Machine Guarding

MACHINE GUARDING OSHA 1910, SUBPART O

INTRODUCTION

This course covers OSHA’s machine guarding requirements. We will begin with a discussion of the general principles of machine guarding. Next, we will cover some of the requirements of OSHA’s machine guarding regulations. We will examine moving parts, hazardous motions, and types of machine guarding. We will look at some important OSHA directives for specific machine guarding issues. Finally, we will look at OSHA’s new initiative to reduce and eliminate hazards on machines that cause, or are likely to cause, amputations.

LEARNING OBJECTIVES Understand the basics of machine

guarding, where hazards occur, hazardous machine motions, machine actions, requirements for safeguards, and employee training.

Learn what OSHA machine guarding requirements are including general requirements for all machines, woodworking machines, abrasive wheel machinery, mechanical power presses, and mechanical power-transmission apparatus.

Learn what types of safeguards are available, and what their common applications are.

KEY TERMS The point of operation where work is performed on material, such as

cutting, shaping, boring, or forming of stock

Power transmission apparatus: all components of the mechanical system which

transmit energy to the part of the machine performing the work. These components include flywheels, pulleys, belts, connecting rods, couplings, cams, spindles, chains, cranks, and gears.

Push stick: means a narrow strip of wood or other soft

material with a notch cut into one end and which is used to push short pieces of material through saws.

KEY TERMS Abrasive wheel: means a cutting tool consisting of abrasive grains

held together by organic or inorganic bonds. Diamond and reinforced wheels are included.

Inorganic wheels: means wheels which are bonded by means of

inorganic material such as clay, glass, porcelain, sodium silicate, magnesium oxychloride, or metal. Wheels bonded with clay, glass, porcelain, or related ceramic materials are characterized as "vitrified bonded wheels”.

Bolster plate: means the plate attached to the top of the bed of

the press having drilled holes or T-slots for attaching the lower die or die shoe.

KEY TERMS

Pinch point: means any point other than the point of

operation at which it is possible for a part of the body to be caught between the moving parts of a press or auxiliary equipment

Press: means a mechanically powered machine that

shears, punches, forms or assembles metal or other material by means of cutting, shaping, or combination dies attached to slides.

Slide: means the main reciprocating press member. A

slide is also called a ram, plunger, or platen.

PRINCIPLES OF MACHINE GUARDING

This lesson focuses on the following topics:

Principles of machine guarding

Hazardous motions and actions

Requirements of safeguarding

Employee training

LESSON 1


Crushed hands and arms, severed fingers, blindness -- the list of possible machinery-related injuries is as long as it is horrifying.

There seem to be as many hazards created by moving machine parts as there are types of machines. Safety guards are essential for protecting workers from needless and preventable injuries.

This man lost his finger when a machine in a foundry cut it off. There was no safety guard in place, as required by federal law, to keep his hand out of the point of operation.

LESSON 1


Where Mechanical Hazards Occur

Dangerous moving parts require safeguarding. Scroll over each area to find out more about:

The point of operation

Power transmission apparatus

Other moving parts

LESSON 1


The point of operation:that point where work is performed on the material, such as cutting, shaping, boring, or forming of stock.

Power transmission apparatus: all components of the mechanical system which transmit energy to the part of the machine performing the work. These components include flywheels, pulleys, belts, connecting rods, couplings, cams, spindles, chains, cranks, and gears.

Other moving parts: all parts of the machine that move while the machine is working. These can include reciprocating, rotating, and transverse moving parts, as well as feed mechanisms and auxiliary parts of the machine.

LESSON 1

HAZARDOUS MOTIONS AND ACTIONS

A variety of mechanical motions and actions may present hazards to the worker. These can include the movement of rotating members, reciprocating arms, moving belts, meshing gears, cutting teeth, and any parts that impact or shear. The basic types of hazardous mechanical motions and actions are the following:

Motions

rotating (including in-running nip points) reciprocating transversing

LESSON 1


Actions

Cutting Punching shearing

bending

LESSON 1


Motions

Rotating motion can be dangerous. Even smooth, slowly rotating shafts can grip clothing, and through mere skin contact, force an arm or hand into a dangerous position. Some examples of common rotating mechanisms which may be hazardous are:

Collars Couplings Cams Clutches Flywheels

LESSON 1


Shaft ends Spindles Meshing gears Horizontal or vertical shafting

The danger increases when projections such as set screws, bolts, nicks, abrasions, and projecting keys are exposed on rotating parts.

LESSON 1


Nip Points

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

Nip points can also occur between rotating and fixed parts which create a shearing, crushing, or abrading action. Examples are: spooked hand-wheels or flywheels, screw conveyors, or the periphery of an abrasive wheel and an incorrectly adjusted work rest.

