Functional Safety 2014

– 5

November 2014

Page 2 of 14

Minimising Systematic Failures in Safety Instrumented System Design

- Achieving Higher Integrity

Cenbee CY Bullock

BEng(Hons), CFSE, CEng, MIMechE, MInstMC

PFS Consulting Ltd

Phone: +44(0)7733 628 050

Keywords

: Systematic Failures and Human Errors

Abstract

“Withmost Safety Instrumented Systems now relying on software to achieve high integrity protection,

how can the probability of dangerous or unexpected failures be minimised?

How does Human Error affect the integrity of Safety Instrumented Systems within different phases of

the Safety Lifecycle activities? How do IEC61508/ IEC16511 apply to the challenges of eliminating

Systematic Failures? How can we apply the IEC61508/IEC61511 Safety Lifecycle to minimise

Systematic Failures within the design, engineering, installation and testing?”

This paper describes how to minimise systematic failures in Safety Instrumented System design by

following the guidance from the International Standards Safety Lifecycle. It includes the different

requirements for verifying electromechanical and programmable electronic systems. It also describes

some typical examples of over estimation of human reliability during design, engineering, installation

and test phases. These result in mistakes in engineering, additional design time and may have led to

some of the unexpected incidents that have occurred in the past few decades.

This paper will touch on some of the Safety Lifecycle activities with emphasis on identifying typical

human errors in the design and engineering process (including both type A and type B system

architecture), and installation and testing. With reference to Human Reliability Analysis from various

research resources, recommendations are made to reduce the incidence of Human Error and thus

increase the integrity of Safety Instrumented Systems.