4. Methods for assessing the probability of failure of safety devices

As we have already seen, risk control is based on MMRs, which can be SISs, SAMSs or safety devices. It should be pointed out that a safety device, whether active or passive, is liable to fail. For example :

• • A fire protection wall will only fulfil its safety function if it has been correctly dimensioned, and if its integrity is maintained and monitored over time.

• • A safety valve on pressure equipment will only fulfil its safety function correctly if it has been correctly sized, and if its maintenance prevents causes of failure, such as deposit formation or clogging, which could influence the set pressure (increase in opening pressure).

For this last category, failure probability assessment methods are still largely based on expert opinion. Indeed, while it is possible to find in the...