Flammability testing ignitability test

One of the most useful laboratory flammability tests is the oxygen index (OI) test (ASTM-D2043). In this test, the specimen is burned as a candle in controlled mixtures of oxygen and nitrogen. The minimum oxygen concentration which produces downward flame propagation is considered the OI of ignitability for the polymer. 

It is necessary, in approaching most problems to obtain the limits of flammability of the particular gas mixture in question. Few industrial fuel gases are composed of pure gases or vapors, but are mixtures in most cases of many different gases. If the equipment and time are available, a number of mixtures of die fuel gas-air mixtures may be prepared and their flammabilities tested by ignition but it is much easier to determine the flammability limits of complex gas mixtures by calculation. Experience has shown that the results obtained are sufficiently dependable. 

Flammability tests evaluate the hazard present when an ignition source is available. These tests range from the determination of flash point, flammable limits and autoignition to the very rapid and destructive burning in a dust explosion. 

A large number of flammability tests have been developed to evaluate the ignition propensity of a wide range of materials exposed, usually for a short duration, to a small heat source. For example, the most recent compilation of ASTM lire standards includes 30 small heat source ignition tests.21 When adding methods that use an electric arc, hot wire, hot surface, etc., instead of a flame and those developed by other standard organizations (NFPA, UL, ISO, IEC, etc.), the total number of tests is in the hundreds. 

A material that does very well in the test might perform very differently in a real fire if any of these factors are different. For example, a V-0 rated material is not expected to ignite when subjected in a real fire to a heat source similar to that in the test. But what would happen if the real source is more severe or persists beyond the exposure time in the test The results could be dramatically different. Ignition might occur and flames might subsequently propagate over the surface and quickly result in a catastrophic fire. There are numerous examples of materials that pass a flammability test successfully, but perform miserably under slightly more severe real fire conditions. 

Higher irradiation levels give better reproducibility, more clearly defined ignition, and shorter measurement times, but correspond to more developed fires. Thus particularly for flame-retarded polymers, a smaller irradiation level often corresponds better to the fire protection goals addressed. Cone calorimeter results for the HRR at small irradiances correspond to flammability tests such as LOI and UL 94, if a reasonable set of materials are compared and the behavior is not dominated by dripping effects. Thus different considerations govern the choice of external heat flux.76 77... 

Another study demonstrating the importance of conducting multiflux flammability tests was conducted by Panagiotou and Quintiere [33], Quintiere used modeling of flame-spread to show that a polymer system can be accurately characterized only if the flammability is measured over a range of heat fluxes ignition time, flame spread, and HRR need to be measured at various fluxes. 

Once ignited, the greater the flammability of a material, the FIGURE 21.11 Temperature index greater will be the hazard associated with it. A small-scale apparatus, flammability test which is very extensively used for plastic... 

FIGURE 26.6 Relationship between FIGRA and THR measured in MCC (i.e., PCFC). FIGRA = PHRR/ TTPHRR, FPI = TTI/PHRR, where PHRR is peak heat release rate, TTPHRR is time to peak heat release rate, and TTI is time to ignition. (Based on Lin, T.S. et al., Correlations between microscale combustion calorimetry and conventional flammability tests for flame retardant wire and cable compounds, in Proceedings of 56th International Wire and Cable Symposium, 2007, pp. 176-185.)... 

Dangerous Goods, Manual of Tests and Criteria, for Ignition distance test, Enclosed space ignition test and Aerosol foam flammability test. 

According to ASTM E918, high-pressure vessels with a minimum volume of 1-L and a minimum diameter of 76-mm should be used for flammability tests at high pressures. A prescribed fuse wire is recommended as the ignition source. A 7% pressure rise is defined as an ignition. 

Flame stability is governed by the limits of flammability and ignition temperature of the fired fuel. Due to the complex chemistry it is generally impractical to predict precisely using CFD modeling. Scale tests and actual field data are used to extend simple ID and 2D models for calibration to predict flame stability. The variables... 

Highly flammable gas ignition temperature 350°C (662°F) forms explosive mixtures with air, with LEL and UEL values of 3.4% and 27% by volnme of air, respectively. It is, however, less flammable than propane-butane mixtnres, as shown by closed drug and flame extension tests. The flame extension of compositions containing 45% methyl ether is 0-15 cm (20-35 cm for propane-butane mixtnre) (Bohnenn 1982) flre-extingnishing method stop flow of gas use a water spray to keep fire-exposed containers cool. 

Many current flammability tests are based on perceived hazards and often involve flames applied to products or materials. Such tests use flames of different type, size, and duration, and test specimens of different size, shape, and orientation, although considerable rationalization has taken place recently. For historical reasons, they are often industry and or product based. The majority of these tests essentially determine whether a product will sustain combustion away from the ignition. source. When assessed in terms of fire hazard analysis, the effective differences between these flames may be minor compared to the actual fire scenario. 

A series of flammability tests and guidance for their use when applied to electrical components is given in the lEC 695 2 scries of tests (individually referenced below). However they include a number of different ignition sources which could be applied to many plastics materials, since these arc frequently used by the electrical industry. These standards are similar to those described above but are important because each standard... 

A flammability test under a 50 % oxygen atmosphere was also carried out. The vinyl polymer 1, ferrocene 6b and benzene polymers 7 are burned out when attacked with flame. The carborane hybrids 3a, 3b are both ignited but extinguished soon in the case of the higher (y + z) contents. The introduction of carborane brings non-flammability to the hybrid polymers along with thermal and mechanieal strength. Transformation of the boron structure to boron oxide was observed around... 

Flammability tests of plastics can be classified in various ways (such as characteristics of the igniting source, size or shape of the test specimen, etc.). In the present discussion, test methods are divided into the following groups testing of materials, testing of products, and full-scale fire tests. 

The first and hitherto most wide-spread standard flammability test for plastics foams, ASTM D 1692 has been withdrawn. The practically identical ISO 3582-1978 prescribes a test specimen of 150 mm x 50 mm with a thickness between 5 and 13 mm, placed on a horizontal wire gauze of 215 mm x 75 mm. 13 mm of the length of the gauze is bent upwards to a right angle as shown in Figure 3.60. The specimen is marked 125 mm from the end to be ignited then placed in a holder (Fig. 3.61). 

ISO 340-1982 concerns the flammability testing of conveyor belts. A rectangular test piece 200 mm x 25 mm is arranged with its major axis vertical and then ignited at its lower edge by a 150 to 180 mm long spirit flame from a burner inclined at 45 deg. for 45 s (Fig. 3.136). The duration of flaming after removal of the burner is measured. 50 to 70 s after removal of the burner, an air stream is directed at the surface of the specimen at a speed of 1.5 m/s and it is observed whether or not the specimen flares up. 6 specimens are cut, 3 warp way and 3 weft way. If covered belts are tested, 6 additional test pieces are prepared in the same manner but the covers are stripped off. The material meets the requirements if the total duration of flame... 

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