Flammable chemical

Certain chemicals pose fire and explosion risks because  

Clearly, flammable chemicals also pose a health risk if the substance or its thermal degradation or combustion products are toxic or result in oxygen deficiency. 

Liquids and solids do not burn as such, but on exposure to heat vaporize or undergo thermal degradation, to liberate flammable gases and vapours. Some chemicals undergo spontaneous combustion (see page 142). 

The vapour pressure of a flammable substance also provides an indication of how easily the material will volatilize to produce flammable vapours the higher the vapour pressure, the greater the risk. Lists of vapour pressures usually contain data obtained under differing conditions but inspection of boiling points (when the vapour pressure equals atmospheric pressure) gives a first approximation of the ease with which substances volatilize. Table 5.1 therefore includes both boiling point and vapour pressure data. 

The flash point represents the minimum temperature at which an ignitable mixture exists above a liquid surface. By definition, flash points are inapplicable to gases. Some solids, e.g. naphthalene and camphor, are easily volatilized on heating so that flammable mixtures develop above the solid surface and hence flash points can be determined. (However, although these substances can be ignited, they generally need to be heated above their flash points in order for combustion to be sustained this is the fire point .) 

Clearly, flammable chemicals also pose a health risk if the substance or its thermal 

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For many years the petroleum industry has defined nonconductive liquids as having conductivities less than 50 pS/m. A higher value of 100 pS/m is used here to address the higher dielectric constants of certain flammable chemicals in relation to petroleum products. For example the dielectric constant of ethyl ether is 4.6 versus 2.3 for benzene from Eq. (2-3.2), ethyl ether therefore has the same relaxation time at a conductivity of 100 pS/m as benzene at a conductivity of 50 pS/m. It is the relaxation time, not the conductivity alone, that determines the rate of loss of charge hence the same logic that makes 50 pS/m appropriate for identifying nonconductive hydrocarbons makes 100 pS/m appropriate for identifying nonconductive chemical products. 

Explosion a confined vapour cloud explosion (CVCE) can result from ignition of vapour within a building or equipment a boiling liquid expanding vapour explosion (BLEVE) can result when unvented containers of flammable chemicals burst with explosive violence as a result of the build-up of internal pressure unconfmed vapour cloud explosion (UVCE) can result from ignition of a very large vapour or gas/air cloud. 

Table 6.11 Control measures for working with flammable chemicals...

Keep flammable chemicals apart from oxidizing agents Design layout to avoid domino effects/fire spread Segregate empty and full containers... 

Train staff in hazards and precautions, and practise emergency evacuation drills Remember that flammable chemicals can also be toxic or asphyxiant... 

Figure 13.3 Procedure for hot work on equipment that contains, or has contained, a flammable chemical (general summary only reference should be made to detailed procedures)...

Special Hazards of Combustion Products Not pertinent Behavior in Fire May explode in fires Ignition Temperature Not flammable Electrical Hazard Not pertinent Burning Rate Not flammable. Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials Dirt and metals can cause rapid decomposition with the liberation of oxygen gas Stability During Transport Pure grades are stable, but contamination by dirt and metals can cause rapid or violent decomposition Neutralizing Agents for Acids and Caustics Not pertinent Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Threshold Quantity - As defined in 29 CFR 1910.119, the minimum amount of a toxic, reactive, or flammable chemical judged by OSHA as being capable of causing a catastrophic event. The threshold quantity triggers application of the rule s requirements, tonnes - A metric ton, i.e., 2,200 lb. 

In plastics, these correlative properties, together with those that can be used in design equations, generally are called engineering properties. They encompass a variety of situations over and above the basic static strength and rigidity requirements, such as impact, fatigue, flammability, chemical resistance, and temperature. 

Fire detection and suppression form the basis of fire control, with emergency back-up procedures to mitigate the consequences. Selected key tactics for working with flammable chemicals are summarized in Table 5.11. 

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