Abstract of TD-No.5

National Institute of Occupational Safety and Health, Japan

Risk assessment and risk reduction for preventing process accidents in chemical process industries

Yukiyasu SHIMADA, Yoshihiko SATO, and Haruhiko ITAGAKI

Implementation of risk assessment is essential as part of Industrial Safety and Health Act, which wasintroduced as "duty to make efforts" on March, 2006 (obligatory risk assessment for the substances subject to preparation and issuance of safety data sheet (SDS) will be made after June, 2014). This approach led to more penetration and implementations of risk assessment in chemical process industries. Over the past few years, major chemical companies had reported number of serious process accidents, which can be prevented if appropriate risk assessment practice is implemented. The relevant ministries and agencies report that riskassessment and risk reduction to prevent process accidents have not been performed sufficiently. Small and medium-sized enterprises (SMEs) of chemical process industries are suffering from the lack of adequate resources, such as time and effort, budget, knowledge, information, etc., to perform the effective risk assessment and risk reduction. Furthermore, SMEs regard assessing risk and taking measures to reduce risk as unnecessary or least priority activities in their business plans, because of the small amount of handling chemical substances, as well as low awareness of process risks.

This technical document introduces a systematic and iterative framework of risk assessment and risk reduction, which specifies logical thinking approach at each step to promote the effective implementation of risk assessment and risk reduction. At first, responses are obtained to questionnaire regarding properties of chemical substances and handling processes, which enhance the consciousness of possible risks and process accidents (leak, fire, explosion, burst, etc.). In views of hazard specifications, other than process behavior, defect factors on field works or plant operations and plant facilities and equipment are identified as hazards, with the occurrences of process accidents in mind. Lists of examples of defect factors are provided so that SMEs can consider them easily. A fault propagation scenario from identified hazards to possible process accidents is specified and the associated risks are estimated. Three major risk estimation steps are performed for confirming the effectiveness of existing and additional risk reduction measures. As part of high risk level scenarios, additional risk reduction measures are studied according to following concepts: a) priority based on reliability; and b) multiple protection measures. These concepts clearly specify the rational ground for studying and implementing risk reduction measure. The rational aspects are written down explicitly on the record sheet. This can make it possible to transfer the stated risk management information to field workers and/or plant operators at production-sites, which contribute to their effective safety management activities. Case studies of risk reduction measures are also provided as reference information for SMEs. In the presence of residual risks, risk reducing measures should be studied and specified to guide field workers or plant operators.

The proposed framework can recognize the possibility of process accidents and the logical grounds for the implementation of risk reduction measures, which are specified in the record sheet, and perform effective safety management activities.

A simple case study is used to show the effectiveness of the proposed framework.

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