-
S a f e g u a r d i n gi n
M a n u f a c t u r i n g
M A C H I N E G U A R D I N G C H E C K L I S TGuarding
Requirements1. Do the guards prevent workers hands, arms,
and other body parts from making contactwith dangerous moving
parts?
2. Are the guards firmly securedand not easily removable?
3. Do the guards ensure that no objects willfall into the moving
parts or explode out?
4. Do the guards permit safe, comfortable, andrelatively easy
operation of the machine?
5. Can the machine be oiled or greasedwithout removing the
guard?
6. Does the machine automatically shutdown when the guard is
removed?
7. Can the existing guards be improved?Mechanical Hazards: Point
of Operation1. Is there a point-of-operation guard
provided for the machine?2. Does it keep the operators
hands,
fingers, body out of the danger area?3. Is there evidence that
the guards have
been tampered with or removed?4. Can you suggest a more
practical, effective guard?5. Can you make changes on the
machine to
eliminate point-of-operation hazard entirely?Mech. Hazards:
Power Transmission Apparatus1. Are there any unguarded gears,
sprockets,
pulleys or flywheels on the apparatus?2. Are there any
exposed
belts or chain drives?3. Are there any exposed set
screws, key ways, collars, etc.?4. Are starting and stopping
controls
within easy reach of the operator?5. If there is more than one
operator,
are separate controls provided?Mechanical Hazards: Other Moving
Parts1. Are guards provided for all
hazardous moving parts of themachine, including auxiliary
parts?
A Companion Guide to
Safeguarding Machineryand Equipment
Yes No
Yes No Yes No
Yes No Yes No Yes No Yes No
Yes No
Yes No Yes No Yes No
Yes No
Yes No Yes No Yes No Yes No
Yes No
Yes No
M A C H I N E G U A R D I N G C H E C K L I S TEducation &
Training1. Do operators and skilled trades workers
have the necessary education and trainingin how to use the
guards?
2. Does the education include examples ofworkers in your
workplace or elsewhere whomight have lost their life or their limbs
fromlack of machine guarding?
3. Have production workers and skilled tradesworkers been
trained in where the guardsare located, how they provide
protection,and what hazards they protect against?
4. Have production workers and skilledtrades workers been
trained in how andunder what circumstances guards can
beremoved?
5. Have workers been trained in the procedureto follow if they
notice guards that aredamaged, missing or inadequate?
6. Do skilled trades workers have thenecessary education and
training in howto build the safety aspects of guards?
Protective Equipment & Proper Clothing1. Is protective
equipment required?2. If protective equipment is required, is
it
appropriate for the job, in good condition,kept clean and
sanitary, and stored carefullywhen not in use?
3. Is the operator dressed safely for the job(no loose fitting
clothing or jewelry)?
Machinery Maintenance & Repair1. Have skilled trades workers
received
up-to-date instructions on the machinesthey service?
2. Do skilled trades workers lock out themachine from all of its
energy sourcesbefore beginning repairs?
3. Is the maintenance equipment itself properlyguarded?
Yes No
Yes No
Yes No
Yes No
Yes No
Yes No
Yes No Yes No
Yes No
Yes No
Yes No
Yes No
This presentation has been formatted by:Flip Productions Ltd
Nanaimo, BC Canada1-888-220-FLIP (3547) www.flipproductions.comMade
in Germany by Infoflip ULM e.K. IF.G.01.00272.A.01
BK10912/2006
-
WorksafeBC makes no representations, warranties, orcondition,
expressed or implied, that this document is andwill remain accurate
at all times. WorkSafeBC is notresponsible for direct, indirect,
special, or consequentialdamages, however caused, arising from the
use of thisdocument and its information. Employers and
workersshould always refer to the Act/Regulation and
applicableguidelines for specific requirements that apply to their
workoperations and activities.
