Selection of inherently safer process routes: a case study

Increased public concern about safety issues and stringent environmental standards has led plant designers to consider inherently safer design. The term ‘inherently safer’ implies that the process is safe by its very nature and not externally constrained to be safe by the use of add-on systems and devices. Such opportunities for developing inherently safer process are highest in the early stages of design. Constraints such as time, lack of knowledge and inadequate inherent safety analysis tools are often cited as obstacles to development and implementation of inherently safer design. In this paper, we describe an inherent safety analysis methodology that can be applied in the early stages of process development. The methodology is based on an inherent safety index for comparing process routes and heuristics for identifying hazards and generating alternative designs. This methodology has been implemented as one module in iSafe, an intelligent system that automates inherent safety analysis. One key benefit of iSafe is substantial reduction in the time and effort required to perform safety analysis. Automation of the inherent safety analysis also makes it more thorough and detailed, minimizes or eliminates human errors, facilitates documentation and makes the study results available online for detailed safety analysis and review in the later stages of process design. The details of inherent safety analysis at the route selection stage are discussed in this paper and illustrated by comparing competing processes for acetic acid manufacture.