There are 3 different ways that devices can be shown to be suitable for use in a 61511 Safety Instrumented Function. If any SIF device isn’t demonstrably compliant by one of these 3 ways, then the entire SIF is non-compliant. The 3 ways (or routes) are:
Route 1 “By Design” is the only way a product manufacturer can launch a new product on the market. By definition “new” means untried and untested in the real world. This Route requires product manufacturers to follow all the requirements of 61508 parts 1 to 4. This is a considerable undertaking – time consuming and often requires additional circuitry being added to the design to add diagnostics.
Route 2 “Proven in Use” allows a product manufacturer to claim that an existing design has turned out to be “good enough for SIL” mainly by reviewing product faults reported by customers. If the returns show that the typical rate of dangerous undetected failures is low enough, then this claim can be made. (There is a statistical significance test included, to ensure confidence in the numbers claimed). This route is defined in 61508.
“Prior Use” is defined in 61511 and follows similar thinking to Route 2 “Proven in Use”. Again the “good enough for SIL?” test is based on a review of actual failures – but this time done by the end user (plant operator) themselves. And again, there is a statistical confidence test for the values obtained from the test data of the device population. (Of course, you must have been keeping good proof test records to be able to do this. A typical operator may not have kept good records and may not have enough devices, that have been installed for long enough for prior use to be a viable option to demonstrate device compliance.)
An update to an earlier SIL verification and PFD calculation exercise.
Industry: Oil and Gas OnshoreFor an oil storage facility, carrying out an exercise to confirm that the SIL requirement was correct (under review changed from SIL 1 to SIL 2), identify a replacement for non-compliant contractor and confirm the compliance of a non-certified galvanic isolator by way of a prior use analysis.
Industry: Oil and Gas OnshoreAn Alarm review at a Scottish distillery. The scope covered all SCADA/HMI systems on the site, a total of 700 alarms were reviewed.
Industry: Brewing and DistillingA "SIL Verification" exercise to confirm the compliance of x6 Safety Instrumented Functions for a Boiler package vendor. Reviewing the design against the SRS, confirming compliance of the SIF components, checking that the correct hardware fault tolerance had been selected and that the PFD calculations were correct.
Industry: Process - GeneralConfirming compliance with 61508/61511 for a number of devices intended for use on an offshore gas platform.
Industry: Oil and Gas OffshoreE: support@methodfs.com. T: 44 (0)1462 713313. W: www.methodfs.com