Table 54 Screening criteria for single external events: C1/Severity C2/Frequency C3/Distance C4/Inclusion C5/Warning C6/Applicability Site-related Site-related Site-related Impact screening Impact screening screening criteria screening criteria screening criteria criteria criteria Screened-out if: Screened-out if: Screened-out if: Screened-out Screened-out if: Screened-out if: if: The event has a The event has a The event The event The event is not damage considerably cannot occur The event can develops in applicable to potential that is lower frequency close enough to be included in such a slow rate the site because less or equal to of occurrence the plant to the definition that there is of other another event than events with affect it. of another enough time to reasons. that the plant is similar event. initiate already uncertainties and counteractions. dimensioned cannot result in for. worse consequences. Screening Criteria for Multiple External Events A combination of external events is considered to be relevant if the combination has more severe or additional effects on the compared to those of the initial single external event. In to arrive at a manageable amount of potential combined external events, the following screening criteria are used based on reference [71]: Table 55 Screening criteria for multiple external events: M1 / Definition M2 / Independence M3 / Impact C1 C6 – Screened-out if: Screened-out if: Screened-out if: Screened-out if: The multiple events The events occur The events do not Any of the single are included in the independently of each independently in time (see external events definition of a single other in time criterion M2) criteria apply to the event, which is already AND AND potential multiple analysed for the plant The probability of The events affect the same plant events simultaneous occurrence safety function is low, i.e., below single AND event frequency The combined effect on the screening criteria C2 safety function is not greater than the effect from the most severe of the single events involved
Table 54 Screening criteria for single external events: C1/Severity Site-related screening criteria C2/Frequency Site-related screening criteria C3/Distance Site-related screening criteria C4/Inclusion Impact screening criteria C5/Warning Impact screening criteria C6/Applicability Screened-out if: The event has a damage potential that is less or equal to another event that the plant is already dimensioned for. Screened-out if: The event has a considerably lower frequency of occurrence than events with similar uncertainties and cannot result in worse consequences. Screened-out if: The event cannot occur close enough to the plant to affect it. Screened-out if: The event can be included in the definition of another event. Screened-out if: The event develops in such a slow rate that there is enough time to initiate counteractions. Screened-out if: The event is not applicable to the site because of other reasons. Screening Criteria for Multiple External Events A combination of external events is considered to be relevant if the combination has more severe or additional effects on the compared to those of the initial single external event. In to arrive at a manageable amount of potential combined external events, the following screening criteria are used based on reference [71]: Table 55 Screening criteria for multiple external events: M1 / Definition M2 / Independence M3 / Impact C1 – C6 Screened-out if: The multiple events are included in the definition of a single event, which is already analysed for the plant Screened-out if: The events occur independently of each other in time AND The probability of simultaneous occurrence is low, i.e., below single event frequency screening criteria C2 Screened-out if: The events do not independently in time (see criterion M2) AND The events affect the same plant safety function AND The combined effect on the safety function is not greater than the effect from the most severe of the single events involved Screened-out if: Any of the single external events criteria apply to the potential multiple events
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