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 with the assistance of the manufacturer and is driven by IEC 61511. Prior use is a facility-based justification method under IEC 61511 and is not itself a certification route under IEC 61508.
Do not confuse prior use with proven in use (PIU). Remember, PIU is essentially 2S and 2S is proven in use and is driven by IEC 61508. Proven in use has very strict requirements per IEC 61508-2. Data that does not meet PIU requirements could still be used for prior use under that framework.
Note prior use, proven in use, and routes are notoriously confusing in functional safety circles.
Key Points:
- Less strict than PIU, which is always manufacturer driven.
- Generally used by the facility, but the manufacturer and CB can use it to bolster their arguments.
- Requires operating hours and failure data.
- Generally a more difficult path than using certified components.
- Database data, like OREDA, can be used for prior use.
Example:
A solenoid valve was used successfully for 10 years in similar conditions by a single operating company. They want to use that solenoid valve in a SIL 1 certification.
- This would not mee PIU requirements
- They use this data as prior use.
- The facility FuSa engineer could justify the use in a SIF using the prior use process in IEC 61511. No Certification Body is needed.
See Also: proven in use, routes
Cited Source:
- IEC 61511:2015, Clause 11.5.3
- IEC 61511:2016, Clause 3.2.51
- The 61508 Association – Proven in Use – policy paper