Layer of protection analysis applied to ammonia refrigeration systems

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Title: Layer of protection analysis applied to ammonia refrigeration systems
Author: Zuniga, Gerald Alexander
Abstract: Ammonia refrigeration systems are widely used in industry . Demand of these systems is expected to increase due to the advantages of ammonia as refrigerant and because ammonia is considered a green refrigerant . Therefore , it is important to evaluate the risks in existing and future ammonia refrigeration systems to ensure their safety . LOPA (Layer of Protection Analysis ) is one of the best ways to estimate the risk . It provides quantified risk results with less effort and time than other methods . LOPA analyses one cause -consequence scenario per time . It requires failure data and PFD (Probability of Failure on Demand ) of the independent protection layers available to prevent the scenario . Complete application of LOPA requires the estimation of the severity of the consequences and the mitigated frequency of the initiating event for risk calculations . Especially in existing ammonia refrigeration systems , information to develop LOPA is sometimes scarce and uncertain . In these cases , the analysis relies on expert opinion to determine the values of the variables required for risk estimation . Fuzzy Logic has demonstrated to be useful in this situation allowing the construction of expert systems . Based on fuzzy logic , the LOPA method was adapted to represent the knowledge available in standards and good industry practices for ammonia refrigeration . Fuzzy inference systems were developed for severity and risk calculation . Severity fuzzy inference system uses the number of life threatening injuries or deaths , number of injuries and type of medical attention required to calculate the severity risk index . Frequency of the mitigated scenario is calculated using generic data for the initiating event frequency and PFD of the independent protection layers . Finally , the risk fuzzy inference system uses the frequency and severity values obtained to determine the risk of the scenario . The methodology was applied to four scenarios . Risk indexes were calculated and compared with the traditional approach and risk decisions were made . In conclusion , the fuzzy logic LOPA method provides good approximations of the risk for ammonia refrigeration systems . The technique can be useful for risk assessment of existing ammonia refrigeration systems .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -3133
Date: 2009-05-15

Citation

Layer of protection analysis applied to ammonia refrigeration systems. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -3133 .

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