Testing methods smoke chamber

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. 

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. 

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. 

ASTM E 1995 Standard Test Method for Measurement of Smoke Obscuration Using a Conical Radiant Source in a Single Closed Chamber, With the Test Specimen Oriented Horizontally. ASTM International, West Conshohocken, PA. 

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. 

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 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. 

Conventional laboratory methods for testing the smoke formation, such as the NBS chamber, involve an area (A) of specimen, a chamber of fixed volume (V) and a measured optical density (D) over a fixed path length (L). In these measurements, the specific optical density is obtained according to the above relation ... 

Smoke testing in the NBS chamber has not gained ground in Europe but it is still the progenitor of several European methods such as of the ISO-boXy and of the smoke chambers used in the USSR and in the COMECON countries. 

At present there are more than fifteen widely used different test methods to evaluate smoke, each employing its own unique set of heating conditions, sample size and orientation, gas flow and means of smoke measurement. The most frequently used tests are those based on optical methods, i.e. attentuation of a light beam due to the sample formulations burning. There are also mechanical methods, those based on separation of liquid and solid aerosol particles from the smoke gases, the Arapahoe method and electrical methods (generation of electrical charges in an ionization chamber). 

ASTM E 84 Steiner Tunnel Test. This test, which uses very large samples (20 ft x 20 1/4 in.) is referenced in all model building codes for evaluating flame spread and smoke emission of foam plastic insulation. The test apparatus consists of a chamber or tunnel 25 ft. long and 17 3/4 X 17 5/8 in. in cross section, one end of which contains two gas burners. The test specimen is exposed to the gas flame for ten minutes, while the maximum extent of the flame spread and the temperature down the tunnel are observed through windows. Smoke evolution can also be measured by use of a photoelectric cell. The flame spread and smoke evolution are reported in an arbitrary scale for which asbestos and red oak have values of 0 and 100, respectively. More highly fire-retardant materials have ratings of 0-25 by this method. 

ASTM E 906 Heat and Visible-Smoke-Release Rate Test (based on Ohio State University Release Rate Apparatus). In this test the specimen is injected into an environmental chamber through which a constant flow of air passes. A radiant-heat source is used to produce the desired heat flux in the specimen, which way be tested horizontally or vertically. Combustion may be initiated by a number of different methods. The changes in temperature and optical density of the gas leaving the chamber are monitored, and from the resultant data the heat-release rate and visible anoke-release rate are calculated. Toxic-gas release and oxygen consumption rates may also be measured. 

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. 

ISO 5659-2 [108] determines the optical density of smoke generated and measured in a single test chamber. The test cabinet and smoke tneasuring equipment is that of the earlier NBS test defined as ASTM E662 and BS 6401. This ISO test uses a horizontal fire model in which the standard test specimen (75 mm square) is supported on a load cell. The specimen is exposed to radiant heat from a conical radiator positioned above the specimen holder see Fig. 19. Although a range of heat flux values can be used, the standard specifies that tests should be carried out at 25 kW.nr with and without a pilot ignition flame, at 50 kW m without a pilot flame. Calculation of results is by the method defined in the earlier tests. 

Part 3 of this standard refers to a draft method in which smoke is measured dynamically. The equipment is similar to that of Part 2. except that a small hood is mounted over the radiator and test specimen. The hood is connected to a duct that passes through the roof of the test cabinet. A smoke measuring system and extraction fan are attached to this duct and the test operated with the chamber cabinet open. 

Thome FA, Heavner DL, Ingebrethsen BJ, Eudy LW, Green CR (1986) Environmental tobacco smoke monitoring with an atmospheric pressure chemical ionization mass spectrometer/mass spectrometer coupled to a test chamber. Proc 79th Annual Meet Air Pollution Control Assoc. Air Pollution Control Assoc, Pittsburgh, paper 86-37.6 Thompson CV, Jenkins RA, Higgins CE (1989) A thermal desorption method for the determination of nicotine in indoor environments. Environ Sci Technol 23 429-435 Thomson BA, Davidson WR, Lovett AM (1980) Applications of a versatile technique for trace analysis atmospheric pressure negative chemical ionization. Environ Health Perspect 36 77-84... 

The XP-2 chamber was further developed by the US National Bureau of Standard (NBS). This NBS chamber as standardized in ASTM E 662-1979 has become the most wide-spread test apparatus in the United States. In this method, the light transmittance is again measured for calculating the specific optical density of the smoke generated on the following theoretical basis ... 

Due to the different dimensions of the laboratory test chambers, the above standardized methods give fairly diverse and not easily compared information. In fact, practical meaning of these test results is very difficult to relate to real-life experience. For this reason, smoke formation has been tested in instrumented large compartments, involving even people, in many countries. 

ANSI/ASTM E 84-79a - method of test for surface burning characteristics of building materials (Steiner tunnel). A 24-foot-long specimen is held horizontally as the roof of a 25-foot-long chamber. The ignition source is two gas burners, applied to the underside of one end. Flame spread is measured visually and instruments are used to determine fuel contribution and smoke density. The test is identical with UL 723 and ULC-S 102 1978, used in Canadian Building Regulations. 

With the dynamic O.S.U. apparatus, a photometer measures the percentage of light transmitted through the gases leaving the apparatus. The O.S.U. method yields dynamic records of smoke (and heat) released during combustion. The test also provides for radiant thermal exposure of a specimen both with and without a pilot source. Chamber dimensions are 890 mm x 410 mm x 200 mm with a pyramidal top section 395 mm high connected to the outlet. Specimens are typically 150 mm X 150 mm x 2 mm and are exposed in the vertical orientation. 

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