Risk analysis reduction

Semi-Quantitative Risk Analysis Reduction Options 150... 

The objective of a risk analysis is to reduce the level of risk wherever practical. Much of the benefit of a risk analysis comes from the discipline which it imposes and the detailed understanding of the major contributors of the risk that follows. There is general agreement that if risks can be identified and analyzed, then measures for risk reduction can be effectively selected. 

The analysis of a risk—that is, its estimation—leads to the assessment of that risk and the decision-making processes of selecting the appropriate level of risk reduction. In most studies this is an iterative process of risk analysis and risk assessment until the risk is reduced to some specified level. The subjec t of acceptable or tolerable levels of risk that coiild be applied to decision making on risks is a complex subject which will not oe addressed in this section. 

The process by which the results of a risk analysis (i.e., risk estimates) are used to make decisions, either through relative ranking of risk-reduction strategies or through comparison with risk targets... 

The Chemical Process Industry (CPI) uses various quantitative and qualitative techniques to assess the reliability and risk of process equipment, process systems, and chemical manufacturing operations. These techniques identify the interactions of equipment, systems, and persons that have potentially undesirable consequences. In the case of reliability analyses, the undesirable consequences (e.g., plant shutdown, excessive downtime, or production of off-specification product) are those incidents which reduce system profitability through loss of production and increased maintenance costs. In the case of risk analyses, the primary concerns are human injuries, environmental impacts, and system damage caused by occurrence of fires, explosions, toxic material releases, and related hazards. Quantification of risk in terms of the severity of the consequences and the likelihood of occurrence provides the manager of the system with an important decisionmaking tool. By using the results of a quantitative risk analysis, we are better able to answer such questions as, Which of several candidate systems poses the least risk Are risk reduction modifications necessary and What modifications would be most effective in reducing risk ... 

This study investigated risks to the public from serious accidents which could occur at the industrial facilities in this part of Essex, U.K. Results are expressed as risk to an individual and societal risk from both existing and proposed installations. Risk indices were also determined for modified versions of the facilities to quantify the risk reduction from recommendations in the report. Nine industrial plants were analyzed along with hazardous material transport by water, road, rail and pipeline. The potential toxic, fire and explosion hazards were assessed for flammable liquids, ammonia, LPG, LNG, and hydrogen fluoride (HE). The 24 appendices to the report cover various aspects of the risk analysis. These include causes and effects of unconfined... 

Guidelines for Chemical Process Quantitative Risk Analysis (CPQRA Guidelines) builds on the earlier work to show the engineer how to make quantitative estimates of the risk of the hazards identified. The quantitative estimates can identify the major contributors to risk. They can also help to define the most effective ways to a safer process by indicating relative risk reduction from proposed alternate process safeguards and measures. 

Deciding which risk-reduction method to use maybe difficult. In many instances, appropriate decisions can be made without resorting to quantitative techniques. However, in some cases, particularly when the options are costly, quantitative risk analysis (QRA) and risk-based decision-making approaches may be an effective basis for measuring the improvement in safety arising from the proposed options. These approaches can also be used in prioritizing safety improvements and balancing cost and production issues. 

Risk is defined as a measure of human injury, environmental damage, or economic loss in terms of both the incident likelihood (probability) and the magnitude of the loss or injury (consequence) (AICHE/CCPS, Guidelines for Chemical Process Quantitative Risk Analysis, 2d ed., American Institute of Chemical Engineers, New York, 2000, pp. 5-6). It is important that both likelihood and consequence be included in risk. For instance, seat belt use is based on a reduction in the consequences of an accident. However, many people argue against seat belts based on probabilities, which is an incorrect application of the risk concept. 

Section 2 above implies that a manufacturer must carry out a risk analysis. A harmonised standard is available on this topic, EN 14 971, which amplifies the methodology for risk analysis, elimination or reduction required by section 2. 

Thus, the risk analysis must be well prepared, meaning that the scope of the analysis must be clearly defined data must be available and evaluated, to define the safe process conditions and the critical limits. Then, and only then, the systematic search for process deviations from the safe conditions can be started. The identified deviations lead to the definition of scenarios, which can be assessed in terms of severity and probability of occurrence. This work can advantageously be summarized in a risk profile, enhancing the major risks that are beyond the accepted limits. For these risks, reduction measures can then be defined. The residual risk, that is, the risk remaining after implementation of the measures, can be assessed as before and documented in a residual risk profile showing the progress of the analysis and the risk improvement. These steps are reviewed in the next sections. 

Based on knowledge of chance and effect (risk characterization), a first risk classification can be made. This will offer some insight into the priorities on risk avoidance or reduction, but it might leave a number of risks open for further risk analysis. Risk communication through the label or by other means then might become necessary. 

Levinson A (1991) Risk communication Talking about risk reduction instead of acceptable risk. In Zervos C, Knox K, Abramson L, Coppock R, eds. Risk analysis Prospects and analysis. New York, NY, Plenum Press, pp. 387-392. 

D.M. Riley, B. Fischhoff, M.J. Small and P. Fischbeck, Evaluating the Effectiveness of Risk-Reduction Strategies for Consumer Chemical Products, Risk Analysis, 2001, 21, 357. 

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