Functional Safety 2016

November, 2016 - London

Page 15 of 17

Conclusion

The impact of imperfect proof testing can have significant impact on the designed risk reduction

requirements and the suitability of the defined proof testing method when the C

is not

considered.

It has been shown the impact imperfect proof testing can impact the PFD

AVG

in relation

hardware calculations, and has been illustrated in the practical example of where the proof test

methodolgy has been based on manufacturers requirements. By following the requirements of

the manufactures testing, inspection and competency requirements within the safety manuals

obtaining a 100% C

is a near impossible target to achieve.

The application of C

should be applied to a project involving a SIS as early as is practicable,

where C

is not available either due to equipment not yet selected or equipment not certified,

using a systematic approach such as the approach identified in (Abdelrhafour, Bajaj, & Boily,

2012) would be benficial.

As shown in Table 4 there is potential for a final system to not provide defined risk reduction

requirements, which may lead to an end-user rejecting or involvement from the HSE.

Therefore, a theoretical and pragmatic approach should be adopted taking into account the

prescribed proof testing methods in the safety manual and its prefined C

for the selected

operation mode. Consideration should also be given to the persons responsible to writing and

conducting the proof testing for their ongoing relevant competency requirements.