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.
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:
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.
- Eliminate the hazard by design
Control the hazard by guarding or devices
- Personal protective 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.
| CONSEQUENCE |
How severely could it hurt someone?
| What is the likelihood of it happening?
First aid only,
|VERY LIKELY: |
|VERY UNLIKELY: |
It could happen,
When designing machine guards the safeguards must
meet these minimum general requirements:
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.
- A guard is a protective device that PREVENTS anyone
from reaching over, under, around or through the guard
or guarding device.
- 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.
- 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.
- 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.
- 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.
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
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.
- 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.
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.
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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