LESSON 1

Transverse motion (movement in a straight, continuous line) creates a hazard because a worker may be struck or caught in a pinch or shear point by the moving part.


Cutting Action

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, or other materials.

Examples of mechanisms involving cutting hazards include band saws, circular saws, boring or drilling machines, turning machines (lathes), or milling machines.

LESSON 1


Punching Action

Punching action results when power is applied to a slide (ram) for 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.

LESSON 1


Shearing Action

Shearing action involves 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.

LESSON 1


Bending Action

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.

LESSON 1

REQUIREMENTS OF SAFEGUARDING

What must a safety guard do to protect workers against mechanical hazards? Safety guards must meet minimum general requirements. Scroll over each requirement below to find out more:

Prevent contact

Be secure

Protect from falling objects

Create no new hazards

Create no interference

Allow safe lubrication

LESSON 1


Prevent contact: The safety guard must prevent hands, arms, and any other part of a

worker's body from making contact with dangerous moving parts.

Be secure: Workers should not be able to easily remove or tamper with the

safety guard, because a safety guard that can easily be made ineffective is no safety guard at all. Guards and safety devices should be made of durable material that will withstand the conditions of normal use. They must be firmly secured to the machine.

Protect from falling objects: The safety guard should ensure that no objects could 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.

LESSON 1


Create no new hazards: . A safety guard 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.

Create no interference: Any safety guard which impedes a worker from performing the job

quickly and comfortably might soon be overridden or disregarded. Proper safety guarding can actually enhance efficiency since 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 safety guards. 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.

LESSON 1

EMPLOYEE TRAINING

Training

Even the most elaborate safety guarding system cannot offer effective protection unless the worker knows how to use it and why. Specific and detailed training is therefore a crucial part of any effort to provide safety guarding against machine-related hazards.

LESSON 1

EMPLOYEE TRAINING

Thorough operator training should involve instruction and/or hands-on training in the following:

A description and identification of the hazards associated with particular machines

The safety guards themselves, how they provide protection, and the hazards for which they are intended

How to use the safety guards and why

LESSON 1

EMPLOYEE TRAINING

How and under what circumstances safety guards can be removed, and by whom (in most cases, repair or maintenance personnel only)

What to do (e.g., contact the supervisor) if a safety guard is damaged, missing, or unable to provide adequate protection.

This kind of safety training is necessary for new operators and maintenance or setup personnel, when any new or altered safety guards are put in service, or when workers are assigned to a new machine or operation.

LESSON 1

OSHA MACHINE GUARDING REQUIREMENTS


General Requirements For All Machines

Woodworking Machinery Requirements

Abrasive Wheel Machinery

LESSON 2

GENERAL REQUIREMENTS

FOR ALL MACHINES

OSHA’s fundamental requirement for employers is that one or more methods of machine guarding be provided to protect the operator and other employees in the machine area from hazards.

These include such hazards as those created by point of operation, in-going nip points, rotating parts, flying chips and sparks. Examples of guarding methods are-barrier guards, two-hand tripping devices, etc.

LESSON 2


FOR ALL MACHINES

General requirements for machine guards

Guards shall be affixed to the machine where possible and secured elsewhere if for any reason attachment to the machine is not possible. The guard shall be such that it does not offer an accident hazard in itself.

The point of operation of machines, whose operation exposes an employee to injury, must be guarded and be designed and constructed to prevent the operator from having any part of his body in the danger zone during the operating cycle.

LESSON 2


FOR ALL MACHINES OSHA encourages the use of special hand tools such as push sticks

to allow for easy handling of material without the operator having to put his hand in the danger zone.

Another general requirement for all machines is that machines designed for a fixed location shall be securely anchored to prevent "walking" or "moving".

LESSON 2

Safety committees or an individual (s) with responsibility for plant safety should perform regular safety audits of machine areas to ensure guards have not been removed, discarded, or are in need of repair or replacement. Machines generally should not be operated unless all the guards are securely in place.

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FOR ALL MACHINESGeneral requirement for guarding fan blades

When the periphery of the blades of a fan is less than 7 feet above the floor or working level, the blades shall be guarded.

The guard shall have openings no larger than 1/2 inch.

The use of concentric rings with spacing between them not exceeding a 1/2 inch are acceptable provided that sufficient radial spokes and firm mountings are used to make the guard rigid enough to prevent it from being pushed into the fan blade during normal use.

