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Chemical and Downstream Oil
Industries Forum
CDOIF is a collaborative venture formed to agree strategic areas for
joint industry / trade union / regulator action aimed at delivering
health, safety and environmental improvements with cross-sector
benefits.
Guideline – Demonstrating Prior Use v4
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A.4 Other techniques for calculating failure rates
Where no failure rate data is available, either from the end users or equipment
manufacturers is may be necessary to perform a detailed analysis of the component
using such techniques as Failure Modes, Effects and Diagnostic Analysis (FMEDA). Any
such analysis should only be completed by a suitably independent and competent
person. Even then, there is no guarantee that any failure rate derived from such an
exercise will match eventual experience.
A.5 Systematic capability
Systematic capability is mentioned in BS EN 61511, but is discussed in detail in BS EN
61508
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. It is particularly relevant in relation to items of equipment containing software.
The techniques and measures that have been employed during the development of the
software limit the safety integrity level that can be claimed for a safety instrumented
function that uses an equipment item containing software. BS EN 61508-2 relating to
hardware and BS EN 61508-3 relating to software contain tables of techniques and
measures and the safety integrity levels to which they apply.
It should be noted that this topic is not related to Prior Use demonstration.
A.6 Safety manuals
The Safety Manual is mentioned in BS EN 61511, and Part 1 defines Safety Manual as
“safety manual: manual which defines how the device, subsystem or system can be
safely applied”.
Note: This could be a stand-alone document, an instructional manual, a programming
manual, a standard document, or included in the user document(s) defining application
limitations.
However, it is a new significantly more prominent requirement in BS EN 61508 Edition 2.
BS EN 61508 Edition 2 introduces a new normative requirement in Part 2, Annex D
“Safety Manual for Compliant Items”. It defines the purpose of the Safety Manual as,
“The purpose of the safety manual for compliant items is to document all the information,
relating to a compliant item, which is required to enable the integration of the compliant
item into a safety-related system, or a subsystem or element, in compliance with the
requirements of this standard”.
In BS EN 61508-3 Edition 2, Annex D, there are further normative requirements for the
safety manual with respect to software, “Safety manual for compliant items – additional
requirements for software elements”. This annex makes it clear that the safety manual
may comprise solely the manufacturer’s documentation, if that is sufficient to meet the
new normative BS EN 61508 Edition 2 requirements, or it should be created as part of
the design of the safety related system.
Thus, the safety manual is documentation that is produced by the supplier or the system
integrator.
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BS EN 61508 Edition 2 Published 2010