The application of QRA should not be limited to large complex expensive studies. It is a technique which can be used quickly and cheaply to help structure the solution to problems for which the solution is not intuitively obvious.
Figure 1: QRA for small as well as large studies
Without the quantification of risk in some situations, we may be in danger of allocating scarce resources for little benefit.
Figure 2: Quantitative versus qualitative assessment
Risk is often defined as a function of the chance that a specified undesired event will occur and the severity of the consequences of the event. When risk is assessed qualitatively a Risk Matrix may be used. When assessed quantitatively, risk is derived from the product of chance and potential consequence. For QRA purposes, chance is usually expressed as the frequency of occurrence. If no attempt is made to estimate the frequency, we may be driven by the consequence into investing heavily on risk reduction measures which are ineffective.
Figure 3: The importance of quantification
Many are concerned about the accuracy of the quantification and use this as a reason why the technique should not be applied. However, whether we realise it or not, we are always making implicit comparative quantification whenever we make a decision. What we gain with QRA is a structured assessment of the risk instead of an intuitive type of quantification. The numbers used in a QRA may be very approximate, but at least we have broken down the problem into its basic elements and made an objective judgement for each of these elements rather than an overall judgement on a largely subjective basis. However, when there are a large number of situations to be analysed, it may be advantageous to precede the QRA study by a consequence analysis. This may filter out the cases where a full QRA would not add additional information.
Concerns Regarding Misuse of QRA
There are several situations in which QRA has and is being misused. This misuse is not necessarily deliberate but can arise from a misunderstanding of the QRA process.
2.1 Reducing risk rather than proving acceptability
A common form of misuse results from the desire to prove that a deviation from company standards or practices is 'acceptably' safe. As with any type of study, it is always possible for the less scrupulous to steer the process so that the conclusions are biased towards a preconceived goal. No-one gains from this. Unless the study is carried out objectively and with an open mind, ill-conceived decisions may be made and the opportunity missed to reduce risks. In principle, the use of QRA to challenge the need for retrofitting to revised standards and to aid in the development of standards and procedures should be encouraged. However, such assessments must be carried out objectively with the overall aim of reducing risks to ALARP (as low as reasonably practicable). Under no circumstances should QRA be used to justify or encourage risk taking.
Figure 4: Reducing risk rather than proving acceptability
Reducing risk to ALARP rather than to a fixed level
Adoption of the concept that something can be 'acceptably' safe is also a source of misuse. The only level of risk which is truly acceptable is zero. Whatever we do has a risk associated with it and therefore, in practice, an acceptable risk level is unattainable. Society and industry tend to agree that the dividing line between tolerable and intolerable risk of fatality to those individuals that obtain commensurate benefits from the activity is around 10-3 per year. Below this level, provided individuals are aware of the risks, enjoy some commensurate benefit and everything reasonable has been done to reduce the risk, risks may be tolerated. The aim of the management of risks in this tolerable region is not to reduce risks to some fixed 'acceptable' level but to reduce them until they are ALARP. The resulting actual risk levels could thereby be different for different projects but with the common feature that they are ALARP for that project.
Figure 5: Reducing risk to ALARP rather than to a fixed level
Representing reality rather than force fitting into a rigid model
Another criticism of the way some of our QRAs are carried out is that they are too mechanistic. Risk assessment is a process by which one tries to represent reality by a much simplified model. It is important that the modelling should not be forced into a preconceived model template structure, but that each study should be modelled to include all areas which impact the risk levels.
Figure 6:Representing reality rather than force-fitting into a rigid model
One criticism of the application of QRA in the past is that studies have focused too much on mitigation of the consequences of hazardous or top events and too little attention has been given to looking for ways to reduce the likelihood or eliminate the top event itself. Once the top events have been identified, their occurrence should not just be accepted but effort should be spent on seeking ways to eliminate them - prevention is better than cure!
Comparing like with like
It is also important that the right boundaries are drawn around the options so that one is comparing like with like.
Figure 7: QRA: comparing like with like
QRA specialists must not work in isolation
In some projects, QRA is still regarded as the sole province of QRA experts. A consequence of this is that the experts, usually consultants, may be asked to carry out a QRA study with insufficient thought having been given to the objectives and benefits of the study. Also, there is a danger that the study will be carried out with a minimum involvement of those that are directly involved in the business being analysed. The possibility then exists that the assumptions (including the operating philosophy) and data used will bear little relationship with reality. The study is then of little value. It is imperative that the relevant staff are involved throughout the study to ensure that the right assumptions are being made and are correctly used. It is also essential that any assumptions made in a QRA study of new projects are carried through into the HSE Case. Also, for existing facilities, the results of a QRA should be fed back into the HSE Case.
Figure 8: QRA studies: QRA specialists must not work in isolation
Handling data
The blind use of data needs to be avoided. There are various sources of data. However, not all are reliable and not all will be applicable to the operation under study. When the reliability or applicability of the available data is in question it is important that this is highlighted. For data which has a significant impact on the risk picture, a separate study should be made to evaluate the probable range of uncertainty. Sensitivity runs should then be carried out to test the robustness of the analysis.
For cases where the data is so uncertain that no conclusions can be drawn regarding the relative safety of the options considered, this should be highlighted in the report.
Figure 9: Handling data uncertainty
Using the correct level of detail
Significant errors can be made in QRA by not using the level of detail appropriate to the objective of the study. The level of detail should be selected such that, for instance, it is possible to identify which combination of event size and probability contributes most to the risk of a particular operation.
Figure 10: QRA: using the correct level of detail