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Background

An entanglement (draw-in) hazard exists wherever a conveyor belt runs over a carry or return idler in addition to other locations along the conveyor. Previous practice has been to guard idlers where the lifting of the belt is restricted such as at skirts, ploughs, convex curves and transitions. Return idlers were typically guarded when their positions were greater than 600mm and less than 2500mm above ground level.

The latest Australian Standard on conveyor safety (AS1755 -2000) has removed the clause that does not require return idler guards up to 600mm above ground level.

Further, belts are now heavier with linear loads increasing. Belt linear masses of 45 to 70kg/m are currently in use and burden loads in excess of 250kg/m are common.

Safety around Conveyor Idlers

Notwithstanding the requirements and changes in safety codes, there has always existed a significant hazard near conveyor idlers. Maintenance personnel have been, and continue to be, exposed to serious risks when working near conveyors.

Return idlers and suspended idlers have been more a problem as the support frame does not permit a limb to pass through to the other side. However the heavier weights applied to base-mounted carry idlers is also very likely to cause serious injury to an entrapped limb.

It could be well argued that such heavy loads in themselves restrict belt lifting as defined by safety codes.

Accidents have been reported during cleaning up operations beneath ploughs typically where shovel handles have been drawn into the conveyor-idler interface and serious injuries have occurred. Unless the user of the shovel lets go immediately it is likely that his arm will be drawn into the belt.

The height of the conveyor is a factor. Low conveyors are difficult to clean under and high conveyors have access problems to the belt. Intermediate heights, where good clean-up access is available, leads to greater exposure to the return idler draw-in hazard.

It has also been argued that length of the conveyor has made conveyor belt guarding impractical, if not then very expensive. The hazard risk is then controlled by limiting access to the conveyor and safety training.

In other cases light weight guarding has been installed and relies on maintenance personnel to correctly reinstate the guarding if removed for idler replacement. More cumbersome guards are less likely to be reinstated and become a hazard in themselves.

Return idler guards (cages) can fill with carry-back.

Access to idlers is also necessary for inspections and belt tracking, perhaps while the belt is operating and guards and fences may impede this access.

Approach to Safety

In the more enlightened age of safety, those who suffer accidents and injuries are less likely to be blamed for the accident and systems and interfaces are hopefully reviewed for possible improvements.

Human error is an unacceptable cause for an accident, particularly in an engineering context. Humans make errors, this is a fact of life. The consequences of such errors need to be minimized.

Once a hazard has been identified, and rated in some quantitative order, the risk relating to the hazard needs to be addressed. In descending order of effectiveness, the following actions are required:

• Eliminate the hazard or substitute with a reduced hazard

• Guard the Hazard

• Minimize exposure

• Provide protective equipment or accept the risk.

In the case of the conveyor idlers, alternatives are currently limited and guarding is the most effective. Guarding may also include secondary guarding where main guards are removed for maintenance access.

Idler Guarding

Idler guards can take the form of a barrier with appropriate ergonomic dimensions to avoid contact with the draw-in hazard or a nip guard. Nip guards are simply barriers to the draw-in zone, which prevent fingers reaching the hazard. Hair and loose clothing may still become entangled under certain circumstances and there is also the possibility of an abrasion injury.

Barrier guards are now required to be removable only by tools.

The leading frame type idler support can provide an inherent nip guard which is not removable and does not impede access to the idler rolls. Such an intrinsically safe idler frame, removes the concern of guards not being reinstated, or being removed for maintenance tasks, which may expose the operator to hazards.

Fig. 1:

Idler Nip Protection

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This type of idler guard can be considered as a secondary guard for areas of frequent access or a primary guard for other idlers, more remote from day to day operations.

The arrangement does not add cost to many base-mounted idler types as a similar quantity of steel is required to support the idler as would be otherwise used.

The protection is not perfect as there are still small apertures through which access can be made, however it is apparent that in the situation of accidental contact, the risk of entanglement is very small if not negligible.

Fig. 2: Typical Arrangement on Carry Side

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Fig. 3. Typical Arrangement on Return Side

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Fig. 4. Typical Arrangement of Carry Idler

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Fig. 5. Typical Arrangement of Return Idler

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Conclusion

Sometimes it does not take much of a change in design or cost to save a life. For example, an extra stanchion on a high landing can avoid a slip through fall; attention to changes in surface friction can avoid slips; stair nosings and gates on access ladders are all minor costs to a project but are very effective in risk reduction.

