Inherent Safety: Eliminate
We continue our series of posts on the topic of Safety in Design. The first four posts were,
The principles of inherent safety vary from organization to organization, but most descriptions of the topic are structured around the following five elements.
Eliminate
Substitute
Minimize
Moderate
Simplify
In this post we consider the first item in the above list: Eliminate.
Risk consists of three components: a hazard, the consequences of that hazard should it occur, and the predicted frequency (not probability) of occurrence.
The only way to reduce risk to zero is to eliminate the hazard. In a 1979 paper Trevor Kletz , one of the founders of the concept of inherent safety, expressed the same concept more pithily when he said, ‘What You Don’t Have, Can’t Leak’.
We can illustrate Trevor’s slogan with the following example.
A liquid is transferred from Unit A to Unit B as shown. There is an intermediate storage tank between the two units. If we can remove the tank then we have eliminated hazards associated with this tank such as overflow or leakage caused by corrosion. To paraphrase Trevor’s words,
If a tank’s not there, it can’t leak.
General questions to do with the elimination of risk include the following:
Can a hazardous material be eliminated?
Can a flammable material be eliminated?
Can an additive be removed?
Can equipment or piping be removed?
Can an activity be eliminated?
Can personnel be removed from the area?
The last item in the above list can better be written as,
If a man’s not there, he can’t be killed
The ‘Eliminate’ term can, however, create a new set of hazards. In the case of the Intermediate Storage Tank, its ability to smooth out operational upsets would be removed. This could create other, more serious hazards in either of the operating units A and B. The Law of Unintended Consequences is always with us.
