbon yields (not recorded in the NFX tests), which are both fairly good indicators of fire condition, for four materials (LDPE, PS, PVC, and Nylon 6.6), at two fire conditions, well-ventilated and under-ventilated. The CO and hydrocarbon yields are shown in Figures 17.9 and 17.10. 

For PA 6.6 all the tests show an increase in CO yield from well-ventilated to under-ventilated, although the values vary from very low (NBS and SSTF) to fairly high (NFX 70-100) for well-ventilated conditions, while all tests except the NBS smoke chamber are able to replicate the higher CO yields of under-ventilated combustion consistently for PA 6.6. For hydrocarbons, a clear, consistent trend is observed between the low yields of well-ventilated combustion and the higher yields of under-ventilated combustion. 

Despite the understanding that smoke obscuration ought to be measured in a large scale, or by a method which can predict large-scale smoke release, the most common small-scale test method for measuring smoke from burning products is the traditional smoke chamber in the vertical mode (ASTM E 662)39 (Figure 21.14). The test results are expressed in terms of a quantity called specific optical density, which is defined in the test standard. This test has now been shown to have some serious deficiencies. The most important problem is misrepresentation of the smoke... 

The cone calorimeter,71 which is a dynamic flow-through fire test, can also be used to assess smoke obscuration. The rankings tend to be quite different from those found with the static smoke chamber and are much more realistic. Several empirical parameters have been proposed to make this compensation for incomplete sample consumption, including one called the smoke factor (SmkFct), determined in small-scale RHR calorimeters.188 It combines the two aspects mentioned earlier the light obscuration (as the total smoke released) and the peak RHR. 

Setchkin) of 535 C and UL rating of V-0. Flame spread in the radiant-panel test is low (I, = 2.7) and the LOI is high — 47. NBS smoke-chamber results show a low specific optical density (Ds 4 min = 0.7, Dm = 31, flaming mode), and combustion-product-toxicity studies show results comparable to polystyrene (10). 

This method is basically the NBS Smoke Density Chamber Test. It covers the determination of the specific optical density of smoke generated by solid materials and assemblies mounted in a vertical position in thickness up to 1 inch (2.54 cm). It measures attenuation of a light beam by smoke accumulating within a closed chamber due to nonflaming pyrolytic decomposition and flaming combustion. 

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