Chapter 2 – Occupational Safety
Module 6:
Title: Occupational Safety
Title of the Lesson: Machine Safety
Duration: 2 hrs
The aim of this module is to introduce to you the principles of machine safety as a means
to eliminate industrial injuries and accidents. As an engineering students taking up BOSH
subject , you must be able to know the basics of machine guarding to avoid accidents,
injuries and deaths happening in your assigned work area in the future.
Machines empower us to do a lot of things that we won’t be able to do otherwise, it make
things easy and comfortable for us. Though machines are very much a part of our lives ,
it is essential for us to be mindful that they may also be the causes of injuries and even
deaths in the workplace if not used properly.
Any part, function or process involving machines may cause injuries. To eliminate the
hazards posed by machines, you must have sufficient understanding of machine safety
particularly of the four major areas: adjustment and repair, servicing and maintenance,
moving parts (machine guarding), and point-of-operation in every machine.
Machine guards are classified into those that prevent access and those that prevent
hazardous motion. However, machine guards alone cannot prevent injuries – there is a
need to educate and train workers on machine safety. Lock-Out/Tag-Out (LOTO) is an
effective system for controlling accidents in servicing and maintenance of machines.
Objectives
Working on this module should help you to
recognize the principles of machine guarding
Know the basic types of hazardous mechanical motions and actions
identify areas where machine guards are needed
enumerate the types of machine guards
Understand the Importance of machine safety
differentiate a lock-out from tag-out
I. Machine Safety
A machine is a tool used to make work easier. It is basically an assemblage of parts that
transmit forces, motion and energy in a predetermined manner. Simple machines are
mechanical devices that change the direction or magnitude of a force. They are the
"building blocks" of which the more complicated machines or compound machines are
made.
A. The Industrial Revolution
It was only during the industrial revolution that modern machines were used extensively.
Prior to this, all operations were manually done. The start of the 18th century marked the
start of the industrial revolution. Modern machines were conceptualized and created.
These enabled factories to produce goods faster, but at the same time lead to poor
working conditions and a lot of accidents, giving rise to a growing concern for machine
safety. Machine safety covers 4 basic areas: adjustment and repair, servicing and
maintenance, moving parts and point of operation.
Source:https://brewminate.com/important-inventions-of-the-industrial-revolution/
B. Hazardous Mechanical Motions and Actions
A wide variety of mechanical motions and actions may present hazards to the operator.
These can include the movement of rotating members, reciprocating arms, moving belts,
meshing gears, cutting teeth, and any parts that impact or shear. These different types of
hazardous mechanical motions and actions are basic in varying combinations to nearly
all machines, and recognizing them is the first step toward protecting operators from the
danger they present.
The basic types of hazardous mechanical motions and actions are:
1. Motions
rotating (including in-running nip points)
reciprocating
transversing
2. Actions
cutting
punching
shearing
bending
Mechanical Motions
1.1. Rotating
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. Injuries
due to contact with rotating parts can be severe.
Collars, couplings, cams, clutches, flywheels, shaft ends, spindles, meshing gears, and
horizontal or vertical shafting are some examples of common rotating mechanisms which
may be hazardous. The danger increases when projections such as set screws, bolts,
nicks, abrasions, and projecting keys or set screws are exposed on rotating parts,
Nip Point
In-running nip point (or points where parts of the hand, body or clothes can get caught
in-between) hazards, are caused by the rotating parts of machinery. There are three
main types of in-running nips.
i. Parts rotating in opposite directions
Parts can rotate in opposite directions while their axes are parallel to each other. These
parts may be in contact (producing a nip point) or in close proximity. In the latter case
the stock fed between the rolls produces the nip points. This danger is common on
machines with intermeshing gears, rolling mills, and calenders
ii. Nip points between rotating and tangentially moving parts. Some
examples are: the point of contact between a power transmission belt and its
pulley, a chain and a sprocket, and a rack and pinion.
iii. Nip points between rotating and fixed parts which create a shearing,
crushing, or abrading action. Examples are: spoked hand wheels or
flywheels, screw conveyors, or the periphery of an abrasive wheel and an
incorrectly adjusted work rest.
-
1.2. Reciprocating
Reciprocating motions may be hazardous because during the back-and-forth or up-and-
down motion, a worker may be struck by or caught between a moving and a stationary
part.
https://www.grainger.com/know-how/safety/machine-safeguarding/people-protection/kh-
osha-requirements-machine-guarding
1.3. Transversing
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.
