Inherent Safety
We continue our series of posts on the topic of Safety in Design. The first three posts were,
The principles of Inherent Safety can be used at any time. However, they are best applied during the early stages of the design process (Concept and Preliminary/FEED Engineering).
The following definition is used for this term.
A process is inherently safer if process hazards can be eliminated, or the risk associated with those hazards can be reduced, without the use of protective systems. This reduction or elimination is accomplished through changes that are permanent and passive.
There are three important features of the above definition.
The definition uses the relative term ‘inherently safer’, not ‘inherently safe’. No process can be absolutely safe, risk can never be zero.
The words permanent and passive mean that inherent safety features cannot be removed or bypassed.
The use of the principles of inherent safety does not mean that the system is fail-safe. Nevertheless, a facility that has been designed using the principles of inherent safety will less dangerous if operations go badly awry.
The Table provides examples of safety features that are inherent, and of others that are not.
The principles of inherent safety vary from organization to organization, but most descriptions of the topic are structured around the following five elements (with considerable overlap between them).
Eliminate
Substitute
Minimize
Moderate
Simplify
These principles should generally be addressed in the order shown, i.e., those at the top of the list provide greater security than those at the bottom.
There is considerable overlap between them. For example, if a company decides to use aqueous ammonia rather than anhydrous ammonia, this action could be either ‘Eliminate’ or ‘Substitute’, or even ‘Moderate’.
