New simple indices for risk assessment and hazards reduction at the conceptual design stage of a chemical process

• Risk indices based on chemical hazards and accident frequency are proposed.
• The indices can be used at conceptual design phase to address risks to process safety.
• Linear dependency of indices on hazard mass fraction conceptualizes inherent safety.
• The risk indices make it possible to evaluate risks independently from process size.
• Indices assess risks at minimum available data as screening tool among design array.

Inherent safety has been of great interest to regulators, process designers and investors. The idea behind this is that a process design is more economic when it is inherently safer. Inherent safety is known as the safety intrinsic to a process; the spirit of which is to mitigate hazards within the process. It is also possible to achieve inherently safer design by diminishing the hazards in multi-component streams during process design. Hazards reduction during the design phase is a challenging task. A decrease in hazards in a process design not only improves process safety, but also protects the environment from potential impacts of the process. Current methodologies for risk assessment at the conceptual design stage of a chemical process need detailed process data, which is usually unavailable at such a phase. This paper presents simple new indices that require minimum data for risk evaluation of chemical processes at the conceptual design phase. The indices are applied to a hydrogenation case study to choose inherently safer designs among different alternatives. As an important result, total capacity of a process among other design array does not suffice for decision making unless the mass fraction of hazards in product streams are appreciably low.