Mechanical Actions
2.1. Cutting
Cutting action hazards involve rotating, reciprocating or transverse motion, where finger,
head and arm injuries can occur and where flying chips and scrap material can strike a
worker’s eyes or face. Cutting actions are dangers with bandsaws, circular saws, and
boring or drilling machines.
Examples of mechanisms involving cutting hazards include band saws, circular saws,
boring or drilling machines, turning machines (lathes), or milling machines.
https://uwm.edu/safety-health/occupational-safety/
2.2. Punching
Punching action results when power is applied to a slide (ram) for the purpose of blanking,
drawing or stamping metal or other materials. The danger occurs where stock is inserted,
held and withdrawn by hand as with power presses.
Typical machines used for punching operations are power presses
2.3. Shearing
Shearing action involves applying power to a shear or knife to trim or shear materials
such as metal. The danger is where stock is inserted, held and withdrawn, as with
hydraulically or pneumatically powered shears.
Examples of machines used for shearing operations are mechanically, hydraulically, or
pneumatically powered shears.
2.4. Bending
Bending action results when power is applied to a slide to draw or stamp metal or other
material. This is a threat where stock is inserted, held and withdrawn, as with equipment
such as power presses.
Equipment that uses bending action includes power presses, press brakes, and tubing
benders.
C. Areas where machine guarding are necessary
Dangerous moving parts in three basic areas require safeguarding:
i. The point of operation: that point where work is performed on the material,
such as cutting, shaping, boring, or forming of stock.
ii. 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.
iii. Other moving parts: all parts of the machine which moves while the machine
is working. These can include reciprocating, rotating, and transverse moving
parts, as well as feed mechanism and auxiliary parts of the machine.
In general, any machine part, function, or process which may cause injury must be
guarded.
D. Importance of machine safety
Why it is necessary to have safety program for machine operations? Because, we know
that machines can cause:
- severe accidents
- loss of trained and skilled employee/s
- loss of production
- damage to equipment
- incurring training cost for new employee/s
- overtime cost
- possible litigation
- accident investigation
Machines can also cause:
- lost time expense
- cost of machine down time
- cost of machine damage and repairs
- lost time due to time spent on accident investigation and other
statutory requirements
- loss of production
E. Types of machine guards
1. Preventing access
Fixed enclosing guards
If the hazard is on a part of the machinery which does not require access, it should be
permanently guarded with fixed enclosing guards.
2. Preventing dangerous motions
When frequent access is required, physical guarding at the hazard is sometimes too
restrictive for part loading or adjustment. In this situation, a device is required to prevent
dangerous motion while allowing unrestricted access by sensing the presence of the
operator and sending a stop signal.
Movable guards with interlocking switches
If access is required in a hazardous area of a machine, an operator can be protected by
an inter-lock with the power source which ensures that whenever the guard door is not
closed, the power is switched off.
Two hand controls
There are other ways of preventing access while the machine is in a dangerous condition.
The use of two hand controls (also referred to as bi-manual controls) is common in certain
types of machinery. Two start buttons have to be operated at the same time to run the
machine. This ensures that both hands of the operator are in a safe position and therefore
cannot be in the hazard area.
Pullback Devices
These are mechanical devices attached to the operator's hands and connected to the
moving portion of the die. If properly adjusted, it withdraws the operator's hands if they
are inadvertently within the point of operation as the dies close.
Photoelectric light curtain
These devices emit a “curtain” of harmless infrared light beams in front of the hazard
area. When any of the beams are blocked, the light curtain control circuit sends a stop
signal to the guarded machine.
Light curtains are extremely versatile and can guard areas many meters wide. By using
mirrors, light beams can be diverted all around the corners to enclose a machine.
There are many applications ranging from totally enclosing perimeter guards for industrial
robots, to point of access guards for certain types of presses.
Safety mats
These devices are used to guard a floor area around a machine. Interconnected mats are
laid around the hazard area and any pressure will cause the mat controller unit to send a
stop signal to the guarded machine.
Pressure-sensitive mats are often used within an enclosed area containing several
machines (e.g., flexible manufacturing or robotics cells). When access into the cell is
required (example: for setting or robot “teaching”), dangerous motion can be prevented if
the operator stays within the safe area.
Pressure-sensitive edges
These devices are flexible edging strips which can be fixed to the edge of a moving part
such as a machine table or powered door where there is a risk of crushing or shearing
hazard. If the moving part strikes the operator (or vice versa), the flexible sensitive edge
is depressed and will send a stop signal to the power source.
Emergency stops
Wherever there is a danger of an operator getting into trouble on a machine there must
be a facility for fast access to an emergency stop device.
