course outline

1. 1
Addis Ababa University
Addis Ababa University Institute of Technology
Department of Mechanical and Industrial Engineering
HUMAN FACTOR ENGINEERING: FUNDAMENTAL OF
BIOMECHANICS (Module)
Kasu Jilcha (PhD)
October 2020

2. 1. Contents
1. Contents .................................................................................................................................................2
Summary.......................................................................................................................................................1
1. Introduction............................................................................................................................................1
2. Applications of Biomechanics.................................................................................................................2
3. Biomechanical Analyses of Work ...........................................................................................................3
4. Anatomy of the Spine.............................................................................................................................4
5. Biomechanics of Safe Lifting...................................................................................................................5
5.1. Back Injuries..................................................................................................................................5
5.2. Lifting Mechanics ..........................................................................................................................6
5.3. Muscle, Ligament, Tendon, and Bone Capacity............................................................................6
5.4. Muscle and Tendon Strain ............................................................................................................6
5.5. Bone Tolerance .............................................................................................................................7
5.6. Ligament Tolerance.......................................................................................................................7
5.7. Ways to Protect Your Back............................................................................................................7
5.8. Assessment Methods and Identification of Low-Back Disorder Risk At Work .............................8
5.9. The three-dimensional static strength prediction program (3DSSPP)..........................................8
5.10. Job Demand Index.....................................................................................................................9
5.11. NIOSH Lifting Guide and Revised Lifting Equation....................................................................9
5.12. Methods of load lifting............................................................................................................10
5.13. Safe Lifting Guidelines.............................................................................................................11
6. Sitting and Chair Design .......................................................................................................................11
6.1. Seating Design criteria ................................................................................................................12
6.2. Generally criteria of sitting design..............................................................................................13
6.3. Chair Design Case Study..............................................................................................................15
7. MANUAL MATERIAL HANDLING...........................................................................................................16
7.1. Manual Material Handling Tips For Safer Performance..............................................................16
7.2. Reduce workplace risk factors with ergonomics ........................................................................17
7.3. Make sure team members are ready to work with a Pre-Shift Warm-up program ...................17
7.4. Make sure team members use proper body mechanics and work technique ...........................18
7.5. Educate team members on self-care..........................................................................................18

3. 7.6. Proactively respond to early reports of fatigue and discomfort ................................................19
7.7. MANUAL MATERIAL HANDLING AND LIFTING TECHNIQUES......................................................19
7.7.1. Hazards and Human Factors ...................................................................................................19
7.7.2. Manual Handling.....................................................................................................................19
7.7.3. Lifting and Carrying................................................................................................................20
7.7.4. Training...................................................................................................................................20
7.8. Minimizing Manual Material Handling Hazards ........................................................................21
7.8.1. Engineering Controls. .............................................................................................................21
7.8.2. Operating Lifting Methods......................................................................................................21
7.8.3. Team Lifting. ..........................................................................................................................23
7.8.4. Carrying Methods. ..................................................................................................................23
7.9. Carrying Items Up or Down Stairways.......................................................................................24
7.10. Manual Material Handling Equipment....................................................................................24
7.11. What should your employees know before moving, handling, and storing materials?...........25
7.12. What are the potential hazards for workers?...........................................................................26
7.13. What precautions should workers take when moving materials manually? ...........................26
7.14. What precautions should workers take when moving materials mechanically?.....................27
7.15. What precautions must workers take to avoid storage hazards?.............................................28
7.16. What safeguards must workers follow when stacking materials?...........................................28
7.17. Important Safety Measures .....................................................................................................29
7.17.1. What safety measures should employer stake regarding conveyors? .....................................30
7.17.2. What safety measures should employer stake regarding cranes? ...........................................30
7.17.3. What must employers do to ensure the safe use of slings? .....................................................32
7.17.4. What must employers do to protect workers who operate powered industrial trucks?...........32
7.17.5. What are the safety requirements for design?.........................................................................32
7.17.6. What are the safety requirements for modification?...............................................................33
7.17.7. What are the safety requirements for designation?.................................................................33
7.17.8. What safety precautions should employers and workers observe when operating or
maintaining powered industrial trucks? ..................................................................................................34
7.17.9. Are there any training requirements for operators of powered industrial trucks?...................35
7.18. Basic Safety and Health Principles .........................................................................................36
8. Hand Tool Design and Musculoskeletal Disorders...............................................................................36

4. 9. Poor Design ..........................................................................................................................................36
10. Biomechanical Considerations in Hand Tool Design ............................................................................36
11. Shape and Size Considerations for Better Performance ......................................................................37
12. Shape the tools to avoid extremes of wrist deviation .........................................................................37
13. Shape the tool to avoid shoulder abduction........................................................................................37
14. Shape the tool to assist the grip...........................................................................................................37
15. Musculoskeletal Disorders (MSDs).......................................................................................................38
15.1. Etiology of MSDs.........................................................................................................................38
15.2. Human vibration .........................................................................................................................39
15.3. Human vibration and why we need to measure it .....................................................................39
15.4. Measuring human vibration........................................................................................................41
15.5. Measured parameters ................................................................................................................43
15.6. Vibration magnitude...................................................................................................................43
15.7. Duration ......................................................................................................................................45
15.8. Whole-body vibration measurement .........................................................................................47
15.9. Hand-arm vibration measurement .............................................................................................49
15.10. Exposure point system................................................................................................................51
15.11. Measurement of seat effective amplitude transmissibility - SEAT.............................................52
15.12. Lumbar spine measurement.......................................................................................................53
15.13. Spinal response in a vertical direction........................................................................................54
15.14. Calculation of acceleration dose.................................................................................................54
15.15. Relationship between acceleration dose and health effects......................................................55
15.16. Assessment of health effects......................................................................................................56
15.17. Example of assessment of adverse health effects......................................................................57
15.18. Human vibration module in Dewesoft........................................................................................60
15.19. Vibrations sensors.......................................................................................................................58
15.20. Measurement modes..................................................................................................................58
16. Reference .............................................................................................................................................58

5. 1
Summary
In summary, this course provides an opportunity to fundamental understanding of biomechanics
is necessary to understand some of the terminology associated with kinesiology (e.g., torque,
moment, moment arms).Although the human body is an incredibly complex biological system
composed of trillions of cells, it is subject to the same fundamental laws of mechanics that
govern simple metal or plastic structures. The study of the response of biological systems to
mechanical forces is referred to as biomechanics. It is the study of the structure and function of
biological systems such as humans, plants, organs and cells by means of the methods of
mechanics. Biomechanics can also be useful in a critical evaluation of current or newly proposed
patient evaluations and treatments.
Objective of this module:
 Define and use concepts and application of biomechanics.
 Explain the principles that form the foundation of biomechanical analysis of rigid bodies
 Analysis the mathematical approaches used to perform safety lift
 State the function of functions of human spine
 Describe basic concepts of statics, kinematics and kinetics.
 State the criteria design of seat
 Determine techniques of lift mechanisms.
1. Introduction
Biomechanics is an interdisciplinary field in which information from both the biological sciences
and engineering mechanics is used to quantify the forces present on the body during work.
Biomechanics is often referred to as the link between structure and function. While a therapist
typically evaluates a patient from a kinesiology perspective, it is often not practical or necessary
to perform a complete biomechanical analysis. However, a comprehensive knowledge of both
biomechanics and anatomy is needed to understand how the musculoskeletal system functions. It
is the application of the mechanical laws of physics and engineering to motion, structure, and
functioning of all living systems, including plants and animals. Human movement biomechanics
is the study of the structure and function of human beings using the principles and methods of
mechanics of physics and engineering. Biomechanics has been defined as the study of the

6. 2
movement of living things using the science of mechanics (Hatze, 1974). Mechanics is a branch
of physics that is concerned with the description of motion and how forces create motion. Forces
acting on living things can create motion, be a healthy stimulus for growth and development, or
overload tissues, causing injury. Biomechanics provides conceptual and mathematical tools that
are necessary for understanding how living things move and how kinesiology professionals
might improve movement or make movement safer.
2. Applications of Biomechanics
Biomechanics is interesting because many people marvel at the ability and beauty in animal
movement. Some scholars have purely theoretical or academic interests in discovering the laws
and principles that govern animal movement. Within kinesiology, many biomechanistshave had
been interested in the application of biomechanics to sport and exercise.
The applications of biomechanics to human movement can be classified into two main areas:
 The improvement of performance and
 The reduction or treatment of injury
Improving Performance: Effective movement involves anatomical factors, neuromuscular skills,
physiological capacities, and psychological/cognitive abilities. Most kinesiology professionals
prescribe technique changes and give instructions that allow a person to improve performance.
Biomechanics is most useful in improving performance in sports or activities where technique is
the dominant factor rather than physical structure or physiological capacity. Since biomechanics
is essentially the body arch are performed poorly.
Preventing and Treating Injury: Movement safety, or injury prevention/treatment, is another
primary area where biomechanics can be applied. Sports medicine professionals have
traditionally studied injury data to try to determine the potential causes of disease or injury
(epidemiology). Biomechanical research is a powerful ally in the sports medicine quest to
prevent and treat injury. Biomechanical studies help prevent injuries by providing information on
the mechanical properties of tissues, mechanical loadings during movement, and preventative or
rehabilitative therapies. Biomechanical studies provide important data to confirm potential injury
mechanisms hypothesized by sports medicine physicians and epidemiological studies.