For more information, please refer to the full
manual:Safeguarding Machinery and Equipment
General Requirements(WorksafeBC #BK101)
Safeguarding Controls
Eliminate human interaction in the process Eliminate pinch
points Automate material handling Mechanical hard stops Interlocked
guards Barrier guards 2-handed controls Presence-sensing devices
Computer warnings Lights, beacons, Warning signs/labels Strobes,
beepers Restricted Space Horns and sirens
painted on floor Safe work procedures Training Safety Equipment
Inspections Lockout Safety eyewear Gloves Hearing protection
Respirator Face shield Hardhat Steel toe safety boots
MOSTEffective
LEASTEffective
1. Elimination/Substitution
2. EngineeringControls
3. Awareness
4. Training &Procedures
5. PPE
This Infoflip is a companion guide and is merelyintended to draw
attention to some hazards andpreventative safeguarding measures:
the user isrequired to do a complete hazard analysis
Hierarchy of Safeguarding Controls
-
This infoflip was produced to help: Employers to comply with the
Occupational
Health and Safety Regulation (OHSR) and Part3 of the Workers
Compensation Act, and toexercise due diligence in providing a safe
workenvironment
Supervisors to assess risks to their workersfrom harmful contact
with machinery andequipment, and to evaluate safeguardingsolutions
that satisfy the competing needs ofsafety, production, and quality
assurance
Workers to gain greater awareness of thehazards associated with
equipment operationand maintenance, and of the
safeguardingprotection they have a right to expect
Suppliers to understand the requirements formachinery and
equipment to conform to theWorkers Compensation Act and the
OHSR
Individuals involved in risk assessment,maintenance, operations
management, andhealth and safety committees.
-
Safeguarding is the first line of defence in ensuring thesafety
of workers operating powered machinery andequipment. It protects
workers when machinery/equipmentis in operation. Safeguarding
should consider the Hierarchyof Safeguarding choose the most
effective option.
Steps to Effective Safeguarding1. Recognize the hazard
(2)Recognize the hazard (2)2. Assess the risk (3)Assess the risk
(3)3. Develop and/or apply safeguarding to eliminate the risk
to
an acceptable level4. Ensure required communication, orientation
and training
is performed5. Evaluate safeguarding for its effectiveness and
make
adjustments as required.Do not confuse safeguarding with
lockout, which protectsworkers when machinery or equipment is shut
down formaintenance (including repairs and clearing jams).
Trainingand supervision are essential to ensure worker safety
forany activity around machinery.
TerminologySafeguards
This is the umbrella term for measures that give
workerseffective protection from harmful contact with
hazardousmoving parts or other harmful conditions.
Safeguardsinclude barrier guards, safety devices, shields,
awarenessbarriers, warning signs, etc., used singly or in
combination.
Guards/Barrier GuardsThese are physical barriersor covers that
are designed,constructed, and installed toprevent contact with
movingparts, e.g., belts and drivechains. They are reliableand
cost-effective solutionswhen access to movingparts is not needed
during operation. They usually requirelow maintenance if properly
designed and installed.Alternatives to barrier guards are
interlocked movable barrierguards, two-hand controls, and
electronic presence-sensingdevices, e.g., light curtains and
pressure-sensitive mats.These solutions are more complex/technical
but may be theonly option when access to danger areas is required
duringnormal operation, e.g., when materials are fed into amachine
for processing.
Personal Protective Equipment (PPE) Personal protective
equipment may have to be used evenwhen other machine hazards are
effectively safeguarded. Insome cases, such as operating a powered
forging hammer,the only protection available to the operator,
besides trainingand safe work procedures, may be eye and face
protection,hearing protection, and hand protection.
1 Overview and Terminology
1 Overview and Terminology
MUST and SHOULDMust a requirement orstandard in Part 12, OHSR
Should a course ofaction that, although notspecified in the OHSR,
willimprove workplace safety
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2 Hazard Recognition
2 Hazard Recognition
Most machines have three principal components: a powersource
(often an electrical motor), a power train thattransfers moving
energy, and tooling where machines workis performed. Hazards from
these components generallyinvolve belts, pulleys, chains,
sprockets, gears, shafts, andcouplings used with the power train,
and the operations andprocesses completed by the tooling.
Recognizing Mechanical HazardsObserve how moving parts of a
machine operate and howparts of a workers body may comeinto contact
with them. Parts that rotate (e.g., shafts or
couplings), present a risk ofentanglement/snagging. Two ormore
parts rotating together(e.g., feed rolls, V-belt and pulleydrives),
create nip points
Parts that slide or reciprocate(e.g., dies in punch
presses),create shearing or crushinghazards.
Parts that rupture or fragment(e.g., abrasive wheel), maycause
impact injuries.
