IEC61508 is a new international standard for safety related systems which sets out a generic approach for all safety lifecycle activities for systems comprised of electrical and/or electronic and/or programmable electronic components that are used to perform safety functions. As David Lewis shows, the part it plays in conceptual design and hazard identification is going to have a profound impact on chemical engineers.

Working in a safe environment is something many people take for granted and do not even think about. However, for personnel working in the chemical, processing, utilities and oil and gas industries, the knowledge that the work environment is as safe as possible will always be of paramount importance (Fig. 1). Ensuring that standards for safety are being continually developed therefore remains a priority for these industries.
Chemical engineers will be aware that the Control of Major Accident Hazards (COMAH) regulation requires operating plants to have a safety management system in place which prevents hazardous events or losses of containment. On most chemical plants, the trip and alarm protection system is fundamental to the prevention of hazardous events, this equipment should have been conceptualised, hazard identified, designed and commissioned with reference to the new international functional safety standard IEC61508. For chemical engineers functional safety is therefore a prime concern.
Functional safety is defined as: "That part of overall safety relating to the equipment under control and the control system which depends on the correct functioning of the electric, electronic and programmable electronic (E/E/PES) safety related systems, other technology safety related systems and external risk reduction facilities." With the increasing use of such systems, the problem of knowing whether a system will work effectively to prevent a catastrophe is a very real one.
IEC61508 is a new international standard for safety related systems which sets out a generic approach for all safety lifecycle activities for systems comprised of electrical and/or electronic and/or programmable electronic components that are used to perform safety functions.
This unified approach has been adopted in order that a rational and consistent technical policy can be developed for all electrically-based safety-related systems. A major objective is to facilitate the development of application sector standards.
For chemical engineers, particularly those involved in new projects or modification, a vital aspect of IEC 61508 is the part it plays in conceptual design and hazard identification where it provides a framework for risk reduction and allocation, giving full justification and traceability to these phases.
Compliance to the criteria set out in IEC61508 allows manufacturers, systems integrators and end-users to demonstrate to customers and the Health and Safety Executive (HSE) that good practice has been followed through the whole lifecycle and that risks are being managed. Purchasers of systems, or system components, are already using the standard to specify their performance requirements in terms of safety functions that have to be considered. If the chemical engineers on plant have implemented an accredited IEC61508 Functional Safety Management System and are procuring products that meet IEC61508 requirements, they will be going a long way to giving the regulator and senior management confidence that they are operating a safe plant.
IEC61508 is based on risk assessment. The standard requires investigation based on evidence to judge functional safety. It calls for independent assessment and recommends minimum levels of independence all related to the consequences of failure of the system, and to the safety integrity levels of the system.
Until now it has not been possible to obtain accredited certification against IEC61508. In September this changed, when Sira Certification Service became accredited to certify the Functional Safety Capability of organisations against IEC61508 using the Conformity Assessment of Safety-related Systems (CASS) scheme as the vehicle (Fig. 2). The scheme is now being developed to certify other phases of the safety lifecycle including 'product', systems and operation and maintenance.
CASS is an initiative that has been developed by industry and supported by the DTI and HSE, which provides an overall framework for a conformity assessment scheme, based on the requirements of IEC61508. The CASS scheme provides a structure whereby third-party accredited certification bodies can offer conformity assessment certification for all activities within a safety lifecycle which meet the requirements of IEC61508. The scheme will:
* Enhance confidence in the safety of complex E/E/PES systems through the availability of an accredited assessment standard.
* Reduce procurement costs by facilitating the re-use of assessed product.
* Reduce long-term operational and capital costs by facilitating the use of a 'building block approach' using certified components with recognised safety characteristics.
* Reduce design and development costs for systems that utilise these components.
* Generate increased end-user confidence in current and emerging technologies that can offer flexibility and cost reductions without compromising safety.
* Promote international trade in certified equipment by providing manufacturers with independent and internationally recognised product endorsement.
* Provide a yardstick to national regulatory authorities assessing 'fitness for purpose' and best practice of installed systems.
Sira received its accreditation in October 2001 from the United Kingdom Accreditation Service (UKAS), based on witnessed assessments carried out over the past few months. Accreditation of the certification process is important as it gives independent assurance of the competence of the certifier and provides consistency of the results of the process.
In order to maintain and improve on high safety standards, chemical companies would be well advised to ensure their safety manuals now build in the specification that products are supplied by IEC certified companies (Fig. 3). This will demonstrate a strong commitment to safety, meeting both industry and international standards to accredited procedures. Using IEC certified suppliers will give engineers and other users the added security of knowing that products have been manufactured for the paramount safety of the industries in which they are utilised.

David Lewis is managing director of Sira Test and Certification Ltd. www.siraservices.com