Inherent safety is a term that describes a system, technology or process that, through various design features, is able to operate in such a state that various failures modes do not present a risk to people, property or environment. The concept was initially introduced by Trevor Kletz of ICI in the 1980's. He applied the term to the study of chemical accident prevention, expressing it as, "Inherently safer plants are plants which can withstand deviations from normal operating conditions without having to rely on safety systems."1 The term continues to be used in the context of the chemical processing industry (CPI), primarily in the context of acute events. It is a concept that has great value well beyond the CPI.
While many will acknowledge that inherently safe systems are ideal, we also realize that, in many systems, risk cannot be eliminated without also eliminating the utility of that system. As a result, the concept of inherently safe has evolved into inherently safer. This acknowledges that, while a comprehensive inherently safe system may not always be achievable; there is value in assessing any system for opportunities to make it inherently safer. At the same time, especially in organizations where there is substantial risk to people, property and the environment, there needs to be an innovation infrastructure in place so that opportunities for achieving inherently safe systems can be identified, promoted, analyzed and implemented.
This paper introduces a simple graphical model for assessing the extent to which various the risk management options create an inherently safer system. Drawing on the concepts of primary prevention, secondary prevention and mitigation, it has been used to represent various acute chemical release events, from the vapor cloud explosion in Flixborough, England to the methylisocyanate (MIC) release in Bhopal, India to the release of mecury-based pesticides into the Rhine River in Basel, Switzerland. It has also been used to demonstrate the gains achieved with inherently safer options, such as transitioning from batch to continuous processing to substantially reduce quantities of hazardous intermediate products.2
To understand the effectiveness of a firm's safety efforts, it is worthwhile to subdivide measures which fall under an organization's definition of prevention. These measures can be classified as:
Mitigation measures generally exist as stand-by systems which perform in response to an event. These measures are intended to minimize the amount of personal injury and property damage given the occurrence of an accident such as a chemical release. They are not intended to actually prevent the event from occurring. Many emergency response measures fall into this category. For adverse consequences to be minimized, it is important that response procedures be properly implemented by those involved. Especially for acute events, such as chemical releases, that have low frequencies of occurrence and great variability in how they manifest themselves, there can be numerous factors that impact whether or not emergency response actions are appropriate and effective.