Fires, accidental combustible materials

Hazardous substances present in the process are identified on the basis of their flammability, explosiveness and toxicity. The flammability of gases and vapours of flammable liquids is a great concern in the process industries. The result of an ignition can be a fire or an explosion or both. Accidental fires and explosions of flammable mixtures with air often follow the escape of combustible materials or inlet of air into process equipment. 

A severely destructive explosion in Los Angeles in 1947 was caused by a mixture of 68—72 % perchloric acid with acetic anhydride used for electropolishing of aluminum plates. " In general, the perchloric acid as usually encountered, in concentrations of 70% or less in water, is rather harmless aside from the fact that it is a very strong acid. However, if it should be soaked up accidentally in combustible material, it would greatly aggravate an existing fire. 

The employer is required to regularly and properly maintain, according to established procedures, equipment and systems installed on heat-producing equipment to prevent accidental ignition of combustible materials. The maintenance procedure must be included in the written fire prevention plan. 

Water-reactive chemicals. Certain chemicals, including sodium, potassium, and many metal hydrides, react with water, producing heat and flammable gases. Other chemicals may burn upon contact with water. Storage areas used to hold water-reactive chemicals should be designed to prevent accidental contact with water. For example, these areas should not be equipped with automatic water sprinkler systems. Segregate water-re-active chemicals from other combustible materials, and be certain that the area is of fire-resistant construction. 

In ideal combustion 0.45 kgs (1 lb.) of air combines with 1.8 kgs (4 lbs.) of oxygen to produce 1.2 kgs (2.75 lbs.) of carbon dioxide and 1.02 kgs (2.25 lbs.) of water vapor. Carbon monoxide, carbon dioxide, nitrogen and water vapor are the typical exhaust gases of ordinary combustion processes. If other materials are present they will also contribute to the exhaust gases forming other compounds, which in some cases can be highly toxic. Imperfect combustion will occur during accidental fires and explosion incidents. This mainly due to turbulence, lack of adequate oxidizer supplies and other factors that produce free carbon (i.e., smoke) particles, carbon monoxide, etc. 

Most combustible liquids do not present a vapor problem if accidentally released into the atmosphere. The probability of a fire, therefore, is considerably less than it would be if the spill was of a flammable material. If, however, the combustible liquid is at a temperature higher than its flashpoint, then it can be expected to behave in the identical manner a flammable liquid. One major difference between the two in a fire situation is that the potential exists for cooling the combustible liquid below its flash point by the proper application of water (generally applied in the form of water spray). In the event the liquid is burning, and if the fire forces are successful in achieving the required reduction in liquid temperature, then vapor production will cease and the fire will be extinguished because of a lack of vapor fuel. Unless this reduction in liquid temperature can be brought about, the fire will necessitate the same control considerations a low-flash liquid fire would. 

Chlorinated and brominated materials are burned or thermally treated in a variety of combustion sources including hazardous and municipal waste incinerators, industrial processes, backyard trash burning, and accidental fires. Chlorinated materials are used in a wide range of applications and brominated compounds are fire retardants used in many devices including electronic circuits. Although there has been some research on the reactions of CHCs and BHCs in the past 20 years, too little is known about their reactions considering the magnitude of the environmental impact. Elementary reaction studies of gas-phase reactions of Cj and C2, CHCs, and BHCs are needed to understand their most fundamental reaction properties. Reactions of the chlorinated and brominated benzenes and phenols are important intermediate steps in the formation of PCDD/F. Recent kinetic models indicate that the gas-phase reactions may be quite important and elementary gas-phase reaction studies have been overlooked by researchers. 

Most combustible liquids do not present a vapor problem if accidentally released into the atmosphere. The probability of a fire, therefore, is considerably less than it would be if the spill was of a flammable material. If, however, the combustible liquid is at a temperature higher... 

Continuous ignition sources should be located away from probable points of release of flammable materials. In particular, pumps and compressors, which are the most likely source of accidental leaks, should be located at least 15 meters from sources of ignition such as fired heaters and internal combustion engines. 

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