Some machinery/equipment can endanger a worker in morethan one
way. For example, an abrasive wheel can explode
Recognizing Health HazardsWithout safeguards, control measures,
and PPE (1)PPE (1), aworker may be exposed to: Toxic/corrosive
chemicals that irritate or pass through skin Airborne substances,
e.g., oil
mist, metal fumes, solvents Heat, noise, and vibration Ionizing
radiation such as X-
rays and gamma rays Non-ionizing radiation such as
ultraviolet light (UV), radiofrequency (RF) energy, lasers
Biological contamination/waste Soft tissue injuries
resulting
from repetitive motion,awkward posture, extendedlifting, and
pressure grip
Recognizing Other Hazards Slips/falls from and around machinery
during maintenance Unstable equipment not secured against falling
over Fire or explosion Pressure injection injuries from the release
of fluids and
gases under high pressure Electrocution from
faulty/ungroundedelectrical components
and cause serious impact injuries. Or, a worker can receiveminor
abrasions from accidental contact with the wheel.
Sliding Milling Table
NipPoint
Hazards from Fragmentsand Projectiles
Common Hazards
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3 Risk Assessment
3 Risk Assessment
The two most important factors affecting risk are: How likely
will an accident occur Measure of Probability How serious will the
injuries be Measure of SeverityCombining the two factors determines
the level of risk. Forexample, if the likelihood that a worker will
come in contactwith dangerous moving parts of a machine is low, and
if hedoes, the expected injury is only a mild abrasion, the
risklevel is very low. However, if harmful contact is almostcertain
and expected injuries are very severe, the risk levelis extremely
high.
Assessing RiskA risk assessment must involve the operator,
maintenancepersonnel, and the supervisor. You should also consult
withmanufacturers, suppliers of safeguards, and
safetyprofessionals. Each party sees the machine from a
differentperspective, and will provide a valuable
contribution.Follow the steps to effective safeguarding (1)steps to
effective safeguarding (1). Gatheringinformation for a risk
assessment may require repeatedobservations, especially when
determining what the workerdoes when normal production flow is
interrupted. Do notlimit your assessment to the question, What is a
workerlikely to do? Try to determine ALL possible actions, i.e.,
ifsomeone can access a hazard, a safeguard is warranted.
Factors Affecting the Probability of InjuryFactors that increase
the probability of contact withunguarded hazardous machine moving
parts include: Lack of familiarity with the machine Hand-feeding a
machine activated by a foot control Reaching into a machine to
clear jams and misfeeds Boredom and repetition Frequent access to
danger areas of the machine for
setup and adjustments Lack of operator training and experience
Machine cycle speed
Machine Risk Assessment Survey A Machine Risk Assessment Survey
form is available at:
www2.worksafebc.com/PDFs/manufacturing/Machine_Risk_Assess_Survey.pdf
The form can be revised and adapted to suit your needs use it to
prioritize your safeguarding measures: Identify/describe each
hazardous machine motion and
condition (e.g., rotating shaft, nip point, shearing
part,punching/impact hazard, flying debris, abrasive/hotsurface,
electrical hazard, hot/toxic fluid or vapour, etc.)
Describe in detail the worst injury that would reasonablyoccur
(e.g., death, loss of sight, spinal damage,amputation/crushing,
respiratory damage, loss ofconsciousness, burns, fracture,
bruising, cuts, abrasions)
Estimate the severity (fatal,
major/irreversible,serious/reversible, minor) and the likelihood
(unlikely,possible, probable, certain) of injury
Calculate the level of risk by factoring the severity of
theinjury multiplied by the likelihood of its occurrence
-
The most effective safeguard is a device or system thatprovides
the maximum protection for the minimum impact onnormal machine
operation. Use the guide below to determinethe most effective
safeguard.
4 Selecting the Right Safeguard
4 Selecting the Right Safeguard
Is there a lowrisk of injury?
Have you completeda risk assessmentfor each machine?
Perform a riskriskassessmentassessment(3)(3)
Install abarrier guard
Full access isrequired duringnormal operation
Install safeguardingdevice
No access isrequired duringnormal operation
Yes
NoYes
No
Safeguard Selection Guide
Fixed powertransmissionbarrier guard
Self-retractingguard (skill saw)Perimeterfencing
Two-hand controls
Barrier guardwith simpleinterlocking
Fixed point-of-operationbarrier guard
Presence-sensing device: Light curtains Radio frequency
Pressure-sensitive mat
Barrier guardwith poweredinterlocking
(Semi)automaticfeed with pointof operationenclosed
Limited machinemovement devices (joginch & set-up modes)
Emergency body contactdevices such as crashbar, panic bar, belly
bar
Self-adjusting feed guard
Passive worker restraintdevices (pull-backs)
Awareness barriers: Protective shield Splash guard
How much accessis required to thedanger area?
