Hazards Calculations

Industrial SafetyLecture 9

Machine Guarding

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Industrial Safety

Some common mechanical hazards.

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Introduction

Crushed hands and arms, severed fingers, blindness - the list of possible machinery-related injuries is as long as it is horrifying. Safeguards are essential for protecting workers from needless and preventable injuries.

A good rule to remember is: Any machine part, function, or process which may cause injury must be safeguarded.

Where the operation of a machine can injure the operator or other workers, the hazard must be controlled or eliminated.

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Causes of Machine Accidents

• Reaching in to “clear” equipment

• Not using Lockout/Tagout

• Unauthorized persons doing maintenance or using the machines

• Missing or loose machine guards

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Where Mechanical Hazards Occur

• Point of operation

• All parts of the machine which move, such as:

– flywheels, pulleys, belts, couplings, chains, cranks, gears, etc.

– feed mechanisms and auxiliary parts of the machine

• In-running nip points

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Point of Operation

That point where work is performed on the material, such as cutting, shaping, boring, or forming of stock must be guarded.

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Rotating Parts

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In-Running Nip Points

Belt and pulley

Chain and sprocket

Rack and pinion

Rotating cylinders

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Requirements for Safeguards

• Prevent contact - prevent worker’s body or clothing from contacting hazardous moving parts

• Secure - firmly secured to machine and not easily removed

• Protect from falling objects - ensure that no objects can fall into moving parts

• Create no new hazards - must not have shear points, jagged edges or unfinished surfaces

• Create no interference - must not prevent worker from performing the job quickly and comfortably

• Allow safe lubrication - if possible, be able to lubricate the machine without removing the safeguards

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Methods of Machine Safeguarding

• Guards

– fixed

– interlocked

– adjustable

– self-adjusting

• Devices

– presence sensing

– pullback

– restraint

– safety controls (tripwire cable, two-hand contol, etc.)

– gates

• Location/distance

• Feeding and ejection methods

– automatic and/or semi-automatic feed and ejection

– robots

• Miscellaneous aids

– awareness barriers

– protective shields

– hand-feeding tools

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Fixed Guard

Provides a barrier - a permanent part of the machine, preferable to all other types of guards.

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Interlocked Guard

When this type of guard is opened or removed, the tripping mechanism and/or power automatically shuts off or disengages, and the machine cannot cycle or be started until the guard is back in place.

Interlocked guard on revolving drum

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Adjustable Guard

Provides a barrier which may be adjusted to facilitate a variety of production operations.

Bandsaw blade adjustable guard

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Self-Adjusting Guard

Provides a barrier which moves according to the size of the stock entering the danger area.

Circular table saw self-adjusting guard

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Pullback Device

• Utilizes a series of cables attached to the operator’s hands, wrists, and/or arms

• Primarily used on machines with stroking action

• Allows access to the point of operation when the slide/ram is up

• Withdraws hands when the slide/ram begins to descend

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Pullback Device (cont’d)

• Hands in die, feeding

• Point of operation exposed

• Pullback device attached and properly adjusted

• Die closed

• Hands withdrawn from point of operation by pullback device

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Restraint Device

• Uses cables or straps attached to the operator’s hands and a fixed point

• Must be adjusted to let the operator’s hands travel within a predetermined safe area

• Hand-feeding tools are often necessary if the operation involves placing material into the danger area

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Safety Tripwire Cables

• Device located around the perimeter of or near the danger area

• Operator must be able to reach the cable to stop the machine

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Two-Hand Control

• Requires constant, concurrent pressure to activate the machine

• The operator’s hands are required to be at a safe location (on control buttons) and at a safe distance from the danger area while the machine completes its closing cycle

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Gate

• Movable barrier device which protects the operator at the point of operation before the machine cycle can be started

• If the gate does not fully close, machine will not function

Gate Open Gate Closed

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Safeguarding by Location/Distance

• Locate the machine or its dangerous moving parts so that they are not accessible or do not present a hazard to a worker during normal operation

• Maintain a safe distance from the danger area

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Automatic Feed(shown on power press)

Transparent EnclosureGuard

Stock FeedRoll

DangerArea

Completed Work

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Robots

• Machines that load and unload stock, assemble parts, transfer objects, or perform other tasks

• Best used in high-production processes requiring repeated routines where they prevent other hazards to employees

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Protective Shields

These do not give complete protection from machine hazards, but do provide some protection from flying particles, splashing cutting oils, or coolants.

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Holding Tools

• Used to place and remove stock in the danger area

• Not to be used instead of other machine safeguards, but as a supplement

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Some Examples of OSHA Machine Guarding Requirements . . . .

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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 must be guarded with a guard having openings no larger than 1/2 inch.

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Abrasive Wheel Machinery

Work rests on offhand grinding machines must be kept adjusted closely to the wheel with a maximum opening of 1/8-inch to prevent the work from being jammed between the wheel and the rest, which may result in wheel breakage.

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Abrasive Wheel Machinery

The distance between the wheel periphery and the adjustable tongue must never exceed 1/4-inch.

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Power-Transmission Apparatus

Power-transmission apparatus (shafting, flywheels, pulleys, belts, chain drives, etc.) less than 7 feet from the floor or working platform must be guarded.

