Selecting a Basis of Safety

Before choosing the safety measures, four important factors need to be considered  

The following sections look at each of these points in turn. 

An important factor in determining the nature and magnitude of the hazard, and the complexity and expense of the safety measures, is the amount of chemicals in the reactor at any one time. 

In a continuous process where the reactants are fed into the reactor continuously the amount of unreacted material is usually small. The same is usually true of a semi-batch process, when the reactor is charged with one reactant and the others are added over a period of time. In a batch process, on the other hand, the full quantities of reactants are mixed together at the start of the reaction if a runaway occurs early in the reaction it will involve large quantities of unreacted material. 

Continuous or semi-batch processes are usually inherently safer than batch processes. The applications of continuous processes are limited, but almost all processes can be designed to operate in a semi-batch mode. 

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Having identified the chemical hazards of a process, it is necessary to decide how to design and operate the process safely — that is, to select a basis of safety. (See also case histories Al 27-30, pages 172-175.)... 

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