Install a shield, anawareness barrier,warning signs
-
5 Barrier Guards
5 Barrier Guards
As per the Hierarchy of Safeguarding Controls, barrierguards
provide the most effective protection to workers.
Fixed Barrier GuardsProtect workers from hazardous moving parts
or harmful fluidsand projectiles, particularly when access is not
normallyrequired during operation. Fixed barrier guards must
Physically prevent a worker from reaching around, over,
under, and through the guard to the danger area. Not create
additional pinch points or other hazards Safely contain broken
parts (such as belts and chains) Allow for safe lubrication and
minor adjustments.Unless interlocked with a control system, barrier
guards mustbe secured with at least one fastener requiring a tool
forremoval. When a barrier guard must be moved aside toenable a
worker access to a point of operation or feed pointduring normal
operation, the guard must be interlocked to
disable the controlsystem until guard isput back in place
andcontrol system is reset. Fixed barrier guardsshould offer
goodvisibility to feed points,stand up to normalwear and tear,
meetnormal production and
quality needs and be difficult to modify or
defeat.Self-adjusting (self-retracting) Guards
Although a self-retractingguard of a handheldcircular saw (as
shownon right) works very well,guards designed for right-handed
people can oftencause problems for left-handed persons.
Adjustable Guards
Guardretracted
Stock
Adjustable BandSaw Guard
Adjustable Power Press Feed Guard
Access to drive belt andpulleys prevented by guard
Requirestool to open
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6 Power Transmission Guards
6 Power Transmission Guards
Chain-Sprocket& V-Belt Guards
Powertransmissionparts typicallyconsist of belts,pulleys,
chains,sprockets, gears,shafts, andcouplings.Contact withthese
movingparts accounts fora large number ofpreventable
injuries. It is usually a straightforward task to fabricate
andinstall guards for these hazards by following appropriategrid
guard design considerations (7)grid guard design considerations
(7).
PTO (Power Take-Off) Drive Shaft GuardsUnguarded PTO drive
shafts are frequently used on tractorsto power portable
agricultural machinery. Because equipmentis powered for frequent,
short periods, installing guards overthese drives is often
neglected. Install a chain or cabletether at each end of the PTO
drive shaft guard so that the
Rotating Shaft and Coupling Guard
guard can be readily secured to the tractor or portableequipment
when not in use.
Wire mesh with openings meetingmaximum requirements
Provision for lubricating withouthaving to remove the guard
Guard secured with atleast one fastener
requiring a tool forremoval
Both underside and backside of guard are enclosed
to prevent access to moving parts
Typical V-Belt/Chain-Sprocket Guard
Flexible rubber boot forconnecting to machinery
Tether Chain
PTO DriveShaft Guardwith tetherchainattached toeach end ofthe
guard
Spline guardattached
to machinehousing
Rotating PTO shaftCutawayview ofPTO DriveShaft
andtypicalguard
PTO shaft guardSpline guard attached tomachine housing
Typical Design of Rotating Shaft and Coupling Guard
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7 Grid Guard Design Considerations
7 Grid Guard Design Considerations
Grid Guards and EnclosuresThese guards generally consist of
woven wire, or expandedor perforated metal and must be installed
with sufficientclearance to prevent any person from reaching
through theopenings and contacting the danger point. This is done
byplacing the guard at a safe distance from hazardous movingparts.
Test the effectiveness of guard openings with themachinery locked
out and safely at rest.
Grid Guard Opening and Distance to Danger Point
Point-of-Operation (Feed) GuardsPoint-of-operation guards (also
known as feed guards) oftenenable the operator to insert flat stock
into a machine. Feedguards must ensure that the workers hands
cannot accessthe danger point. Note in the table below how the
openingsbetween the horizontal guarding members decrease as
theworkers fingers come closer to the pinch point.
