Machine Guarding Applications and Attributes

Machine Guarding Applications and Attributes - Safety Engineering Network (SAFTENG)

Written by Bryan HaywoodMonday, 18 June 2012 19:58

Applications and Attributes

(Informative: the safeguarding and complementary equipment contained in the chart below, aswell as their applications and attributes, are NOT intended as an all-inclusive list, but merely asadditional information or guidance on some potential uses and capabilities of the listedsafeguarding and complementary equipment)

Safeguarding

Application(s)

(for safeguarding hazard areas where: )

Attribute(s)

Fixed barrier guard

• access, by individuals, to the hazard area is not required during normal operation of the machine;

• the barrier guard slot or opening, required for entry and removal of the material, workpiece or scrap, is of a size or location that will not allow a body part to reach the hazard area.

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• protects individuals in the vicinity of the hazard area being safeguarded;

• is not dependent on any interaction with the individual(s) being safeguarded.

Interlocked barrier guard

• regular access to the hazard area is required for tool changes or adjustments, coil changes, scrap removal, et cetera;

• access to the hazard is not required during normal operation of the machine.



Adjustable barrier guard

• access, by individuals, to the hazard area is not required during normal operation of the machine;

• the guard slot or opening, required for entry and removal of the material, workpiece or scrap is of a size or location that will not allow a body part to reach the hazard area.

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• is not dependent on any interaction with the individual(s) being safeguarded;

• requires adjustment to suit each job set-up;

• is dependent on the training and supervision of set-up personnel for effective safeguarding.

Movable barrier guard

access to the hazard area is necessary during normal operation of the machine.



Use of a movable barrier device can significantly decrease machine productivity by increasing the time required to complete a production cycle.

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Pullback (pull out) and restraint devices

access to the hazard area is necessary during normal operation of the machine.

• protects only the individual(s) using the device;

• provides no obstruction between the operator and the operation being performed;

• is dependent on the training and diligence of set-up and supervisory personnel.

Presence-sensing device; electro-optical, R.F. and area scanning, safety mat and edge devices

the manufacturing process requires access to the hazard area, by individuals, during normal operation of the machine.


• provides no obstruction between the operator and the operation being performed;


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Drop probe device

the manufacturing process requires access to the hazard area, by individuals, during normal operation of the machine.

• Protects only the individual(s) using the device;


Two-hand control device

• the machine is provided with a part-revolution clutch, hydraulically or pneumatically actuated, or electrically or electronically driven (servo and variable speed drives);

• the manufacturing process requires access to the hazard area, by an individual(s), during normal operation of the machine.

• protects only the individual operating the device;

• provides no obstruction between the operator and the operation being performed.

Two-hand trip device

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• the machine makes one complete machine cycle after the trip controls are momentarily actuated;




Single control device

• the machine is provided with a part-revolution clutch, hydraulically or pneumatically actuated, or electrically or electronically driven (servo and variable speed drives);

• the machine makes one complete machine cycle after the trip controls are momentarily actuated;




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Awareness devices and signals

awareness devices or signals alert individuals of a pending or approaching hazard.

An awareness device or signal alerts individuals by means of audible sound or visible light.

Safe distance safeguarding

workpiece positioning and operator location eliminates the need for the operator to be in or near the hazard area during the hazardous portion of the machine cycle.

• protects only the operator who is required to maintain a position at a safe distance from the hazard area during hazardous motion of the machine;

• is not dependent on any interaction with the individual being safeguarded.

Safe holding safeguarding

the operator is required to hold the workpiece with both hands outside of the hazard area during the hazardous portion of the machine cycle.

• protects only the operator who is required to hold the workpiece with both hands outside of the hazard area during the hazardous portion of the machine cycle.

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Safe opening safeguarding

an opening in a barrier guard with the workpiece in place prevents an individual(s) from reaching into the hazard area.

• protects individuals in the vicinity of the hazard area being safeguarded when the workpiece is in place;


Safe positioning safeguarding (hostage control)

operators or helpers assigned to the production process are not required to have access to the hazard area during normal production. The control must be located at a distance from the hazard area such that the operator or helper cannot reach the hazard before hazardous motion has ceased.

• protects only the individual(s) operating the control device provided;


Safe work procedures

procedures developed by the user to ensure proper use and operation of the safeguarding or the machine for a particular task.

The user determines whether a safe work procedure is required to ensure that a safe work practice is achieved.

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Factors to consider in determining whether a safe work procedure is required may include, but are not limited to, the following:

• where tasks are complex;

• where tasks have high risk;

• where training, skill or work experience is limited;

• where other safeguarding is removed or bypassed;

• where required to augment other safeguarding.

