Accident Prevention Manual
for Business & Industry:
Engineering & Technology
13th edition
National Safety Council
Compiled by
Dr. S.D. Allen Iske, Associate Professor
University of Central Missouri
CHAPTER 6
SAFEGUARDING
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Safeguarding
• A primary method to reduce worksite hazards
• Prevents personnel from contact with moving parts
• Key is to identify hazards
• Includes barriers, guards, signs, lockout/tagout, safety
design, enclosures, fences
Definitions
• Safeguarding—Any means of preventing personnel from
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coming in contact with moving parts of machinery or
equipment, that would potentially cause harm
Device—a mechanism or control designed for
safeguarding at the point of operation
Guard—barriers designed for safeguarding
Enclosure—safeguarding by fixed physical barriers that
are mounted on or around the machine to prevent
accidents
Fencing—safeguarding by means of a locked fence or rail
Location—safeguarding when a hazard is physically
inaccessible under normal operating conditions or use
Definitions (Cont.)
• Nip points or bites—the hazardous area created by two
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or more mechanical parts, rotating in opposite directions
within the same plane
Pinch point—the point where any body part can be
caught between two moving parts or one fixed and one
moving
Point of operation—the area of a machine where
material is positioned or work is performed on material
Power transmission—all mechanical parts (gears, cams,
shafts, pulleys, belts, clutches) that transmit energy and
motion from a source of power to equipment or a machine
Shear points—the hazardous area created by the cutting
movement of a mechanical part
Point-of-Operation Protection Devices
• Openings used for safeguarding
• should not exceed 3/8”
• prevents entry or contact
• first 1.5” from danger line should not exceed 1/4” opening
Point-of-Operation Safeguards
• Guard construction
• must be sturdy and secure (substantially constructed)
• secured to minimize distortion or movement.
• sufficiently strong to withstand stress and exposure
• usually made of metal
Point-of-Operation Safeguards (Cont.)
• Proper guard characteristics:
• integration with machine
• adequate construction, durability, and strength
• handle workpiece in-feed and ejection
• protection from the hazards
• ease of inspection and maintenance
• tamper-proof or foolproof
• Proper guard should NOT:
• Create additional hazards
• Interfere with production
• Cause work discomfort
Point-of-Operation Safeguards (Cont.)
• Types of safeguards
• built-in safeguards
• barrier guards
• interlocking barrier guards
• automatic safeguard devices
• guarding by location
• Substitution
• Match machine or equipment to the operator
• Study and review Table 6–A
Types of Safeguards
• Built-in safeguard
• factory made, conforms to the machine—appearance, placement,
and function
• eliminates hazards
• withstands normal wear and tear
• costs less than improvised/modified safeguard
Types of Safeguards (Cont.)
• Barrier guard
• prevents physical access to dangerous point of operation or work
area
• usually adjustable for different sets of tools or kinds of work
• once adjusted, must not be moved or detached
Types of Safeguards (Cont.)
• Interlocking barrier guard
• can be electrical, mechanical, pneumatic or combination
• prevents operation of machine control mechanism until guard
moves into predetermined position
• when open, machine cannot operate and mechanism is locked.
• when machine is in motion or operation, guard cannot be opened
until machine comes to rest or fixed position
Interlocking Barrier Guards
• Effective interlocking barriers must meet three
requirements:
• guard hazardous area before machine can be operated
• stay closed until the rotating equipment is at rest
• prevent operation of the machine if the interlocking device fails
Types of Safeguards
• Automatic safeguarding devices
• prevent operator from coming in contact with dangerous parts of a
machine while the machine is in motion
• stop the machine in the event of a sub-normal operating condition
(shuts down operation)
• types of devices:
• presence-sensing devices
• pull-backs
• restraints
• two-handed controls
Guarding by Location
• Location of the exposed part will be sufficient for guarding
purposes.
• OSHA 29 CFR 1910.219
• All exposed parts of horizontal shafting seven (7) feet or less from
floor or working platform, excepting runways used exclusively for
oiling or running adjustments, shall 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.
Types of Safeguards (Cont.)
• Substitution
• Substitute a less hazardous machine or piece of equipment for a
more hazardous one.
• Eliminates or reduces machine hazards
Types of Safeguards (Cont.)
