By David E. Hendrix
President, The Hendrix Group, Houston, TX
With more EPA mandates on the way, companies must foster a safety culture equipped with an effective risk management plan. The 1990 Clean Air Act Amendments contain provisions requiring the US Occupational Safety and Health Administration (OSHA) and the US Environmental Protection Agency (EPA) to promulgate rules requiring facilities that handle extremely hazardous substances to prepare a risk management plan that assesses hazards from accidental releases, provides measures from preventing such releases, and sets forth specific actions to be taken in response to an accidental release. In response to this mandate, OSHA issued 29 CFR 1910.119, Process Safety Management of Highly Hazardous Chemicals, as a final rule on February 24, 1992. The roots of today’s rules extend back over 20 years and are a response to a series of industrial accidents such as the Flixborough explosion and the Seveso dioxin release. International attention was galvanized by the 1984 release in Bhopal. In the United States, the 1989 Phillips explosion fueled concerns that industry was not moving quickly enough to institute effective process safety management programs (PSM).
There are nine core elements common to the OSHA PSM regulation:
Facilities that are setting up PSM programs have quickly recognized that this effort is resource intensive. As a result, it is imperative that resources spent to comply with regulations produce the greatest benefit to the facility and the corporation.
One method for optimizing limited resources and minimizing serious equipment failures, while helping to comply with the mechanical integrity section of the OSHA PSM requirements, is risk-based inspection. This inspection approach has been in use in the nuclear industry for some time now. Risk-based inspection is a procedure for ranking or prioritizing equipment for inspection purposes based upon risk. Risk is defined as the combination of probability and consequence. Probability is the likelihood of an event occurring, in this case an equipment failure. Consequence is a measure, both in lives and property, of the damage that would occur if an equipment item failed.
Risk-based inspection procedures can be based on either qualitative or quantitative methods. Qualitative procedures provide a ranking of equipment based largely on experience and engineering judgment. Quantitative risk-based methods use engineering disciplines to set priorities and develop programs for equipment inspection, including non-destructive examinations, system and component design and analysis, fracture mechanics, probabilistic analysis, failure analysis, and operation of facilities. However, quantitative analysis methods can be expensive, time consuming, and tedious. Often, insufficient information is available for conducting a quantitative risk analysis. Two organizations currently working on quantitative risk-based analysis procedures for use by the chemical industry are the American Society of Mechanical Engineers and the American Petroleum Institute.
One approach for ranking process equipment is a procedure developed by this writer based on internal probability of failure (POF). The procedure is based on a set of rules based on past inspection histories, equipment design and existing condition, knowledge of potential corrosion and cracking environments, and information concerning normal and upset conditions. Using this information, it ranks equipment on a numerical scale. Proper use of the procedure requires engineering judgment and experience; therefore, the results depend on the background and expertise of the analyst. However, one person can effectively develop rankings for fixed equipment in a reasonable time if the appropriate information is available. The POF ranking is then combined with a consequence ranking to provide a true risk-based ranking.
Equipment rankings will not stay constant, but will require updating as additional knowledge is gained, process conditions change, and equipment ages. Maximum benefits of the procedure depend on fixed equipment inspection programs that permit the capture, documentation, and retrieval of inspection, maintenance, and corrosion/failure mechanism information.
At this writing, the procedure has been used to rank more than two thousand equipment items and has proven to be practical, effective, and efficient. Its usefulness lies in its facilitating the most efficient use of finite inspection monies and personnel where 100% inspection is not practical.
Additional information on this procedure is available to interested parties upon request. Carmagen Engineering can also assist in implementing this inspection approach as necessary.