7. 3
Kinematics is the study of motion without considering mass or the causes of motion. While
Kinetics is the study of the forces and actions that change the motion of masses. The study of
dynamics considers both of these specialties and focuses on forces that are not in equilibrium. If
an unbalanced force acts on a body, the body will accelerate; the magnitude of acceleration is
proportional to the unbalanced force and the direction of acceleration is in the direction of the
unbalanced force.
The famous equation in engineering f = ma, stated several times previously, comes directly from
this law. Motion starts with a force being applied. If this force exceeds other friction or other
restraining forces, acceleration changes from zero to a positive value and the body starts moving
in the direction of the force at some velocity. If no additional force is applied, motion continues
at a fixed velocity. When the velocity is constant, the distance traveled is equal to the velocity
multiplied by the movement time.
A static biomechanical model is used in 3DSSPP to compute forces on critical joints of the
worker during job segments. The computed forces are reported as percentiles of the male and
female American working populations expected to have sufficient strength to handle the load.
NIOSH recommends strength limits that can be met by 99% of the male population and 75% of
the female population. NIOSH also recommends a maximum back compressive force of 765 lb
(3400 N) for safety-related reasons.
3. Biomechanical Analyses of Work
Kinesiology is the scholarly study of human movement, and biomechanics is one of the many
academicsubdisciplines of kinesiology. Biomechanics in kinesiology involves the precise
description of human movement and the study of the causes of human movement. The study of
biomechanics is relevant to professional practice in many kinesiology professions. Biomechanics
has been defined as the study of the movement of living things using the science of mechanics
(Hatze, 1974).
Mechanics is a branch of physics that is concerned with the description of motion and how forces
create motion. Forces acting on living things can create motion, be a healthy stimulus for growth
and development, or overload tissues, causing injury. Biomechanics provides conceptual and

8. 4
mathematical tools that are necessary for understanding how living things move and how
kinesiology professionals might improve movement or make movement safer.
Kinesiology is the term referring to the whole scholarly area of human movement study, while
biomechanics is the study of motion and its causes in living things. Biomechanics provides key
information on the most effective and safest movement patterns, equipment, and relevant
exercises to improve human movement. In a sense, kinesiology professionals solve human
movement problems every day, and one of their most important tools is biomechanics.
4. Anatomy of the Spine
Muscles are attached to the bones by tendons. A bone depression or protrusion is normally
present at the spot where the tendon attaches. The surface layers of a bone are hard and dense,
and tend to be smooth except for roughened areas where ligaments and tendons are attached.
Several small holes allow arteries, veins, and nerves to pass into the soft and spongy interior of
the bone. Joints occur at the locations where bones come together, or articulate. Joints tend to be
complex structures, made from many different materials beside bone. Within a joint, ligaments
and muscles hold the bones together. Most ligaments and tendons are made from inelastic
collagen fibers. Some joints (especially in the spine) are held together by stretchable ligaments
made from elastic fibers. The contact surfaces of bones in a joint are normally covered with a
thin, smooth, and very slippery layer of collagen fibers, referred to as cartilage. This cartilage
layer acts as a shock absorber and also helps minimize friction forces.
The diagnostic accuracy of advanced imaging techniques like magnetic resonance imaging
(MRI) for identifying spinal abnormalities (e.g., disk hernia ion) that correlate with function and
symptoms of low-back pain is poor (Beattie & Meyers, 1998). The causes of low-back pain are
complicated and elusive. Biomechanics can contribute clues that may help solve this mystery.
Mechanically, the spine is like a stack of blocks separated by small cushions (McGill, 2001).
Stability of the spine is primarily a function of the ligaments and muscles, which act like the guy
wires that stabilize a tower or the mast of a boat. These muscles are short and long and often
must simultaneously stabilize and move the spine. Total spine motion is a summation of the
small motions at each intervertebral level (Ashton-Miller & Schultz, 1988). Biomechanical

9. 5
studies of animal and cadaver spines usually examine loading and rotation between two spinal
levels in what is called motion segment.
The range of movement allowed by a joint is influenced by many factors including
• The shape of the articulation surfaces
• The distribution of the muscles and ligaments
• Muscle bulk
A basic understanding of the spine’s anatomy and its functions is extremely important to patients
with spinal disorders.
The three main functions of the spine are:
1. Protect the spinal cord, nerve roots and several of the body’s internal organs.
2. Provide structural support and balance to maintain an upright posture.
3. Enable flexible motion.
5. Biomechanics of Safe Lifting
Anthropometry is the study of all measurements of the human body and the uses of this
information. It naturally progresses to workspace design and some related issues in
biomechanics. Biomechanical analyses must consider not only the loads imposed upon a
structure but also the ability of the structure to withstand or tolerate a load during work. This
section will briefly review the knowledge base associated with human structure tolerances.
5.1. Back Injuries
More than one million workers suffer back injuries account annually, and these account for one
in five workplace injuries (Bureau of Labor Statistics). 80% of these injuries are to the low back
(lumbar spine). Back injuries cost the US economy billions of dollars each year.
The human spine (see spine) has 33 bones (vertebrae) separated by cartilaginous shock-absorbers
(discs). The spine is supported by ligaments and muscles. The natural shape of the spine creates
three balanced curves (lodrotic cervical region, hypnotic thoracic region and lord tic lumbar
region). Many postures can produce a change in the geometry of the spin. but moving from
moving from standing up to bending down, and then from bending down to standing up (during
these movements the lumbar spine goes from being lord tic to hypnotic to lord tic), and when this
is combined with lifting or lowering a load it creates a particular risk for a low back injury.

10. 6
5.2. Lifting Mechanics
Biomechanical analyses must consider not only the loads imposed upon a structure but also the
ability of the structure to withstand or tolerate a load during work. This section will briefly
review the knowledge base associated with human structure tolerances.
If you lift and bend at your waist and extend your upper body, this changes the back's alignment
and the center of balance (center of mass) in the abdomen. Consequently, the spine has to
support both the weight of the upper body and the weight of the load being lifted or lowered.
The forces being transmitted through the low back can be estimated by calculating the moment
and forces created by the weight of the load being lifted and the weight of the upper body
Moment = (Force) x (Distance)
This is the same as: Moment = (Weight of load) x (Distance from center of weight of load to a
fulcrum) {Equation A}.
5.3. Muscle, Ligament, Tendon, and Bone Capacity
The precise tolerance characteristics of human tissues such as muscles, ligaments, tendons, and
bones loaded under various working conditions are difficult to estimate. Tolerances of these
structures vary greatly under similar loading conditions. In addition, tolerance depends upon
many other factors, such as strain rate, age of the structure, frequency of loading, physiological
influences, heredity, conditioning, as well as other, unknown factors. Furthermore, it is not
possible to measure these tolerances under in vivo conditions. Therefore, most of the estimates of
tissue tolerance have been derived from various animal and/or theoretical sources.
5.4. Muscle and Tendon Strain
The muscle is the structure within the musculoskeletal system that has the lowest tolerance. The
ultimate strength of a muscle has been estimated to be 32 MPa (Hoy et al., 1990). In general, it is
believed that the muscle will rupture prior to the (healthy) tendon (Nordin and Frankel, 1989)
since tendon stress has been estimated at between 60 and 100 MPa (Hoy et al., 1990;Nordin and
Frankel, 1989). It is commonly believed that there is a safety margin between the muscle failure
point and the failure point of the tendon of about two- (Nordinand Frankel, 1989) to threefold
(Hoy et al., 1990). Thus, tendon failure it generally thought to occur at around60–100 MPa.

