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Discipline guidance - Guidance for retrospective application
Guidance for retrospective application and non 61508 based standards on
- HSE recognises BS IEC 61511 as relevant good practice for safety
functions implemented by safety instrumented systems in the Process
Industry sector in the context of assessing compliance with the law in
individual cases and the use of good practice: http://www.hse.gov.uk/dst/alarp2.htm
- Hardware and Software Issues.
2.1 This standard can be used when reviewing
health or safety measures on an existing plant/installation or situation
(such as when considering retrofitting, safety reviews or upgrades),
duty holders should compare existing measures against current good
practice. The good practice measures set out should be adopted so far as
is reasonably practicable. It might not be reasonably practicable to
apply retrospectively to existing plant, for example, all the good
practice expected for new plant. However, there may still be ways to
reduce the risk e.g. by partial solutions, alternative measures
2.2 Based on this information, it would appear
logical that, if a COMAH site hasn’t already done so, it should review
its existing measures for managing the risks from use of safety
instrumented systems against the provisions of BS IEC 61511. As a
general rule, sites should be aware of which safety-instrumented
functions are the most critical. It would make sense, therefore, that
every site using non-61508 based standards should carry out a review of
at least a sample of their installation to get some idea of how well the
existing design compares with those required by BS IEC 61511. The
findings from this review should then be used to make a decision as to
whether or not further work is required.
- Management Systems Issues.
3.1 About half of the provisions in BS IEC 61511
relate to management systems, rather than pure technological issues. It
is strongly recommended that sites review any existing relevant systems
against BS IEC 61511 as a part of their ongoing review of safety