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FUNCTIONAL SAFETY

A GENERAL OVERVIEW

Sira Test & Certification Ltd Form 7000

Hazardous Area Centre, Rake Lane, Eccleston, Chester, England. CH4 9JN. Issue 3Tel: +44 (0)1244 670 900, Fax: +44 (0)1244 681 330, e-mail: info@siracertification.com

Certification and EU Notified Body activities are undertaken by Sira Certification Service (SCS), the independent certification body of Sira

Functional Safety A General Overview

Challenges faced by industry today includeunremitting pressure to reduce costs coupled withshorter product life-cycles, a need for ever shortertime to market, and pressure to maximise the useof the asset base. Industry continually strives toimprove performance and profitability whilemaintaining and improving safety. In addition,there are regulatory and social requirements forsafety and reliability, and for protecting theenvironment.

Against this background industry is experiencinga revolution in rapidly evolving safetytechnologies, all which have an increasing

reliance on computer-based control and safetysolutions.

It is important to exploit this modern technologyso as to facilitate improvements in both safety andeconomic performance. But this must be donewithin an overall safety framework whichmaintains an appropriate level of safety and whichprovides confidence that this is being achieved.

Where do most Hazards Occur?

Studies carried out by HSE of incidents involvingprocess control systems show that the majoritystem from relatively few causes.

(From Out of Control A compilation of incidents involvingcontrol systems, by the UK HSE)

In addition, computer control and embeddedsoftware were becoming more commonplace,

thereby increasing concerns about the possibilityof hidden risks buried within complex coding.

Due Diligence

In the UK, the Consumer Protection Act requiresthat goods supplied into the market are ofmarketable quality, expecting suppliers to exhibitdue diligence to ensure this. Similar legislationexists in other countries. Where national orinternational standards exist for this purpose, anysupplier not applying them would have difficultypleading due diligence'.

What is the HSE Position?

It is recognised by the UK Regulators, the Healthand Safety Executive (HSE), that good practicesuch as that laid down in the functional safetystandards can help to achieve good heath andsafety performance. The HSE may use IEC61508 and related industry-specific standards asa reference for determining whether a reasonablypractical level of safety has been achieved.

So what is Functional Safety?

Functional Safety is concerned with equipment

whose failure could have an impact on the safetyof persons and/or the environment. The relevantstandards which are now widely accepted are:

IEC 61508 - the generic standard. It provides afirm basis for the specification, design andoperation of electrical or electronic (includingsoftware controlled) safety systems and allowsthe potential of this technology to be realised fullyand safely. It also forms the basis for the followingrelated industry-sector standards.

IEC 61511 - Functional safety of safetyinstrumented systems for the process industry.

IEC 61513 - Nuclear power plants:Instrumentation and control for systems importantto safety.

IEC 62061 - Safety of machinery: Functionalsafety of safety-related E/E/PE control systems.

changes aftercommissioning20% specification

operations & 44%maintenance

15%

installation & design & commissioning implementation6% 15%

7/30/2019 61508 Overview Sira

2/2

FUNCTIONAL SAFETY

A GENERAL OVERVIEW

Sira Test & Certification Ltd Form 7000

Hazardous Area Centre, Rake Lane, Eccleston, Chester, England. CH4 9JN. Issue 3Tel: +44 (0)1244 670 900, Fax: +44 (0)1244 681 330, e-mail: info@siracertification.com

Certification and EU Notified Body activities are undertaken by Sira Certification Service (SCS), the independent certification body of Sira

Other Benefits

By following best practice for managing plant

safety as set out in these standards, not only caninsurance premiums be reduced, but also healthand safety inspections may be more easilyprogressed.

IEC61508

What is the Scope of Functional Safety?

The approach used covers all the activitiesdescribed in the HSE pie chart describedoverleaf, from entire systems down tocomponents contributing to safety, includinghardware, software and procedures.

Safety Integrity Level (SIL)

Four levels (SILs) of safety performance arespecified for a safety function: SIL 1 being thelowest and SIL 4 the highest, according to thedegree of risk that must be reduced. The SIL is anindication of the probability of failure of the safetyfunction. Safety functions with higher SILs requiremore rigour in terms of the design, testing andmethods used in the development.

Organisation and Competence of Personnel

An important aspect which is assessed is theability of an organisation to manage any of its

activities that could have an impact on functionalsafety, such as its quality process and thecompetence of its staff.

What Else Does it Cover?

Being generic, the principles in the standard canalso be applied to other technologies such asmechanical, hydraulic or pneumatic which areused, for example, in pipeline emergencyshut-down systems.

Studies have shown that perhaps 50% ofproblems in the field are the result of valves,actuators and/or solenoids failing to respond,often because they remain in one position for longperiods, making them difficult to operate when

needed. IEC 61508 provides a framework todefine the reliability of such devices usingwhatever technology. Analysis of historicalreliability data for these elements can determinethe components suitability for use in a safetyfunction with a given SIL.

Protection of Environment and Assets

An identified hazard may not be one that affectsthe safety of individuals directly, but one whichcompromises the integrity of the environment orof costly assets. Again the strategy of thestandard is valid, and the only difference is in the

choice of criteria for quantifying the hazards andthe integrity levels for the risk reduction factors.

How can Sira Help?

Sira provides a range of services to enable you tobenefit from the advantages of functional safety.

More Information

For further information please contact Sira:

Tel: +44 (0) 1244 670 900Email: functionalsafety@siracertification.com

Web: www.siracertification.com

Note: The SIL relates to the overall safety functionbeing performed not to the individual componentparts of the system. Any use of the term SIL in

relation to components must be treated with extremecaution and looked at in the context of theirapplication.

Technical advice & Training.Product certification.Company certification.Independent third party assessments.Staff competence.