11. 7
5.5. Bone Tolerance
Bone tolerances have also been estimated in the literature (Ozkaya and Nordin, 1991). The
ultimate stress of bone depends upon the direction of loading. Bone tolerance can range from 51
MPa in transverse tension to over 133 MPa in transverse compression and from133 MPa in
longitudinal loading tension to 193 MPa in longitudinal compression and 68 MPa in shear.
5.6. Ligament Tolerance
In general, ultimate ligament stress has been estimated to be approximately 20 MPa. However,
ligament properties vary greatly depending on their location within the body. Note the much
greater tolerances associated with greater body load bearing.
A strong temporal component to ligament recovery has also been identified. Solomonow found
that ligaments require long periods of time to regain structural integrity during which
compensatory muscle activities are observed (Solomonow, 2004; Solomonow et al.,1998, 1999,
2000, 2002; Stubbs et al, 1998; Gedaliaet al, 1999; Wang et al., 2000). Recovery time has been
observed to be several times the loading duration and can easily exceed the typical work–rest
cycles observed in industry.
5.7. Ways to Protect Your Back
Give yourself a lot of support. For stability, spread your feet at least as for apart as your shoulder
width. Distribute weight evenly throughout the soles of both feet and keep your feet firmly
planted, with your center of gravity in your abdominal cavity.
Tighten your abdominal muscles. The abdominal cavity consists of the abdominal muscles in
front, the diaphragm and ribs above the pelvic floor below. Pressure in the abdomen that helps
share the loads placed upon the spine.
Bend form your knees. Always bend from our knees, so the legs can serve as shock absorbers.
The pelvis to find its balance over the hips when the knees are slightly bent, so that weight
comes first into the thighs and hips instead of the spine. Don't lift with locked knees because they
tighten the hamstring muscles and lock the pelvis into an unbalanced position. Don't bend from
the waist because it puts tremendous pressure on the lumbar vertebrae.
Keep your spine in balance. Balance your shoulders and chest over the lower spine, to lessen the
force placed on it. A balanced back, with its normal 3 curves, keeps the spinal muscles active so
they can share the load placed on the bones, ligaments and discs.

12. 8
5.8. Assessment Methods and Identification of Low-Back Disorder Risk
At Work
The logic associated with various risk assessment approaches has been described in previous
sections. These approaches have been used to develop a rich body of literature that describes
spine loading and subsequent risk in response to various work-related factors that are common to
workplaces (e.g. one-hand vs. two-hand lifting). These studies can be used as a guide for the
proper design of many work situations. However, there is still a need to assess unique work
situations that may not have been assessed in these in-depth laboratory studies. High-fidelity
spine-loading assessment techniques (e.g., EMG-assisted models) may not be practical for the
assessment of some work situations since they require extensive instrumentation and typically
require the task to be simulated in laboratory environment. Therefore, tools with less precision
and accuracy may be necessary to estimate risk to the spine due to the work.
5.9. The three-dimensional static strength prediction program
(3DSSPP)
The three-dimensional static strength prediction program (3DSSPP) has been available for quite
some time. The computer program considers the load–tolerance relationship from both the spine
compression and joint strength aspects. Spine compression is estimated with a linked segment–
single equivalent muscle model and compared to the NIOSH-established compression tolerance
limit of 3400 N.Strength tolerance is assessed by estimating the joint load imposed by a task on
six joints and comparing these loads to a population-based static strength database. This strength
relationship has been defined as a lifting strength rating (LSR) and has been used to assess low
back injuries in industrial environments (Chaffin and Park, 1973). The LSR is defined as the
weight of the maximum load lifted on the job divided by the lifting strength. The assessment
concluded that “the incidence rate of low back pain (was) correlated (monotonically)with higher
lifting strength requirements as determined by assessment of both the location and magnitude of
the load lifted.” This was one of the first studies to emphasize the importance of load moment
exposure (importance of load location relative to the body in addition to load weight) when
assessing risk. The study also found that exposure to moderate lifting frequencies appeared to be
protective, whereas high or low lift rates were associated with jobs linked to greater reports of
back injury.

13. 9
5.10. Job Demand Index
Ayoub developed the concept of a sob severity index(JSI), which is somewhat similar to the LSR
(Ayoubet al., 1978). The JSI is defined as the ratio of the job demands relative to the lifting
capacities of the worker.
Job demands include the variables of object weight (lifted), the frequency of lifting, exposure
time, and lifting task origins and destinations. Liles and associates (1984) performed a
prospective study using the JSI and identified a threshold of a job demand relative to worker
strength above which the risk of low back injury increased.
5.11. NIOSH Lifting Guide and Revised Lifting Equation
The NIOSH has developed two lift assessment tools to help those in industry assess the risk
associated with materials handling. The objective of these tools was to “prevent or reduce the
occurrence of lifting-related low back pain among workers” (Waters et al., 1993). These
assessments considered biomechanical, physiological, and psychophysical limits as criteria for
assessing task risk.
The original tool was a guide to help define safe lifting limits based upon biomechanical,
physiological, and psychophysical tolerance limits ((NIOSH, 1981).This method requires the
evaluator to assess workplace characteristics. Based upon these work characteristics, the guide
estimates that the magnitude of the load that must be lifted for spine compression reaches 3400N
[the action limit (AL)] and 6400N [the maximum permissible limit (MPL)]. From a
biomechanical standpoint, the AL was defined as the spine compression limit at which damage
just begins to occur in the spine in a large portion of the population. Based upon this logic, “safe
“work tasks should be designed so that the load lifted by the worker is below the calculated AL
limit. The AL is calculated through a functional equation that considers four discounting
functions multiplied by a constant. The constant (90 lb, or 40 kg) is assumed to be the magnitude
of the weight that, when lifted under ideal lifting conditions, would result in a spine compression
of 3400 N.
The four workplace-based discounting factors are:
 horizontal distance of the load from the spine,
 the vertical height of the load off the floor,

14. 10
 the vertical travel distance of the load, and
 The frequency of lifting.
These factors are governed by functional relationships that reduce the magnitude of the
allowable load (constant) proportionally according to their contribution to increases in spine
compression.
The MPL is determined by simply multiplying the AL by a factor of 3. If the load lifted by the
worker exceeds the MPL, it is assumed that more than 50% of the workers would be at risk of
damaging the disc. Under these conditions engineering controls would be required. If the load
lifted is between the AL and the MPL values, then the task is assumed to place less than half the
workers at risk. In this case, either engineering or administrative controls were permitted. If the
load lifted is less than the AL, the task is considered safe. This guide was designed primarily for
sagittally symmetric lifts that were slow (no appreciable acceleration) and smooth. Only one
independent assessment of the guide’s effectiveness could be found in the literature (Marraset
al., 1999b). When predictions of risk were compared with historical data of industrial back injury
reporting, this evaluation indicated an odds ratio of 3.5 with good specificity and low sensitivity.
5.12. Methods of load lifting
 Basic Lift (Diagonal Lift): this lift is the most common method of good lifting
technique. Use the basic lift for objects small enough to straddle where you have enough
room to use a wide stance.
 Power Lift: in the power lift, the object shifts your center of gravity forward, and
you must push your buttocks out to compensate. (Professional weight lifters lift
using this position.)
 Tripod Lift - use the tripod lift for objects with uneven weight distribution (example:
sacks of food). Recommended for people with decreased arm strength. Not recommended
for people with bad knees.
 Partial Squat Lift: use the partial squat lift for small light objects with handles close to
knee height.
 The Golfers Lift: use the golfers’ lift for small light objects in deep bins and to pick
small objects off the floor. Recommended for people with knee problems or decreased
leg strength.

15. 11
 Straight Leg Lift: use the straight leg lift when obstacles prevent you from bending your
knees. Be careful! Lifts over obstacles that prevent you from bending your knees put you
at increased risk for muscle strain. If possible, avoid this lift. Only use this lift when
absolutely necessary (i.e. lifting out of a grocery cart, car trunk)
 Overhead Lift: use the overhead lift to place objects on an overhead shelf. This lift
begins with the object in your hands. Be careful! Overhead lifts put you at increased risk
for muscle strain. It can be difficult to maintain balance during the lift. If possible, avoid
this lift.
5.13. Safe Lifting Guidelines
 Lifting safely will protect your back while you lift. Before you lift an object ask yourself
the following questions:
 Do you think you can lift it alone?
 Is the load too big or too awkward?
 Does the load have good handles or grips?
 Is there anything to obstruct proper lifting?
 Could the contents of the load shift while being lifted?
 For safe lifting, remember to:
 Stand as close to the load as possible
 Bend at your knees NOT your waist
 Hug the load close to your body, don't hold it away from you
 Raise yourself up with the strong thigh muscles.
6. Sitting and Chair Design
Sitting is a body position in which the weight of the body is transferred to a supporting area
mainly by the Ischia tuberoses of the pelvis and their surrounding soft tissue. Human anatomy
plays an important role in the design of seating. People experimented with chair designs long
before ergonomists focused on this issue. The fact is that people enjoy sitting down, as verified
many years ago by Vernon (1924) when he studied a shop of women employees.

