It is a matter of considerable practical importance to recognize metastable, potentially hazardous chemical compositions so that suitable thermal hazard management means can be provided as a part of process safety management. This communication is a report on our evaluation of the oxygen balance criterion as a screening technique for thermal hazard assessment.
Numerous chemical compositions are subject to spontaneous self-reaction, i.e. reaction within themselves to yield more stable products. Some substances of this nature are stable in storage though capable of vigorous or explosive reaction if heated or otherwise disturbed. Commercial and military explosives, usually organic nitro compounds, are obvious examples of such compositions. Additional examples include other nitrates, many peroxy and diazo compounds azides nitrides, and fulminates, and many metastable composition made up of oxidizing and reducing components that can be mixed or compounded without reaction.
Hazard assessment may be accomplished by heating, mechanical impact and explosive impact tests, by thermochemical and kinetic studies, and by other means. The oxygen balance test, widely used in explosives technology, is one of the simplest of such means.
Most explosives are metastable redox compositions. If the proportions oxidant and fuel are such that all of the oxygen m the composition appears in the form of water and/or carbon dioxide in the reaction products, the composition is said to be "oxygen balanced", or simply "balanced". It is reasonable to look for correlations between oxygen balance and other characteristics of potentially hazardous compositions. As noted, most commercial and military explosives are organic nitro compounds or nitrate esters. In general such compounds are not exactly oxygen balanced. Glycerol trinitrate (nitrogly-cerm), is a (rare) example of an oxygen-rich explosive.
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