Discipline guidance - Guidance for retrospective application

Guidance for retrospective application and non 61508 based standards on COMAH sites.

1. 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: Risk management: Expert guidance.


2. 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 etc."
   
   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.
   
3. 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 management systems."