Risk assessment/acceptance methods

Section 2 deals with flood risk analysis. The conceptual model somce pathway-receptor onsequence for flood risk analysis is presented and its components are analjraed further. The methodology to extract the predicted probabihty of coastal flooding from risk sources and pathways, as well as the expected damages from risk receptors are introduced and examined. Reliability analj is of a coastal system is also briefly discussed in the subsection dealing with the pathways of risk. Section 3 concentrates on risk assessment. Quantitative methods to define acceptable flooding... 

Risk-Based Inspection. Inspection programs developed using risk analysis methods are becoming increasingly popular (15,16) (see Hazard ANALYSIS AND RISK ASSESSMENT). In this approach, the frequency and type of in-service inspection (IS I) is determined by the probabiUstic risk assessment (PRA) of the inspection results. Here, the results might be a false acceptance of a part that will fail as well as the false rejection of a part that will not fail. Whether a plant or a consumer product, false acceptance of a defective part could lead to catastrophic failure and considerable cost. Also, the false rejection of parts may lead to unjustified, and sometimes exorbitant, costs of operation (2). Risk is defined as follows ... 

Risk analysis A methodical examination of a process plant and procedure that identifies hazards, assesses risks, and proposes measures that will reduce risks to an acceptable level. 

When performing human reliability assessment in CPQRA, a qualitative analysis to specify the various ways in which human error can occur in the situation of interest is necessary as the first stage of the procedure. A comprehensive and systematic method is essential for this. If, for example, an error with critical consequences for the system is not identified, then the analysis may produce a spurious impression that the level of risk is acceptably low. Errors with less serious consequences, but with greater likelihood of occurrence, may also not be considered if the modeling approach is inadequate. In the usual approach to human reliability assessment, there is little assistance for the analyst with regard to searching for potential errors. Often, only omissions of actions in proceduralized task steps are considered. 

The Rijnmond area is that part of the Rhine delta between Rotterdam and the North Sea. The Commission for the Safety of the Population at large (COVO) commissioned the study for six chemicals and the operations associated with them acrylonitrile, liquid ammonia, liquid chlorine, LNG, propylene, and part of a separation process (diethanolamine stripper of a hydrodesulfurizer). The study objectives were to evaluate methods of risk assessment and obtain experience with practical applications of these methods. The results were to be used to decide to what extent such methods can be used in formulating safety policy. The study was not concerned with the acceptability of risk or the acceptability of risk reducing measures. 

It is the general consensus within the worldwide fire community that the only proper way to evaluate the fire safety of products is to conduct full-scale tests or complete fire-risk assessments. Most of these tests were extracted from procedures developed by the American Society for Testing and Materials (ASTM) and the International Electrotechnical Commission (IEC). Because they are time tested, they are generally accepted methods to evaluate a given property. Where there were no universally accepted methods the UL developed its own. 

Today, when a pesticide with no detectable residues is registered for use, a Tolerance or maximum residue limit (MRL) is established at the lowest concentration level at which the method was validated. However, for risk assessment purposes it would be wrong to use this number in calculating the risk posed to humans by exposure to the pesticide from the consumption of the food product. This would be assuming that the amount of the pesticide present in all food products treated with the pesticide and for which no detectable residues were found is just less than the lowest level of method validation (LLMV). The assumption is wrong, but there is no better way of performing a risk assessment calculation unless the limit of detection (LOD) and limit of quantification (LOQ) of the method were clearly defined in a uniformly acceptable manner. 

Government risk assessment methods used to determine acceptable residues in foods (governed by tolerances) were not designed to detect or quantify the majority of these unique risks. 

The total risk assessment process used by the Swiss is shown in Fig. 38. In Switzerland, an acceptable individual risk has been established to be 3 x 10-/Vyear. It is interesting to note that this value is not far from that footnoted in Table VI, which converts to 10 3/year. But, methods of calculating probabilities in Refs. 41 and 42 are quite different. 

In use of risk assessment methods, you will find that the methodology for calculating overall risk probabilities is quite well defined. But, assigning realistic values to individual probabilities can be quite difficult, and a matter of personal opinion of the analyst. So, the analyst must have intimate knowledge of the system being evaluated, as well as all effects being considered, before he can make an acceptable risk assessment. 

Haynes alloy 25 (L605), composition of wear-resistant alloy, 7 22 It Haynes alloy 188, composition of wear-resistant alloy, 7 22 It Hayward Tyler agitator, 1 739 HAZARD I method, 11 449 Hazard acceptance, 13 170 Hazard Analysis and Critical Control Point (HACCP) protocol, 15 260 Hazard analysis and risk assessment,... 

In animal experiments exposures can be carefully controlled, and dose-response curves can be formally estimated. Extrapolating such information to the human situation is often done for regulatory purposes. There are several models for estimating a lifetime cancer risk in humans based on extrapolation from animal data. These models, however, are premised on empirically unverified assumptions that limit their usefulness for quantitative purposes. While quantitative cancer risk assessment is widely used, it is by no means universally accepted. Using different models, one can arrive at estimates of potential cancer incidence in humans that vary by several orders of magnitude for a given level of exposure. Such variations make it rather difficult to place confidence intervals around benefits estimations for regulatory purposes. Furthermore, low dose risk estimation methods have not been developed for chronic health effects other than cancer. The... 

The liquid and solid effluents are well characterized. As the ACW I Committee noted in its original and supplemental reports, the gaseous process emissions will have to be characterized for health risk assessments and environmental risk assessments required by EPA guidelines (NRC, 1999, 2000a). These results, along with the results of analyses of metals emissions (including chromium VI), can be used to assess the environmental impact of a facility through accepted risk-assessment methods (EPA, 1998). 

Some critical differences in risk assessment procedure lead to confusing situations on a worldwide basis. These differences are due to some very controversial areas of safety issues including the calculation of the acceptable daily intake (ADI), the assignment of the ADI to maximum residue limit (MRL)/tolerance, the validation of the analytical methods needed to regulate drug residues, and the fitness of legislation to toxicology. 

Finally, the diversity of extrapolation techniques relates to the diversity of technical solutions that have been defined in the face of the various extrapolation problems. Methods may range from simple to complex, or from empirical-statistical methods that describe sets of observations (but do not aim to explain them) to mechanism-based approaches (in which a hypothesized mechanism was guiding in the derivation of the extrapolation method). In addition, they may range from those routinely accepted in formal risk assessment frameworks to unique problem-specific approaches, and from laboratory-based extrapolations consisting of 1 or various kinds of modeling to physical experiments that are set up to mimic the situation of concern (with the aim to reduce the need for extrapolation modeling). 

The project enables risk assessments (or components thereof) to be performed using internationally accepted methods, and these assessments can then be shared to avoid duplication and optimize use of valuable resources for risk management. It also promotes sound science as a basis for risk management decisions, promotes transparency in risk assessment and reduces unnecessary testing of chemicals. Advances in scientific knowledge can be translated into new harmonized methods. 

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