LESSON 2

WOODWORKING MACHINERY REQUIREMENTS

Many of the woodworking requirements apply to specific types of equipment such as cut-off saws and circular saws. One of the first requirements of the section (1910.213 (a)(4)) covers automatic cutoff saws. On October 30, 1978 OSHA issued a directive (OSHA Instruction STD 1-12.15) that clarified it’s position on automatic cutoff saws.

LESSON 2


In work situations where employees are not exposed to any hazards involving automatic cut-off saws, such saws that stroke continuously without the operator being able to control each stroke, may be used.

In work situations where employees are exposed to any hazards involving automatic cut-off saw, (e.g., load, clamp, cut-off, unload, etc.) such saws that stroke continuously without the operator being able to control each stroke are in violation of 29 CFR 1910.213(a)(4) and shall be cited.

LESSON 2


One on the most hazardous situations involving woodworking machinery is the re-starting of a machine after the power has been cut. Any time injury to the operator might result if motors were to restart after power failures, a safety guard must be implemented to prevent machines from automatically restarting upon restoration of power (usually an in-line anti restart cord with a built-in reset button).

LESSON 2


It is important that machine operators can cut power to the machine anytime it is necessary, and as soon as possible. To accomplish this, OSHA has another requirement: A mechanical or electrical power control shall be provided on each machine so the operator can cut off the power from each machine without leaving his position at the point of operation.

Safety and practicality are important consideration when setting up woodworking machines for operator use. Power controls and operating controls should be located within easy reach of the operator while he is at his regular work location, making it unnecessary for him to reach over the cutter to make adjustments.

LESSON 2


For circular saws where there is a possibility of contact with the portion of the saw either beneath or behind the table, that portion of the saw shall be covered with an exhaust hood, or, if no exhaust system is required, with a guard that shall be so arranged as to prevent accidental contact with the saw.

Each circular hand-fed ripsaw shall be guarded by a hood which completely encloses that portion of the saw above the table and above the material being cut.

LESSON 2


The hood and mounting must be arranged so that the hood will automatically adjust itself to the thickness of, and remain in contact with, the material being cut. On October 30, 1978, OHSA released directive STD 1-12.18 to clarify this requirement.

Automatically adjusting guards are not required where fixed enclosures or fixed barrier guards provide protection equivalent to the protection of automatically adjusted guards, thereby preventing employee exposure to the saw blade.

LESSON 2

Other woodworking tools addressed by OHSA in the regulations include: Self-feed circular saws, swing cutoff saws, radial saws, band saws, jointers, and many other specialized machines, a detailed discussion of which is beyond the scope of this lesson.


Radial saws must be equipped with special safety features to protect operators. These include:

a guard that encloses the upper portion of the blade

an adjustable guard for the sides and lower portion of the blade, to the full diameter of the blade, by a device that will automatically adjust itself to the thickness of the stock

LESSON 2


Non-kickback fingers or dogs located on both sides of the saw so as to oppose the thrust or tendency of the saw to pick up the material, or to throw it back toward the operator; an adjustable stop shall be provided to prevent the forward travel of the blade beyond the position necessary to complete the cut in repetitive operations; and a retracting device to automatically bring the saw back to the starting position are other required safety guards.

LESSON 2

ABRASIVE WHEEL MACHINERY

Safety guards are required on abrasive wheel machines except when they are used for internal work while within the work being ground; mounted wheels, used in portable operations, 2 inches and smaller in diameter; or special listed operations where the work offers full protection (see 1910.215 (a)(1)(iii).

The safety guard shall cover the spindle end, nut, and flange projections.

LESSON 2


Work rests must be kept closely adjusted, maximum gap = 1/8", to prevent work from jamming & breaking wheel. The adjustable tongue guard must be kept adjusted within 1/4" of the grinding wheel. It is important to remember that these guards require continual adjustment as the diameter of the grinding wheel decreases with use, they must be securely clamped after each adjustment, and adjustments are made only after the wheel has stopped.

LESSON 2


Other important requirements for abrasive grinding machinery:

The rpm rating on the grinding wheel must be rated at or higher than the rpm rating of the grinding machine it is being installed on. If the rpm rating is lower than that of the grinder the wheel could break apart causing possible serious injury to the operator.

Wheels should be tapped gently with a light nonmetallic implement, such as the handle of a screwdriver for light wheels, or a wooden mallet for heavier wheels. If they sound cracked (dead), they shall not be used. This is known as the "Ring Test".

LESSON 2


Guard exposure angles

The amount of grinding wheel that can be exposed, varies with the type of grinder used.

Visors or other accessory equipment shall not be included as a part of the guard when measuring the guard opening, unless such equipment has strength equal to that of the guard.

