Inherently safe systems in the process industries

In process industry plants, the concept of more inherently safe design is a recurring theme in the three reports of the Advisory Committee on Major Hazards (ACMH - set up in the UK after the Flixborough accident). These reports set the general principles of new process industry safety in the UK and they represent in their field what, for example, the IAEA Safety Fundamentals documents do in the nuclear industry. 

A full account of the developments of this concept is given in Lees, Kletz (1984) and UMIST (1982). The Loss Prevention Bulletin (published by the Institution of Chemical Engineers, England) is also a must for interested people. It is available in most technical libraries and a list of its main articles over the years is included in Lees. The basic principles of inherently safer designs in the process industry are  

Interesting examples of proposals in the process industry foUow 

This kind of process continued to be used until fifty years ago with a number of casualties and complete plant losses. The same reaction is now obtained in a small injector where the acid jet entrains the correct amount of glycerin and, due to the turbulent mixing, the reaction time has been reduced down to minutes. The reaction is complete at the exit of the injector. The amount of nitroglycerine in the reactor is reduced to a few kilograms and the operators can be protected by a blast wall. 

Another reaction, the adipic acid reaction (used in the manufacture of nylon), was previously performed in a huge reactor with external circuits for cooling. Today, it is carried out in a smaller integral vessel with internal cooling and agitation, and with a very smaller possibility for leaks. A similar evolution has taken place in nuclear reactors which changed from external to internal recirculation units (or to integral proposals for future reactors). 

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