Maximum Permissible Openings in Feed GuardsBarrier Opening Size
Minimum Distance From Hazard(smallest dimension)
mm in Slotted opening Square opening6.1 11 1/4 3/8 64 mm (2-1/2
'') 48mm (2 '')11.1 16 3/8 5/8 89 mm (3-1/2 '') 66 mm (2-5/8
'')16.1 32 5/8 1-1/4 166 mm (6-1/2) 166 mm (6-1/2 '')32.1 49 1-1/4
2 445 mm (17-1/2 '') 445 mm (17-1/2'')49.1 132 2 5 915 mm (36 '')
915 mm (36 '')
If a is between4 mm and 8 mm(3/16 '' and 3/8 ''),b must be at
least15 mm (5/8 '')
If a is 20 mm 30 mm(3/4 '' 11/8 ''), b must beat least 200 mm (7
7/8 '')
If a is 30 mm 150 mm(11/8 '' 6 ''), b must beat least 850 mm
(331/2 '')
If a is 8 mm 12 mm (3/8 '' 1/2 ''),b must be at least 80 mm (3
1/8 '')If a is 12 mm 20 mm (1/2 '' 3/4 ''),b must be at least 120
mm (4 3/4 '')
a
aa
a
bb
bb
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8 Protective Barriers
8 Protective Barriers
Protective barriers such as rail enclosures or perimeterfences
should be at least 1.8 m (6 ') high. If this is notpractical, use
the figure and table below to find the reachdistance from the
guardrail or perimeter fence to the dangerpoint. For example, if
the height of the danger zone (A) is1,400 mm (55 '') and its
horizontal distance (C) from theproposed protective barrier is
1,000 mm (40 ''), the height ofthe protective barrier (B) must be
at least 1,120 mm (44 '').
Recommended Height of Protective BarrierBased on Distance to
Hazard
DangerZone (A) 1000 1120 1400 1600 1800 2000 2200 2400
2500Height (40) (44) (55) (63) (71) (78) (86) (94) (98) mm ('')
2500 (98)
2400 100 100 100 100 100 100 100 100 (94) (4) (4) (4) (4) (4)
(4) (4) (4)
2200 600 600 500 500 400 350 250 (86) (24) (24 ) (20) (20) (16)
(14) (10)
2000 1100 900 700 600 500 350 (78) (43) (36) (28) (24) (20)
(14)
1800 1100 1000 900 900 600 (71) (43) (40) (36) (36) (24)
1600 1300 1000 900 900 500 (63) (51) (40) (36) (36) (20)
1400 1300 1000 900 500 100 (55) (51) (40) (36) (20) (4)
1200 1400 1000 900 500 (48) (55) (40) (36) (20)
1000 1400 1000 900 300 (40) (55) (40) (36) (20)
800 1300 900 600 (32) (51) (36) (24)
600 1200 500 (24) (48) (20)
400 1200 300 (16) (48) (12)
200 1100 200 (8) (43) (8)
0 1100 200 (0) (43) (8)
Fixed Barrier/Protective Structure Height (B)mm ('')
Horizontal Distance to Danger Zone C, mm ('')
Danger Point
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Legal Background Information
Topics discussed in this infoflip, and other relatedissues, are
based on the following legislation:Safeguarding: Operational Health
and SafetyRegulation (OHSR), Part 12
Safeguarding protects workers whenmachinery or equipment is in
operation
Training & Supervision: Workers CompensationAct, Sections
115-17
Training and Supervision is needed for allaspects of equipment
operation andmaintenance.
Lockout: Operational Health and SafetyRegulation (OHSR), Part
10
Lockout protects workers when machinery orequipment is shut down
for maintenance.
The OHSR, associated policies and guidelines,
andexcerpts/summaries of the Workers CompensationAct are available
on www.worksafebc.com. Somepublications may also be available in
print:
(604) 232-9704 or toll-free 1-866-319-9704
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9 Two-Hand Controls and Trips
9 Two-Hand Controls and Trips
Two-Hand ControlsBoth controls (buttons, levers, sensors) must
be activated atthe same time and kept engaged throughout the
hazardousportion of the machine cycle. If the controls are released
themachine either stops or returns to top of stroke (the
positionthat opens the dies).This type of machine operation is
calledpart revolution clutch (12) or friction clutch, and is
foundwith pneumatic clutches/brakes andwith hydraulically powered
machinerysuch as brake presses.
Two-Hand TripsBoth controls must be activated atthe same time to
initiate the machinecycle but releasing the controls willnot
interrupt the machine cycle. Thistype of machine operation is
calledfull revolution clutch (12) ormechanical clutch.Two-hand
controls and trips must be: Protected against unintended or
accidental operation, i.e.,
surrounding the activating button with a ring guard Separated or
otherwise designed to require both hands to
activate controls (no hand-and-elbow operation) Designed so that
both hands must be released before
another cycle can be initiated (anti-repeat feature). Thedesign
should also prevent the operator from tying downone of the controls
by using tape, rubber band, wedge,etc., (anti-tie down feature
Located a safe distance from the nearest hazard so thatthe
operator cannot reach it with a hand/other body partbefore the
hazardous machine cycle has stopped. Thissafe distance is
calculated using a Hand Speed Constantof 1,600 mm (63 '') per
second (sec.), considered thespeed of a person reaching into a
machines point ofoperation to retrieve an object or correct a
fault.
