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Thread: Inherent Safety in Conveyor Idler Design

  1. #1
    Author Guest

    Inherent Safety in Conveyor Idler Design

    Inherent Safety in Conveyor Idler Design

    by
    David Sheehy, MSc BE and Nick Murphy BE
    GHD Pty Ltd
    Australia

    Date: 5th September, 2004




    ABSTRACT

    Conveyor Idlers have traditionally consisted of rolls mounted directly above a supporting frame. It is proposed to mount the rolls from a frame located on the leading side of the idler rolls to provide a physical barrier to the draw-in hazard between the belt and idler roll, thus improving the inherent safety attributes of conventional idler assemblies.
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  2. #2
    Author Guest

    Inherent Safety in Conveyor Idler Design

    - Page 2 -


    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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  3. #3
    Author Guest

    Inherent Safety in Conveyor Idler Design

    - Page 3 -


    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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  4. #4
    Author Guest

    Inherent Safety in Conveyor Idler Design

    - Page 4 -



    Fig. 3. Typical Arrangement on Return Side
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  5. #5
    Author Guest

    Inherent Safety in Conveyor Idler Design


    - Page 5 -


    Fig. 4. Typical Arrangement of Carry Idler
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  6. #6
    Author Guest

    Inherent Safety in Conveyor Idler Design

    - Page 6 -


    Fig. 5. Typical Arrangement of Return Idler
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  7. #7
    Author Guest

    Inherent Safety in Conveyor Idler Design

    - Page 7 -



    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.

  8. This looks like a good idea from Dave at GHD.

    We have over 25 conv. on site that have been operating for over 20 years and I do not know of a serious incident wrt humans.

    We are going thur the process of adding more guarding to meet current AS's

    The risk reduction hierarchy pyramid always has eliminate or engineer out the hazard/risk.

    But I really wonder how far we are going with designed solutions.

    I have seen safety alert reports several cases of serious or worse injuries involving conveyors and very disturbing TV program on one USA steel company's safety record and attittude.

    To me, it seems that people involved with conveyors incidents is because there is some thing wrong with the conveyor that requires action.

    If the conveyor is well designed to minimise spillage (and enable safe cleaning), uses good parts and is appropriately maintained > then the inherent hazards are reduced.

    Further, the people maintaining or cleaning the conveyors are sometimes hired help or unskilled with probably little training or safety awareness of the hazards with belt conveyors. In these cases, the owners need to recognise this and ensure that people are adequately trained and supervised.

    Considering that some conveyors are getting very heavy and operate at high speeds, even with the safety pull wire system, there is little chance of the belt stopping quickly.

    At installations where there are a lot of belt conveyors, there is also usually large mobile equipment. Care has to be taken by pedestrians and others to avoid this machinery - the risk controls used in this case is usually "administrative" and not "engineered" as per conveyor guarding eg looking before entering or crossing.

    Hence, are we taking a balanced view towards risk management on bulk materials handling sites?

    When do we say that the "residual risk" is acceptable??

    I am interested in others opinons and thoughts on risk management wrt belt conveyors.

    Cheers

    James

  9. #9
    Kinder Guest

    Inherent Safety in Conveyor Idler Design

    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

  10. #10
    Lawrence K. Nordell

    Lawrence K. Nordell

    President and CEO

    Conveyor Dynamics Inc.

    Conveyor Dynamics Inc.

    Professional Experience 62 Years / 8 Month Lawrence K. Nordell has 62 Years and 8 Month professional experience

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    I agree with safety first. I have doubts this design will be an attractive alternative.

    1. There is another way to achieve the protections -- reference Australia's Channar, Muja Collie, Warkworth and BHP Yandi where the carry side idler nip is inherently covered by the stringer and additionally by the hood covers.

    2. The design shown will be significantly more expensive than what is practiced today by using this sqare tubing, its cutting welding, jigging, quality control and need to keep multi-degree of freedom compliance within design limits to control vibration.

    3. The cut and jigged square tube will be difficult to hold installation tolerances for high speed, high capacity, and large pitched roll sets with its many more parts to cut, fit, and assemble.

    It does make a better selling job for point 1.

    Lawrence Nordell
    www.conveyor-dynamics.com

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