Combustion fires and explosions

Historically, combustion synthesis (both SHS and VCS) is a direct descendant of classic works on combustion and thermal explosion (e.g.. Mallard and Le Chatelier, 1883 Semenov, 1929 Zeldovich and Frank-Kamenetskii, 1938 Williams, 1965 Glassman, 1977) see Hlavacek (1991) and Merzhanov (1995) for additional comments in this regard. We discuss later in Section IV how the theory of SHS grew directly from these works. The progress in combustion science made it possible to organize self-sustained exothermic reactions in powder mixtures that were controllable and predictable, hence avoiding the uncontrollable evolution of the reaction that is commonly associated with the terms combustion, fire, and explosion. 

In Chapter 1 we briefly considered the critical phenomena in branching chain reactions consisting in the qualitative transfer from the slow mode of reaction to the intensive (self-accelerated) one at negligible changes in the parameters of a reaction system. Investigations of critical phenomena are still urgent. Increased interest in this problem is closely associated with the practical tasks of combustion, fire and explosion safety, inhibition of oxidation processes, etc. [1-3, 26-50],... 

Example 9.1 A process involves the use of benzene as a liquid under pressure. The temperature can be varied over a range. Compare the fire and explosion hazards of operating with a liquid process inventory of 1000 kmol at 100 and 150°C based on the theoretical combustion energy resulting from catastrophic failure of the equipment. The normal boiling point of benzene is 80°C, the latent heat of vaporization is 31,000 kJ kmol the specific heat capacity is 150 kJkmoh °C , and the heat of combustion is 3.2 x 10 kJkmok. ... 

Fire and Explosion Prevention. Prevention of fire and explosion takes place in the design of chemical plants. Such prevention involves the study of material characteristics, such as those in Table 1, and processing conditions to determine appropriate ha2ard avoidance methods. Engineering techniques are available for preventing fires and explosions. Containment of flammable and combustible materials and control of processes which could develop high pressures are also important aspects of fire and explosion prevention. 

A concentration of 35,000 ppm in air produces unconsciousness in 30—40 minutes. This concentration also constitutes a serious fire and explosion hazard, and should not be permitted to exist under any circumstance. Any person exposed to ethyl ether vapor of any appreciable concentration should be prompdy removed from the area. Recovery from exposure to sublethal concentrations is rapid and generally complete. Except in emergencies, and then only with appropriate protective equipment, no one should enter an area containing ether vapor until the concentration has been found safe by measurement with a combustible-gas indicator. 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials Contact with most combustible materials may cause fires and explosions. Corrosive to most metals with formation of flammable hydrogen gas, which may collect in enclosed spaces Stability During Transport Unstable if heated Neutralizing Agems for Acids and Caustics Flush with water, rinse with dilute sodium bicarbonate or soda ash solution Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

The conditions imposed on oils by compressors - particularly by the piston type - are remarkably similar to those imposed by internal combustion engines. One major difference is, of course, that in a compressor no fuel or products of combustion are present to find their way into the oil. Other contaminants are broadly similar. Among these are moisture, airborne dirt, carbon and the products of the oil s oxidation. Unless steps are taken to combat them, all these pollutants have the effect of shortening the life of both the oil and the compressor, and may even lead to fires and explosions. 

R = 8.3145 kJ-K 1-kmol 1 and T is the reactor temperature (K). T is also the supply temperature of A whose yet unknown inventory mA is in the form of a superheated liquid. The total amount of B to be produced is 1000 kmol. T and mA are to be selected with the additional consideration of safety. The normal boiling point of A is 70°C, its latent heat of vaporization is 25,000 kJ-kmol-1, the liquid specific heat capacity is 140 kJ-kmol K 1, and its heat of combustion is 2.5 x 106 k.bkrnol. The residence time of the reactor is 1 min, and the safety is measured in terms of fire and explosion hazards on the basis of the theoretical combustion energy resulting form catastrophic failure of the equipment. 

Figure 6-5 Maximum pressure for methane combustion in a 20-L sphere. The flammability limits are defined at 1 psig maximum pressure. Data from C. V. Mashuga and D. A. Crowl, Process Safety Progress (1998), 17(3) 176-183 and J. M. Kuchta, Investigation of Fire and Explosion Accidents in the Chemical, Mining, and Fuel-Related Industries A Manual, US Bureau of Mines Report 680 (Washington, DC US Bureau of Mines, 1985).

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. 

General References Crowl and Louvar, Chemical Process Safety Fundamentals with Applications, 2d ed., Prentice-Hall, Upper Saddle River, N.J., 2002, Chaps. 6 and 7. Crowl, Understanding Explosions, American Institute of Chemical Engineers, New York, 2003. Eckoff, Dust Explosions in the Process Industries, 2d ed., Butterworth-Heinemann, now Elsevier, Amsterdam, 1997. Kinney and Graham, Explosive Shocks in Air, 2d ed., Springer-Verlag, New York, 1985. Lewis and von Elbe, Combustion, Flames and Explosions of Gases, 3d ed., Academic Press, New York, 1987. Mannan, Lees Loss Prevention in the Process Industries, 3d ed., Elsevier, Amsterdam, 2005, Chap. 16 Fire, Chap. 17 Explosion. 

Petroleum and chemical related hazards can arise from the presence of combustible or toxic liquids, gases, mist, or dust in the work environment. Common physical hazards include ambient heat, bums, noise, vibration, sudden pressure changes, radiation, and electric shock. Various external sources, such as chemical, biological, or physical hazards, can cause work related injuries or fatalities. Although all of these hazards are of concern this book primarily concentrates on fire and explosions hazards that can cause catastrophic events. 

Hydrocarbon materials have several different characteristics that can be used to define their level of hazard. Since no one feature can adequately define the level of risk for a particular substance they should be evaluated as a synergism. It should also be realized that these characteristics have been tested under strict laboratory conditions and procedures that may alter when applied to industrial environments. The main characteristics of combustible hydrocarbon materials which are of high interest for fire and explosion influences are described below. 

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. 

A-2.11.1 Storage Vessel Failure. The release of GH2 or LH2 may result in ignition and combustion, causing fires and explosions. Damage may extend over considerably wider areas than the storage locations because of hydrogen cloud movement. Vessel failure may be started by material failure, excessive pressure caused by heat leak, or failure of the pressure-relief system. 

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