The question of whether companies follow good site safety practices is an interesting one. Firstly, what do we mean by good site safety practices?  I think most companies believe they follow good site safety practices but do they really? Are they really measuring and tracking this?

The basis of having good site safety practices is how well companies follow Clause 16 of IEC61511 for Operations and Maintenance.  For example, how well are the maintenance team sticking to the proof test intervals defined in the SRS and if not, by how much are they missing the time interval? It can be shown that once the Proof Test interval exceeds more than 10% of the original interval, as defined and used in the Safety Instrumented Function (SIF), SIL verification, then the risk reduction will reduce and will effectively increase the Probability of Failing on Demand in Low Demand application SIFs.  Another key indicator is whether the Useful Life of the SIF devices is being tracked and the devices are being replaced/refurbished before they reach the end of the Useful Life; instead of implementing a run-to-fail strategy. 

Another consideration is the competency, training and assessments of the maintenance staff, plus number of audits and/or functional safety assessments performed.  For example, is the periodic SIS performance assessment (Functional Safety Assessment 4) being undertaken?  The 2016 edition of IEC61511 now requires a periodic performance review to be carried out.  But how many companies are really doing this?

What other metrics are being tracked in order to assess performance?  Are real or false trips being tracked; near misses and/or incidents; alarms; failures; and whether repair and restore times are within requirements. All these should be being tracked and subject to audit.

To understand better how companies perform site practices, they can take the challenge by initially completing the questionnaire which can be found at The Site Safety Index web site which will provide a ranking based upon 5 levels of Site Safety Index (SSI): SSI0 to SSI4.  

SSI0 will indicate a poor functional safety culture with a bear, minimum approach, missed and/or delayed proof testing; run to fail strategy; higher initial failure rates; more incidents, ineffective repairs and/or reactive maintenance, compared to SSI4 where testing is performed per the SRS, repairs are implemented effectively and in-keeping with the Mean Time To Restore requirements; useful life is being tracked and adhered to; personnel and SIS performance assessments are being undertaken; performance data is used for improvements, where the safety culture is much more endemic.  Companies should at least be at SSI2, which indicates a “good” level of maintenance capabilities.

One other thing that should be considered is the cost of downtime and/or startup after a trip. Not only is this expensive but it also increases risk.  By spending more on proactive maintenance practices and less on reactive maintenance following incidents, companies will improve ROI, at the same time as effectively mitigating risk.

If this article has peaked your interest, then look out for the upcoming webinar on the subject, which will highlight more on this issue.

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Tagged as:     Steve Gandy     SRS     Site Safety Index     SIS     SIL verification     SIF     proof test intervals     IEC61511     Failure Rates  

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