Lower flash point

Fig. 1. Effect of temperature on limits of flammabiUty of a pure Hquid fuel ia air, where = lean (or lower) flash point = rich (or upper) flash point ...

Substanees may be heated to their flash points by other substanees with lower flash points burning in elose proximity. Storage of flammable ehemieals, therefore, needs eareful eonsideration. 

The lowest temperature of a flammable liquid at which it gives off sufficient vapor to form an ignitable mixture with the air near the surface of the liquid or within the vessel used. The flash point has been commonly determined by the open cup or closed cup method but recent research has yielded higher and lower flash points dependent on the surface area of the ignition source. Because of this aspect ASTM and other standard test methods have been recently withdrawn. They are under review until an adequate determination of a practical and comprehensive standard is composed and agreed upon. 

The flash point of a petroleum product is also used to detect contamination. A substantially lower flash point than expected for a product is a reliable indicator that a product has become contaminated with a more volatile product, such as gasoline. The flash point is also an aid in establishing the identity of a particular petroleum product. 

Sb sulfide, BafNOj), or CaSi, by McNutt (Ref 56) LA with KClOj/S/Pb thiocyanate 40/ 10/50% by duPont (Ref 58) LA/natural, synth or rubber substitute by Snelling (Ref 63) LA/ Ba(NOj)j/tetracene by Weale (Ref 62) LA/ diazoguanidine picrate with or without tetryl by Imperial Chem lads (Ref 67) LA/nitro-soguanidine by Olsen Seavey (Ref 61) LA/ nitratohypophosphite by Brun Burns (Ref 68) LA/ground glass by Hatch (Ref 70) LA/ various expl additives,which lower flash point, by Dynamit-AG (Ref 72) LA/Pb nitrosores-orcinate by Kerone Carroll (Ref 71) LA/... 

Temperature at which a liquid produces ignitable vapors. Lower-boiling compounds typically have lower flash points. Any liquid with flash point below 15°C should be considered dangerously flammable and suitable precautions should be put in place. ... 

The Pensky-Martens closed tester (ASTM D-93, IP 34) and the tag closed tester (ASTM D-56) are normally used for determining the flash point of fuel oil and similar products. The Cleveland open cup method (ASTM D-92) is most commonly used, although the Tag open cup (ASTM D-3143) is applicable to cutback asphalt. As noted above, the flash point of asphalt is an indication of fire hazard and is frequently used to indicate whether asphalt has been contaminated with materials of lower flash point. 

Flammability, the tendency of a material to burn, can only be subjectively defined. Many materials that we normally do not consider flammable will burn given high enough temperatures. Neither can flammability be gauged by the heat content of materials. Fuel oil has a higher heat content than many materials considered more flammable because of their lower flash point. In fact, flash point has become the standard for gauging flammability. 

Flash point is the temperature at which the volatile products are evolved at such a rate that they are capable of being ignited but not supporting combustion. A crude cottonseed oil with a free fatty acid content of 1.8% was found to have a flash point of 560°F (293°C). Solvent-extracted oils can have a lower flash point due to a solvent residue. A flash point test identifies this crude oil deficiency and so prevents accidental fire or explosion in an atmosphere that is not explosion-proof. Crude vegetable oil shipments received with a flash point below 250°F can be rejected under most trading rules. 

METHYLENE OXTOE (50-00-0) CHjO An extremely flammable gas. Forms explosive mixture with air [explosion limits in air (vol %) 7 to 73 flash point (gaj) 185°F/85°C solution), [methanol content (usually 10 to 15%) lowers flash point] 122 to 176°F/50 to 80°C Fire Rating (37% by weight solutions) 4 (no methanol) 2 (15% methanol)]. Aqueous solutions (37 to 55% by weight) are combustible and may explode above their flash points. Aqueous solutions slowly oxidize in air to formic acid. May polymerize unless properly inhibited (usually... 

