ISO 13849 is a safety standard which applies to parts of machinery control systems that are assigned to providing safety functions. 

A new version now replaces ISO 13849-1:2015. Once listed in the Official Journal (OJEU) as a harmonised standard there may be a transition period of up to three years before the superseded version loses its presumption of conformity. However, once it is listed (which at the time of writing we are still awaiting), this new standard will have a presumption of conformity with corresponding EU rules, and it will be also become listed as a designated standard in the UK.

What does ISO 13849-1 cover?

ISO 13849-1 provides safety requirements and guidance on the principles for the design and integration of safety-related parts of control systems (SRP/CS). This includes the design of software, and the standard includes specific requirements for SRP/CS using programmable electronic systems. It also specifies characteristics that include the Performance Level required for carrying out safety functions. The standard applies to SRP/CS for high demand and continuous mode, regardless of the type of technology and energy used (electrical, hydraulic, pneumatic, mechanical, etc.), for every type of machinery.

The whole document has been reorganised to better reflect the design and development process for control systems and the following discusses some key highlights, but not every change. 

New focus on risk assessment recommendations

The standard now includes a focus on risk assessment recommendations. For example, Figure 2 of Clause 4 is an enhanced version of Figure 1 in the current version – breaking out the ‘three-step process’ of risk reduction. Alongside this, Clause 4.6 (subsystems) is new, while significant parts of Clause 4 have been moved to their own clauses for specification, design, and verification.

There is also a new Clause 7 on software safety requirements. Changes and additions include explaining the differences between ‘limited variability language’ and ‘full variability language’ and guidance in deciding between them. 

Functional safety management

Clause G.5 of Annex G covers the management of functional safety, requiring a functional safety plan to be drawn up and documented for each SRP/CS design project, which should be updated as any changes to the system are made. Key features of a functional safety plan should include:

• The identification of the relevant activities in the SRP/CS design process and confirmation of the order in which they should take place. 
• The identification of the roles and resources required for actioning and reviewing every activity.
• The creation of a validation plan.

There is also a new Annex L on electromagnetic interference (EMI) immunity. It provides a scoring methodology (table L.1) that can be used where equipment that integrates electronics can be assessed by considering various measures to achieve immunity.

Annex M includes additional information for safety requirements specification, while Annex N also introduces the concept of fault-avoiding measures for the design of safety related software. It Is intended to help users of the standard apply the requirements of Clause 7 on software safety requirements. Meanwhile, Annex O now covers safety-related values of components or parts of the control systems. This is extracted from a data library format created by the German machinery manufacturers association (VDMA). It has been around for some years and is used in applications like SISTEMA and PAScal to help with the calculations for hardware reliability.

Stewart Robinson is principal engineer and functional safety expert at TÜV SÜD

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