Flammability testing propagation

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. 

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. 

The ignition, combustion, and fire propagation behaviors of polymer are examined in various flammability test standards, where polymers are intentionally degraded, and the degradation products are ignited and burned under controlled exposure and environmental conditions. Various countries and agencies promulgate these types of flammability test standards ... 

The autoignition temperature is the minimum temperature required for self-sustained combustion in the absence of an external ignition source. The value depends on specified test conditions. Tht flammable (explosive) limits specify the range of concentration of the vapor in air (in percent by volume) for which a flame can propagate. Below the lower flammable limit, the gas mixture is too lean to burn above the flammable limit, the mixture is too rich. Additional compounds can be found in National Fire Protection Association, National Fire Protection Handbook, 14th ed., 1991. 

The UL flammability ratings describe the relative ease of ignition and combustibiUty of plastics. Tests include the measurement of flame propagation, time to self-extinguish, melt and drip with and without flame, and oxygen indexes. Some engineering plastics, eg, polyetherimides, are, as ranked by this test, inherently nonflammable. Others can be made nonflammable by compounding with flame retardants (ERs) such as bromine... 

The Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances (UL 94) has methods for determining whether a material will extinguish, or burn and propagate flame. The UL Standard for Polymeric Materials-ShortTerm Property Evaluations is a series of small-scale tests used as a basis for comparing the mechanical, electrical, thermal, and resistance-to-ignition characteristics of materials. 

The above flame retardants, HMPN and TMP, along with another commercially available alkyl phosphate, triethyl phosphate (TEP), were systematically characterized by Xu et al. To quantify the flammability of the electrolytes so that the effectiveness of these flame retardants could be compared on a more reliable basis, these authors modified a standard test UL 94 HB, intended for solid polymer samples, and measured the self-extinguishing time (SET) instead of the universally used flame propagation rate. Compared with the UL 94 HB, this new quantity is more appropriate for the evaluation of the electrolytes of low flammability, since the electrolytes that are determined to be retarded or nonflammable by this method all showed zero flame propa-... 

ASTM E 2058 Standard Test Methods for Measurement of Synthetic Polymer Material Flammability Using a Fire Propagation Apparatus. Annual Book of Standards, Vol. 04.07, ASTM International, West Conshohocken, PA. 

Flammability limits. The range of flammable vapor-air or gas-air mixtures between the upper and lower flammable limits. Flammability limits are usually expressed in volume percent. Flammability limits are affected by pressure, temperature, direction of flame propagation, oxygen content, type of inerts, and other factors. The precise values depend on the test method. 

Effect of temperature on flammable limits. The higher the temperature at the moment of ignition, the more easily the combustion reaction will propagate. Therefore, the reference temperature (initial temperature) of the flammable mixture must be stated when flammable limits are quoted. There are not a lot of data for flammable limits under different conditions of initial temperature. The behavior of a particular mixture under different conditions of initial temperature usually must be determined by tests. 

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