Definition:
Prior use is a concept that is used when there is no SIL assessment or certification of the equipment, but good historical data exists. Prior Use refers to demonstrating that a device is suitable for use in a safety function based on its successful operating history. This responsibility is driven by the facility owner and not the manufacturer. It is this distinction that makes it different from proven in use (PIU). Remember, PIU is essentially 2S and 2S is proven in use. Prior use is a pathway that IEC 61511-1 permits.
Note prior use, proven in use, and routes are notoriously confusing in functional safety circles.
Key Points:
- Can substitute for formal SIL certification if sufficient documented experience exists.
- Requires operating hours and failure data.
- Generally a more difficult path than using certified components.
- This process can be used to help justify 2S or 2H routes.
Example:
A solenoid valve used successfully for 10 years in similar conditions by a single operating company may be justified under prior use.
See Also: proven in use, routes
Cited Source:
- IEC 61508-2:2010, Clause 7.4.9
- IEC 61511-1:2016, Clause 3.2.51
- The 61508 Association – Proven in Use – policy paper