New Conveyor Safety Standards Are Here!

As of August 2015, AS 1755 has been superseded by a new set of conveyor safety standards. For those who aren’t familiar with AS 1755, this is why it's a big deal:

• AS 1755 has been the Australian standard for conveyor safety since 1986
• It is the code of practice for conveyor safety in South Australia and referenced as guidance for conveyor safety in every other state and territory’s code of practice
• Conveyors are one of the most prevalent types of machinery in Australian industry and a significant cause of work safety incidents 

So why are we changing the standard? 
The main issue with AS 1755, is there are many different types of conveyors used in many different industries and it’s difficult for one standard to effectively cover all of this. For example, a low torque conveyor of 5m length placed in a manufacturing plant which has high exposure to human operators has vastly different safety requirements then a conveyor that transports tons of material over 500m and has very infrequent exposure to human operators.

To deal with these different conveyor options we now have 4 new standards to replace AS 1755:

1. AS/NZS 4024.3610 - Conveyors - General requirements
2. AS/NZS 4024.3611 - Conveyors - Belt conveyors for bulk material handling
3. AS/NZS 4024.3612 - Conveyors - Chain conveyors and unit handling conveyors
4. AS/NZS 4024.3614 - Conveyors - Mobile and transportable conveyors

The general requirements for conveyor safety can be found in 3610 and additional requirements can be referenced in 3611, 3612 and 3614 for specific conveyor types. This should allow the series of standards to better cover the safety aspects of common conveyor applications in Australia and New Zealand.

The standards are now placed in the 3000 series of the AS 4024 family. This makes more sense rather than having the conveyor standard being separate to the AS 4024 collection of safety standards. The 3000 series consists of machine specific standards and now covers the following types of machines:

• Presses: Mechanical (AS 4024.3001), Hydraulic (AS 4024.3002)
• Milling machines (AS 4024.3101)
• Robotic cells (AS 4024.3301)
• Conveyors (AS 4024.3610 - AS 4024.3614)

If you have any machines covered by a 3000 series standard this will provide the best guidance for safety requirements.

• Express interest in a Safety Standards Workshop

What Should I Design To: Performance Levels Or Safety Categories?

With last year's revision of AS 4024.1:2014 designers of safety control systems now have two options:

1. Design to Safety Categories (AS 4024.1501), or 
2. Performance Levels (AS 4024.1503)

Why does the series have 2 options? Which option should be used? Wouldn't it be much easier if there was one direction for design guidance?

As explained in AS 4024.1100:2014, the standards are in a transition phase and are mimicking the process followed by international standards. In international standards, Performance Levels replaced Safety Categories in 2012 after a 5 year transition period where the two standards ran in parallel. The Australian standards are now entering a similar transition phase. It was decided that an instant changeover would not be achievable because it would take a period of time for the industry to become familiar with Performance Levels and the two methods would run in parallel during this period.

Which design method should you use? 
Most safety control systems can be designed to Performance Levels or Safety Categories, but here are some reasons why you may want to use certain sections of AS 4024.1503.

• Common Cause Failures (CCF). To learn more about CCFs and for guidance, refer to a previous post titled 'New series provides guidance on Common Cause Failure'. I would recommend using the common cause method in Annex F of AS 4024.1503 for any CAT 2, 3 or 4 system
• Guidance for developing safety software. If you are developing/maintaining software for safety programmable devices then section 4.6 of AS 4024.1503 is the only guidance on software development that you will find in the AS 4024.1:2014 series
• Component reliability. If you are designing a CAT 1 system I would recommend calculating a Mean Time To dangerous Failure (MTTFd) for your safety system using section 4.5.2 of AS 4024.1503. CAT 1 is highly dependent on component reliability and thus ensure your CAT 1 system has a MTTFd of HIGH.
• Architecture flexibility. Safety Categories using AS 4024.1501 can be inflexible on the architecture of the safety system and will generally push the design towards conservative architectures with redundancy. By using Performance Levels you will find greater flexibility with the architecture of the safety system; for example observing Table 7 of AS 4024.1503, it can be seen that a CAT 1, 2 or 3 architecture can be used to achieve the same risk reduction level.

So, be aware that the standards are transitioning away from Safety Categories. During this phase Safety Categories and Performance Levels will run in parallel, this should be seen as providing more choice to safety designers, not confusion. As mentioned above, there are some useful sections in AS 4024.1503 that will improve safety systems' design, even if the systems are designed to the requirements of Safety Categories. By using these sections of AS 4024.1503, you will design improved safety systems, have more flexibility in your system design, and be better placed to cope with future changes of the AS 4024.1 series.

New Guidance on Machinery Risk Assessments

Risk assessment on machinery is a major area of uncertainty for a large proportion of industry. It's quite common for people given the responsibility of risk assessment to be unsure of the process and fearful of being held accountable for results of the risk assessment.

While codes of practice do provide good guidance for the general process of risk assessment, they don't cover the unique challenges of machinery applications. Unfortunately, the 2006 version of the Australian Machine Safety Standards (AS 4024.1) provided only theoretical guidance for risk assessment and left many people still confused on issues such as:

• Who should be involved in the process of risk assessment?
• Systematic methods to identify hazards on the equipment
• What risk estimation tools are available and how do they work?
• What does documentation of risk assessment actually looks like?

Guidance is now available in the 2014 revision of Australian Machine Safety Standards (AS 4024.1). A new standard, AS 4024.1303:2014, has been created, which provides practical guidance on risk assessment for machinery.

