It is an approach that encourages the designer to attempt to eliminate or minimize hazards (physical, inhalational, etc.) identified at each stage in the process life cycle, and at every level of process and plant design, rather than accepting the existence of the hazards and designing safety systems to control those hazards. It may not always be feasible to eliminate or reduce hazards, but the ISP philosophy requires that this be attempted before moving on to specification of risk management equipment and procedures. Note that describing a process as “inherently safer” can only be done in the context of specific hazard or subset of hazards and that management of all liazards must be considered in order to design a safer process. Thus, a substitution (inherent) might eliminate one type of hazard but require the development of new standard operating procedures (procedural) to manage a different one.

The terms “inherently safer processes” (ISPs),1 and variations such as “inherently safer technology” (IST) and “inherently safer design” (ISD) were first used in discussions about PSM in the 1970s after serious process industry incidents around that time.2 These incidents focused industry, government, and public attention on PSM, and resulted in the initial development of many of the PSM techniques and regulations that are in common use throughout the world today.

The ISP philosophy was first fully articulated in 1977 by Trevor Kletz, a senior safety advisor for Imperial Chemical Industries (ICI). That year Kletz presented the Jubilee Lectufre to the Society of Chemical Industry in Widnes, England, which he titled “What you don’t have, can’t leak.” In his talk, Kletz challenged the practice of storing large quantities of flammable or toxic materials at manufacturing plants and questioned the need for the use of elevated temperatures and pressures in processing (Kletz, 1978). He also suggested that risk management efforts should aim at elimination of hazards where feasible, instead of using safety systems and procedures to manage the risk. This should be accomplished, for example, by reducing the amounts of hazardous material used in processes, using less-hazardous materials, or developing technology that allows for processes to proceed under milder conditions. Kletz described this as “inherently safer.”3

In subsequent years, a set of principles for ISPs were established within the chemical community, an effort supported by Kletz (1984, 1985, 1991, 1998) and others in the chemical industry (Puranik et al., 1990; Ashford, 1993; Windhorst, 1995; Mannan, 2005; See also additional references at the end of this chapter). As

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1 The term “inherently safer processes” is used here in accordance with the language of the statement of task.

2 These included a 1974 explosion at a chemical plant in Flixborough, England that resulted in the deaths of 28 and injuries to another 36 individuals and a 1976 chemical release at Seveso in Milan, Italy that sickened many in the surrounding area.

3 In his 1977 lecture, Kletz used the term “intrinsically safer.” This was later changed to “inherently safer” to avoid confusion with the use of “intrinsically safe” to describe electrical equipment designed to meet specific hazardous area classification requirements.



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