In a simple example, thesafe location of a two-handcontrol for a
machine thatcomes to a complete stop1 sec. after the controls
arereleased is 1,600 mm (63 '')from the nearest point ofoperation.
For a machinethat stops in 1/2 sec., thesafe distance is 800 mm
(31-1/2 ''), etc.
To find the precisestopping time of amachine cyclerequires
specializedmeasuring equipment.
Two-Hand ControlsPower Press
WARNINGTwo-hand controls alonemay not provide
sufficientsafeguarding. Additionalbarrier guards may berequired to
protect workersother than the operator.
Two-Hand Controls (Paper Guillotine)
Safeguarding ofMachinery: CSAStandard Z432 ?
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10 Presence-Sensing Devices
10 Presence-Sensing Devices
Devices such as light curtains, proximity sensors, and
safetymats do not prevent access to hazardous points of
operation.They simply prevent dangerous machine motion by sendinga
stop signal if any part of a workers body is in the dangerarea when
a machine cycle is initiated. Choose this type ofsafeguard when
frequent access is needed for loading partsand making adjustments,
and physical guarding is restrictive.There are many technical
factors, such as machine controlreliability and safety distance,
that affect the proper selectionand positioning of presence-sensing
devices.
Presence-Sensing Device Limitations They may not provide
sufficient safeguarding when used
alone; additional barrier guarding may be required Do not use
for machines with a full-revolution clutch Review the requirements
of relevant standards before
installing a presence-sensing device Use only during production,
not as substitute for lockout.
Photoelectric Light CurtainsThese devices emit a curtain of
harmless infrared lightbeams in front of the hazardous area. When
any of thebeams is blocked, the light curtain control circuit sends
astop signal to the machines control system. This type ofsafeguard
offers the maximum protection with the minimum
impact on normal machineoperation. It is particularly wellsuited
to safeguarding brakepress operations. Note: steam ordust can
inadvertently affect alight curtain.Pressure-Sensitive Safety
MatsThese devices are used to guardthe floor area around a
machine.A matrix of interconnected matsis laid around the hazard
area,
and the proper amount of pressure (such as an operatorsfootstep)
will cause the mat control unit to send a stopsignal to the
guardedmachine. Pressure-sensitivemats are often used withinan
enclosed area containingseveral machines, such asflexible
manufacturing orrobotics cells. When accessinto the cell is
required (forexample, in the case ofrobot teaching), the
matsprevent dangerous motionif the operator strays fromthe safe
area. Safety Mat: Stamping Machine
Light Curtain: Brake Press
CSA Standard Z432, Safeguarding of MachineryCSA Standard Z142,
Punch/Brake Press OperationCSA Standard Z434, Industrial
Robots/Robot System ?
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11 Safety Interlocks
11 Safety Interlocks
Movable openable barrier guards interlocked with themachines
power source (electrical, pneumatic or hydraulic)can be a reliable
and cost-effective solution. The controlpower is routed through
theinterlocks safety contact so themachine will not operate if
theguard is in the open position.
Simple InterlockingThe interlocked guard can be opened during
operation, andthe machine will stop.
Power InterlockingThe power interlocking device locks the guard
door closed
and will not release ituntil the machinecomes to a safe stop.It
is used withmachinery such astumblers andcentrifuges, where
thecoasting-down timemay take severalseconds to severalminutes,
such as ahouseholds spin cyclewashing machine.
Considerations For System Selection Most interlock switches are
intended for use in production
processes. They may not have the integrity and
reliabilityrequired for worker safety; check with the
manufacturer
Where the risk assessment (3)risk assessment (3) indicates a
high levelof risk, the integrity of the safety interlock circuit
mayrequire monitoring. In addition, the use of redundantinterlocks
may be required
Safety-rated interlock switches feature positive-breaknormally
closed contacts. This ensures that the electricalcontacts are
forced open by a non-resilient mechanicalaction. This means that
they do not rely on spring actionto open the contacts. The
international symbol forpositive-break contacts is
Interlock switches should be tamper-resistant and difficultto
defeat or bypass using readily available means (pieceof wire, tape,
simple hand tool, etc.). Safety interlockmanufacturers address this
by designing two-piece keyedinterlocks or interlocks using coded
magnet sensors
Interlocks should be installed using positive-modemounting. When
mounted in the positive mode, the non-resilient mechanical
mechanism that forces the normallyclosed (NC) contacts to open is
directly driven by thesafety guard. In this mounting mode, opening
the safetyguard physically forces the NC contacts to open
Power interlocks may require that certain parts of themachine
retain a supply of power when the machine isshut down. The
implementation of lockout proceduresshould address this concern.