16. 12
People do many of their tasks while standing or sitting in front of tables, work benches, desks,
conveyer belts, or other flat work surfaces. In some cases, as when people write on a piece of
paper, the activity is performed on the surface itself. In others, much of the activity is performed
immediately above the surface, as when people pick up an object and manipulate it in some way,
before setting it down again.
6.1. Seating Design criteria
Depending on chair and posture, some proportion of total body weight is transferred to the floor
via the seat pan and feet, armrests, and backrests. An estimated 50% of people in the
industrialized world suffer some form of back complaint and many of these are related to poor
seat design. A number of design principles for seating have been recognized over the years
(Courtesy of NIOSHguide lines, Washington, DC; adapted in part from Grand jean, E., Fitting
the Task to the Man: An Ergonomic Approach, 1982). Some principles appear to be simply
common sense.
However, over time, precise value limits and design recommendations have been developed that
go well beyond ordinary perceptions. Grand jean’s results lead us to a basic ergonomic design
principle, stated as follows:
For high precision work, tables should be up to 10 cm (around 4 in.) higher than the normal
elbow height and for heavy work as much as 20 cm below normal elbow height.
For seated people, the appropriate table height depends on chair height: This principle also holds
the other way around, but chairs that are too tall are obviously problem. In general, chair heights
above 26 in. are discouraged. Another comment is that since chair heights vary, and many can be
adjusted, it is hard to guess where the work surface will end up relative to the elbow of seated
workers in the real world.
The design should allow the sitter to change posture; This principle appears in a number of
different places and reflects the fact that posture changes are necessary for blood to flow
properly to different parts of the body. Posture changes help muscles relax and prevent people
from becoming stiff and sore.

17. 13
The chair should provide support in the lumbar region of the sitter’s back; Support of the lumbar
region of the spine should be provided starting at a point about20 cm (8 in.) above the bottom of
the seat and extend upward at least 10 cm (4 in.) higher. Because of the curvature of the human
body in the horizontal plane at the lumbar region, many people recommend that the portion of
the seat back providing lumbar support be curved with an approximately 41 cm (16 in.) radius.
Space should be provided under the seat and in front of the person for their feet: It is important to
provide adequate space under the chair and under the bench or table in front of the operator. This
allows a person to change the position of their feet. Foot room under the chair is most important
for getting out of the chair. To demonstrate, observe yourself as you get out of a chair and then
try to execute the same maneuver with both feet in front of the chair. Adequate leg room
becomes a special concern when people must remain seated for long time periods. What seems to
be more than adequate, when seated for a few minutes, is often far from adequate, after sitting
for 8 h, as is often the case in airplanes, automobiles, and in certain jobs where motion is
restricted.
Chairs must be matched to the use related context. Typical multipurpose chairs are adequate for
many applications, but do not meet the requirements of offices, comfort seating, or elderly users.
There are many different types of seating. Each has some special design elements that need to be
considered. Multipurpose chairs are used in a variety of places including schools, waiting rooms,
and sometimes in offices. Typically, these chairs are simple molded plastic units with metal or
plastic legs and frames.
6.2. Generally criteria of sitting design
 Seat Height - Optimum seat height is controversial.
Traditional Criterion - Seat height should be adjusted to support a knee angle of 90-degrees to
prevent leg swelling. However 75% of leg swelling may be due to low leg muscle activity rather
than chair.
 Minimum Height - should be 15" (38cm) which designs to the 5th percentile of women
with 1" heels. The seat should adjust 9" (23cm).

18. 14
 Fixed Height - should be about 17" (43cm). This is a compromise. A chair that is too
high leads to increased pressure at the political fold (underside of knees), decreasing
blood circulation and increasing pressure on the nerve. A chair that is too low increases
weight on the Ischia tuberosities.
 Seat Pan -
 Seat Depth - recommended is 16.5" for fixed seats and 14-18.5" for adjustable seats. If
the seat depth is greater than the buttock-political length (fifth percentile woman is at
17") then the user won't be able to use the backrest.
 Seat Pan Contours - Half body weight is supported by an 8% area under the "seat
bones" (ischial tuberosities). If the seat is hard and flat the pressures can be 85-100 p.s.i.
Seat contouring and cushioning can be used to distribute pressure over a larger area and
rotate the pelvis forward the promote better posture.
 Seat Cushioning - recommended thickness at 1.5-2". Cushion should be firmer in back
and thicker while less firm and thinner at front. Too much cushioning can cause the body
to sink into a chair constraining movement. A soft chair may be comfortable at first, but
as the body sinks blood circulation lowers, skin temperature rises in affected areas, and
compression under thighs increases. These factors combine to increase discomfort.
 Cushion Compressibility - Compressibility is termed indentation load deflection (ILD)
or indentation force deflections (IFD). An ideal combination is a soft top layer (25%
ILD) over a firm bottom layer (65% ILD). Top and bottom layer increased ratios between
the two, is greater than 2.6, leads to better quality support.
Seat Width – is around 20 - 22" to accommodate clothed persons. If seat has armrests then
elbow to elbow breadth may be more relevant.
Seat Angle - Positive seat angle helps user to maintain good contact with backrest. For most
purposes, a 5 - 10 angle is recommended.

19. 15
Armrests - give additional postural support and aid in standing up and sitting down. Armrests
should be padded and engage the fleshy part of the forearm. They should not engage the bony
parts of the elbow where sensitive lunar nerve is close to the surface so a gap of approximately
4" between the armrest and seat back is recommended. Cantilevered elbow rests should be 8-10"
above the seat surface height. Armrests should be at least 17.2" apart to exceed thigh breadth of
95th percentile females.
Backrests -
Height - Higher backrests give better trunk weight support. Three categories:
Low-level backrest - supports the lumbar region only. Depth of the lumbar curve of the backrest
should be 0.6 - 2.0". Backrest heights of 5, 7, and 9" seem equally effective.
Medium-level backrest - gives full shoulder support (e.g. car seat, office chair) and may need to
be about 26" high to accommodate the 95th percentile man.
High-level backrest - full support of head and neck (e.g. plane seat) and may need to be about
36" for a 95th percentile man.
Angle - Optimal angle seems to be between 100-110-degrees.
6.3. Chair Design Case Study
Consider the problem of the elderly getting up out of a chair. Seats that are flat require that the
person rise from a position in which the leg is bent 90°, which is difficult for those who do not
have adequate leg strength or flexibility. A study was commissioned to examine how to design
chairs for the elderly to help with this problem.
The study, which resulted in a chair whose seat pan lifted at the rear, involved the use of
questionnaires, interviews, and television recordings of people using two models of these chairs
and riser-mechanisms. The piston and associated mechanism was found to be one of the difficult
features. Various design issues were identified by observing users while they learned how to use
the chairs.
Some pistons were too forceful, particularly in certain phases of getting up or sitting down. The
study also found that some people could not lean forward far enough to see the release button on
the chair front. An alternative second release button was consequently recommended on the chair
side. The researchers determined that users needed instructions on how to properly use this chair,
so they recommended that a video tape be made showing entry and exit procedures with and

20. 16
without use of walking devices. They also prescribed improvements in the existing written
instructions for how to make adjustments. Finally, they recommended a way marketing people
could work effectively with ergonomics personnel, particularly in selling the chairs to people
who to some extent are not independently mobile.
7. MANUAL MATERIAL HANDLING
Handling and storing materials involve diverse operations such as hoisting tons of steel with a
crane; driving a truck loaded with concrete blocks; carrying bags or materials manually; and
stacking palletized bricks or other materials such as drums, barrels, kegs, and lumber.
The efficient handling and storing of materials are vital to industry. In addition to raw materials,
these operations provide a continuous flow of parts and assemblies through the workplace and
ensure that materials are available when needed. Unfortunately, the improper handling and
storing of materials often result in costly injuries.
Manual material handling is the process of moving or supporting an object by physical force.
Pushing, pulling, lifting and carrying are all examples of manual handling tasks. These tasks can
be found in every workplace, whether you are in an office, on a construction project, a ranch or
anywhere in between.
Manual Material Handling poses several risks to employees. Strains and sprains are commonly
reported by employees who perform manual handling tasks. Backs, knees, hips, shoulders, and
elbows, necks: they are all body parts threatened by manual handling tasks. The contributing
factors for these risks vary, but include the weight, size, shape and stability of the object;
frequency and distance of the move; and the body mechanics and overall health of the employee.
Understanding the risk factors in your workplace from manual handling tasks is the first step in
controlling these injuries.
7.1. Manual Material Handling Tips For Safer Performance
Manual material handling tasks can sometimes expose workers to risk factors that eventually turn
into costly injuries and lost productivity. Following are five tips for smarter and safer work
performance.

