Evaluation of available indices for inherently safer design options

Inherent safely is a proactive approach for loss prevention during process plant design. It has been proven that, considering the lifetime costs of a process and its operation, an inherent safety approach can lead to a cost-optimal option. Application of inherent safety at the early stages of process design yields the best results with respect to process selection, conceptual design, and engineering design. However, in spite of being an attractive and cost-effective approach to loss prevention, it is not widely used. Reasons have been suggested for this lack of widespread use, but the lack of systematic tools to apply inherent safety principles is perhaps the most important one. A detailed study was conducted to analyze the performance of available hazard indices with reference to various inherent safety principles (guidewords). The performance of four main indices (Dow, Mond, Inherent Safety, and Safety Weighted Hazard [SweHI] indices) was studied for five inherent safety guidewords. None of the indexing procedures can capture all of the inherent safety guidewords, although the SWeHI and Dow Index were found to be robust on many accounts. It is recommended that a new specific index be developed for inherently safer design evaluation. The SWeHI and Dow indexing procedures may be a good basis on which to build.