Unguarded beltand pulley

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Machine Safety Responsibilities

• Management– ensure all machinery is properly guarded

• Supervisors– train employees on specific guard rules in their areas– ensure machine guards remain in place and are functional– immediately correct machine guard deficiencies

• Employees– do not remove guards unless machine is locked and tagged– report machine guard problems to supervisors immediately– do not operate equipment unless guards are in place

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Training

• Hazards associated with particular machines

• How the safeguards provide protection and the hazards for which they are intended

• How and why to use the safeguards

• How and when safeguards can be removed and by whom

• What to do if a safeguard is damaged, missing, or unable to provide adequate protection

Operators should receive training on the following:

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Summary

• Safeguards are essential for protecting workers from needless and preventable machinery-related injuries

• The point of operation, as well as all parts of the machine that move while the machine is working, must be safeguarded

• A good rule to remember is: Any machine part, function, or process which may cause injury must be safeguarded

Common Mechanical Injuries

• The most common mechanical injuries are:

– Cutting and tearing

– Shearing

– Crushing

– Breaking

– Straining

– Spraining

– Puncturing

Machine-Operator Contact Injuries (1 of 2)

• Safeguarding involves devices or methods that minimize the

risk of accidents resulting from machine-operated contact.

Machine-Operator Contact Injuries (2 of 2)

• The contact may result from an individual making contact with:

– A machine

– Flying metal chips

– Chemical

– Hot metal splashes

– Stock kickbacks

– Mechanical malfunction

Risk Assessment (1 of 2)

• In addition to the Decision Tree the following model can be

used for risk assessment in machine operations:

– List all machines/processes in the facility.

– Collect pertinent information about the

machines/processes.

– Remove all safeguards.

Risk Assessment (2 of 2)

– Observe the machine/processes in operation without the

safeguards.

– Choose an established method for labeling risk levels.

– Choose safeguards on the basis of the level of risk

identified.

OSHA Standard for Machine Guarding(1 of 2)

• The OSHA standard containing the general requirements for

machine guarding is 29 CFR 1910.212.

OSHA Standard for Machine Guarding(2 of 2)

• This standard contains requirements in the following areas:

– Types of guarding

– General requirements

– Guarding the point of operation

– Machines requiring point-of-operation guards

– Exposure of fan blades

– Anchoring fixed machinery

Characteristics of Safeguards

• All safeguards should have the following characteristics:

– Prevent contact.

– Be secure and durable.

– Protect against falling objects.

– Create no new hazards.

– Create no interference.

– Allow safe maintenance.

Types of Point-of-Operation Devices (1 of 2)

• Point-of-operation devices come in a variety of different types

including:

– Photoelectric

– Radio frequency

– Electromechanical

– Pullback

– Restraint

Types of Point-of-Operation Devices (2 of 2)

– Safety trip

– Two-hand controls

– Trips

– Gates

– Wireless controls

Types of Feeding and Ejection Systems

• Feeding and ejection systems can be effective safeguards if

properly designed and used.

• These systems come in two types:

– Automatic

– Semiautomatic

Mechanical Hazards Associated with

Robots (1 of 2)

• The main mechanical hazards associated with robots are as

follows:

– Entrapment of a worker between a robot and a solid

surface

– Impact with a moving robot arm

– Impact with objects ejected or dropped by the robot

Mechanical Hazards Associated with

Robots (2 of 2)

• The best safeguard for a robot is a barrier around the

perimeter of its work envelope.

• Sensitized doors or gates in the barrier can also decrease the

hazard potential.

OSHA’s Standard for the Control of

Hazardous Energy

• OSHA’s standard for the control of hazardous energy (29 CFR

1010.147) is often referred to as the lockout/tagout standard.

• The overall purpose of the standard is to prevent injuries from

the accidental or inadvertent energizing of machines or

equipment while they are shut down for maintenance or

servicing.

Permanent Electrical Safety Devices in

Lockout/Tagout Programs

• An emerging technology in electrical safety is the permanent

electrical safety device (PESD).

• PESDs have excellent potential to help workers safely isolate

electrical energy, especially when used as part of an

organization’s lockout/tagout procedures.

• Properly installed and validated before each use, PESDs can

avoid the risky endeavor of verifying voltage, thereby

improving electrical safety and the chance of accidently

instigating the operation of a machine.

Key Concepts of the Lockout/Tagout

Standard

• Key concepts in this standard are as follows:

– Affected employee

– Authorized employee

– Energy control program

– Lockout

– Lockout device

– Tagout

– Tagout device

Key Provisions in the Lockout/Tagout

Standard (1 of 2)

• Key provisions in the standard include:

– Energy control program

– Energy control procedure

– Energy-isolating devices

– Requirements for lockout/tagout

– Employee training

Key Provisions in the Lockout/Tagout

Standard (2 of 2)

– Periodic inspections

– Application of controls

– Lockout/tagout devices

– Removal of locks and tags

Respond Immediately to Hazards

• When hazards or hazardous behaviors are observed,

corrective action should be taken immediately.

• Waiting to act can be fatal.