334 / 1143
Functional Safety 2016
November, 2016 - London
Page 4 of 17
Methodology to determine Proof Test Coverage
The definition of the Proof Test Coverage Factor (C
PT
) is the percentage of dangerous failures
detected by the Proof Test usually in relation to the undetected dangerous failures, where
internal diagnostics are available.
The BS EN 61511:2004, UK HSE and EEMUA 22 guidance provides little technical guidance on
methodology, therefore the assessment is usually carried out as a combination of a review of
the proof test procedures with a comparison against the available guidance and vendor
recommendations.
The UK HSE is clear that partial (imperfect) proof testing must be accounted for in the hardware
calculations and SPC/Technical/General/48 and CRR 428/200 provides some guidance.
The methodology for the identified SIF Loops is:
1. Review the Safety Requirements Specification (SRS) to identify specific loop
components and equipment model / type.
2. Source the vendor Safety Manual for the equipment model / type and identify any
specific testing requirements and any coverage claims.
3. Review the PT procedure for the identified SIF Loop.
4. Review the SIL hardware assessment report with respect to test coverage claims and
failure rate data used.
5. Assess the current C
PT
based on the proposed testing regime in comparison to vendor
and UK regulator expectations and requirements.