Lockout must be performedif this safeguard becomes ineffective.
Interlocked Gate Guard HorizontalInjection Molding Machine
Hinged Doorwith TransparentView Panel
HiddenTamperproofInterlock
Safeguarding ofMachinery: CSAStandard Z432 ?
-
12 Movable Gates
12 Movable Gates
complete a typical cycle: Place part in machine and initiate the
cycle. As long as
there are no obstructions, the gate will close. Once the machine
reaches the portion of the cycle where
the point-of-operation hazard has been eliminated, andbefore the
cycle has ended, the B gate opens, allowingthe operator to remove
the formed part.
can only be used to safeguard machines with partpartrevolution
clutches (9)revolution clutches (9). It uses the following steps
to
This unique safeguarding application provides protection toan
operator when hand-feeding parts into various machinessuch as a
punch press.When the machine completes its cycle or returns to top
ofstroke (in the case of a power press), the gate
automaticallyopens, allowing the operator to remove the formed
part. Theoperator then places a feed stock (blank) into the
machineand activates the controls to start another cycle. This can
bedone with either a foot control, a single hand control,
orpreferably two-hand controls (9)two-hand controls (9). The gate
must closebefore the machine can cycle. A low-pressure air
cylinderattached to the gate performs this closing function. If
thereare any obstructions under the gate (such as the
operatorshands), the gate will not fully close. The interlock
switch willprevent further machine operation until the obstruction
hasbeen removed and the controls reset.There are A Type and B Type
movable gate guards.A Type safeguards machines with full revolution
clutchesfull revolution clutches(9)(9) and uses the following steps
to complete a typical cycle: Place part in machine and initiate the
cycle. As long as
there are no obstructions, the gate will close. The machine
makes one complete cycle. The gate opens after the cycle has
ended.The B Type protects the operator only on the downstrokeof
press cycle (or closing stroke of a machine). Therefore, it
Movable Interlocked Gate Mounted on a Punch Press
Air cylinder(moves gate upand down)
Movable gateguard (slides upand down)
Electric safetyinterlock switch
Fixed panelbarrier guards
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13 Pull Wires Trip Wires Contact Bumpers
13 Pull Wires Trip Wires Contact Bumpers
These safeguarding devices function somewhat
likepresence-sensing devices. The difference is that they maypermit
access to the actual danger area before they areactivated and send
a stop signal to the machine.Consequently, they entail a limited
risk of injury, however,they may be the only reasonable choice of
safeguardingwhen other, more effective means are not
practical.Whenever possible,grab wires, pullwires, and contactbars
such as crashbars, belly bars,and similar devicesshould be
mountedso that they will be
activated involuntarily asthe worker approaches thedanger area.
For example,a worker accidentally fallingonto a conveyor belt
wouldautomatically activate theemergency trip wire.A pre-shift
inspection andtest should be donewherever these devices
areinstalled.
Grab Wire and Pull Wire DevicesThese devices usually allow the
worker a first/last chanceto stop the machine in the event of
accidental contact. Theymust be selected and mounted so that
pulling the wire/cablefrom any direction will activate the
emergency stop. Theactivating switch must also sense a broken or
slack cablecondition, and automatically activate the emergency
stop.
Pull Wire
Emergency Trip Wire (Conveyor)
Safety Contact Bumper Overhead Door Machine
Pressuresensitiveedge
Pull Wire System With Two Emergency Stop Switches.The switch is
activated by a pull from any direction.
SlackCableIndicator
SlackCableIndicator
PCV-CoveredRope grips Steel Rope Tensioner Eye Bolts Reset
Knob
PCV-Covered TensionerRope grips Steel Rope Tensioner Eye Bolts
Spring
Pull Wire System With One Emergency Stop Switch. Note
wall-mounted tension spring; activation by pulling from any
direction.
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14 Shields Awareness Barriers
14 Shields Awareness Barriers
ShieldsShields, oftenin the form oftransparentbarriers,
aretypicallyinstalled onlathes, millingmachines,drill pressesand
boringmachines.They can alsobe used on woodworking machines. They
are generallyintended to deflect chips, sparks, swarf, coolant, or
lubricantaway from the operator and other workers in the
machinearea. Besides providing some protection as a barrier,
mostshields also provide good visibility into the point
ofoperation.
