Sunday 28th Feb, 2021

BULKtalk: The evolution of guarding

Conveyor guard standards have evolved over time to reflect higher safety expectations. Steve Davis, Senior Bulk Handling Expert at Advisian, explains how the technology has developed and what is available now.

My first up close involvement with machines that could cause injury was as a machine hand at a small fabrication shop in the UK. We had every kind of pre- computer numerical control metal fabrication machine in use, and not too much thought in guarding.

I managed to survive with only a few cuts and scrapes and an allergy to cutting fluid and some regard for my own safety. Everyone else in the shop had lost at least one finger. Many had scars and disfiguration from various entanglements. These were almost badges of honour.

After graduating, I moved into an automated fabrication facility, initially using cam timers, and then early cassette-controlled programmable logic controllers (PLC). We even had a robot. Guarding was taken seriously here, and automated systems were fully enclosed with Castell interlocks to prevent any possible contact. We soon learned that the tape in a cassette stretches and confuses the PLC with consequential random machine operation. Guards were designed to surround the total locus of movement, so it would be virtually impossible to get hurt. Small machines and easily managed.

In South Africa where I started my materials handling career as a maintenance engineer at a gold mine, guards were random steel and mesh barriers and a total contrast to previous experience.

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Safety was an arbitrary concept and guards were poorly conceived with little thought. Many were heavy, difficult to remove, even more difficult to replace, fragile and rusty. In reality these were only a small part of a non-existent mine safety culture.

Over the years and movement into the design field, I saw guards and health, safety and environmental standards gradually improve, but not much further than identifying the region that needed guards on a design arrangement drawing for the fabricator to develop.

The outcome was predictable, random attempts to provide guards that were easy to fabricate and install and did not consider operation and maintenance. The gaps between, under and over would not come close to current Australian Standards. There was never any pushback from end users and only a vague safety culture. A recent visit to an older plant in South Africa was a stark reminder of some of the issues.

On to Australia, a few years after AS1755 was first published, and set a good standard for guarding for the first time. Sadly, it was still common to identify the areas requiring guarding on the drawings, but now the note would say “Guards to AS1755”. The assumption being that the fabricator would know what this meant, have read the Standard, and diligently applied it.

Over the last 20 years, I have seen many well-meaning failures in providing guards that meet the standard. Being yellow, looking like guards and in the way of contact does not mean that they comply. I am intrigued by the lack of pushback by end users when the safety focus today is a primary concern. We are improving but not always as good as we should be.

AS1755 has improved and now is part of the AS4024 series. These are good standards, but the end results do not just happen because of a note on a drawing. Compliant guards must be designed to meet the key reasons of limiting access to moving parts, nip points and so on, and gaps and limitations are clearly defined. Guards must also resist the loads defined in the Standard.

What is not defined in the Standard are the other aspects that should be considered in design. Guards are an impediment to operation and maintenance, and many often need to be maintained frequently themselves. Guards are often an ergonomic nightmare for removal and replacement, as this aspect has not been considered in design. Guards should be designed to be easily removed and replaced using the obligatory tool, should be lightweight, should be corrosion resistant, should consider where they will be stored when removed and meet all the safety aspects. Guards that are fastened with more than two tool removable fixings are too complex.

Fortunately, the supplier industry in Australia and other countries observed the shortfall in guard performance in recent years, and we now are able to choose from well thought out, and well-defined guard systems. These guard systems comply with gap and distance, strength and are operation and maintenance friendly.

I favour Australian sourced and supported products for Australian use. ESS have an excellent modular guard system in steel or aluminium and supply other conveyor safety accessories.

There are two suppliers of modular guard systems that have taken practicality to new levels. Both DIACON Australia and DYNA Engineering supply excellent conveyor guard systems that are specifically designed for Australian conditions and to the Australian Standard.

Both guard systems use HDPE as the main guard component, and both are fully modular custom fit for application. Expected life is more than 15 years and the self-coloured guards are fully recyclable at end of life. Key issues are:

  • Guards are made to measure for every installation
  • Significantly lighter weight than steel, most are easy single operator lifts, weight is permanently marked
  • Simple, consistent fixing methods that facilitate removal and reinstallation
  • No corrosion, no sharp edges, no mesh to snag
  • Shape is retained, so no force fits back into place
  • 100 per cent Australian made

There are many differences between the two systems, but both have considered the operation and maintenance aspects in detail. In my view both systems also look great when installed and should stay this way for many years.

Another guard system that has impressed me is from a Canadian company, soon to establish in Australia. Enduride supply a curtain guard system which has application in confined spaces, and wider application elsewhere. The system complies with North American and European Standards and has been tested to meet Australian Standards.

The system is novel in that the curtains are suspended between upper and lower steel cables and have a latch system that, when released with an Allen key, allows the curtains to slide back to provide access. Quick access, no lifting, storage in situ and easy reinstallation. Corrosion-resistant materials and they offer a completely different solution to safety.

There are two suppliers in the USA and one in Canada that provide well thought out modular systems for conveyor guards and for many guard and other safety accessories, being Martin Engineering, Asgco and Belt Conveyor Guarding. The systems favour metal guard systems with flat panels and modular supports. These systems are specifically suited to North American Regulations but are functionally able to meet Australian needs.

While we are discussing guards, we should not forget those other tricky components such as chute doors, guards for belt cleaner, drive components, idlers and the like, all of which are available from specialist suppliers, including those already mentioned and from others such as BendTech in Australia.

There really is no excuse for having noncompliant conveyor guarding on new installations, with several excellent choices, and I doubt there is any difference in cost over “traditional” methods. For older installations direct fit made to measure guard systems are readily available. I am certain there are similar suppliers that I am not yet aware of.

Excellent guarding makes a safer environment. Lightweight low maintenance easy to remove guards reduce hazards, reduce maintenance time, and save operating cost.