Technological progress in functional safety
Functional safety is becoming ever more significant as products continue to be further digitalised and automated. Improving the functional safety of products also introduces economic opportunities, including safe product design, early prevention of conformity-related problems, fewer product recalls, and shorter time to market. Stewart Robinson MIET MInstMC, Principal Engineer and Functional Safety Expert at TÜV SÜD discusses.
As the many different functional safety requirements are quite broad and complex, a management framework is required to regulate the processes and organisation of activities. A holistic approach is therefore needed, which requires expertise in various application fields across all project phases – from design and development to manufacturing and installation, testing, certification, placing into service, and decommissioning.
In the past, dangerous machinery movements could be reliably stopped by opening one of the monitored doors in the safety guarding. However, the increasing connectivity of systems and plants, plus the growing possibilities of remote control, has seen a paradigm shift – away from the prevention of access and the reliable shutdown of machines, and through to the reliable identification of people and continued operation. Such an improvement minimises disruption to the production line.
As digitalisation, automation and connectivity have progressed, safety requirements for machines and machine systems have grown more comprehensive and complex. A safety-related control function is one of the measures that contribute to the overall reduction of risk in machinery use. Consequently, electrical, electronic or programmable electronic systems (E/E/PES) are used increasingly in the field of safety applications. However, as what is considered to be ‘state-of-the-art’ moves on at a dramatic pace (particularly in view of innovations such as Industry 4.0), new components and systems must frequently become available which are too technologically advanced for current standard requirements.
Machinery manufacturers must now show compliance with the European Machinery Directive 2006/42/EC or the UK Supply regulations. To demonstrate compliance with legislation, machine builders can choose to work to the harmonised/designated standards EN ISO 13849 (Safety of machinery - Safety-related parts of control systems - General principles for design) or EN IEC 62061 (Safety of machinery - Functional safety of safety-related control systems). These can be used to achieve compliance in the field of functional safety; plus, as neither is technology-specific, they can both be applied for safety systems using any technology.
Increasing system connectivity requires even more suitable approaches to protect systems, such as automated operator identification and the shutdown of machines. With such high levels of automated safety, the safety-related parts of controls systems will become more complex.
An analysis by the Health and Safety Executive (HSE) of incidents connected with the safety-related parts of control systems revealed that poor design and implementation, together with incorrect specification, accounted for 59% of the primary causes identified. These are the types of problems that a full validation process could have uncovered before the control systems went into service.
A new version of EN ISO 13849-1 will include requirements for the verification and validation of Safety-Related Parts of Control Systems that is currently in EN ISO 13849-2.
EN ISO 13849-2 spells out the basic validation requirements very clearly in Section 4.1, Validation Principles. It states: “The validation shall demonstrate that each safety-related part meets the requirements of ISO 13849-1, in particular (for example):
the specified safety characteristics of the safety functions provided by that part, as set out in the design rationale, and
the requirements of the specified performance level (see ISO 13849-1:2006, 4.5)
It also explains: “Validation should be carried out by persons who are independent of the design of the safety-related part(s).”
Carrying out the calculations required by EN ISO 13849-1 and EN IEC 62061 remains a complex task. While there are software packages that help to guide users through the compliance process, the growing complexities caused by ever greater technology innovations and integration means that is becoming a more complex and resource-hungry task to ensure compliance with these standards.
Innovative technologies have contributed significantly to greater efficiency and a higher degree of automation, therefore allowing improvements in operability and profitability. Alongside this, the importance of machinery functional safety has increased continuously, as the safety system contributes significantly to risk reduction and must therefore be aligned to these more versatile and complex applications.
To mitigate against systematic faults, the effectiveness of safety measures must also be fully verified. This will confirm the robustness of components, as well as the complete lifecycle; plus of course, the development process must also be considered during such an assessment. As mentioned previously, a holistic approach to functional safety is therefore required.