PL and SIL merger cancelled. What does it mean for AS 4024.1?

For those who are designing machine safety control systems to achieve international standards you may have been aware of the process in place to merge the two current standards. This would result in a new standard, IEC/ISO 17305, which would merge the methods of Performance Levels (PL as per ISO 13849.1:2015) and Safety Integrity Level (SIL as per IEC 62061).

This process was seen as a positive step for machine safety designers as we would finally have one unified standard that everyone would design their systems to, instead of the confusion of having multiple standards running concurrently. However this merger process has now been cancelled without a guarantee of when or if the process will be restarted.

So what is the relevance of this to Australian Standards?
Our Australian Standard, AS 4024, adopts directly from international standards and as stated in AS 4024.1100 the future direction of the control system section was dependent on the merged standard:
It is envisaged that on completion of the work of Joint Working Group 1 of ISO/TC 199 and IEC/TC 44, combining ISO 13849-1:2006 and IEC 62061, the resulting unified Standard will replace both
Parts 1501 and 1503 in the next revision of the AS 4024.1 series

So what does this mean for the future direction of AS 4024.1? Well that seems to be up in the air at the moment.

Potentially the next revision of AS 4024.1 will see Safety Categories disappear and Performance Levels remain. Another option may be Safety Categories remain as an option for safety control systems that consist of simple devices, such as safety relays, safety contactors, safety valves, etc.

There may be advantages of this second option for the following reasons:

• The Australian industry has much more familiarity and knowledge of Safety Categories compared to PL or SIL
• Safety Categories provide a simple method to design safety control systems
• When applied correctly Safety Categories provide adequate risk reduction
• International systems using PL will still be designed to a Safety Category architecture

What do you think? 
If you have a comment or opinion on what the future direction of safety control systems should be in AS 4024.1 please leave a comment below.

Feedback from the industry is essential so the committee can ensure the standard reflects the industry’s needs.