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Anomaly between BS62061 and 61508

Rob Eagle

I am designing a control system for a very big heavy door which has the capability to crush a person and potentially to death although extremely unlikely.  In determining the SIL requirement for the system using BS61508-5 I get the following:



 



Looking at Table E.1 I can derive a qualitative assessment



 



Consequence – Serious permanent injury to one or more persons; death to one person – C2



Frequency of exposure – Rare to more often exposure in the hazard zone – F1



Probability of avoiding the hazard – Possible under certain conditions – P1



Probability of the unwanted event – A slight probability – W2



 



Looking at Figure E.2 this equates to ‘a’ = “No special safety requirements”



 



However if I use BS62061 looking at table A.1 I find “Irreversible: death, losing an eye or arm” Severity Se = 4, then I go to Table A.6 and irrespective of any other criteria it demands a minimum of SIL2.



 



The question is why is there such disparity?  And which is correct?



Thank you,



Rob


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  • 0
    Robert,



    Just a few thoughts...



    In the context of UK Health and safety law neither path that you describe is, on its own, entirely credible in my view.



    The qualitative approach really requires a multidisciplinary risk and hazard assessment (e..g. HAZOP review) with all the relevant stakeholders, including representatives of the operations and maintenance staff, that is both consistent with the relevant HSE risk assessment guidelines and the ALARP principle?

    http://www.hse.gov.uk/risk/index.htm

    http://www.hse.gov.uk/risk/resources.htm



    There is a lot of inter-disciplinary and multi-disciplinary things to think about before applying the relevant quantitative and qualitative disciplinary safety standards to your design. 



    Below is a link to an unfortunate and sad example of a crush accident that happened in the process of operating a crane; that the HSE investigated and prosecuted. 



    Do you think it possible to prevent accidents such as this one below, by the following just the narrow disciplinary methodologies you have outlined?



    Jaguar Land Rover in court over Halewood death (11 September 2015)

     http://press.hse.gov.uk/2015/jaguar-land-rover-in-court-over-halewood-death/





    [You may counter that the example of operating a crane is different and complex compared with operating your door, but you have not told the reader whether or not there is more than one way or mode of operating the door, or indeed if extra modes of operation exist for maintaining the door. You have not told us about operator and maintenance training requirements, the practicality and feasibility for incorporating fully interlocked human exclusion area around the hazardous crush zone whilst the door is operating (ALARP), the frequency at which the door must open and close (operations per day/hour), the hazards associated with maintaining the equipment, whether or not untrained and inexperienced staff will be in the area when the door is operating, the potential for noise and other distractions leading to operator mistakes etc etc]



    Please don't fall into the trap of trying to solve multi-disciplinary problems solely from within the framework of a single way of thinking.



    James
Reply
  • 0
    Robert,



    Just a few thoughts...



    In the context of UK Health and safety law neither path that you describe is, on its own, entirely credible in my view.



    The qualitative approach really requires a multidisciplinary risk and hazard assessment (e..g. HAZOP review) with all the relevant stakeholders, including representatives of the operations and maintenance staff, that is both consistent with the relevant HSE risk assessment guidelines and the ALARP principle?

    http://www.hse.gov.uk/risk/index.htm

    http://www.hse.gov.uk/risk/resources.htm



    There is a lot of inter-disciplinary and multi-disciplinary things to think about before applying the relevant quantitative and qualitative disciplinary safety standards to your design. 



    Below is a link to an unfortunate and sad example of a crush accident that happened in the process of operating a crane; that the HSE investigated and prosecuted. 



    Do you think it possible to prevent accidents such as this one below, by the following just the narrow disciplinary methodologies you have outlined?



    Jaguar Land Rover in court over Halewood death (11 September 2015)

     http://press.hse.gov.uk/2015/jaguar-land-rover-in-court-over-halewood-death/





    [You may counter that the example of operating a crane is different and complex compared with operating your door, but you have not told the reader whether or not there is more than one way or mode of operating the door, or indeed if extra modes of operation exist for maintaining the door. You have not told us about operator and maintenance training requirements, the practicality and feasibility for incorporating fully interlocked human exclusion area around the hazardous crush zone whilst the door is operating (ALARP), the frequency at which the door must open and close (operations per day/hour), the hazards associated with maintaining the equipment, whether or not untrained and inexperienced staff will be in the area when the door is operating, the potential for noise and other distractions leading to operator mistakes etc etc]



    Please don't fall into the trap of trying to solve multi-disciplinary problems solely from within the framework of a single way of thinking.



    James
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