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Proof Testing of Process Plant Safety Instrumented Systems
The Institute of Measurement and Control, Pub. InstMC-ETP-001.1 Page 2/12
Proof Testing of Process Plant Safety Instrumented Systems
1. PREFACE
1.1.
This paper has been developed from an article (
Who’s Afraid of Proof
Testing)
that was originally published in the February 2010 edition of the Institute
journal.
1.2.
This document provides information, which should not be considered as
definitive or exhaustive. Adherence to any guidance in this paper does not
necessarily mean that regulatory and legal obligations will be met. Users remain
responsible for identifying the relevance and correctness of the guidance in any given
application.
1.3.
The Institute welcomes comments on this paper which should be addressed
to The Publications Department at the Institute of Measurement & Control, 87 Gower
Street, London WC1E 6AA
1.4.
No part of this publication may be reproduced in any form without prior
permission in writing of the Institute of Measurement & Control.
2. INTRODUCTION
2.1.
This paper explores some of the possibilities in a pragmatic approach to proof
testing of process plant safety instrumented systems, with particular regard to the
functional safety system standards BS EN 61508 & 61511 (Ref 1 & 2). It is
preferable that a proof test should reflect real operating conditions; in this respect,
the ideal approach is to drive the process variable to a point where it triggers the
safety system action, but without placing a real demand on the protection, i.e., with
no risk of a hazard should the protection fail during the test. In practice end-to-end
testing with 100% coverage is usually difficult or impossible to implement on a
practicable basis on real plant.
2.2.
The following observations on approaches to proof testing are by no means
exhaustive, but are intended to highlight the considerations that will allow users to
identify the specific requirements for their own installations. Recognition of these
same considerations should also allow more effective design of an installation to
facilitate proof testing.
2.3.
‘New build’ systems should be specifically engineered to accommodate proof
testing requirements. Existing installations should be critically reviewed to identify
where upgrades are appropriate.
3. UNDERPINNING PHILOSOPHY
3.1.
The overall requirement is to establish a proof testing regime that will identify
all dangerous failures within an appropriate timescale to ensure the safety function
Probability of Failure on Demand (PFD) requirement is met.