A risk-based model to establish threshold planning quantities of hazardous substances

The Threshold Planning Quantity (TPQ) is the minimum quantity of any hazardous substance stored or processed at an industry that can pose a defined level of risk up to a certain distance from the industrial premises should an accidental release occur. These are recommended by the concerned government departments of the respective countries. Often, concerned regulatory authorities focus on simple screening tools to prescribe TPQs of hazardous chemicals rather than on more detailed technical aspects. This is illustrated with the help of TPQs presently administered in India, which are followed based on Control of Industrial Major Accident Hazard regulations of the United Kingdom. In this paper, the risk ranking matrix (RRM) approach is described to evaluate the recommended TPQs and prescribe these for some extremely hazardous chemicals (EHS) commonly used in industries. The RRM presented here is unique in the sense that various acceptable risk criteria are reviewed to appropriately rank the risk potential and provide suitability criteria in terms of individual risk factors and geosocietal risk factors (GSRF). Based on this concept, an attempt has been made to develop a risk-based model to determine the TPQs of various EHS (acrolein, ammonia, chlorine, hydrogen fluoride, and phosgene).