The usual way of providing this is in the form of a mushroom headed push-button which
the operator strikes in the event of an emergency. The emergency stops must be
strategically placed, in sufficient quantity around the machine to ensure that there is
always one in reach at the occurrence of hazard.
Grab wire switches
For machinery such as conveyors etc., it is often more convenient and effective to use a
grab wire device along the hazard area. These devices use a steel wire rope connected
to latching pull switches so that pulling on the rope will operate the switch and cut off the
machine power.
Telescopic trip switches
Other variations include telescopic antenna switches where deflection of the antenna
causes the switch to cut off the machine power. These devices are more commonly used
as trip devices on machinery such as pillar drills. The switch is mounted on the drill and
the antenna is extended down next to the drill bit. In the event that the operator becomes
entangled with the drill, he will be pulled onto the antenna thus operating the switch.
Robotics application
This depends on the nature of the machine and the hazard.
F. Requirements of effective safeguards (Rule 1200)
Must prevent contact
Safeguards should prevent human contact with any potentially harmful machine part. The
prevention extends to machine operators and any other person who might come in
contact with the hazard.
Must be secured and durable
Safeguards should be attached so that they are secured Workers should not be able to
render them ineffective by tampering with or disabling them. This is critical because
removing safeguards to speed-up production is a common practice. Safeguards must
also be durable enough to withstand the rigors of the workplace because worn-out
safeguards can’t protect workers properly.
Must provide protection against falling objects
Objects falling into moving machine mechanisms increase the risk of accidents, property
damage, and injury. Objects that fall on a moving part can be thrown out, creating
dangerous projectile. Therefore, safeguards must do more than just prevent human
contact. They must also shield the moving parts of machines from falling objects.
Must not create new hazards
Safeguards should overcome the hazards in question without creating new ones. A
safeguard with a sharp edge, unfinished surface or protruding bolts introduces new
hazards while protecting against the old.
Must not create interference
Safeguards can interfere with the progress of work if they are not properly designed. Such
safeguards are likely to be disregarded or disabled by workers due to the pressure of
production deadlines.
Must allow safe maintenance
Safeguards should be designed to allow the more frequently performed maintenance
tasks (e.g., lubrication) to be accomplished without removal of guards. For example,
locating the oil reservoir outside the guard with a line running to the lubrication point will
allow for daily maintenance without removing the guard.
G. The Hierarchy of Measures
Each measure must be considered according to the hierarchy below. This may result in
a combination of measures being used.
1. Fixed Enclosing Guards - If access to dangerous parts is not required, the
solution is to protect them by some type of fixed enclosing guard.
2. Movable (interlocked) guards or protection devices (e.g., light curtains,
presence sensing mats, etc.) - If access is required, things get a little more
difficult. It will be necessary to ensure that access can only be permitted while
the machine is safe. Protective measures such as interlocked guard doors and/
or trip systems will be required. The choice of protective device or system
should be based on the operating characteristics of the machine.
3. Protection appliances (e.g., jigs, holders, push sticks, etc) - These are used
often in conjunction with guards to feed a work piece while keeping the
operator’s body away from the danger zone.
4. Information, instruction, training and supervision - It is important that operators
have the necessary training in safe working methods for a machine. However,
this does not mean that measures (a), (b) or (c) can be omitted. It is not enough
to merely tell an operator that he/she must not go near dangerous parts (as an
alternative to guarding them). Operators must be trained on the hazards of their
work and how to use and maintain the safety devices as well as give safety
reminders to make them aware all the time.
5. Personal Protective Equipment - In addition to the above measures, it may also
be necessary for the operator to use equipment like special gloves, goggles,
etc. The machinery designer should specify what sort of equipment is required.
The use of personal protective equipment is not the primary safeguarding
method but should complement the measures shown above.
The protective device must be appropriate for the type of work being undertaken.
H. Lock-out/Tag-out System
Another aspect of machine safety is during maintenance work and servicing. The
lockout/tag-out system is effective for preventing accidents during maintenance works.
https://www.emedco.com/safety-training-labels-lock-out-tag-out-saves-lives-hd647-ssk.html
It is a method that is especially designed to protect against the unexpected startup of a
machine that is supposed to be turned off. This is important because statistics indicate
that six percent of all workplace fatalities are caused by the unexpected activation of
machines while they are being serviced, cleaned, or otherwise maintained. The Lock-
out/Tag-out System is designed to protect against the unexpected startup of machine that
is supposed to be "OFF" or an unexpected release of energy (hazardous energy).