21. 17
According to NIOSH, “manual material handling (MMH) work contributes to a large percentage
of the over half a million cases of musculoskeletal disorders reported annually in the United
States.”In other words, manual material handling tasks can become a major problem if you don’t
take proactive measures to reduce injury risk in your workplace. The good news is that these
injuries are preventable. Follow these five tips and action steps to reduce risk in your workplace.
7.2. Reduce workplace risk factors with ergonomics
Ergonomic risk factors are commonly found in the manual material handling environment.
Ergonomic risk factors are problems with the work environment that cause unnecessary physical
fatigue. The three primary ergonomic risk factors are:
 Awkward postures (bending, twisting)
 Highly repetitive motions (frequent reaching, lifting, carrying)
 Forceful exertions (carrying or lifting heavy loads)
A proactive ergonomics improvement process ensures that jobs and tasks are within the worker’s
physical capabilities. It’s about identifying these ergonomic risk factors in your work
environment and putting control measures in place to limit exposure.
This process is the foundation for preventing back injuries for manual material handling tasks.
An ergonomically designed work environment reduces fatigue and discomfort for workers. This,
in turn, limits the risk of an injury occurring.
7.3. Make sure team members are ready to work with a Pre-Shift Warm-
up program
Manual material handling tasks require workplace athletes to be ready for their workday. For
example, what is the last thing Peyton Manning does before he takes the field on Sundays?
He goes through his pre-game stretching and warm-up routine to prepare his body and mind for
the game. It’s the final ritual in his preparation for work, and he never misses it. Neither do any
of his teammates or other teams around the league. They would never miss their pre-game
stretching and warm-up routine.

22. 18
Workplace athletes prepare themselves for work in a similar way with “pre-shift stretching” or
“pre-shift warm-up stretching”. They take a few minutes before they begin their work day by
preparing their body and mind for work with a pre-shift warm-up routine.
Well-designed workplace stretching programs (Work Readiness Systems) ensure workplace
athletes are physically ready for their work day.
7.4. Make sure team members use proper body mechanics and work
technique
By definition, manual material handling tasks require workers to handle materials using their
body. As workplace athletes it’s important they use their bodies properly, using good
biomechanics and work technique.
When workplace athletes use poor body mechanics and work technique, they introduce
unnecessary MSD risk. By educating workers to use better body mechanics and spending the
necessary time out on the shop floor to make sure they’re getting the job done properly, you are
greatly reducing the MSD risk in your workplace.
7.5. Educate team members on self-care
Physical wear and tear on the body is a normal part of the aging process. Every day, we go
through the process of fatigue and then recovery. Each day we fatigue the body. Each night we
sleep as the body’s natural process to recover from the day.
Well, with manual material handling workers, it’s as important as ever to know how to recover
from each workday. Manual material handling tasks are physically demanding on the body and
require and above average process in place to recover from the day.
Workplace athletes that do a great job at self-care are able to recover from each workday and
minimize the risk of an MSD from forming.

23. 19
The only way your workplace athletes will know how to properly care for themselves and
recover from each workday is if you educate and train themselves on self-care tools and
techniques.
7.6. Proactively respond to early reports of fatigue and discomfort
As we just covered in the previous section, fatigue and physical wear and tear is a normal part of
the aging process. In manual material handling tasks, there will be additional fatigue and
discomfort that is just a natural part of life under these circumstances. Even with a proactive
ergonomics process that makes sure the work fits the workers’ capabilities, this work day in and
day out can take a toll on the workplace athlete’s body.
Because cumulative fatigue will eventually turn into an MSD, it’s important to encourage early
reports of fatigue and discomfort so you can proactively respond and put control measures in
place to prevent fatigue from developing into an injury.
Next action: The earlier you discover signs of fatigue and discomfort, the better. That way you
can actually do something about fatigue and discomfort before it develops into an injury that
requires medical treatment. Start encouraging early reports and when you receive them, respond
quickly and with enthusiasm.
7.7. MANUAL MATERIAL HANDLING AND LIFTING TECHNIQUES
7.7.1. Hazards and Human Factors
Strains, sprains, hernias, fractures, bruises, and lacerations may result from poor manual material
handling and lifting practices. Lifting, carrying, dropping, and lowering are the common physical
acts responsible for injuries. Many strains are the direct result of improper lifting techniques,
lifting with no assistance, or failure to use required and available manual material handling
equipment.
7.7.2. Manual Handling.
Influencing factors when manually lifting materials include the size, shape, and weight of the
object to be lifted (and distance to be moved). Proper lifting techniques are as important as the
weight of the object to be lifted. Heavy weights or awkward positions may require mechanical
assistance or team lifting to be used.

24. 20
7.7.3. Lifting and Carrying.
There are several variables, which influence the ability of people to manually handle and lift
materials. Physical capabilities of individuals and variables in the work environment need
consideration. Proper consideration and knowledge of limitations and the use of correct lifting
and carrying techniques will reduce the possibility of injury.
Physical characteristics include factors such as strength, mobility, fatigue, and motor functions
of the individual.
Psychological considerations might be the motivation, emotional state, job satisfaction, and
attitude of the individual toward work. Pre-existing worker injuries may also bear consideration.
Task variables might include the weight, size, shape, distribution, degree of shift (of the load in
the container), and the location of the center of gravity (CG) of the load to be handled.
Workplace layout and the degree of movement required, obstacles, distances moved, and
direction of movement must be factored.
Level of demand to include frequency of lift, duration of lifting task, accelerations and velocities
of lift, shift duration, degree of precision, and relative proportion of muscles involved in the lift
shall be considered.
Environmental variables can have an impact, consider heat and cold stress, noise and vibration,
lighting, toxic agents, traction, stability of the work platform, and atmospheric contaminants that
could affect the task.
7.7.4. Training
Department Heads, Managers and Supervisors must train personnel who regularly perform
manual lifting duties. Supervisors will ensure their personnel receive thorough instructions on
the proper techniques to use and what PPE is required. In addition, personnel will be instructed
in the use of available manual lifting devices and the procedures for performing routine or high
risk manual handling activities. To the new worker, hand trucks and wheelbarrows look
deceptively easy to use. Supervisors will instruct workers on their use. Seeking improvements in
the methods used for accomplishing the work and eliminating manual material handling hazards;
and an understanding of the stresses involved during manual handling which cause injuries are

25. 21
important and should also be addressed during training. This training should include both verbal
and written materials that explain how to do the task correctly with practice and proper motions.
Training will be documented.
Information to assist the supervisor in establishing a program may be found in this chapter and in
the National Safety Council (NSC) Accident Prevention Manual for Industrial Operations,
Engineering, and Technology.
7.8. Minimizing Manual Material Handling Hazards
7.8.1. Engineering Controls
A preferred method of minimizing the risk of manual lifting is the use of engineering controls
such as employing mechanical assists to decrease the force, the repetition, distance of travel, and
frequency of the manual handling activities. Some examples might include employing scissor
tables, elevators, conveyors, and gravity chutes
Administrative Controls. Job rotation schedules and mandatory work-rest cycles can be useful to
reduce mishap potential, but do not eliminate the hazard and are not as reliable as engineering
controls.
Work Design Principles. Conduct a job safety analysis to identify potential hazards, and when
practical, arrange tasks and select workstations using the following principles:
Place objects to be lifted at the approximate height of the knuckles when the arms dangle at side
of the body.
Limit stacks height to shoulder level. If items must be stacked higher, provide step-up access to
eliminate lifting above shoulder level. Use grips, handles, and other devices to provide better
control of items. Slide materials instead of lifting, whenever possible. Use gravity assist in
moving materials. Ensure adequate maneuvering space to eliminate the need to twist the body.
Consider team lifting when items are known to weigh more than 25 pounds.
7.8.2. Operating Lifting Methods
No single technique for preventing injury during lifting and material handling has been
discovered despite numerous research efforts. The best prevention strategy is to ensure

