Acceptable risk and safety priorities

If the consequences of an incident can be predicted quantitatively (property loss and the possible number of fatalities), then a quantitive assessment can be made of the risk. 

Quantitive assessment f Frequency of 1 f loss per 1 of risk — I incident f incident  

If the loss can be measured in money, the cash value of the risk can be compared with the cost of safety equipment or design changes to reduce the risk. In this way, decisions on safety can be made in the same way as other design decisions to give the best return of the money invested. 

Hazards invariably endanger life as well as property, and any attempt to make cost comparisons will be difficult and controversial. It can be argued that no risk to life should be accepted. However, resources are always limited and some way of establishing safety priorities is needed. 

One approach is to compare the risks, calculated from a hazard analysis, with risks that are generally considered acceptable such as, the average risks in the particular industry, and the kind of risks that people accept voluntarily. One measure of the risk to life is the Fatal Accident Frequency Rate (FAFR), defined as the number of deaths per 108 working hours. This is equivalent to the number of deaths in a group of 1000 men over their working lives. The FAFR can be calculated from statistical data for various industries and activities some of the published values are shown in Tables 9.8 and 9.9. Table 9.8 shows the relative position of the chemical industry compared with other industries Table 9.9 gives values for some of the risks that people accept voluntarily. 

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The nuclear industry, for example, has a very low social tolerance of voluntary exposure to risk. The same is true in civil aviation, so here the trade-offs tend to be made in favour of safety initiatives, while targeting full and centralised coherence (and working to prevent isolated local actions). The same has not been true (at least until recently) in international finance, medicine, fishing and motoring, to cite just a few examples in these cases, senior management—or the institution in the broad sense—gives priority to exposure to risk and safety activities are mostly conducted at the local level, and it is accepted that they are local and limited in scope. 

Considering the NORSOK Standard Z-013 model for risk estimation, analysis and evaluation this proposed framework can be used as a framework to deal further risk reducing measures after achieving the acceptable risk levels and there still safety improvements that can be implemented. And also held decisions about which risk reduction measures should be implemented, the priority of each action, the risk involved in different parts of the process. 

Maintenance standards are a matter for the organisation to determine there must be a cost balance between intervention with normal operations by planned maintenance and the acceptance of losses because of breakdowns or other failures. From the health and safety aspect, however, defects requiring maintenance attention which have led or could lead to increased risk for the workforce should receive a high priority. Linking inspections with maintenance can be useful, so that work areas and equipment are checked regularly for present and possible future defects. Some plant items may be subject to statutory maintenance requirements, and the manufacturer s instructions in this respect should be complied with as well. 

Tasks with high risk are given a higher priority and may require immediate actions. A step may, on the other hand, include tasks with only marginal risk and have limited safety requirements. If a job step is shown to have catastrophic potential, the job is immediately shut down until the risk is brought to an acceptable level with immediate controls implemented. 

The role of risk assessment is to provide the necessary information on which to make decisions regarding the cost-effective commitment of resources to prevent loss. Risk assessment can also be used to determine if appropriate action is acceptable where it is impractical to totally eliminate hazards. Risk assessment will indicate where the greatest gains can be made with the least effort, and which action(s) should be given priority. This prioritization will bring about greater safety with the minimum level of effort. 

Software requirements in non-critical software are usually tested wifli a coverage that depends on factors such as ftie quality system, criticahty to the project, resources and schedule. Execution priority and regression execution will also depend on these factors. In the case of safety critical software it cannot be accepted to work in the same way. Risk mitigations shall be completely and reliably tested before releasing to the public. In oftier words, test coverage for risk related requirements shall be 100% in all cases. This is a very important check that ensures that risk mitigations are put into place and effectively work. 

Based on today s methods and results of probabilistic safety assessments (PSAs), it is acceptable and considered safe to measure and adjust maintenance strategies according to the frequencies involved and levels of risk (risk informed strategies). The risk informed approach gives better transparency and background for maintenance priorities and for the cost effectiveness of maintenance efforts (personnel, money, dose, waste). The IAEA has discussed this approach in greater depth in Refs [8,9]. 

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