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10 proof testing principles

Author : Harvey T. Dearden, HTS Engineering Group

22 January 2021

The following is a briefing note on 10 proof testing principles from the Functional Safety Special Interest Group (FS-SIG), a group within the Institute of Measurement & Controls that is responsible for promoting the awareness and understanding of safety-related topics associated with measurement and control.

1. Proof testing provisions and procedures should be arranged to facilitate *coverage as far as is practicable. 100% coverage is rarely achievable.

2. Proof test procedures should be suitably explicit with detailed instructions so that coverage is not inadvertently compromised by unauthorised deviations from the intended approach. Where available, consult vendor safety manuals for guidance on testing approaches.

3. Test procedures should include clear pass/fail criteria and should record all ‘as-found’ values.

4. Test records should be traceable to the person(s) carrying them out and include details of any test equipment employed.

5. If during proof testing, any rectification work is undertaken, this must be recorded and reported to the responsible engineer. Appropriate re-testing post rectification must be undertaken.

6. Disturbance of the installation for testing purposes should be minimised as far as is practicable with the intended test coverage.

7. Proof testing should be so arranged that it will reveal dangerous failures in any redundant channel; a simple function test might not reveal a failed redundant channel.

8. ‘End-to-end’ testing may be ideal, but is not a requirement, and may not be practicable (particularly in relation to point 7 for example). Tests may be divided across different sections of the function but with the aim that, as far as is practicable, no untested gaps remain.

9. Any override used to facilitate testing should be under suitable management control.

10. All persons engaged with proof testing should be competent for that purpose with an understanding of the principles and the need for due diligence.

*Proof Test Coverage: The dangerous failures modes that would be revealed by a given test. It is typically difficult to arrange testing that will reveal all possible dangerous failure modes. Some obscure failure modes might remain untested.

This document is distributed by the FS-SIG as an information service to the SIG membership. No guarantee is made by the institute or the author(s) concerning the accuracy, reliability or completeness of the information provided. This document should not be construed as providing advice. Readers should satisfy themselves of the applicability of the information provided. Readers make use of the information provided at their own risk.

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