26. 22
workstations are properly designed, loads are manageable in both size and weight distribution,
the frequency and duration of lifting are not excessively stressful, and workers can demonstrate
knowledge of proper techniques for material handling. There are three basic methods of lifting,
that is, straight back-bent knees, free style, and kinetic. Each has advantages and limitations:
The kinetic method is the most widely accepted and taught because it provides more stability for
the worker while reducing load on the back muscles and intervertebral disks. Instructions and
diagram on how to lift properly follow:
Before an object is lifted, it should be inspected to make certain no grease or slippery substance
will cause the object to slip. Also inspect the objects for slivers, sharp edges, and rough or
slippery surfaces before attempting to lift.
Position feet correctly. Place far enough apart for balance with one foot to the rear of the
object and the other foot slightly ahead of the other and to the side of the object.
Crouch close to the load. Crouching is preferred to squatting. Stay close to the load to
Minimize strain on the back muscles.
Always keep the back as straight as possible. It may not be possible to keep the back in
The vertical plane but avoids arching the back. Bend from the hips and not from the middle of
the back.
Pick up materials with a full palm grip. Do not attempt to pick up items using a fingertip grip.
Gloves (Leather or Leather-palmed) shall be worn when lifting objects which have sharp or
burred edges or splintered surfaces.
With the arms, slide the object towards the body putting it in motion (kinetic energy).
At the same time, lift the object with the legs and bring them back to a vertical position. Keep the
object close to the body; avoid twisting while lifting.

27. 23
Fig 1. Lifting Technique
5.4.1 Setting the Object Down
. Use the same motion as when lifting, but reverse it to set an object down. Lower the load by
bending the legs and crouching with the back straight. Take care when releasing the load to
prevent injury to fingers, hands, or feet.
7.8.3. Team Lifting
When it’s required to move heavy or unusual shaped items manually, always seek and obtain
assistance when it is not practical to use mechanical equipment assign additional workers to the
task. When two or more people are required to move or carry an object, adjust the load so each
person carries an equal part. If possible use workers similar in size and train them in team-lifting.
Workers need to understand that if one worker lifts too soon, shifts the load, or lowers
improperly, that person or their partner(s) may be overloaded and strained. Test lifts should be
made before proceeding. The key to lifts using two or more personnel is to make every move in
unison. Assign one person to give orders to ensure the necessary coordination for movement.
The supervisor and workers are responsible for assessing all available methods to safely handle
materials described above and using mechanical assistance whenever possible.
7.8.4. Carrying Methods
Acceptable carrying methods differ, based upon the type of material, distance, and number of
workers. Workers should be instructed during initial training in each procedure--for example,
neck, shoulder, side, tray, two-person, and under-arm carry methods, etc. Points to remember:

28. 24
 Use appropriate PPE as determined for each task, such as gloves, to protect the hands and
protective footwear to protect the feet.
 Keep fingers away from pinch and shear points.
 Do not carry a load that obstructs the view of the direction of travel. Make sure that the
path of travel is clear.
 Do not turn at the waist to change direction or to put an object down. Turn the whole
body and crouch down to lower the object.
7.9. Carrying Items Up or Down Stairways
 Adhere to the guidance provided by the supervisor.
 Try to reduce the bulk or size of the object carried to allow for maximum visibility.
 Use assistance when required and available.
 Use mechanical material handling equipment whenever loads are too heavy or bulky to
be
Lifted or carried efficiently or safely by hand. Forklifts, hand trucks, rollers, conveyors, or cranes
(When properly used) simplify materials handling and greatly reduce the hazards of handling
supplies and equipment.
7.10. Manual Material Handling Equipment
This equipment will be used whenever loads are too heavy or bulky to be lifted or carried
efficiently or safely by hand. Hand trucks, dollies , two-wheeled hand trucks and wheelbarrows
(when properly used) simplify materials handling and greatly reduce the hazards of handling
supplies and equipment.
 Hand Trucks, Dollies and Wheelbarrows. Hand trucks, dollies, wheel barrows or other
manual devices shall be used to lift and (or) carry bulky or heavy items whenever
possible.
 Hand trucks. Tip the load to be lifted forward slightly so the tongue of the truck goes
Under the load.
 Make sure the tongue of the truck is all the way under the load prior to movement.
 Keep the center of gravity of the load as low as possible. Place heavy objects on the
bottom of the load. Keep feet clear of the wheels.

29. 25
 The center of gravity of the load on both the hand truck and wheelbarrow will be Kept as
low as possible. The weight should be forward so it will be carried by the axle, not the
Handles. If loaded correctly, the hand truck should carry the load—the operator need
only balance and push.
 Place the load so it will not slip, shift, or fall. Load only to a height that will allow a clear
view ahead. For added safety, strap or chain bulky or dangerous cargo (such as cylinders
or drums) to the hand truck’s frame.
 Avoid walking backward with a hand truck if possible. This eliminates the need for a
worker to look over their shoulder to see clearly.
 Never break a hand truck by putting your foot on its wheel; keep your feet clear of the
wheels at all times.
 When going down an incline, keep the hand truck ahead of you. When going up, pull the
hand truck behind you.
 Move the truck at a safe speed. Do not run. Keep the truck constantly under control.
 Secure and store unused trucks in a designated area where they don't create a hazarder
traffic obstruction.
 When a hand truck is loaded in a horizontal position, proper lifting procedures will be used to
prevent operator injury.
7.11. What should your employees know before moving, handling, and
storing materials?
In addition to training and education, applying general safety principles such as proper work
practices, equipment, and controls can help reduce workplace accidents involving the moving,
handling, and storing of materials. Whether moving materials manually or mechanically, your
employees should know and understand the potential hazards associated with the task at hand
and how to control their workplaces to minimize the danger.
Because numerous injuries can result from improperly handling and storing materials, workers
should also be aware of accidents that may result from the unsafe or improper handling of
equipment as well as from improper work practices. In addition, workers should be able to
recognize the methods for eliminating or at least minimizing the occurrence of such accidents.
Employers and employees should examine their workplaces to detect any unsafe or unhealthful
conditions, practices, or equipment and take corrective action.

30. 26
7.12. What are the potential hazards for workers?
Workers frequently cite the weight and bulkiness of objects that they lift as major contributing
factors to their injuries. In 1999, for example, more than 420,000 workplace accidents resulted in
back injuries. Bending, followed by twisting and turning, were the more commonly cited
movements that caused back injuries.
Other hazards include falling objects, improperly stacked materials, and various types of
equipment. You should make your employees aware of potential injuries that can occur when
manually moving materials, including the following:
 Strains and sprains from lifting loads improperly or from carrying loads that are either too
large or too heavy,
 Fractures and bruises caused by being struck by materials or by being caught in pinch points,
and
 Cuts and bruises caused by falling materials that have been improperly stored or by
incorrectly cutting ties or other securing devices.
7.13. What precautions should workers take when moving materials
manually?
When moving materials manually, workers should attach handles or holders to loads. In addition,
workers should always wear appropriate personal protective equipment and use proper lifting
techniques. To prevent injury from oversize loads, workers should seek help in the following:
 When a load is so bulky that employees cannot properly grasp or lift it,
 When employees cannot see around or over a load, or
 When employees cannot safely handle a load.
Using the following personal protective equipment prevents needless injuries when manually
moving materials:
 Hand and forearm protection, such as gloves, for loads with sharp or rough edges.
 Eye protection.
 Steel-toed safety shoes or boots.
 Metal, fiber, or plastic metatarsal guards to protect the instep area from impact or
compression.

