Instead, a methodical approach can ensure that the lifetime cost is proportional to the risks that are being managed.
As safety systems become more complex and software plays an increasingly prominent role, so the need grows for better communications between the parties involved in specifying, supplying, implementing and operating these systems.
"Critical safety systems need people you can rely on as well as products," says Clive de Salis, the newly elected Chair of The 61508 Association. "Sixty per cent of industrial control accidents are traceable back to either a failure to specify properly or a failure to design and implement the specification properly. People and quality systems are often the forgotten critical component."
It was against this background that the international standard IEC 61508 and its derivatives (such as IEC 61511 and IEC 62061) were created. IEC 61508 provides a detailed process covering the whole lifecycle of a safety system starting from the specification of the safety requirements to be met by the system. For each lifecycle phase, the person or company involved is guided through the inputs, actions and outputs such that the resulting system will meet the specified requirements.
The actions have to be carried out by competent people working within organisations which operate an effective safety management system. The standard also requires that, at every stage, the correct actions are verified and that adequate records are maintained.
With so many different parties involved, a clear and consistent method for each to achieve conformance with the standard is required. Companies from all parts of the supply chain have teamed up with end users to form The 61508 Association, with the express intent of promoting demonstrable conformance to IEC 61508 and related standards. The Association works closely with the UK's Health and Safety Executive (HSE) and with CASS to promote the cost effective application of the standard. (CASS, or Conformity Assessment for Safety Systems, is managed by The CASS Scheme Ltd, a not-for-profit organisation created by industries where safety systems play a prominent role.)
Among the activities being undertaken by The 61508 Association is the development of requirements to be met by certification bodies involved with verifying the conformance of companies, systems and components with the standard's requirements. The aim of the CASS system is to provide certification which has integrity, transparency and consistency. CASS is open to all certification bodies that sign up to apply the CASS method.
A key factor in the successful application of IEC 61508 and related standards is the competence of everyone involved in the safety system lifecycle. The 61508 Association is developing guidelines for companies to follow in order to achieve the necessary standard of competence management. The guidelines draw on work already carried out by the Institution of Electrical Engineers (IEE) and the British Computer Society (BCS), and The 61508 Association maintains close links with these professional engineering bodies as well as the Institute of Measurement and Control (InstMC).