1996

Koivisto, Raija

Safety is one of the most important features of modern chemical processes. The foundation for the safety of a process is formed when designing the process. It is common practice to analyse the process with regard to safety during or at least at the end of the design. Accident and incident data together with other experiences, however, suggest that a considerable portion of process accidents and incidents are ultimately due to inadequate design. Based on the literature, this study strives first to identify the deficiencies and problems in current process design practice. Three common practices to address safety have been studied: adherence to good practice, safety analyses and inherently safer design. The problems in their use include the deficient coverage of the problem area and the analytic (not synthesizing) way to consider safety which often is too late because the important safety-related decisions have been made already. With regard to inherently safer design, there are no good tools available. To sum up, safety is not being taken continuously and systematically into consideration during process design. This study suggests a new process design approach, Safety-conscious process design methodology, which strives to raise the designer's safety-consciousness of the process to a level surpassing that of the current descriptive-analytical approach (i.e. safety is the result of the design decisions and can be analysed), the outcome being a prescriptive-synthetical approach (awareness of what the process safety should be after some design decision). Safety-conscious process design methodology is built on Phenomenon-driven process design methodology and Performance-driven design strategy. Safety has been defined in the same object hierarchy as 'process', thus including safety in the description of process and process design (in object form). This association makes safety considerations systematic and continuous during the process design. A new concept, safety balance, was developed to aid the safety assessment during the process design. Safety balance also offers a means of assessing the safety-consciousness of a design decision. The novel advantage of safety balance (when compared to current practices) is that balance control volume must be defined, i.e. the area or extent included in the safety consideration must be defined and this has not been self evident previously. Safety-conscious process design methodology still suffers from some deficiencies, such as the quantification of safety and the definition of aggregation operators which enable the safety assessment of the entire process based on the safety values of its parts. The Safety-conscious process design approach was tested in one industrial design case. The results were promising, even without proper tools for knowledge handling and safety assessment.