31. 27
See OSHA's booklet, Personal Protective Equipment (OSHA 3077), for additional information.
Employees should use blocking materials to manage loads safely. Workers should also be
cautious when placing blocks under a raised load to ensure that the load is not released before
removing their hands from under the load. Blocking materials and timbers should be large and
strong enough to support the load safely. In addition to materials with cracks, workers should not
use materials with rounded corners, splintered pieces, or dry rot for blocking.
7.14. What precautions should workers take when moving materials
mechanically?
Using mechanical equipment to move and store materials increases the potential for employee
injuries. Workers must be aware of both manual handling safety concerns and safe equipment
operating techniques. Employees should avoid overloading equipment when moving materials
mechanically by letting the weight, size, and shape of the material being moved dictate the type
of equipment used. All materials-handling equipment has rated capacities that determine the
maximum weight the equipment can safely handle and the conditions under which it can handle
that weight. Employers must ensure that the equipment-rated capacity is displayed on each piece
of equipment and is not exceeded except for load testing.
Although workers may be knowledgeable about powered equipment, they should take
precautions when stacking and storing material. When picking up items with a powered
industrial truck, workers must do the following:
 Center the load on the forks as close to the mast as possible to minimize the potential for the
truck tipping or the load falling,
 Avoid overloading a lift truck because it impairs control and causes tipping over,
 Do not place extra weight on the rear of a counterbalanced forklift to allow an overload,
 Adjust the load to the lowest position when traveling,
 Follow the truck manufacturer's operational requirements, and
 Pile and cross-tier all stacked loads correctly when possible.

32. 28
7.15. What precautions must workers take to avoid storage hazards?
Stored materials must not create a hazard for employees. Employers should make workers aware
of such factors as the materials' height and weight, how accessible the stored materials are to the
user, and the condition of the containers where the materials are being stored when stacking and
piling materials. To prevent creating hazards when storing materials, employers must do the
following:
 Keep storage areas free from accumulated materials that cause tripping, fires, or explosions,
or that may contribute to the harboring of rats and other pests;
 Place stored materials inside buildings that are under construction and at least 6 feet from
hoist ways, or inside floor openings and at least 10 feet away from exterior walls;
 Separate non compatible material; and
 Equip employees who work on stored grain in silos, hoppers, or tanks, with lifelines and
safety belts.
In addition, workers should consider placing bound material on racks, and secure it by stacking,
blocking, or interlocking to prevent it from sliding, falling, or collapsing.
7.16. What safeguards must workers follow when stacking materials?
Stacking materials can be dangerous if workers do not follow safety guidelines. Falling materials
and collapsing loads can crush or pin workers, causing injuries or death. To help prevent injuries
when stacking materials, workers must do the following:
 Stack lumber no more than 16 feet high if it is handled manually, and no more than 20 feet if
using a forklift;
 Remove all nails from used lumber before stacking;
 Stack and level lumber on solidly supported bracing;
 Ensure that stacks are stable and self-supporting;
 Do not store pipes and bars in racks that face main aisles to avoid creating a hazard to
passersby when removing supplies;
 Stack bags and bundles in interlocking rows to keep them secure; and

33. 29
 Stack bagged material by stepping back the layers and cross-keying the bags at least every
ten layers (to remove bags from the stack, start from the top row first).
During materials stacking activities, workers must also do the following:
 Store baled paper and rags inside a building no closer than 18 inches to the walls, partitions,
or sprinkler heads;
 Band boxed materials or secure them with cross-ties or shrink plastic fiber;
 Stack drums, barrels, and kegs symmetrically;
 Block the bottom tiers of drums, barrels, and kegs to keep them from rolling if stored on their
sides;
 Place planks, sheets of plywood dunnage, or pallets between each tier of drums, barrels, and
kegs to make a firm, flat, stacking surface when stacking on end;
 Chock the bottom tier of drums, barrels, and kegs on each side to prevent shifting in either
direction when stacking two or more tiers high; and
 Stack and block poles as well as structural steel, bar stock, and other cylindrical materials to
prevent spreading or tilting unless they are in racks.
In addition, workers should do the following:
 Paint walls or posts with stripes to indicate maximum stacking heights for quick reference;
 Observe height limitations when stacking materials;
 Consider the need for availability of the material; and
 Stack loose bricks no more than 7 feet in height. (When these stacks reach a height of 4 feet,
taper them back 2 inches for every foot of height above the 4-foot level. When masonry
blocks are stacked higher than 6 feet, taper the stacks back one-half block for each tier above
the 6-foot level.)
7.17. Important Safety Measures
To reduce the number of accidents associated with workplace equipment, employers must train
employees in the proper use and limitations of the equipment they operate. In addition to
powered industrial trucks, this includes knowing how to safely and effectively use equipment
such as conveyors, cranes, and slings.

34. 30
7.17.1. What safety measures should employer stake regarding
conveyors?
When using conveyors, workers may get their hands caught in nip points where the conveyor
medium runs near the frame or over support members or rollers. Workers also may be struck by
material falling off the conveyor, or they may get caught in the conveyor and drawn into the
conveyor path as a result. To prevent or reduce the severity of an injury, employers must take the
following precautions to protect workers:
 Install an emergency button or pull cord designed to stop the conveyor at the employee's
work station.
 Install emergency stop cables that extend the entire length of continuously accessible
conveyor belts so that the cables can be accessed from any location along the conveyor.
 Design the emergency stop switch so that it must be reset before the conveyor can be
restarted.
 Ensure that appropriate personnel inspect the conveyor and clear the stoppage before
restarting a conveyor that has stopped due to an overload.
 Prohibit employees from riding on a materials-handling conveyor.
 Provide guards where conveyors pass over work areas or aisles to keep employees from
being struck by falling material. (If the crossover is low enough for workers to run into it,
mark the guard with a warning sign or paint it a bright color to protect employees.)
 Cover screw conveyors completely except at loading and discharging points. (At those
points, guards must protect employees against contacting the moving screw. The guards are
movable, and they must be interlocked to prevent conveyor movement when the guards are
not in place.)
7.17.2. What safety measures should employer stake regarding
cranes?
Employers must permit only thoroughly trained and competent workers to operate cranes.
Operators should know what they are lifting and what it weighs. For example, the rated capacity
of mobile cranes varies with the length of the boom and the boom radius. When a crane has a

35. 31
telescoping boom, a load may be safe to lift at a short boom length or a short boom radius, but
may overload the crane when the boom is extended and the radius increases.
To reduce the severity of an injury, employers must take the following precautions:
 Equip all cranes that have adjustable booms with boom angle indicators.
 Provide cranes with telescoping booms with some means to determine boom lengths unless
the load rating is independent of the boom length.
 Post load rating charts in the cab of cab-operated cranes. (All cranes do not have uniform
capacities for the same boom length and radius in all directions around the chassis of the
vehicle.)
 Require workers to always check the crane's load chart to ensure that the crane will not be
overloaded by operating conditions.
 Instruct workers to plan lifts before starting them to ensure that they are safe.
 Tell workers to take additional precautions and exercise extra care when operating around
power lines.
 Teach workers that outriggers on mobile cranes must rest on firm ground, on timbers, or be
sufficiently cribbed to spread the weight of the crane and the load over a large enough area.
(Some mobile cranes cannot operate with outriggers in the traveling position.)
 Direct workers to always keep hoisting chains and ropes free of kinks or twists and never
wrapped around a load.
 Train workers to attach loads to the load hook by slings, fixtures, and other devices that have
the capacity to support the load on the hook.
 Instruct workers to pad sharp edges of loads to prevent cutting slings.
 Teach workers to maintain proper sling angles so that slings are not loaded in excess of their
capacity.
 Ensure that all cranes are inspected frequently by persons thoroughly familiar with the crane,
the methods of inspecting the crane, and what can make the crane unserviceable. Crane
activity, the severity of use, and environmental conditions should determine inspection
schedules.

36. 32
 Ensure that the critical parts of a crane such as crane operating mechanisms, hooks, air, or
hydraulic system components and other load-carrying components are inspected daily for
any maladjustment, deterioration, leakage, deformation, or other damage.
7.17.3. What must employers do to ensure the safe use of slings?
As an employer, you must designate a competent person to conduct inspections of slings before
and during use, especially when service conditions warrant. In addition, you must ensure that
workers observe the following precautions when working with slings:
 Remove immediately damaged or defective slings from service.
 Do not shorten slings with knots or bolts or other makeshift devices.
 Do not kink sling legs.
 Do not load slings beyond their rated capacity.
 Keep suspended loads clear of all obstructions.
 Remain clear of loads about to be lifted and suspended.
 Do not engage in shock loading.
 Avoid sudden crane acceleration and deceleration when moving suspended loads.
7.17.4. What must employers do to protect workers who operate
powered industrial trucks?
Workers who handle and store materials often use fork trucks, platform lift trucks, motorized
hand trucks, and other specialized industrial trucks powered by electrical motors or internal
combustion engines. Employers must make these workers aware of the safety requirements
pertaining the design, maintenance, and use of these trucks.
7.17.5. What are the safety requirements for design?
All new powered industrial trucks, except vehicles intended primarily for earth moving or over-
the-road hauling, must meet the design and construction requirements for powered industrial
trucks established in the American National Standard for Powered Industrial Trucks, Part
II, ANSI B56.1-1969. Trucks approved for fire safety also must bear a label, or some other
identifying mark, indicating acceptance by a nationally recognized testing laboratory.

