Measuring Inherent Safety

Despite the many attempts to develop a tool for measuring the degree of inherent safety of a process/chemical, inherent safety indices have not been widely used in industry due to many reasons. Some indices are developed to assess the inherent safety of a certain hazard, while some are more general and attempt to include the main hazards in a process. All of them have different tradeoffs that motivate one to keep searching for a better metric. Following is a brief background on some of the indices reported in the literature. Table 1 shows previously developed indices, parameters included in each one of them, and their advantages and disadvantages.

Dow’s Fire & Explosion Index (F&EI) is widely used by industry as a measure of inherent safety, though not originally developed for that purpose, but to determine the need for fire protection . The index is calculated for selected units of the process as the product of a material factor (MF) and a process unit hazards factor (PUHF). The MF is a measure of the potential energy release from the material, since it takes into consideration reactivity and flammability. The PUHF is obtained as the product of the General Process Hazards (GPHs) penalty factor and the Special Process Hazards (SPHs) penalty factor. GPHs are the sum of penalties due to type of reaction/process, material handling and transfer, and spill control factors of the chemical. SPHs are the sum of penalties due to chemical properties, process hazardous conditions and the quantity of hazardous chemical in the unit1, 2. Furthermore, Dow’s F&EI and PUHF are combined to obtain the Damage Factor (DF), which is used to calculate the base Maximum Probable Property Damage (MPPD). Loss control credit factors are then taken into acco...

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