This standard gives detailed information on how to set-up and prepare for a risk assessment. Advice is provided on who should be part of the team and what information should be collected to prepare for the risk assessment.

The standard also explains systematic approaches for hazard identification. For example, the top-down approach starts with defining the hazardous situations of a machine and then analyzing the hazard zones.

One of the major improvements with this standard is the information that is provided for risk estimation. This standard now explains various risk estimation tools such as Risk Matrix, Risk Graphs, Numerical Scoring and Hybrid Tools.

If you are confused about how the process is actually implemented and what the documentation looks like then Annex A of AS 4024.1303:2014 should provide some answers. This Annex explains step by step the risk assessment process carried out on a molding machine, it also shows all the documentation created during this process and explains what risk reduction measures were used.

With this new standard, AS 4024.1303:2014, you have access to information to help you facilitate risk assessments on your machinery. If you would still like assistance with the risk assessment process contact NHP's customer service team or contact your NHP sales representative.

What did Australian Standards get wrong with AS/NZS 4024.1:2014?

If you're not aware, AS/NZS 4024.1 series of machine safety standards was revised late last year. In this revision most of the parts were revised, some were unchanged, some new parts were added and some parts were removed. If you want more information on what's revised, unchanged, new and removed check out this previous NHP blog topic: New Revision of AS 4024.1 Series of Machinery Safety Standards.

The 2014 dated parts of the series are "direct text adoptions" of international standards. This is confirmed by looking at the first page of each part, the adopted international standard is printed below the AS/NZS title. In figure 1 we can see that AS/NZS 4024.1602:2014 is a direct text adoption of ISO 14119:2013.

Fig 1. Part title, appears in top right corner on the first page of the part

OK, so you're thinking what's the big deal about direct text adoption?

Direct text adoption means that nothing can be changed from the international standard's wording, even references. So if AS/NZS 4024.1602:2014 is referencing a clause from AS/NZS 4024.1503:2014, the reference will appear as the international standard, ISO 13849-1:2006. This obviously makes the series a little difficult to use. Assistance can be found in the "Preface" section of each part, which will list the international standards that are referenced and will show the equivalent AS/NZ 4024 part. There is also a cross reference list available in Appendix B of the application guide, AS/NZS 4024.1100:2014.

In the previous version of the AS 4024.1 series, the parts were based on international standards but some changes were allowed. In this series the references were changed from international standards to the relevant AS 4024.1 part. As mentioned previously some parts of the series have been unchanged in the 2014 revision, for example AS 4024.1501-2006. Thus this standard still has references to clauses and parts from the 2006 version.

For example AS 4024.1501-2006 references standards AS 4024.1202 and AS 4024.1301, both of these standards are now superseded by AS/NZS 4024.1201:2014 and no longer exist in the AS 4024.1 series. So be aware of this issue when using any of the 2006 version parts of AS/NZS 4024.1:2014

Hopefully this blog topic can help you avoid this gotcha when using AS/NZS 4024.1:2014.

Have you come across anything strange with this series? Or do you have some useful hints and tips? If so please share in the comments section.

New series provides guidance on Common Cause Failure (CCF)

What is a common cause failure (CCF)? CCF is a term that has much more significance in the new AS 4024.1 series. A good description of CCF can be found from a very trusted reference...TV! If you have ever watched Air Crash Investigation then you may be familiar with the 'Swiss Cheese Model'.

From this Swiss cheese model, it can be seen that if the holes in the multiple layers of cheese line up then a single path through the layers can exist and thus the safety critical system has failed. CCF is an example of this occurring in machine safety systems. If we think of a dual channel system; a CCF would be both channels failing at the same time due to a common event, for example:

• Two independent switches on a guard failing because the ambient temperature is above their rating
• Two independent safety channels having erroneous signals induced on them from the same source of electromagnetic noise
• Two mechanical switches on a guard fracturing due to the one impact event of that guard door

The above explanation shows how threatening common cause failure can be to a safety system. We will generally design machine safety systems with two channels when the risk of the application is high; this provides redundancy so the system can tolerate a fault on a single channel. However if the system hasn't been designed to avoid CCF, then there is a real chance that a certain event will defeat both channels and the system will fail.

For this reason, whether you are designing systems to categories (AS 4024.1501) or performance levels (AS 4024.1503) CCF should be a consideration for any multiple channel architecture. Unfortunately the previous version of AS 4024.1 didn't have any usable process to avoid CCF, however this has been rectified in the new version of the series released in 2014.

AS 4024.1503:2014 Annex F contains a test for common cause failure that can be used to determine if the safety system has been designed to avoid CCF to an acceptable level. I would recommend any machine safety system designed to architectures cat. 2, 3 or 4 should be analysed with the process from Annex F. This is the only usable guidance in the AS 4024.1 series for designing safety control systems to avoid CCF.

Other parts in the 2014 version of AS 4024.1 also provide guidance on designing to avoid CCF for common safety functions. For example, AS 4024.1602:2014 Clause 8.3, provides excellent guidance on how to prevent common cause failures in interlock guard functions.

This is an example of the improvements that have been made with the new 2014 version of AS 4024.1 series. We will be exploring some of the new features of AS 4024.1 in many of the safety blog topics this year. If you missed our last topic Safety Systems Must Be Designed For Productivity, be sure to to check it out as this topic explored how the 2014 version of AS 4024.1602 can help you design interlock guards that operators won't defeat.

Don't be a Robbo or Danny boy, protect yourself from common cause failure.