The “Fatal Five” Main Causes of Maintenance Injuries:
iv. Failure to stop equipment
v. Failure to disconnect from power source
vi. Failure to dissipate (bleed, neutralize) residual energy
vii. Accidental restarting of equipment
viii. Failure to clear work areas before restarting
Hazardous Energy Sources Found in the Workplace
Electrical - sudden turning on of power source or stored energy in capacitors
Mechanical
Thermal - such as steam or due to chemical reaction
Potential - stored energy that may be due to gravity, hydraulics, pneumatics,
vacuum or springs
Types of Lock-out Devices
Plug Locks
Ball Valve Lock-out
Gate Valve Lock-out
Group Lock-out Hasp
Electrical
Hydraulic, pneumatic, and other pressurized systems
Lock-out Procedure
Alert the operator(s) that power is being disconnected.
Preparation for Shutdown
Equipment Shutdown
Equipment Isolation
Application of Lock-out Devices
Control of Stored Energy
Equipment Isolation-Verification
Removal of Lock-out
Ensure equipment is safe to operate
Safeguard all employees
Remove lock-out/tag-out devices. Except in emergencies, each
device must be removed by the person who placed it.
Last person to take off lock
Follow checklist
To observe proper LOTO procedures, most firms maintain some forms of documentation.
The Assignment/Course Requirement Guide will give the student a clear direction upon
his/her completion for the listed learning activities that can be found in each of the
provided modules or study guides. Aside from the instructions provided, this course
requirement guide will intend to specify the rubrics on grading the activities and also the
guidelines for both the schedule and means of submission if in case the student will not
be able to submit his/her assignment via online platforms.
RUBRIC FOR ASSESSMENT:
For Problem Solving Type Item in a Quiz, assignment or Examination:
Criteria Points Ratin
per Item g
5 4 3 2 1 0
Multiple One No
choice point answ
questions for er
every
correc
t
answ
er
Enumerati Five Four Three correct Two One No
on correct correct answers w/ correct correc corre
answe answers correct spelling answers t ct
rs w/ w/ w/ correct answ answ
correct correct spelling er w/ er
spellin spelling correc
g t
spelli
ng
Identificati Correct Corre No
on answer ct answ
with answ er
correct er but
spelling wrong
spelli
ng
Definition Complet Good solid Explanati Misse No
, e response with on/ s key answ
Discussio response clear definition points er
n or for a definition/discus of
explanatio detailed sion or discussio
n definition explanation n is
/ unclear
discussio
n or
explanati
on
Total
Guidelines for Submission and Evaluation
1. For those students who choose either synchronous (SL) or asynchronous
online learning (AOL) as the mode of learning that is suited for them, all
activities must be submitted online (Google Classroom, Google Mail, or
Messenger). Otherwise if the student prefers for remote print learning mode
(RPL), the instructor will give two (2) weeks for them to accomplish and submit
a printed/hand-written copy of their output.
2. Feedback for the submitted outputs will be through e-mail (for SL or AOL)
Summary:
1. Remember that any machine part, function, or process which many cause injury must
be safeguarded. When the operation of a machine or accidental contact with it can
injure the operator or others in the vicinity, the hazards must be either controlled or
eliminated.
References:
https://www.proprofs.com/quiz-school/story.php?title=NjU2OTU45HVB
http://www.ehsdb.com/resources/Safety_Quiz/Safety_quiz_documents/Equipmen
t.pdf
Machine
https://ehs.princeton.edu/workplace-construction/workplace-safety/physical-
safety/machine-guarding/hazardous-mechanical-motions-and-actions
https://www.osha.gov/Publications/Mach_SafeGuard/chapt1.html
https://www.osha.gov/Publications/Mach_SafeGuard/chapt1.html
https://www.grainger.com/know-how/safety/machine-safeguarding/people-protection/kh-
osha-requirements-machine-guarding
https://uwm.edu/safety-health/occupational-safety/
https://www.osha.gov/sites/default/files/2018-12/fy11_sh-22300-
11_MachineGuardingQuiz.pdf
https://quizizz.com/admin/quiz/5cfe4f2f91cb5f001afe0259/machine-guarding
https://www.proprofs.com/quiz-school/story.php?title=fire-safety-quiz_2
https://www.mysafetysign.com/fire-safety-quiz/questions/how-many-americans-die-in-
fires-every-year
Compiled By:
Jovita SP Domingo REE, MAE- Math
Faculty
Check By:
Reynaldo Alejandria REE, MAE-Math
Department Head EE
Approved By:
Dr. Ma. Magdalena V. Gatdula
Dean College of Engineering
