From time to time, it may be necessary to evaluate alternative spacing requirements between process units and adjacent equipment, hazards and facilities. This action may be taken where site limitations reduce the space available for process unit separation from adjacent units or where neighboring plants
and communities must be considered. In either case, the procedure that follows offers guidelines for the evaluation of alternatives proposed to reduce spacing or for examination of required spacing.
Evaluation Procedure for Determining Alternative Spacing Requirements | Plant Layout Levels
a. Identify the hazards inherent in the process unit, plant, or exposing facility.
b. Estimate the consequences that could result from accidents involving the hazards identified. Identify the opportunities to reduce the consequences.
c. Calculate the heat radiation, blast pressure, and/or fire effects on exposed process or offsite equipment or facilities or areas adjacent to unit. For toxic hazards, calculate the extent of a possible toxic cloud dispersion. When these calculations are performed, it should be assumed that any measures taken to reduce the consequences of accidents are effective.
d. Identify measures to reduce the impact of the calculated effects and recalculate the consequences assuming the implementation of these measures.
e. Based on the results of Item 5, review spacing based on Tables 1A and 2A and determine new separation distance. In general, the radiation levels in the target area shall not exceed 4.73 kW/m2 for personnel exposure and 18 kW/m2 for process equipment exposure. Blast wave pressure shall not exceed 3.4 kPa and NIOSH-recommended and IDLH levels shall not be exceeded at the property boundary.
f. All scenarios, calculation methods, and formulas, will be presented to Buyer for review prior to conducting the analysis. Once preliminary results are obtained, the recommendations for spacing and the results of the studies will be presented for review and approval.
