PSI - Issue 28

Dmitry O. Reznikov et al. / Procedia Structural Integrity 28 (2020) 1360–1368 D.Reznikov, N.Makhutov,O.Yudina / Structural Integrity Procedia 00 (2019) 000–000

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2 { } 10 [ ] R R    (5) A negligible (broadly acceptable) individual risk is a risk comparable to other risks that people face in their everyday life and which are considered insignificant (for example, the risk associated with a meteorite falling on a residential building). The limit value (upper limit) of negligible risk is defined by the regulatory authorities of the country with accounting for the level of its economic development, safety culture and attitude to human life. In industrially developed countries the probability of death per year { R i } =10 -6 (1 in a million) has been established as the upper limit of broadly acceptable (negligible) individual risk. Usually it is established two orders of magnitude below the limit value of tolerable risks (Health and Safety Executive, 2001; Health and Safety Executive, 2002). The criteria values { R i } and [ R i ] divide the probability axes of individual risks into the regions of broadly acceptable R i <{ R i }, tolerable({ R i } < R i <[ R i ]) and unacceptable ( R i >[ R i ]) risks (fig.2): - If the HIF generates risk that are estivated according to equation (1) falls into the region III of broadly acceptable(negligible) risks, the legislator does not require that any additional measures aimed at risks reduction be taken. The operation of the facility that generates such a low level of risk can be continued without any additional efforts aimed at risk reduction. Accordingly it is believed that the operation of industrial facilities that generate such small risks may not be controlled by technical supervision authorities. -When the individual risks associated with operation of the HIF lie within unacceptable region I, any regular operation of the facility is prohibited until the moment when protective measures are implemented that allow transferring risks to the region of tolerable (conditionally acceptable) ones. Moreover risk reduction to a level lower than [ R i ] should be carried out, regardless of the cost of protective measures. - If the individual risk induced by HIF belongs to the region of tolerable (conditionally acceptable) risks than a special risk reduction strategy should be implemented that stipulates that these risks are to be reduced to a specific level R i * that is practically feasible. These risks the society is ready to put up with in order to secure benefits from HIF in the condition that these risks are carefully monitored and minimized in compliance with practical considerations according to ALARP principle should be benefits of operating the system, people (or society as a whole) are willing. According to standards [5-8], conditionally acceptable risks lie in the range: 6 10 i i     . 3. Application of ALARP principle in individual risk management As was indicated in the previous section if the facility in question generates risks falling into the regions of broadly acceptable (negligible) or unacceptable risks than risk reduction procedures are quite simple: - If risks induced by the facility fall in to the region III of broadly acceptable risks than no special risk reduction actions are required. It is only necessary to monitor the state of the system, confirming that over time risks do not exceed the limit of value of broadly acceptable risks. - If the operation of the facility causes risks falling into the region I unacceptable risks than any regular operation of such a facility should be immediately stopped and urgent measures are to be taken to reduce the risk to the tolerable level. Risk management activity in the case when risks generated by the facility at hand fall into the region of conditionally acceptable risks require more detailed consideration. As was pointed out above risk regulation should take into account two competing groups of requirements related to ensuring safety and economic efficiency. Obviously due to limited resources and the imperfection of existing technologies, an excessive decrease in the value of individual risk is practically impossible and would lead to the fact that any economic activity become unprofitable. Therefore activities that are carried out in the region of conditionally acceptable risks must comply with some compromise principle that provides for the implementation of measures aimed at reducing risks to the level of practical feasibility, which is also called the level of tolerable risk R i * . Thus, if risks associated with the operation of a technical facility fall into the region of conditionally acceptable risks, the company operating this facility should take measures to reduce the risk to the level that is considered as practical. Here term “practical” 6 4 { } 10 R    [ ]     i tol R R i  10 i   .