Risk Criteria

As described previously in this Chapter, risk assessment involves imeertainties. Therefore it may not be suitable to use risk criteria as inflexible rules. The rqrplication of numerical risk criteria may not always be appropriate because of uncertainties in inputs. Accordingly, acceptance of a safety case is unlikely to be based solely on a numerical assessment of risk. 

Risk criteria may be different for different individuals. They would also vary between societies and alter with time, accident experience and changing expectation of life. Risk criteria can therefore only assist judgements and be used as guidelines for decision making. 

In different industries, risk criteria are also different. For example, in the aviation industry, a failure with catastrophic effects must have a frequency less than 10 per aircraft flying hour. In the nuclear industry, the basic principles of the safety policy recommended by the International Commission Radiologicrd Protection (ICRP) are that no practice shall be adopted unless it has a positive net benefit that all exposures shall be kept As Low As Reasonably Achievable (ALARA), taking economic and social factors into account and that individual radiation doses shall not exceed specific criteria (ICRP (1977)). There are no explicit criteria used by ICRP. 

As far as risk criteria for ships are concerned, the general criteria may include (1) the activity should not impose any risks which can reasonably be avoided (2) the risks should not be disproportionate to the benefits (3) the risks should not be unduly concentrated on particular individuals and (4) the risks of catastrophic accidents should be a small proportion of the total (Spouse (1997)). More specifically, individual risk criteria and social risk criteria need to be 

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Arrester Testing and Standards Regulatory and approval agencies and insurers impose acceptance testing requirements, sometimes as part of certification standards. The user may also request testing to demonstrate specific performance needs, just as the manufacturer can help develop standards. These interrelationships have resulted in several new and updated performance test procedures. Listing of an arrester by a testing laboratoiy refers only to performance under a defined set of test conditions. The flame arrester user should develop specific application requirements based on the service involved and the safety and risk criteria adopted. 

While the F-N curve is a cumulative illustration, the risk profile shows the expected frequency of accidents of a particular category or level of consequence. The diagonal line is a line of constant risk defined such that the product of expected frequency and consequence is a constant at each point along the line. " As the consequences of accidents go up, the expected frequency should go down in order for the risk to remain constant. As the example illustrates, if a portion of the histogram sticks its head up above the line (i.e., a particular type of accident contributes more than its fair share of the risk), then that risk is inconsistent with the risk presented by other accident types. (Note There is no requirement that you use a line of constant risk other more appropriate risk criteria for your application can be easily defined and displayed on the graph.)... 

Health and Safety Executive (HSE), Risk Criteria for Land-Use Planning in the Vicinity of Major Industrial Hazards, London HMSO, 1989. 

S. B. Gibson, The Use of Risk Criteria in the Chemical Industry, ASME Winter Annual Meeting, November 30-December 1, 1988. 

Objective-based risk criteria established as goals or guidelines for performance... 

Starr, C., 1980, Risk Criteria for Nuclear Power Plants A Pragmatic Proposal ANS/ENS International Conference, Washington, DC, November 16-21. 

Flashpoint is the temperature at which an inflammable liquid builds enough vapour so that this, together with air, forms an inflammable mixture in the presence of an igniting flame.The inflammation has to be very brief when this parameter is measured. If the combustion lasts for longer than five seconds, this temperature is defined as fire point. Fire point is never used because it is really difficult to obtain an accurate value. Flashpoint is the most important parameter in fire hazard. It plays an essential role in the determination of risk criteria related to the inflammability of a substance. 

O A risk assessment should be performed at presentation of febrile neutropenia to identify low-risk patients for potential outpatient treatment. Patients who do not meet low-risk criteria should be hospitalized for immediate parenteral administration of broad-spectrum antibacterials before culture results are obtained. 

The company has developed internal aggregate risk criteria. A comparison of these criteria with the calculated aggregate risk for personnel occupying the cafeteria shown in Figure 4.7 indicates the calculated aggregate risk curve is above the upper limit of tolerability for high values of N. 

New South Wales. "Risk Criteria for Land Use Safety Planning." Hazardous Industry Planning Advisory Paper No. 4. Department of Planning, Sydney. 1990. 

Figures 6.3 and 6.4 show the adjusted F-N curves. With this risk reduction, the company s aggregate risk criteria would be met Therefore, the emergency shutdown system was installed and no further action was required.

For companies to make risk-based decisions from risk screening or quantitative risk assessments, company-specific risk tolerance criteria or methodologies should be developed for both individual risk and aggregate risk. Chapter 4 provides a discussion of risk criteria and methodologies, and offers guidance for companies to consider in developing their own approaches to risk tolerability. 

Health and Safety Executive. "Risk Criteria for land-use planning in the vicinity of major industrial hazards." London, HMSO. 1989. 

Layers-of-protection analysis (LOPA) is a semiquantitative methodology for analyzing and assessing risk. It is typically applied after a qualitative hazards analysis has been completed, which provides the LOPA team with a listing of hazard scenarios with associated safeguards for consideration. LOPA uses simplified methods to characterize the process risk based on the frequency of occurrence and consequence severity of potential hazard scenarios. The process risk is compared to the owner/operator risk criteria. When the process risk exceeds the risk criteria, protection layers are identified that reduce the process risk to the risk criteria. 

An H RA involves a review of the process design and its control, operation, and maintenance practices. The review is conducted by a multidisciplinary team with expertise in the design and operation of the process unit. The team uses a systematic screening process to determine how deviations from normal operation lead to process hazards. The H RA identifies areas where the process risk is too high, requiring the implementation of safety functions. The team s objective is to reduce the risk to below the owner/operator s risk criteria. 

The gap between the process risk and the owner/operator s risk criteria establishes the requirements for risk reduction. The risk gap can be managed by a single safety function or by multiple functions allocated to protection layers. The team defines the risk reduction that must be provided by each safety function and allocates the safety function to a protection layer that is designed and managed to achieve the allocated risk reduction. 

Usually the petroleum industry level of risk for a particular facility is may be based one of two parameters. The average risk to the individual (FAR or PLL) or the risk of a catastrophic event at the facility (QRA). The risk criteria can be specified in two manners. Risk per year (annual) or facility risk (lifetime). For purposes of Consistency and familiarity all quantifiable risks are normally specified as annually. Where value analysis is applied for cost comparisons of protection options, a lifetime risk figure is normally used. 

Layer of Protection Analysis (LOPA) Scenario- based Order-of- magnitude By preidentified scenario Processes likely to require independent protection layers, such as safety instrumented systems, to meet predefined risk criteria Dependent on comprehensiveness of scenario list identified by other method(s) Higher... 

If the level of risk does not meet the risk criteria, then additional protection is required. The options for reducing the risk are identified and selected and the analysis is recalculated to determine the impact on the risk. Some options provide significant risk reduction others have very little impact on the risk. 

For the purpose of prioritising regulatory action under REACH, this thesis proposes to reduce the nine risk criteria identified by Klinke and Renn to four categories that can be used to characterise risk levels hazard, exposure, social mobilisation and probability. The grouping of the nine specific risk criteria into the four fundamental prioritisation criteria relevant for regulatory chemical risk management is shown in Table 5.6. 

Automatic bans for carcinogenic, mutagenic or reprotoxic (CMR) substances following the restrictions procedure under Directive 76/769 have been excluded (step 2) because these will continue to apply under REACH. The result of the risk criteria evaluation for each substance according to the decision-making matrix is shown in Table 6.1 (step 3). Based on the selection procedure detailed in Section 5.3.2, the most suitable regulatory outcome... 

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