Specific optical density

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 ... 

Flaming mode, sample thickness unkown, Dm-maximum specific optical density. cAlumina trihydrate. 

SPECIFIC OPTICAL DENSITY 10-2 SPECIFIC OPTICAL DENSITY 10-2... 

Specific Optical Density of Smoke Generated by Solid Materials [NIST (NBS) Smoke Chamber], 1993. 

The specific optical density is a dimensionless quantity that is defined as follows ... 

Smoke density is measured based on the attenuation of a light beam by the smoke accumulating in the closed chamber. A white light source is located at the bottom of the enclosure, and a photomultiplier tube is mounted at the top. A modified version of Equation 14.19 is used to calculate the specific optical density from the measured transmittance ... 

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. 

ISO 5659-2 Plastics—Smoke Generation—Part 2, Determination of Specific Optical Density. 

Chapter 6 Smoke test. The test is based on the National Bureau of Standards (NBS, now NIST, National Institute of Standards and Technology) smoke density chamber, which has also been standardized as ASTM E 66239 (see also Section 4.1.1). The test exposes a vertical test specimen ca. 75 mm x 75 mm (3 in. x 3 in.) to an incident radiant heat flux of 25kW/m2, from a radiant heat burner for 4 min, in the presence of an open-flame pilot burner. The test applies to the same materials as the heat release rate test. The acceptance criterion is an average maximum specific optical density of smoke that does not exceed 200 (no units). 

Tray cable, listed via UL 1581-1160 (UL tray), plus low specific optical density of smoke via ASTM E 662 (specific optical density of smoke at 4min into the test that does not exceed... 

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... 

ASTM E 662 Test Method For Specific Optical Density Of Smoke Generated By Solid Materials, ASTM, West Conshohocken, PA, 2006. 

Gross et al. (1967) and Imhof and Stueben (1973) developed a smoke density index (Dm) based on the maximum specific optical density, ranging from 0 to 1000. High Dm values are found for polymers with LOI values between 0.18 and 0.30. 

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. 

The time to reach a critical smoke density, also called the obscuration time, is a measure of the time available before a typical occupant in a typical room would find his vision obscured by smoke sufficiently to hinder escape. The value of specific optical density describing this critical level is 16, based on 16 per cent light transmittance under certain specific conditions of room dimensions. 

Specimens of 3 in. by 3 in. size and up to 1 in. by thickness are predried for 24 h at 60°C (140°F) and then conditioned to constant weight at ambient temperature. The ASTM test describes calculations to obtain specific optical density of smoke. 

BS 6401 [103] and ASTM E662 [104] are based on the NBS smoke test and are essentially the same test although some differences occur see Fig. 18. A 75 mm square specimen of up to 25 mm thick is combusted in a vertical orientation at 25 kW m incident heat flux. Tests are carried out with and without a scries of pilot flames along the lower edge of the specimen. The smoke is contained in a cabinet of 0.51 m and measured using a vertical photomultiplier lamp system. The results are typically expressed as specific optical density, which relates the optical density of the smoke to the volume of the cabinet, the length of the smoke-measuring path, and the area of the specimen exposed in the test. Other methods have been used in which specific optical density is related to the mass of the specimen combusted and/or to time. 

BS 6401 (1987). Method of measurement in the laboratory of specific optical density of smoke generated by materials. 

ISO 5659 2 (1994), Plastics - Smoke generation Part 2. Determination of specific optical density. 

Maximum specific optical density — National Bureau of Standards, NFPA 258, specimen thickness = 1.3-1.5mm 5 (smoldering) 170 (flaming) (8,9)... 

ASTM E662-13 (standard test method for specific optical density of smoke generated by solid materials) and ISO 5659-2 2012 (plastics - smoke generation - part 2 determination of optical density by a single-chamber test) for smoke production. 

---