Awareness BarriersAwareness barriers include installations such
as electricallyinterlocked pull cable assemblies installed in the
rear area ofmachines such as brake presses and shears to
restrictworker entry. These areas are often out of the
operatorsview. The machine is stopped if someone pulls or
loosens
Although shields and awareness barriers offer some degreeof
safeguarding, they cannot be considered guards becausethey only
restrict but do not prevent access to danger areas.When installing
these devices and before moving them fromtheir normally applied
position, always turn off power to themachine; follow lockout
procedures if there is a risk ofaccidental startup.
the cable. It is recommended that a sign denoting thedanger be
placed on the pull cable.
TransparentShield
LatheChuck
Awareness Barrier: Lathe Chuck
Pull Cable withInterlock Switch
Warning Sign
Awareness Barrier: Sliding Table
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15 Safeguarding by Location
15 Safeguarding by Location
With the body upright and standing at full height, the
safeclearance when reaching upward to an unguarded hazard isa
minimum of 2.5 m (8 ') (see below). Any hazardous movingparts
beyond this distance are considered to be guarded bylocation. If
access to hazardous locations is gained by useof ladders,
scaffolds, and so on, temporary guarding orlockout procedures must
be used.
Safeguarding Equipment With Infrequent AccessWhen the question
is raised of safeguarding equipment thatis located out of the way
of normal work areas, commentssuch as nobody ever goes there or we
access thatequipment only when it is locked out are sometimes
heard.The fact that a worker can access unguarded moving partsthat
are not already safeguarded by location means thataccidental
contact can occur. And an accident will occurover time, although
the level of risk on any given day maybe quite low. It is not a
question of whether these locationswill be safeguarded but rather
of establishing priorities anddetermining which machinery in the
plant will besafeguarded first based on a risk assessment (3)risk
assessment (3) andmachine survey.
The Occupational Health and SafetyRegulation permits
safeguardinginstallations in place before January 1,1999, to have
unguarded parts morethan 2.1 m(7 ') but less than 2.5 m (8 ')above
the floor, walkway, or platform,unless the work process presents
anundue risk to workers or until suchtime as the installation is
substantiallyoverhauled or renovated.
Safe Distance For Reaching Up To An Unguarded Hazard
Overheadunguarded hazard
Hazards abovethis plane areconsideredguarded bylocation
Guard all hazardsfrom referenceplane to here
Reference plane(floor, walkway)
8' (2
.5
m)
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16 E-Stops
The following requirements apply to all E-stop installations:
Mushroom-shaped and red in colour Located within immediate and
unimpeded reach of the
operator or other persons directly affected by themachine
operation
Designed to allow immediate activation with any part ofthe body
(no ring guards or recessed position)
Requires a manual push to activate and a manual pull toreset;
remains in the depressed position when activated(not a hold-to-run
type switch)
A check for safe machine operation is required before anE-stop
is reset
Must be hard-wired into the control circuit to allow themagnetic
coil to drop out (cannot be routed through aProgrammable
LogicController [PLC] except formonitoring purposes)
The machine must notrestart merely by pulling outand resetting
the E-stop. Asecond, independentcontrol must also beactivated
before themachine will restart.
16 E-Stops
E-stop is the industry term forEmergency Stop. It is a
redmushroom-shaped stop buttonthat is manually depressed in
theevent of an emergency condition,upset condition, or accident.
Anemergency stop is not considereda primary safeguarding
device.Because it requires intentionalactivation, an
emergency-stopdevice seldom preventsaccidents; it is an
after-the-factdevice. It may, however, prevent
an unsafe machine operationfrom continuing and, whenactivated,
will stop a machineafter an accident has occurred.The various
publishedsafeguarding standards containspecific requirements for
E-stops, including how many arerequired and where they shouldbe
located.
E-Stop Installation Requirements
E-Stop With Run Button& Main Power Disconnect
Standard E-Stop
E-Stop With Run Button
Hierarchy of Safeguarding Controls1 Overview and Terminology2
Hazard Recognition3 Risk Assessment4 Selecting the Right Safeguard5
Barrier Guards6 Power Transmission Guards7 Grid Guard Design
Considerations8 Protective Barriers9 Two-Hand Controls and Trips10
Presence-Sensing Devices11 Safety Interlocks12 Movable Gates13 Pull
Wires - Trip Wires - Contact Bumpers14 Shields - Awareness
Barriers15 Safeguarding by Location16 E-Stops