In several of our technical papers over the years, we have noticed that failure rates for the manufacturer, model number are different at different sites, even when the processes were quite similar.  When I have mentioned this to end users and manufacturers, often the response is “Yes, I have noticed.  Why does this happen?”  exida finally has enough field failure data to create a simple model for this based on concepts from IEC 61508.  We call our model the Site Safety Index™ (SSI).

A wide range of factors seem to contribute to the SSI.  After gathering lots of expert opinion on these factors, it became clear that they had everything to do with the requirements of IEC 61511.  In other words, IEC 61511 tells us the right things to do.  One must then simply ask, are they being done?  Of course not everything listed in IEC 61511 impacts failure rates of devices, so exida gathered input from end users and created a simple questionnaire SSI evaluation.  To see how well your site does, click here. To read more about the evaluation concept, see our White Paper titled Assessing Safety Culture via the Site Safety Index.  

Given an evaluation, the impact of that rating can be seen by using the model in a PFDavg calculation.   The SSI model is being incorporated into the exSILentia® tool from exida for that purpose.  exida is also adding new failure rate tables to our FMEDA reports starting with final element devices.  To see an example calculation and read more about the failure rate modeling, see our White Paper titled Quantifying the Impacts of Human Factors on Functional Safety. 

The SSI is a good start but it is a simple model meant to be very easy to use.  As more data becomes available, the models will be enhanced.  But for now it is great to be able to actually model an issue that many have agreed is very real.  One of the end users who reviewed the initial model is using it to justify better safety culture.  Another is using it to show the impact of poor safety culture.  This seems like good stuff.