Flammable mixture

Deflagration. In a deflagration, the flame front travels through the flammable mixture relatively slowly, i.e., at subsonic velocity. 

Similarly, instead of installing vacuum relief valves the vessels can be made strong enough to withstand vacuum. In addition, if the vessel contains flammable gas or vapor, vacuum relief valves will often need to admit nitrogen to avoid flammable mixtures. A stronger vessel often may be safer and cheaper. 

Low pressure. Low pressures are not in general as hazardous as the other extreme operating conditions. However, one particular hazard that does exist in low-pressure plants handling flammable materials is the possible ingress of air with the consequent formation of a flammable mixture. 

The flash point measures the tendency of a petroleum material to form a flammable mixture with air. It is one of the properties to be considered when evaluating the flammability of a petroleum cut. 

It should be noted finally that adding gasoline to diesel fuel which was sometimes recommended in the past to improve cold behavior conflicts with the flash point specifications and presents a serious safety problem owing to the presence of a flammable mixture in the fuel tank airspace. Adding a kerosene that begins to boil at 150°C does not have the Scune disadvantage from this point of view. 

Potential health and safety problems of acryflc polymers occur in their manufacture (159). During manufacture, considerable care is exercised to reduce the potential for violent polymerizations and to reduce exposure to flammable and potentially toxic monomers and solvents. Recent environmental legislation governing air quality has resulted in completely closed ketde processes for most acryflc polymerizations. Acryflc solution polymers are treated as flammable mixtures. Dispersion polymers are nonflammable. 

Most of the world s commercial formaldehyde is manufactured from methanol and air either by a process using a silver catalyst or one using a metal oxide catalyst. Reactor feed to the former is on the methanol-rich side of a flammable mixture and virtually complete reaction of oxygen is obtained conversely, feed to the metal oxide catalyst is lean in methanol and almost complete conversion of methanol is achieved. 

The ignition temperature or autoignition temperature is the minimum temperature of a flammable mixture that is required to initiate or cause self-sustained combustion without ignition from an external source of energy such as a spark or flame (ASTM D2155). 

Stabilized tetrachloroethylene, as provided commercially, can be used in the presence of air, water, and light, in contact with common materials of constmction, at temperatures up to about 140°C. It resists hydrolysis at temperatures up to 150°C (2). However, the unstabilized compound, in the presence of water for prolonged periods, slowly hydrolyzes to yield trichloroacetic acid [76-03-9] and hydrochloric acid. In the absence of catalysts, air, or moisture, tetrachloroethylene is stable to about 500°C. Although it does not have a flash point or form flammable mixtures in air or oxygen, thermal decomposition results in the formation of hydrogen chloride and phosgene [75-44-5] (3). 

Ignition can also be produced by a heated surface. During the process of heat transfer from a hot surface to a flammable mixture, reactions are initiated as the temperature rises and the combination of additional heat transfer from the surface and heat release by chemical reactions can lead to ignition of the mixture. 

Alternatives to Arresters Alternatives to the use of flame arresters include fast-ac ting isolation valves, vapor suppression systems, velocity-type devices in which gas velocity is designed to exceed flashback velocity, and control of the flammable mixture (NFPA 69 standard, Explosion Prevention Systems ). The latter alternative frequently involves reduction of oxygen concentration to less than the limiting oxygen concentration (LOC) of the gas stream. 

There is a maximum safe gap measured experimentally which will prevent the transmission of an explosion occurring within a container to a flammable mixture outside the container. Critical and maximum experimental safe gaps for a number of materials in air are listed in Lees (1980, pp. 491-492). These quenching effects are important in the design of flame arresters and flameproof equipment. 

Gases At ambient temperature and pressure, form flammable mixtures at 13 percent or less by volume. 

The test gas must be of uniform and known composition. This generally requires on-line gas analysis if flammable mixtures are not supplied from a suitable reservoir. If concentration gradients are created in the surrounding air, errors can be introduced by releasing the test gas stream from a perforated probe doubling as an electrode. The maximum effective energy of a... 

The resistance to ground should be sufficiently small to prevent spark ignition at the maximum anticipated charging current to the system. This can be achieved by ensuring either that the energy stored is less than the MIE or that the minimum ignition voltage cannot be attained (A-4-1.3). The necessary resistance depends not only on the flammable mixture but also on the electrical circuit. 

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