Explosive atmosphere ignition sources

Ignition of flammable atmosphere for open filters or solvent may be above flash point with air present when cleaning or unplugging closed filters. This may necessitate tight control of ignition sources to prevent a fire/explosion. 

The fluoro compound is resistant to nitration and an operating temperature of 90°C is necessary to ensure formation of the 5-nitro derivative. Under these conditions, the atmosphere (containing the fluoro compound, its nitro derivative and nitric acid vapours) in the nitration vessel is explosive and above the flash point. An unknown ignition source led to an explosion and rupture of the 3 cu. m vessel, and a maximum explosion pressure of 50 bar was confirmed experimentally. Such explosive atmospheres are not found in low temperature nitration reactions. 

Atmospheric dispersion of any rupture disc discharges would result in a vapor cloud with gas concentrations above the lower explosive limit. Thus, such releases must be avoided, and other mitigation procedures should be used. However, as an additional check on the situation, mapping of the potential gas cloud versus the plant layout was conducted with the conclusion that no ignition sources were likely to be present in the region where the vapor cloud would be flammable. 

To protect against the explosion and fire hazard, a plant manager should (a) have qualified plant personnel field monitor for explosive atmospheres and flammable vapors, (b) keep all potential ignition sources away from an explosive or flammable environment, (c) use nonsparking, explosion-proof equipment, and (d) follow safe practices when performing any task that might result in the agitation or release of chemicals. 

The explosibility of a carbonaceous dust is governed by its fineness and its volatile content. A hazardous dust would, in general, have a fineness greater than 200 mesh and a volatility greater than 13%. A governing factor for a metal or alloy would be its fine ness and for a plastic, molecular configuration plays a part. Other factors that play important roles in the initiation and development of an explosion are composition of the dust, concentration of the dust cloud, composition of the atmosphere and the ignition source. 

The following operating procedures will xeduce explosion hazards to a minimum good housekeeping, prevention of dust dissemination, elimination of igniting sources, use of inert atmospheres or explosion suppression devices and venting... 

In general, an explosion is an exothermic chemical reaction between two components. A well-known example is the reaction between the oxygen content of the atmospheric air and a combustible substance like petrol. As an exception, there are very few substances - such as acetylene - which are thermodynamically unstable and tend to exothermic self-decomposition. An explosion can start only with an ignition source and a volume or mass ratio of the two components in such a manner that the reaction zone is sustained by itself. Typical values of the peak explosion pressure - when starting with components at atmospheric pressure in a constant volume - are 1 MPa (10 bar) and a propagation velocity of the reaction zone up to 102m/ s (as an order of magnitude). 

Explosivity Fine dust dispersed in air in sufficient concentrations and in the presence of an ignition source, is a potential dust explosion hazard. Minimum concentration for explosion is 0.25 oz. ft The recommended fire extinguishing media is water spray, dry chemical, alcohol foam, or carbon dioxide. Acetaminophen is capable of generating a static electrical charge. Processes involving dumping of acetaminophen into flammable liquid, inert atmosphere in the vessels, or temperatures of flammable liquid should be maintained below its flashpoint. 

Methane is highly flammable and is therefore an explosion and fire hazard the lower explosive limit is 5-15% by volume. Extreme care must be taken to keep areas of high concentration free from ignition sources, such as sparks from static electricity. Explosion-proof equipment should be used in these areas. Many people believe that methane is an important greenhouse gas, and that the apparent threefold increase in atmospheric concentrations over the last 200 years affects the stratospheric ozone layer and the oxidizing capacity of the atmosphere. 

A fire hazard can be defined as any fluid, product, piece of equipment, process, etc. that has the potential to cause or contribute to a fire. The fuel delivery system is a primary fire hazard because of the potential for a leak of the fuel into the surrounding environment or atmosphere which is almost always air. This is an immediate hazard because of the possibility of an uncontrolled fire or an explosion depending upon the size and location of the leak and the availability of an ignition source. 

If evolution or formation of an explosible atmosphere cannot be prevented and all sources of ignition cannot be reasonably eliminated or excluded, then the possibility of a dust cloud explosion persists. Under such conditions, explosion protection measures should be taken to protect people and minimize damage to the plant. It should be noted that explosion protection measures should be considered in addition to taking all reasonable steps to reduce the possibility of formation/spread of dust clouds and exclude potential ignition sources. Explosion protection measures include the following. 

If an explosive atmosphere exists, ignition can be prevented by elimination and control of all potential ignition sources. Open flames, improper electrical equipment and industrial trucks should not be allowed in areas where there is potential for an explosive atmosphere. In some cases, autoignition can also occur during decomposition or contact with temperature extremes. Chapter 3 contains additional information on control of ignition sources. 

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