Most importantly a detailed consideration of all operations that are not just necessary, but are likely, or even just possibly, to be undertaken near a hazard, can prevent injury.

In this case, an old and accepted design for idler support frames may need a minor rethink to improve the inherent safety of a common machine that is inherently hazardous.

REFERENCES

Stevenson Mike. Safety by Design, Published by Mike Stevenson Ergonomics 2004.

Patent Application 2004.

Mines Occupational Safety & Health Advisory Board Minesafe Vol 10 No 1 1999

Mineral Resources Publication Safety Alert Report No SA 02-12-2002

Standards Association of Australia AS1755 Conveyors –– Safety Requirements. 2000

Standards Association of Australia AS1755 Conveyors – Design, Construction, Installation and operation – Safety Requirements. 1986. ■

Practical innovation. The problem I see is the issue of accountability for the safety aspect. Because of our litigious society no one will take responsibility because if they warrant that the design falls within the safety guideless do they then accept the consequences of potential injury or death? The best answer we have received from authorities to safety guarding innovations is referal to the standard. Ask the question - does this design comply? .........Cheers , Neil Kinder ■

This looks like a great idea - there were requirements where I worked for guards on all moving equipment to eliminate, or minimise the hazard, but conveyor guards had a tendancy of not making their way back onto the conveyor after maintenance, and action was very rarely taken. (Frustrating)

Only questions I am interested in are:

1. Could product build-up around idlers (in a poorly housekept area) find its way between the guard & the belt? - if so, this would cause belt deterioration??

2. Could high product surges cause enough sag in the belt to rub against the guard? - would this design require more closely spaced idlers than a standard design to avoid this? - we all know what would happen if it did - maintenance would increase tension in the belt to 'protect' the belt, resulting in decreased life, spillage issues etc. ■

EN 620:2002 Continuous handling equipment and systems - Safety and EMC requirements for fixed belt conveyors for bulk materials

Figure 1 lists typical nip points on a belt conveyor.

Carry and return idlers are NOT included except at loading and transition points, thus implying that nip guards are not required at other positions. ■

In response to the replies to our paper: Thank you for your interest and I would like you to consider the principle first rather than the details.

The proposed frame arrangement is considered as a last means of protection, not necessarily a primary guard. The main application is for idlers that would be otherwise unguarded or where it is possible that guards or covers may be removed for maintenance or inspections. There have been numerous reported accidents where operators have been injured or killed while cleaning up beneath belts, often with guards removed.

Although the frame arrangement may not completely comply with standards or protect against loose clothing or long hair, the practical real world improvement in protection against the most likely accident ie draw-in of a tool handle or limb would be significant.

The draw-in happens very, very quickly.

The latest Australian conveyor safety code permits nip guards, and the frame arrangement can generally be made to comply. However, adherence to standards is no longer sufficient in itself a defence against Workplace Health & Safety actions. Risk Assessment processes are essential and documented actions are to be taken to recognize and address risk.

Idlers with guards or covers that can be removed during maintenance or non-routine operations are a potential risk and are not inherently safe.

There are a number of manufacturing details and frame arrangements using this principle that are not too dissimilar than current designs for 10o return idler frames. Just the position of the frame is changed to the leading side of the rolls. Again I stress the principle of an inherent degree of safety rather than the manufacturing details which can be developed and optimized. I agree there are some issues to be overcome wit the frame design to make it competitive with existing idler frames.

There are many examples in industry and other areas where such approaches (ie looking at things differently) have been successful, but do take some development and overcoming resistance to change.

I must stress it is the principle that is important and with positive and proactive attitude these dreadful accidents can be nearly eliminated.

Again thank you for your interest and we will be looking to develop and test this concept in the near future. I will keep you posted.

David Sheehy

Nick Murphy

GHD Pty Ltd

Australia ■

I should also add we are looking initially at 10 deg return idlers, with frame options including SHS on edge, bent round tube, angle, as well as the SHS as shown in the initial paper for development and testing.

David Sheehy

Nick Murphy

GHD Pty Ltd ■