# THE RAILWAYS (SAFETY MANAGEMENT) REGULATIONS (NORTHERN IRELAND) 2006, Paragraph 10


(1) The second assessment step shall deem the safety performance acceptable if the MWA does not exceed the NRV plus a 20% range of tolerance.
(2) If this condition is not satisfied, the Department for Infrastructure must obtain the specifics of the single highest-consequence accident, in terms of FWSIs, in the most recent years of observation as referred to in paragraph 6, excluding the years used to set the NRV.
(3) If this single accident is more severe, in terms of consequences, than the most severe single accident included in the data used for setting the NRV, it must be excluded from the statistics.
(4) The MWA is then recalculated to check whether it lies within the above-mentioned range of tolerance. If this is the case, the safety performance must be considered acceptable. If this is not the case, the procedure must continue with the third assessment step.

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Source: https://www.legislation.gov.uk/nisr/2006/237/schedule/7/paragraph/10 (the official version)
Page: https://openlegislation.uk/railways-safety-management-regulations-northern-ireland-2006/schedule-7/paragraph-10
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.