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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.