Inherently safer design: implementation challenges faced by new and existing facilities. (Process Safety).

Applying inherent safety design in existing hydrocarbon processing facilities is challenging. A major hurdle is simply to measure the degree of inherent safety in a way that allows alternative designs comparisons, which may or may not increase safety, or may simply redistribute risk. Also, inherent safety is an intrinsic design feature that is best implemented early in the process plant's design phase. Developing inherently safer designs are significant technical challenges that require research and development efforts that have limited economic reward.

These challenges make regulating inherent safety very difficult. A coordinated long-term effort involving government, industry and academia is essential to develop and implement this concept. Similar approaches have been successful in related fields such as green chemistry, energy conservation and sustainable development.

Inherent safety. This principle is centered on technologies and chemical usage which have intrinsic properties that reduce or eliminate hazards. Based on concepts that have existed for more than 100 years, it is an approach to chemical incident and pollution prevention that is, in some ways, contrary to traditional accident prevention and mitigation methods. (1) Traditional safety practices typically reduce risk probability by lowering an incident and/or mitigating incident consequence. This approach alone, although extremely important and generally effective, does not reduce serious chemical incident hazards. Inherent safety is especially important in today's world where terrorists may cause a chemical release by methods that bypass or defeat normal safety systems. The concept, as applied to chemical process plant design, has been discussed elsewhere. (2)

Consider that the most common accident at home is falling on the stairs. A home without stairs, i.e., a one-story house, is inherently safer with regard to falling on stairs than a two-story house. Even if the stairs are equipped with handrails, nonslip surfaces, good lighting and gates for children, the hazard is still present. (1)

Obviously, choosing an inherently safer house implies positive and negative consequences, which may include aesthetics, cost and other hazard types. An elevator could reduce stair use, but requires a large capital expense. During construction, there would be significant hazards to residents and construction workers, and the stairs would still be necessary for emergency egress. Few families would conclude that installing an elevator is the best resource use.

Measuring. While inherent safety is based on well-known principles, difficulties have been encountered in adopting the principles as a routine industrial practice. One problem encountered during application is the subjectivity involved. The principles are descriptive rather that prescriptive, thus subject to interpretation based on previous experience, knowledge and personal perception. A subjectivity consequence is that a systematic methodology measuring inherent safety does not exist. It is presently not possible to know how inherently safe a plant or an equipment item is because it is nor possible to evaluate how well the principles have been applied. If we cannot measure how inherently safer the one-story house is with respect to the two-floor home, how can we choose the safer option?

Several measurement and analysis tools have been proposed during the past...