Two years ago, a worker at a meat processing plant in Ajax, Ont., was loading frozen blocks of meat into a grinding machine. To load one block of meat, which was too frozen to be drawn into the grinder by the rotating feed screw, the worker pushed down on it. When the meat unexpectedly moved, the worker’s hand was pulled down into the hopper. As a result, part of the hand was amputated.
An investigation concluded the company had failed to equip the grinder with a guard to prevent contact with the rotating feed screw.
Unguarded and inadequately guarded machines can lead to severe workplace injuries. The result for the worker is often amputation and permanent disability. Most incidents take place in the manufacturing sector, but incidence is also high in construction, agriculture, service industries and the wholesale and retail trade. Such accidents may also take a financial toll on a company when entire operations are shut down.
Machine safeguards fall into two broad categories, barrier guards (the most common type) and safeguarding devices. While the terms “guards” and “safeguarding” are often used interchangeably, they have precise, different meanings when talking about machine safety.
The barrier guard prevents access by the worker to the moving part. It prevents a worker from “reaching over, under, around or through” the barrier to the hazard.
In addition to preventing access from all directions, according to WorkSafeBC, barrier guards must:
• not create additional pinch points or other hazards
• safely contain broken parts (such as belts and chains)
• be secured by at least one fastener requiring a tool for removal, unless properly interlocked with the machine control system
• allow for safe lubrication and minor adjustments.
Typical barrier guards include the fixed power transmission guard, adjustable band saw guard, adjustable power press feed guard and circular saw guard.
In contrast, a “safeguarding device” is often selected as an alternative to a barrier guard (though it may also be installed as a supplement to a guard). It detects a person’s presence near the hazard and may prevent contact with it by stopping the machine, such as light curtains, safety mats and area scanners.
“If a person needs to reach into a machine to load it, you’re not going to be able to put a fixed guard there because they need to be able to reach in to put the part in or take it out,” says Renée Frigault, president of Toronto-based Lucid Engineering. “This is where the fancier things, like the interlocked doors and the light curtain come into play — places where people might need to reach in to un-jam something on a regular basis or to feed the machine when it runs out of widgets to process.”
Barrier guards are often classified into four groups, says Jason Foster, assistant professor of human resources and labour relations at Athabasca University in Alberta. The first are fixed guards, which are permanent, designed not to be removed and may be regarded as the only acceptable type.
The main advantage of the fixed guard is that it is the most secure, Foster says. There is less opportunity for human error and for someone to remove the guard and try and operate the machine without it. The principle disadvantage is lack of access to the machine. Thus, a fixed guard can be impractical for changing production requirements and make repair more time consuming.
A second type is adjustable. The guard itself stays in place, but it can be adjusted according to different production operations; for example, the opening may adjust to allow materials of varying quantities to be fed into the machine.
Adjustable guards allow for some flexibility during operation, he says. However, that adjustability means there’s a potential for workers to come into contact with the hazard. In adjusting the size of the opening, for example, a person may make the opening too wide. If workers are going to adjust a guard, it’s essential they are properly trained to know how to make the adjustment and to not make the adjustment while the machine
Another type of guard is interlocked. These are designed to be lifted or moved aside when required during normal production work. When the guard is lifted, the control system is disabled and the machine stops.
“It’s called interlocked because it’s interconnected to the machinery itself, so it’s impossible to operate the machinery when the guard is removed or open,” Foster says.
Interlocking guards also provide some potential for contact. They have the advantage that they’re integrated into the machine; however, even if the machine shuts off, the hazardous parts, a rotary blade, for example, may not instantly stop moving.
The fourth type is the self-adjusting guard. Used on power tools, this guard remains in place when the machine is not running but moves out of the way when material starts entering the point-of-operation and retracts according to the size of the material.
The self-adjusting guard is probably the one with the highest risk level, Foster says, because it creates imperfect protection from the hazard. The advantages are for production.
“It will adjust itself to fit the material, so the operator doesn’t have to be constantly adjusting it. It’s a facilitator of production. The problem is that it’s the lowest level of protection because if it can move to allow material in, it could also move to allow in a body part,” he says.
Selecting a guard depends largely on the kind of machine and how it is being used. The two main factors to consider are how much protection the guard offers and how it will affect production. The best guard is one that provides the highest protection with the least impact on normal operations.
The first step should be a risk assessment. If the risk is deemed high, as with feed rolls, which are found in many industries (such as paper products manufacturing), a fixed barrier guard is needed. However, where the risk is deemed low or medium, a perimeter fence or rail enclosure could be selected to protect workers from accessing hazardous machine parts.
In assessing the guard’s effect on production, the key issue is how much access workers need to perform their work, says Frigault.
However, if regular access is not needed, fixed guards should always be the safety manager’s first choice, she says.
The main standard used in Canada for machine guards is CSA Z-432-4 Safeguarding of Machinery. It discusses the design, performance and application requirements, selection and application of guards and safeguarding devices. It also covers risk assessment, maintenance and training procedures.
“That one standard is the one that every manufacturer in Canada should have,” says Jeff Winter, director of safety practice at Burlington, Ont.-based Grantek Integration Systems and member of the committee tasked with the rewrite of ANSI B11.19:2010, Performance Criteria for Safeguarding.
Safety managers should consult the standard to determine what sizing of guards is appropriate, he says. The charts and tables identify, for example, the minimum height of a guard based on how far away the worker is from the hazard, or a maximum opening size based on distance to hazard.
“There is proper dimensioning and sizing of guards and location of guards that you need to consider so that you can’t just reach your arm in or over it. There are height requirements, and that’s both height off the ground and overall height. You need to account for the ability to reach over, under, around or through,” Winter says. “That’s one aspect that’s often overlooked and that needs to
Linda Johnson is a freelance journalist based in Toronto. She can be reached at firstname.lastname@example.org.
This article originally appeared in the August/September 2016 issue of COS.
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