LESSON 2

Maximum wheel exposure = 90º

Maximum angle of exposure abovethe horizontal = 65º

Angular exposure for wheel periphery

Horizontal plane of the spindle

For bench and floor stand grinders


The angular exposure of the grinding wheel periphery and sides for safety guards used on machines, known as bench and floor stands, should not exceed 90 degrees, or one-fourth of the periphery.

This exposure shall begin at a point not more than 65 degrees above the horizontal plane of the wheel spindle, according to the chart.

LESSON 2

Maximum wheel exposure = 90º

Maximum angle of exposure abovethe horizontal = 65º

Angular exposure for wheel periphery

Horizontal plane of the spindle

For bench and floor stand grinders


Protective eyewear should always be used when working with abrasive wheel machinery. Either safety glasses with side shields, or safety goggles should be worn to protect the eyes from sparks and flying particles, and from the wheel itself, should it break apart during use. Face shields are just that: shields that protect the face. They are not designed to provide eye protection, and should only be used in conjunction with appropriate eye protection.

LESSON 2

POWER PRESSES, FORGING MACHINES, POWER-

TRANSMISSIONThis lesson focuses on the following topics:

Mechanical Power Press Safety

Forging Machine Safety

Mechanical Power Transmission Apparatus

LESSON 3

MECHANICAL POWER PRESS SAFETY

Mechanical power presses are powerful machines that can easily produce many tons of pressure at the point of operation. Because they are so powerful, injuries resulting from mechanical power presses can be severe.

Point of operation guards are required that prevent entry into the point of operation during the operating cycle. It is the responsibility of the employer to provide and insure the usage of point of operation guards

LESSON 3


Machines using full revolution clutches must incorporate a single-stroke mechanism.

Foot treadles (a foot pedal that can cycle a power press), if used, must be done so with extreme caution. The pedal mechanism must be protected to prevent unintended operation from falling or moving objects or by accidental stepping onto the pedal, and include a non-slip bottom.

LESSON 3


Two hand trip controls are one means for protecting operators’ hands during the press cycling operation. Each hand control must be protected against unintended operation and arranged so that the concurrent use of both hands is required to trip the press.

On part revolution presses, a red color stop control shall be provided with the clutch/brake control system. Momentary operation of the stop control shall immediately deactivate the clutch and apply the brake.

LESSON 3


Presence sensing devices are another way to protect operator’s hands.

They must prevent and/or stop normal stroking of the press if the operator's hands are inadvertently placed in the point of operation, and they must be interlocked into the control circuit to prevent or stop slide motion if the operator's hand, or other part of his body, is within the sensing field of the device during the down stroke of the press slide.

Presence sensing devices are not allowed on full revolution presses

LESSON 3


Pull-out devices are another method of protecting hands form press point of operations. The requirements for pullbacks include the following:

Each pull-out device in use shall be visually inspected and checked for proper adjustment at the start of each operator shift, following a new die set-up, and when operators are changed.

Necessary maintenance or repair, or both, shall be performed and completed before the press is operated.

LESSON 3


A record of the inspection must be kept including the date of the inspection, the signature of the person performing the inspection, and an identifier of the press that was inspected.

This is usually done by keeping an inspection card at each press that is formatted to include the above requirements plus additional data fields.

LESSON 3


Hand feeding tools are another way to protect operator’s hands by keeping them out of the point of operation, but hand feeding tools are not point of operation guards. They are supplements to other guarding systems.

It is the employer’s duty (and requirement) to train and instruct the operator in the safe method of work before starting work on any power press. The employer must also insure by adequate supervision, that the correct operating procedures are being followed.

LESSON 3


Where the operator feeds or removes parts by placing one or both hands in the point of operation, then a two hand control, presence sensing device of Type B gate or movable barrier (on a part revolution clutch) is used for safeguarding.

A brake monitor is required so that a failure within the system does not prevent the normal stopping action from being applied to the press when required, but does prevent initiation of a successive stroke until the failure is corrected.

LESSON 3

FORGING MACHINE SAFETY

Forging is the shaping of steel (usually steel bars of varying thickness). Forging usually involves heating the steel until it is ‘red’ hot, and can then be formed into the desired shape. It is required that personal protective equipment (gloves, goggles, aprons, and other items) be worn for forging operations.

LESSON 3


It is the responsibility of the employer to maintain all forge shop equipment in a condition which will insure continued safe operation. This responsibility includes the following:

Establishing periodic and regular maintenance safety checks. Keeping certification records of these inspections which include the date of inspection, the signature of the person who performed the inspection and the serial number, or other identifier, for the forging machine which was inspected.

