FEATURE Machine Safety
Keeping pace with functional safety innovation
By Stewart Robinson, principal engineer and functional safety expert at TÜV SÜD, a global product testing and certification organisation
A
s digitalisation, automation and connectivity progress, so safety requirements for machines and systems have
grown more comprehensive and complex. A safety-related control function is one of the measures that makes a contribution to the overall reduction of risk with machinery. Consequently, electrical, electronic or programmable electronic systems (E/E/PES) are used increasingly in the fi eld of safety applications.
Machinery manufacturers must show compliance with the European Machinery Directive 2006/42/EC or the UK Supply regulations. In order 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 fi eld of functional safety and as neither is technology specifi c, they can both be applied for safety systems using any technology.
Over the years, both ISO 13849-1 and IEC 62061 have seen revisions. EN IEC 62061 edition 2 was published in 2021, with a scope that includes the design of low- complexity subsystems and the integration of other subsystems. The design of complex programmable electronic subsystems or subsystem elements is not within the scope of the standard, but in the scope of IEC 61508 or standards linked to it.
EN ISO 13849-1 is in the later stages of being revised and will also have a scope
28 April 2022 | Automation
statement that it “… does not give specifi c requirements for the design of products/ components that are parts of SRP/CS. Specifi c requirements for the design of components of SPR/CS are covered by applicable ISO and IEC-standards”. The new version will, however, still include some information that is directly relevant to the design of electronic subsystems and measures for Safety-Related Embedded Software (SRESW). So, there may be some confusion about which requirements apply to a particular situation, resulting in machine builders perhaps misinterpreting how they should apply the standard.
Stepping up a gear The increasing connectivity of systems, plus the growing possibilities of remote control, further require suitable approaches to protect systems. To minimise disruption to the production line and enable continuous machine operation, some safety applications are moving away from access prevention and the reliable shutdown of machines to the automated identifi cation of people. 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 safety-related parts of control systems revealed that poor design and implementation, together with incorrect specifi cation, accounted for 59% of the primary causes identifi ed. These are exactly the type of problems that a full validation process could have uncovered before the control systems entered service. The new version of EN ISO 13849-1 will include requirements for the verifi cation and
validation of Safety-Related Parts of Control Systems that is currently in EN ISO 13849- 2. This clearly explains the basic validation requirements in Section 4, Validation Principles: “The validation shall demonstrate that each safety-related part meets the requirements of ISO 13849-1, in particular: • the specifi ed safety characteristics of the safety functions provided by that part, as set out in the design rationale, and • the requirements of the specifi ed performance level (see ISO 13849-1:2006, 4.5). • 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 guide users through the compliance process, the growing complexities caused by technology innovations and increased integration mean ensuring compliance with these standards is becoming a more complex and resource hungry task.
Innovative technologies have contributed
signifi cantly to greater effi ciencies and a higher degree of automation, improving operability and profi tability. Alongside this, the importance of machinery’s functional safety has continued to increase, as the safety system contributes signifi cantly to risk reduction and, hence, must be aligned to these more versatile and complex applications.
CONTACT:
TÜV SÜD
www.tuvsud.com
automationmagazine.co.uk
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