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Category: Miscellaneous
Volume: 28
Issue: 3
Article No.: 4600

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Back To Article Directory - May/Jun-07

SAFETY SOLUTIONS: Machine Guarding

The primary function of all machine guarding is to prevent an operator or bystander from being injured by a potentially dangerous portion of a machine. Often the hazard involves moving parts with the potential to cut, crush or draw-in body parts, although barrier guards may also be necessary when electrical, thermal or chemical dangers are present.

Guarding or protecting people from harm may be accomplished with simple physical shielding of machine parts, or more advanced techniques such as photo light curtains. It is also often necessary to employ interlocks to disable power to the machine when a guard has been removed.

Accident risks can be reduced with adequate machine safeguarding. Identifying obvious and hidden hazards should be the first step in planning and reviewing the need for machine tool safeguarding. Some hazards are subject to the ‘seven-foot rule, which dictates that these potentially dangerous operations be enclosed or guarded if they are located less than seven feet above the floor or platform level. Guards are required to have one-half-inch or smaller openings. Blades and other overhead hazards— such as pulleys, belt rope and chain drives, overhead horizontal belts, vertical and incline belts, gears, sprockets and chains—must comply with this rule.

Most incidents leading to injury are the result of inadvertent or unwise contact with moving machine parts. Because of the great diversity of machine designs and functions, appropriate safeguarding to protect workers from such hazards may also have numerous forms. Certain principles, however, are basic to any effective safeguarding design.

Machine Safeguarding Evaluation and Design

A uniform process should be applied and used to evaluate each of the hazards on the machine to develop the required level of safeguarding. The evaluation can be performed by a knowledgeable and experienced person or, for more complicated machine designs and safeguarding issues, the evaluation can be conducted by a qualified third party.

The OSHA/ANSI hierarchy for controlling machine hazards is as follows:

  1. Eliminate the hazard by design
  2. Control the hazard by guarding or devices
  3. Warnings
  4. Personal protective equipment
  5. Training
If the results of the hazard evaluation show the equipment to be safe (that is, poses no hazard to the employee), changes to the equipment may not be necessary. This may be true for manually-powered equipment.

Assessing the Risk: Many times the employer will want to know the answer to this question, “What do we fix first?” Once you have identified the danger areas (hazards), you should assess the risk (how likely it is to cause injury, and how severe the injury could be.)

For every hazard that you identify on a machine, you must then assign a risk factor to it. On the Probability chart listed below, decide what is the most predicable injury that could occur, then assign a risk number to it.

If you score a 1 or 2, do something NOW.
If you score a 3 or 4, plan to do something soon.
If you score a 5 or 6, plan to review the risk in the future.


How severely could it hurt someone?
What is the likelihood of it happening? CATASTROPHIC
Kills, disables, permanently injures
Significantly injures, NOT permanently
First aid only, no work time lost
It could happen
It could happen occasionally
It could happen, although uncommon
It could happen, although probably never will

When designing machine guards the safeguards must meet these minimum general requirements:

  1. A guard is a protective device that PREVENTS anyone from reaching over, under, around or through the guard or guarding device.
  2. An awareness barrier or chip shield can be used to warn a person that they are coming in close proximity to a danger area. Other protective measures such as training or color coding must also be used so the person is reminded that they could potentially be injured if proper procedures are not followed.
  3. Prevent contact: The safeguard must prevent hands, arms, and any other part of the operator’s body from making contact with dangerous moving parts. A good safeguarding system eliminates the possibility of the operator or another worker placing parts of their bodies near hazardous moving parts.
  4. Secure: Operators should not be able to easily remove or tamper with the safeguard, because a safeguard that can easily be made ineffective is more dangerous than no safeguard at all.
  5. Protect from falling objects: The safeguard should ensure that no objects can fall into moving parts. A small tool which is dropped into a cycling machine could easily become a projectile that could strike and seriously injure someone.
  6. Create no new hazards: A safeguard defeats its own purpose if it creates a hazard of its own, such as a shear point, a jagged edge, or an unfinished surface which can cause a laceration. The edges of guards should be rolled or bolted in such a way that they eliminate sharp edges.
  7. Create no interference: Any safeguard which impedes a worker from performing the job quickly and comfortably might soon be overridden or disregarded. Proper safeguarding can actually enhance efficiency as it can relieve the worker’s apprehensions about injury.
  8. Allow safe lubrication: If possible, one should be able to lubricate the machine without removing the safeguards. Locating oil reservoirs outside the guard, with a line leading to the lubrication point, will reduce the need for the operator or maintenance worker to enter the hazardous area. Guards and safety devices should be made of durable material that will withstand the conditions of normal use.
  9. OSHA 1910.212 requires guards to be attached to the machine where possible or secured elsewhere if attachment is not possible. The guard or guarding device can not create a hazard in itself.
In summary, employees working on or near machinery with hazardous moving parts must be protected. OSHA requires that such parts be guarded to ensure worker safety. If unguarded, those parts could entangle a worker’s hands, hair or clothing and lead to injury or even death. Employers therefore should inspect equipment daily to make sure that all guards are intact—especially after maintenance or repair.

For more information, click on the author biography at the top of this page.
This article was written by Jack and Alan Podojil.

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