Covers

For safeguarding lubrication or inspection openings in guards or machine components, where such openings may provide access to a hazard.



Shields

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• necessary to contain chips or coolant, or

• a potential exists for the ejection of broken tooling or workpiece fragments.



Hazardous Energy Types that need guarding

Rotating motion can be dangerous; even smooth, slowly rotating shafts can grip hair and clothing, and through minor contact force the hand and arm into a dangerous position. Injuries due to contact with rotating parts can be severe. Collars, couplings, cams, clutches, flywheels, shaft ends, spindles, meshing gears, and horizontal or vertical shafting are some examples of common rotating mechanisms which may be hazardous. The danger increases when projections such as set screws, bolts, nicks, abrasions, and projecting keys or set screws are exposed on rotating parts.

In-running nip point hazards are caused by the rotating parts on machinery. There are three main types of in-running nips.Parts can rotate in opposite directions while their axes are parallel to each other. These parts may be in contact (producing a nip point) or in close proximity. In the latter case, stock fed between two rolls produces a nip point. As seen here, this danger is common on machines with intermeshing gears, rolling mills, and calendars.

Intermeshing Gears

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Rolling Mill

In-running Nip Points on a Calender

Common Nip Points on Rotating Parts

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Nip points are also created between rotating and tangentially moving parts. Some examples

would be: the point of contact between a power transmission belt and its pulley, a chain and a

sprocket, and a rack and pinion.

Point of Contact Between a Power Transmission Belt and Its Pulley

Point of Contact Between a Chain and a Sprocket

Point of Contact Between a Rack and Pinion

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http://www.osha.gov/SLTC/etools/machineguarding/animations/rack1.html









Nip Points Between Rotating Elements and Parts with Longitudinal Motions Nip points can occur between rotating and fixed parts which create a shearing, crushing, orabrading action. Examples are: spoked handwheels or flywheels, screw conveyors, or theperiphery of an abrasive wheel and an incorrectly adjusted work rest and tongue. Spoked Flywheel

Nip Point Between Rotating Screw Conveyor and Fixed Trough

Rotating Abrasive Wheel on a Grinder

Nip Points Between Rotating Machine Components Reciprocating motionsmay be hazardous because, during the back-and-forth or up-and-down motion, a worker may be struck by or caught between a moving and a stationary part. Worker Caught Between a Reciprocating Table Piece a Stationary Part

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Hazardous Reciprocating Motion Transverse motion(movement in straight, continuous line) creates a hazard because a worker may be struck or caught in a pinch or shear point by the moving part. Point of Contact Between a Power Transmission Belt and Its Pulley

Transverse Motion of Belt

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Cutting action may involve rotating, reciprocating, or transverse motion. The danger of cutting action exists at the point of operation where finger, arm and body injuries can occur and where flying chips or scrap material can strike the head, particularly in the area of the eyes or face. Such hazards are present at the point of operation in cutting wood, metal, and other materials.Examples of mechanisms involving cutting hazards include bandsaws, circular saws, boring and drilling machines, turning machines (lathes), or milling machines.

Hazardous Drilling Action

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Punching action results when power is applied to a slide (ram) for the purpose of blanking, drawing, or stamping metal or other materials. The danger of this type of action occurs at the point of operation where stock is inserted, held, and withdrawn by hand. Typical machines used for punching operations are power presses and iron workers.

Typical Punching Operation

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Shearing actioninvolves applying power to a slide or knife in order to trim or shear metal or other materials. A hazard occurs at the point of operation where stock is actually inserted, held, and withdrawn. Examples of machines used for shearing operations are mechanically, hydraulically, or pneumatically powered shears.

Typical Shearing Operation

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Bending action results when power is applied to a slide in order to draw or stamp metal or other materials. A hazard occurs at the point of operation where stock is inserted, held, and withdrawn. Equipment that uses bending action includes power presses, press brakes, and tubing benders.

Typical Bending Operation

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The A,B,C’s of Machine Guarding

A GOOD Rule to remember: Any machine part, function, or process which may cause

injury must be safeguarded.

All machines consist of three fundamental areas:

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1) the point of operation,

2) the power transmission device, and

3) the operating controls.

Despite all machines having the same basic components, their safeguarding needs widely differ

due to varying physical characteristics and operator interface.

