TECHNIQUES FOR EVALUATING CHEMICAL REACTION HAZARDS

It is clearly not safe to test unknown reactions or compounds in a full-size reactor, as a vigorous exotherm may overcome the protection systems provided. Various theoretical techniques and small-scale tests have therefore been devised to provide data on the likelihood and severity of a runaway reaction. They vary from simple calculations and basic heating tests to sophisticated simulations of full-size plant. This chapter describes the main theoretical techniques and experimental tests available for identifying chemical reaction hazards, and suggests how to select a suitable test regime. 

The tests tend not to give absolute results, in that the experimental conditions may affect the data obtained. Factors such as sample size, container material, heating rate, thermal inertia and endothermic effects (gas evolution. 

An example showing the application of the testing procedures in practice to a particular reaction is given in Appendix 2. 

The existing literature is no substitute for chemical hazard testing, but it often makes a good starting point for assessing the hazards of a new reaction — in particular when the process designer wants to know whether it is safe to carry out laboratory work or to start process development. 

A literature search should be thorough, covering all the chemicals to be used in the process, including any solvents, and using more than one source if possible. If a particular compound is not listed then data on chemically-related compounds may be useful. References 17 and 18 and any relevant company files should be consulted. 

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Committee E-27, Hazard Potential of Chemicals, was formed in 1967, in response to the need for some agency to develop standardization techniques for the evaluation of the potential of chemicals to cause fires and explosions. Several subcommittees were formed and the one on Condensed Phase Reactions was given the assignment of devising a computational method for screening chemicals for their ability to cause an explosion. The task group that wrote the program, now... 

The introduction of a reaction to the pilot plant often proceeds without determining the chemical hazards involved with the scale up process. The reasons for this vary. In cases where a hazards evaluation laboratory is not available, it is the responsibility of the development chemist to assure the safety of the reaction. The development chemist may not be familiar with hazard evaluation techniques, and the instrumentation used to evaluate a reaction for safety may not be readily available. 

The CSB survey identified examples of modified or hybrid techniques to identify reactive hazard scenarios and ensure the implementation of adequate safeguards. For example, companies conducting reactions in batch chemical reactors often conduct HAZOP studies by evaluating deviations from... 

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