• Match operator to the machine
• Workplace—arrange equipment to minimize work
• Work height—adjust for operator
• Controls and displays—make them readily accessible
• Material handling aids—handles, hoists, belts, conveyors, lifts
• Operator fatigue—reduced when job is well designed
Guarding Power Transmissions
• Rotating, reciprocating, and transverse motions
• In-running nip points
• Cutting actions
• Punching, shearing, and bending actions
Guarding Power Transmissions (Cont.)
• Methods of guarding actions and motions
• Similar to point-of-operation safeguards.
• Machine movements can be dangerous.
• Guards must cover all moving parts.
• Guards must allow for routine maintenance and service, but only
when equipment is properly locked out.
• Guards must be fixed in place with bolts, hinges, sliding doors, etc.
• Guards must be durable.
Guarding Power Transmissions (Cont.)
• Types of mechanical actions and motions
• rotating, reciprocating, and transverse motions
• in-running nip points
• cutting actions
• punching, shearing and bending actions
Typical Nip Points
Guarding Power Transmissions (Cont.)
• Guarding Materials
• Material must be sturdy.
• Metal is preferred.
• If visibility is required, use plastic, polycarbonate, or Lexan.
• Use aluminum, another soft metal, or plastic if rust is a concern.
• Wood has limited application due to lack of durability and strength,
relatively high cost, combustibility, and tendency to splinter.
• Provide ample ventilation through the guard.
Maintenance and Service
• Plan for routine maintenance when designing guards.
• Apply engineering techniques that reduce the frequency
of, or eliminate, a job/task.
• Design guards for easy routine maintenance access.
• Equip machines with automatic controls for lubrication,
adjustment, or service.
Control of Hazardous Energy Source
• OSHA Standard 29 CFR 1910.147
• Lockout/tagout procedures
• Purpose
• Scope
• Sequence of Lockout
• Restoring equipment to service
• Other requirements
Lockout/Tagout Procedures
• Procedures
• must be written
• lockout preferred
• tagout used when machine can’t be locked
• combination of the two is best
• strict compliance is required
Lockout/Tagout Procedures (Cont.)
• Purpose
• minimum requirements
• isolates energy for routine maintenance and service
• guards against accidental restart
Lockout/Tagout Procedures (Cont.)
• Scope
• All employees are required to comply with the restrictions and
limitations imposed during use of lockout.
• Authorized employees are required to perform the lockout in
accordance with procedure.
• All employees upon observing a machine or equipment piece that
is locked out should not attempt to start, energize, or use that piece
of equipment or machine.
Lockout/Tagout Procedures (Cont.)
• Sequence
• Notify employees of servicing or maintenance on a machine or
equipment—shut down and lock out.
• Authorized employee refers to and follows procedures to identify
the type and magnitude of energy source.
• Shut down by normal procedure.
• Deactivate the energy—isolating device—machine isolated from
energy sources (lockout/tagout)
• Dissipate stored or residual energy and gas/air/steam
• Verify isolation before performing service.
• Machine is now LOCKED OUT!
Lockout/Tagout Procedures (Cont.)
• Restore service
• Remove non-essential items from the work area.
• Make sure machine is intact.
• Remove all employees from the area.
• Put controls in neutral.
• Remove locks and reenergize the equipment.
• Notify employees that maintenance or servicing is completed.
Equipment or machine is ready for use.
• Group lockout—for a piece of equipment or power source, each
employee shall have an individual lock and apply the lock to the
device.
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Lockout/Tagout Procedures (Cont.)
• Training
• Train all employees in lockout/tagout.
• Retrain annually.
• Audit training program annually.
• Conduct remedial training as needed for individuals for nonconformance actions .
• Lockout equipment
• Devices shall be durable, marked, color coded, or otherwise
identified for each facility and supplied to authorized personnel.
Correct tag labels and strength.
Robotics Safeguarding
• Principal hazards
• being struck by the moving parts of a robot while in the operating
envelope or movement zone
• caught between moving parts of the robot and other machinery or
objects within or near the robots movement zone
• being struck by objects or tools the robot has dropped or ejected
Robotics Safeguarding (Cont.)
• Safeguarding methods
• Restrict robot movement zone to required range of motion for
particular operation
• Install an amber light on a robot, which turns on when the robot is
“live” or operational.
• Install barriers and fixed guards.
• Have emergency stop or “deadman” buttons hardwired to robot
power source and easy to reach.
• Program so operator cannot place into automatic cycle until all
interlocked gates are closed and operator is at master control panel
outside of robot movement zone.
Guards and Noise
• If well designed and mounted, guards:
• may reduce noise
• act as a barrier
• absorb, reflect, or confine sound waves