Risk Assessment in Re nery by Various Quantitative Methods and their Comparison

Abstract

The hazardous chemical accidents in past remain a matter of major concern. Therefore, in order to provide more accurate management plan, risk assessment has become a critical issue in chemical process industry. Risk assessments in particular have been used in the chemical industry for many years to support decision-making on the choice of arrangements and measures associated with chemical processes, transportation and storage of dangerous substances. The assessments are on risk perspective which is measured in terms of economic loss, human injury and environmental loss which is product of frequency and consequences. There are various risk assessment methods based on the techniques like qualitative, semi-quantitative and/or quantitative approaches. High level of accuracy in terms of risk analysis is obtained from the quantitative method as compared with other two techniques. Literature survey concluded that in the field of chemical process industries risk assessment are mainly done by quantitative methods to achieve high accuracy. The Event Tree Analysis, Fault Tree Analysis, F-N (Frequency-Number of Fatality) curve, Location Specific Individual Risk (LSIR) and consequence contour are the quantitative risk assessment methods by which the frequency and consequences are combined to give risk. The F-N curve is product of frequency F of events causing N number of fatalities. For F-N curve, LSIR and consequence contour method the practical case study of the chemical process industries has been analyzed. For the analysis of the F-N curve, LSIR and consequence contour the Phast and Phast Risk software are utilized. The accidental scenario input as source model to the software is identified from the major consequences of HAZOP study. Various models in Phast for discharge, dispersion as well as flammable, explosive and toxic effects have been studied. Based on calculated estimates of consequence (software modeling) from Phast is imported to Phast Risk and likelihood (failure rate data), local population distribution, source ignition and local prevailing weather conditions are input in Phast risk to obtain risk which is presented in terms of individual risk and societal risk . This provides a calculated value of risk. The risk estimated is compared with the risk criteria whether it is in Intolerable or ALARP or Tolerable based on the fatality rate. If the risk is intolerable then risk measures controls are identified to bring down the risk levels into ALARP or Broadly Acceptable range. In this way, the objective is to analyze Hydro Cracker Unit by applying Quantitative Risk Assessment method. The risk found after the study for the Hydro Cracker Unit was in ALARP region.