Relative flammability

If the material in two process alternatives is both flammable and highly toxic, then they can be compared on both bases separately. If the assessments of the relative flammability and toxicity are in conflict, then we can only resort to a safety index. 

A 6x2 ioch strip of fabric, clamped in a rack inclined at 45°, is exposed at its lowest part to the flame of a micro jet burner fbr a period of 1 second. If the sample catches fire, the time of flame travel over 5 inches of the sample is used as an indication of the relative flammability of the fabric... 

Flash Point — This is defined as the lowest temperature at which vapors above a volatile combustible substance will ignite in air when exposed to a flame. Depending on the test method used, the values given are either Tag Closed Cup (C.C.) (ASTM D56) or Cleveland Open Cup (O.C.) (ASTM 093). The values, along with those given below, provide an indication of the relative flammability of the chemical. In general, the open cup value is about 10° to 15 °F higher than the closed cup value. 

Flammable Limits in Air — The percent concentration in air- (by volume) is given for the lower (LFL) and upper (UFL) limit. The values, along with those for flash point and ignition temperature, give an indication of the relative flammability of the chemical. The limits are sometimes referred to as "lower explosive limit (LEL) and "upper explosive limit" (UEL). Chapter 3 provides a detailed technical explanation. 

Sevecek P, Filipi B, Zapletalova I. Modification of the oxygen index test for better evaluation of the relative flammability. Fire Mater. 1981 5 39-40. 

The limiting oxygen index (LOI) measures the minimum oxygen content that is required to sustain a flame [10]. The specimen in this test is in a vertical orientation, but it is the top of the specimen that is ignited. Because the specimen burns in a candle-like fashion, LOI may not be representative of fire situations. However, LOI does give quantitative information and may be useful for ranking the relative flammability of samples. 

Applications. The test illustrates the relative flammability of materials by measuring the minimum concentration of oxygen in atmosphere required to initiate and support flame for more than 3 min. 

RELATIVE FLAMMABILITY CRITERIA FOR LIQUIDS HAVING A FLASH POINT ... 

The method provides means for the determination of relative flammability of plastics by varying the oxygen to nitrogen concentration (see Table 12.31). The oxygen indexer is shown in Figure 12.32. 

Hilado, C. J., Gumming, H. J. and Casey, C. J. Relative flammability and toxicity of pyrolysis gases from cellular plastics. /. Cell. Plast., 15, 205, 219 (1979)... 

This is the minimum temperature at which the material will ignite without a spark or flame being present. Along with the values of flash point and flammable limits in air, it gives an indication of the relative flammability of the chemical. It is sometimes called the autoignition temperature. The method of measurement is given in ASTM A2155. 

To determine relative flammability of plastic by measuring the minimum concentration of oxygen in a flowing mixture of oxygen and nitrogen that will just support flaming combustion. The apparatus is shown in Fig. 10.60... 

Some elastomers will bum rapidly when ignited whereas others are selfextinguishing when the source of ignition is removed. Hame resistance is the relative flammability of an elastomer. 

This means that polymer flammability decreases when LOI increases. This method is also used to test the efficiency of flame retardants, but it is necessary to mention the direction of gas flow while testing (i.e., if the gases are coming from above or below the burning sample) [11]. Relative flammabilities as determined by LOI do not always agree with results from other tests it is thus necessary to know these results for a good evaluation of the flammability of plastic materials. Table 12.2 shows that there is no direct relation between LOI and the enthalpy or heat content for some polymers. 

Flash point is one important indicator of the relative flammability hazard of solvents and solvent-containing products therefore. 

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