Thermal Stability Indicators

Chemical process hazards cannot be effectively managed if they first cannot be properly identified. This is especially true for reactive chemicals storage, processing, and management. Reaction rates can be significantly influenced by the presence of contaminants, inhibitors, incompatible chemicals, etc. Runaway reactions usually involve undesired reactions although many industrial accidents have occurred because of desired chemistry runaway reactions.

Information pertaining to chemical reactivity is required under the Process Safety Information element of the PSM standard in the USA. This requirement is rarely satisfied by a safety data sheet. Information about chemical reactivity needs to be provided for both desired and undesired chemistries. In addition to regulatory compliance, this information is used to develop safe operating limits for storage and processing.

This paper describes several thermal stability indicators that should be provided as critical process safety information for reactive chemicals. This information often requires both laboratory measurements and computer modeling for proper scale-up to plant conditions.

Inhibitors are chemical substances that are used in small amounts to suppress the polymerization reaction of a monomer. An inhibitor has to be completely consumed before a polymerization reaction can proceed at normal rates. The time required to completely consume the inhibitor is often referred to as an ”induction” time. Inhibitors react with polymerization initiation radicals to produce products that cannot induce further reaction. Inhibitors are different from reaction ”retarders”. A retarder does not suppress the reaction but merely slows it down, i.e. the reaction continues to increase at a slower rate until the retarder is consumed. Some impurities in monomers can act as retarders.

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