Quantitative Risk Assessment: A Useful Management Tool for Minimizing Risk, 1999 Pulping Conference Proceedings

Sami Atallah & Naveen Gupta

Trinity Consultants, Inc.

The Risk Management Plans required by EPA have limited usefulness to industry. Since frequency of occurrence is never considered in selecting Worse Case accident scenarios, the results of an RMP may be very misleading and downright "scary", especially to the uninformed public. This is particularly true for facilities which handle highly toxic and irritating materials like chlorine, chlorine dioxide, ammonia, sulfur dioxide and similar chemicals. An accidental release of even small quantities of these chemicals may result in a hazard zone which extends several miles.

Quantitative Risk Assessment (QRA) has been around for a long time. It was originally developed and used by the nuclear industry. In the 1960's, the use of QRAs was extended to the then budding liquefied natural gas (LNG) industry. In more recent years, QRAs have been increasingly applied to a variety of facilities which handle highly hazardous chemicals. Trinity has, for example, applied QRA to chlorine manufacturing plants, an HF alkylation plant, an aluminum plant which utilized chlorine as a fluxing agent, a PVC manufacturer who utilized large volumes of vinyl chloride monomer, a manufacturer of sulfuric acid and oleum, etc.

A QRA is based on the premise that the risk of an accident is a function of both its frequency and severity. In its simplest form, risk is the product of frequency (occurrences per year) and severity (loss per occurrence). Thus risk would have the units of loss/year, where loss can be measured in terms of dollars, downtime, environmental impact, exposure to hazardous levels or fatalities.

QRA may be used to estimate the absolute risk of plants which handle, store or process highly hazardous chemicals and to compare their risks with those set by international standards such as those adopted by several European countries. By quantifying the risks of all accidents that can take place at a given plant, one may utilize the results to identify high risk accidents requiring immediate mitigation. One may also use QRA to compare the costs and benefits (as measured in terms of risk reduction) of optional mitigation measures.