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Safeguards must meet these minimum general requirements:

1. The safeguard must prevent hands, arms, and any other part of a worker's body from

making contact with dangerous moving parts. A good safeguarding system eliminates the

possibility of of the operator or another worker placing parts of their bodies near hazardous

moving parts.

2. Workers should not be able to easily remove or tamper with the safeguard, because a

safeguard that can easily be made ineffective is no safeguard at all. Guards and safety devices

should be made of durable material that will withstand the conditions of normal use. They must

firmly be secured to the machine.

3. 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 injure

someone.

4. 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. for instance, should be rolled or bolted in such a way that they eliminate sharp edges.

5. Any safeguard which impedes a worker from performing the job quickly and comfortably

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might soon be overridden or disregarded. Proper safeguarding can actually enhance efficiency

as it can relieve the worker's apprehensions about injury.

6. 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.

7. Material used in the construction of barrier guards should be of such design and strength

as to protect individuals from identified hazards.

8. Barrier guards MUST be free of sharp edges, burrs, slag welds, fasteners, or other

hazards that may injure individuals when handling, removing or using the guards or equipment.

9. The design and construction of the barrier guard MUST ensure that individuals cannot

reach the hazard by reaching over, under, around, or through the barrier guard.

10. The guard should be designed and constructed to provide visibility of the hazard area

appropriate to the particular operation.

11. Interlocked barrier guards shall be designed and constructed to meet the following

additional requirements: Attachment of the barrier guard to the machine or the hazard

area shall ensure that individuals cannot reach the hazard by reaching over, under, around, or

through the barrier guard.

- Interlock devices used in conjunction with barrier guards are to be specifically designed

and constructed for use in safeguarding applications.

- Handles placed on interlocked barrier guards shall be secured to the guard so as not to

create a pinch point between the handles and the guard, frame or machine.

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- The interlocked section of the interlocked barrier guard(s) shall be prevented from opening

until hazardous motion has ceased, or shall be located so that an individual cannot reach the

hazard before cessation of the hazardous motion when the interlocked section is open.

- The user shall ensure that barrier guards that are frequently removed or that have

movable or hinged sections are interlocked.

Machine Guarding Assessment Checklist

Mechanical Hazards

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YES

NO/NA

□

□

Is there a point-of-operation safeguard provided for the machine?

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□

□

Does it keep the operator's hands, fingers, body out of the danger area?

□

□

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Is there evidence that the safeguards have been tampered with or removed?

□

□

Could changes be made on the machine to eliminate the point-of-operation hazard entirely?

Comments/Notes

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Power Transmission Apparatus

YES

NO/NA

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□

□

Are there any unguarded gears, sprockets, pulleys, or flywheels on the apparatus?

□

□

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Are there any exposed belts or chain drives?

□

□

Are there any exposed set screws, key ways, collars, etc.?

□

□

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Are starting and stopping controls within easy reach of the operator?

□

□

If there is more than one operator, are separate controls provided?

Comments/Notes

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Other Moving Parts

YES

NO/NA

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□

□

Are safeguards provided for all hazardous moving parts of the machine, including auxiliary parts?

□

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□

Have appropriate measured been taken to safeguard workers against noise hazards?

□

□

Have special guards, enclosures, or personal protective equipment been provided, where necessary to protect workers from exposure to harmful substances used in machine operation?

Electrical Hazards

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YES

NO/NA

□

□

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Are there loose conduit fittings?

□

□

Is the machine properly grounded?

□

□

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Is the power supply correctly fused and protected?

Guard Checklist

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YES

NO

If the machine has a guard(s) does it meet these requirements?

□

□

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Do the safeguards prevent workers' hands, arms, and other body parts from making contact with dangerous moving parts?

□

□

Are the safeguards firmly secured and not easily removable?

□

□

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Do the safeguards ensure that no objects will fall into the moving parts?

□

□

Do the safeguards permit safe, comfortable, and relatively easy operation of the machine?

□

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□

Can the machine be oiled/greased without removing the safeguard?

□

□

If the machine is designed for a fixed location, is it securely anchored to prevent walking or moving?

□

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□

When the periphery of the blades of a fan is less than seven (7) feet above the floor or working level, are the blades guarded? NOTE: The guard must not have openings larger than one-half (½) inch.

□

□

Areas where there are revolving barrels, containers, and drums, is the area guarded by an enclosure interlocked with the drive mechanism, so the barrel, gun, or container cannot revolve unless the guard enclosure is in place?

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□

□

Is there a system for shutting down the machinery and locking/tagging out before safeguards are removed?

□

□

Can the existing safeguards be improved?

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Machine Guarding Applications and Attributes

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