SMOKE CHAMBER

Applications. Smoke evolution of commercial materials and the effect of various additives including fillers on smoke production rate. 

Major results General fillers do not affect smoke formation by any means other than simple dilution. Fire retardant fillers such as Mg(0H)2 decrease smoke formation only at high concentrations. Materials which are known catalysts of degradation (e.g., copper) increase smoke formation.  

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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 ... 

Smoke density. Optical density measurements on the smoke evolved from burning plastic samples were carried out using an NBS Smoke Chamber. The samples, which measured 75mm x 75mm, with a thickness of 0.6 - 4mm, were burned in the flaming mode in accordance with ASTM E662-79. Specific smoke density (Ds) values reported are the averages of three independent determinations. 

Figure 3. Effect of inorganic additives on the density of the smoke evolved from brominated polyester resin in the NBS-type Smoke Chamber.

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

Table VIII. NBS Smoke Chamber Data for EMI Coated Structural Foam Samples Average Non-Flaming Data ...

Figure 3. NBS Smoke Chamber results (non-flaming) for two grades of polycarbonate structural foam. Continued on next page.

Figure 4. Continued. NBS Smoke Chamber results (flaming) for modified-polyphenylene oxide and RIM polyurethane structural foam.

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

Table XIV. Comparison of NBS Smoke Chamber Data (Flaming) with Arapahoe Smoke ...

In general, for NBS Smoke Chamber data, coated samples have a tendency to show an increase in smoke formation under non-flaming conditions. Smoke results under flaming conditions are unremarkable and specific coating dependent. 

In the present study DSC and TGA data were run on DuPont 910 and DuPont 951 instruments, respectively. Arapahoe Smoke Chamber results were obtained on a commercial apparatus. Coated samples used were commercially prepared zinc arc spray samples on Noryl FN 215 Structural Foam. 

An initial experiment involved determination of Arapahoe Smoke Chamber results for samples with and without the zinc coating present. Data are presented in Table II. Depending upon orientation of the sample, an increase in char occurred for some samples with zinc present, while no change in smoke formation was seen. Initial pyrolysis GC/mass spectroscopy results at 90CPC in helium showed no difference in volatiles formed with or without zinc. These results suggested enhanced char formation as the origin of the Radiant Panel results for zinc on modified-polyphenylene oxide (m-PPO). Zinc oxide is a known, effective thermal stabilizer in the alloy. The next work then focused on DSC/TGA studies. 

Table II. Arapahoe Smoke Chamber Data for Modified-PPO and Zn ...

Smoke has usually been measured in the NBS smoke chamber. Such results cannot be correlated with full scale fire results and do not predict fire hazard. Rate of heat release (RHR) calorimeters (e.g. NBS Cone (Cone) and Ohio State University (OSU)) can be used to determine the best properties associated with fire hazard, as well as smoke. Results from the Cone RHR correlate with full-scale fire results. The best way to determine the fire hazard associated with smoke, for materials which do not burn up completely in a fire, is by using RHR to measure combined smoke and heat release variables, such as smoke parameter or smoke factor. 

This work measured smoke and heat released from burning 17 materials, in the Cone and OSU and smoke in the NBS smoke chamber. Results from the RHR calorimeters correlate well with each other while those from the smoke chamber do not. This suggests that the smoke parameter and smoke factor, from either RHR calorimeter, are excellent measures of smoke hazard. 

The traditional way in which smoke obscuration has been measured is by determining the maximum smoke density (or the specific maximum smoke density) by means of a smoke density chamber developed by the National Bureau of Standards (NBS smoke chamber, ASTM E662). This instrument measures the obscuration inside a static 500 L chamber, after a sample has been exposed, vertically, to a 2.5 W/cm2 radiant source. 

Other deficiencies of the NBS smoke chamber will also be discussed. 

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

The incident flux used in the NBS smoke chamber is only a single value, at 2.5 w/cm2, which is a relatively mild flux for a fire, and cannot, thus represent all the facets of a fire. The light source is polychromatic, which causes problems of soot deposits and optics cleaning, as compared to measurements done using a monochromatic (laser) beam. Finally, the units of the normal output of this smoke chamber are fairly arbitrary and the data is of little use in fire hazard assessment. 

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. 

Figure 4. Correlation between the OSU smoke factor and the cone smoke parameter at an incident heat flux of 40 kW/m2 (dark points) and also NBS smoke chamber results (light points).

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