For a liquid that is a mixture of compounds that have different volatility and flash points, its flash point shall be detemined as specified above on the material in the form in which it is to be shipped. If it is determined by this test that the flash point is higher than 20°F (-6.67°C) a second test shall be made on a sample of the liquid evaporated from an open beaker (or similar container), under ambient pressure and temperature (20° to 25°C) conditions, to 90 percent of its original volume or for a period of 4 hours, whichever comes first. The lower flash point of the two tests shall be the flash point of the material. 

Mixtures of two or more solvents may, because of the presence of azeotropes, have a lower flash point than their components have separately. 

For safety reasons numerous attempts have been made to raise the flash point of solvent mixtures [14.84]. Azeotropes having a lower flash point than those of the pure components can be formed on mixing solvents use of solvent mixtures to raise the flash point is therefore extremely problematic. The flash point of toluene can, for example, be significantly raised above 21 °C by adding chlorinated hydrocarbons [14.85], [14.86]. However, the flash point is first lowered instead of raised if dichloro-methane is added. Non-flammability is achieved only above a minimum addition of dichloromethane. 

Isobutyl acetate has a higher volatility and lower flash point than butyl acetate, and is therefore used in the production of quick-drying cellulose nitrate lacquers. On account of its low water content it can be used as a solvent and diluent for polyurethane paints. Isobutyl acetate is used as a viscosity-reducing auxiliary solvent in low-solvent paints. 

Technical grades contain acetone and thus have a much lower flash point (starting at - 18 C). 

Since regulations may vary so much from country to country and, even within one country, may vary according to use or method of transport, it is usually necessary to know accurately the flash point of any paint. The flash point of a mixture of liquids can be lower than the flash point of any of its constituents, so measurements should always be made on the actual sample. These are usually carried out in closed or open cups of varying design and it is important to state which cup was used. Closed cups give lower flash points. 

LPG has strong volatOity, lower flash point and wide explosion limits. Its minimum ignition energy is 0.2-0.3 mJ, and it is easy to get fire and even lead to secondary disasters once encounter fire. Subjected to external heat pressure vessels wall will destructed suddenly and hquid is overheated and then released and hghted therefore the fireball emerged. Consequence analysis of first accidents. 

The flash point is not the temperature at which the vapor pressure in air equals the lower flammable limit. Although both parameters have some correspondence there are large differenees between groups of solvents. There is a general tendency for solvents with a lower flammability limit to have a lower flash point. The flash point determination uses a... 

Azeotropes. One solvent may form azeotropes with another solvent due to molecular association. This physical principle can be exploited in several ways. The most important in solvent applications is the possibility of reducing the boiling temperature (some azeotropes have lower boiling point) therefore an applied product such as a coating may lose its solvents and dry faster. The formation of such azeotrope also lowers flash point by which it increases hazards in product use. The formation of an azeotrope is frequently used to remove water from a material or a solvent. It affects the results of a distillation since azeotrope formation makes it difficult to obtain pme components from a mixture by distillation. Azeotrope formation can be suppressed by lowering the boiling point (distillation under vacuum). One benefit of azeotropic distillation is the reduction in the heat required to evaporate solvents. 

The tag open cup is a larger unit equipped with water-glycol bath for temperature control or a solid carbon dioxide-acetone bath for lower flash points. A much larger sample is used with this equipment and the temperature is gradually increased at a rate of TC/min. A taper flame is passed for 1 s in 1 min intervals until the flash point is detected. The tag closed tester can use either a manual or an automated procedure. A sample volume of 50 ml is used. Either a gas flame or an electric ignitor is used. In the automated mode, the equipment is programmed to perform the standard procedure. 

A combustion characteristic which appears to be outside the usual range of characteristics is spontaneous combustion. This is the phenomenon of the apparently inexplicable bursting into flame or smoke of some substances such as oil-soaked rags or overalls, oil-soaked lagging, hay and straw. The explanation is simple a slow oxidation of the oil gives off heat with the formation of substances with lower molecular weights which also have lower flash points. As the oxidation continues the temperature of the... 

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