LESSON 3


Scheduling and recording the inspection of guards and point of operation protection devices at frequent and regular intervals. Recording of inspections must be in the form of a certification record which includes the date the inspection was performed, the signature of the person who performed the inspection and the serial number, or other identifier, of the equipment inspected.

Training personnel for the proper inspection and maintenance of forging machinery and equipment.

LESSON 3

MECHANICAL POWER-TRANSMISSION APPARATUS

Belts, pulleys, chains, rotating shafts, gears, pinions, and sprockets can all be potentially hazardous to work near or around. Workers can get hands caught in pinch or nip points, or can be drawn into the moving parts of machines. All moving parts of machines that could injure employees should be guarded.

LESSON 3


Flywheels seven feet or less above the floor or working platform must be guarded with an enclosure of sheet, perforated, or expanded metal, woven wire or a guardrail.

Wherever flywheels are above working areas, guards shall be installed having sufficient strength to hold the weight of the flywheel in the event of a shaft or wheel mounting failure.

LESSON 3


All exposed parts of horizontal, vertical, and inclined shafting seven (7) feet or less from floor or working platform (excepting runways used exclusively for oiling, or running adjustments), must be protected by a stationary casing enclosing shafting completely, or by a trough enclosing sides and top or sides and bottom of shafting as location requires.

Projecting shaft ends shall present a smooth edge and end and shall not project more than one-half the diameter of the shaft unless guarded by non-rotating caps or safety sleeves. Unused keyways shall be filled up or covered.

LESSON 3


All belts, pulleys, gears, chains and sprockets must all be guarded if they are lower than seven feet from the floor or working platform.

Horizontal belts higher than seven feet must be guarded if located over passages or work location and traveling over 1800 feet per minute, if the center to center distance between pulleys is over ten feet, or if the belt is 8 inches or more in width.

Hand operated gears are exempt from the requirement for guarding, but it is highly recommended that they also be guarded.

All projecting keys, setscrews, and other projections in revolving parts shall be removed or made flush or guarded by metal cover.

LESSON 3

TYPES OF MACHINE GUARDS AND THEIR

APPLICATIONS


Guard Materials

Methods Of Machine Guarding

LESSON 4

GUARD MATERIALS

Materials for guards should be made from expanded metal, perforated or solid sheet metal, wire mesh on a frame of angle iron, or iron pipe securely fastened to floor or to frame of machine.

All metal should be free from burrs and sharp edges.

Guards should be rigidly braced every three (3) feet or fractional part of their height to some fixed part of the machinery or building structure.

Where the guard is exposed to contact with moving equipment, additional strength may be necessary.

LESSON 4

FOUR TYPES OF GUARDS

There are four types of guards available. They are: fixed, interlocked, adjustable, or self-adjusting. Scroll over each type of guard to find out more about the following:

Fixed Guards

Interlocked Guards

Adjustable Guards

Self-Adjusting Guards

LESSON 4


Fixed guards: Are permanent, independent of moving parts, and are made of substantial material such as steel or Plexiglas (see mesh pulley guard below).

LESSON 4

Interlocked guards:

Removing or opening the guard trips the interlock.


Adjustable guards:

Have the advantage of being able to accommodate variable sized parts.

LESSON 4

Self-adjusting guards:

Have the added advantage of adjusting automatically. When stock is removed, the guard returns to original position.


There are four accepted methods of guarding machine hazard areas, they are: guards, devices, location, and parts loaders/ejectors. Scroll over each method to learn more about the following:

Devices

Electromechanical

Safety Gates

Feeding and Ejection Methods

LESSON 4


Devices:

Includes presence sensing, pullbacks and holdouts, body bars, tripwires, safety gates, and two-hand controls and trips. Of these, presence sensing devices are the most sophisticated. One type is a photo electric beam of light that runs across the entrance to a point of operation. If the plane of the beam is broken by any object, the machine will not cycle.

Electromechanical:

This type of guard can be a probe or a contact bar. Any obstruction will prevent the machine from cycling. They are excellent for sewing or riveting operations. An example of an electromagnetic guard is a ring guard

LESSON 4


Safety Gates: Are removable barriers that protect the operator before the machine

cycle starts. Usually they are interlocked so if the gate is opened the machine will stop, and a cycle will not initiate until the gate is closed.

Feeding and Ejection Methods:

Can keep the operator’s hands out of the point of operation at all times. Parts are placed in a feeder, and are automatically ejected from the machine.

LESSON 4

Machine Guarding

Documents

osha machine

machine parts

machine guarding osha

types of machine guarding

machine actions

specific machine

powered machine

basics of machine guarding