37. 33
7.17.6. What are the safety requirements for modification?
You and your employees must not make modifications and additions affecting capacity and safe
operation of the trucks without the manufacturer's prior written approval. In these cases, you
must change capacity, operation, and maintenance instruction plates and tags or decals to reflect
the new information. If the truck is equipped with front-end attachments that are not factory
installed, the user must request that the truck be marked to identify these attachments and show
the truck's approximate weight including the installed attachment when it is at maximum
elevation with its load laterally centered.
7.17.7. What are the safety requirements for designation?
There are 11 different designations of industrial trucks, and each designation is suitable for use in
certain locations and under specific conditions. Workers must not use powered industrial trucks
in atmospheres containing hazardous concentrations of the following substances:
 Acetylene
 Butadiene
 Acetaldehyde
 Cyclopropane
 Ethylene
 Isoprene
 Hydrogen (or gases or vapors equivalent in hazard to hydrogen)
 Ethylene oxide
 Propylene oxide
 Diethyl ether
 Unsymmetrical dimethyl hydrazine
In addition, workers may not use these trucks in atmospheres containing hazardous
concentrations of metal dust, including aluminum, magnesium, and other metals of similarly
hazardous characteristics. In atmospheres containing carbon black, coal, or coke dust, workers
may use only approved powered industrial trucks designated as EX. Where dusts of magnesium,

38. 34
aluminum, or bronze may be present, fuses, switches, motor controllers, and circuit breakers of
trucks must have enclosures specifically approved for such locations.
Some powered industrial trucks are designed, constructed, and assembled for use in atmospheres
containing flammable vapors or dusts. These include powered industrial trucks equipped with the
following:
 Additional safeguards to their exhaust, fuel, and electrical systems;
 No electrical equipment (including the ignition);
 Temperature limitation features; and
 Electric motors and all other electrical equipment completely enclosed.
Workers may use these specially designed powered industrial trucks in locations where volatile
flammable liquids or flammable gases are handled, processed, or used. The liquids, vapors, or
gases should be confined within closed containers or closed systems and not allowed to escape.
These trucks are approved and generally designated as DS, DY, ES, EE, EX, GS, or LPS. See
Title 29 of the Code of Federal Regulations (CFR) Part 1910.178(b) for more detail on these
designations.
7.17.8. What safety precautions should employers and workers observe
when operating or maintaining powered industrial trucks?
When operating or maintaining powered industrial trucks, you and your employees must
consider the following safety precautions:
 Fit high-lift rider trucks with an overhead guard if permitted by operating conditions.
 Equip fork trucks with vertical load backrest extensions according to manufacturers'
specifications if the load presents a hazard.
 Locate battery-charging installations in designated areas.
 Provide facilities for flushing and neutralizing spilled electrolytes when changing or
recharging batteries to prevent fires, to protect the charging apparatus from being damaged
by the trucks, and to adequately ventilate fumes in the charging area from gassing batteries.
 Provide conveyor, overhead hoist, or equivalent materials handling equipment for handling
batteries.

39. 35
 Provide auxiliary directional lighting on the truck where general lighting is less than 2
lumens per square foot.
 Do not place arms and legs between the uprights of the mast or outside the running lines of
the truck.
 Set brakes and put other adequate protection in place to prevent movement of trucks, trailers,
or railroad cars when using powered industrial trucks to load or unload materials onto them.
 Provide sufficient headroom under overhead installations, lights, pipes, and sprinkler
systems.
 Provide personnel on the loading platform with the means to shut off power to the truck
whenever a truck is equipped with vertical only (or vertical and horizontal) controls
elevatable with the lifting carriage or forks for lifting personnel.
 Secure duckboards or bridge plates properly so they won't move when equipment moves
over them.
 Handle only stable or safely arranged loads.
 Exercise caution when handling tools.
 Disconnect batteries before repairing electrical systems on trucks.
 Ensure that replacement parts on industrial trucks are equivalent to the original ones.
7.17.9. Are there any training requirements for operators of powered
industrial trucks?
Employers must also evaluate the operator's performance in the workplace and certify that each
operator has successfully received the training needed. The certification must include the name
of the operator, the date of training, the date of evaluation, and the identity of the person(s)
performing the training or evaluation. In addition, you must conduct an evaluation of each
powered industrial truck operator's performance at least once every 3 years.
You must also conduct such an evaluation as well as refresher training if one of the following
applies:
 Operator is observed operating the vehicle in an unsafe manner;
 Operator is involved in an accident or near-miss incident;
 Operator receives an evaluation revealing unsafe operation of the truck;

40. 36
 Operator is assigned to drive a different type of truck; or
 Condition in the workplace changes in a manner that could affect safe operation of the truck.
For more information contact your Regional OSHA office or visit our website at For more
detailed information on powered industrial trucks, overhead and gantry cranes, and slings, see
29 CFR Part 1910.178 through 1910.184 Subpart N.
7.18. Basic Safety and Health Principles
Employers can reduce injuries resulting from handling and storing materials by using some basic
safety procedures such as adopting sound ergonomics practices, taking general fire safety
precautions, and keeping aisles and passageways clear.
8. Hand Tool Design and Musculoskeletal Disorders
Hand tools are anything that can be manipulated by the hand. The economic and political
stability of early cultures often depended directly on the sophistication of available hand tools,
e.g. weapons, instruments. The use of hand tools is ubiquitous and poorly designed hand tools in
an industrial plant may affect more than 10% of workers per year.
9. Poor Design
May cause decreases in productivity with slower work and more errors. Increases in injuries to
the wrist, forearm, and shoulders may also occur. Illnesses may also increase due to the effects of
long term injury effects. Accidents may also increase as will compensation costs.
10.Biomechanical Considerations in Hand Tool Design
Forceful grip exertions of hand rely on muscle contractions in forearm, and muscle forces are
transferred to fingers via tendons.
 Grip Configuration - determines level of muscle exertion and tendon tension, and there
is some effect of hand and wrist anthropometry.

41. 37
 Wrist Angle - during grip-type exertions directly affects the amount of intra-wrist
supporting forces acting normal to the direction of tendons and synovia (the lubricating
sheaths around tendons).
11.Shape and Size Considerations for Better Performance
12.Shape the tools to avoid extremes of wrist deviation
Allowing hand and forearm to remain in alignment during forceful grip exertion often
requires special handle design such as:
o Bend in the Tool Handle - This has been effective in reducing wrist-related
disorders in users of pliers and knives.
o Pistol grip vs Cylindrical grip designs - Especially applicable to motorized hand
tools. Here driving the torque of tool creates tendency for the tool to rotate in
worker's hand unless firmly gripped. Any wrist deviation leads to significantly
increased risk of injuries. Pistol-shaped tools allow for greater control with less
force and wrist deviation.
13.Shape the tool to avoid shoulder abduction
 If the tool requires extreme wrist deviation, the usual reaction is to raise the arm to
decrease wrist stress. This biomechanical tradeoff increases stresses on the shoulder joint.
Abduction up to 20 reduces excessive load on the shoulder, but as angles increase beyond
20° so the increase in shoulder load leads to an increase in muscle fatigue. If shoulder
abduction exceeds 30° then you get a rapid increase in fatigue. If shoulder abduction is
60° , then muscles fatigue 3X as fast. If shoulder abduction is 60°, then muscles fatigue
6X as fast. Keeping arms down as close as possible to the body can minimize fatigue.
14.Shape the tool to assist the grip
 Slight contouring of the grip or flared handles can increase comfort and reduce slippage
in sweaty hands. Handles should be at least 4 - 5" long for power grip. Longer handles
help distribute forces on fingers. Smooth handles for tools requiring wrist rotation should

42. 38
be avoided because of the increased risk of slippage and rotational wrist damage. Padding
handles reduces the force needed to grip the tool.
o For Forceful Squeezing - ensure that tool can be gripped by men and women,
starting grip distance isn't too great, and that forces aren't concentrated on a few
fingers or the center of the palm.
o Anatomical Limitations - are the locations of the median nerve, arteries,
synovial for finger flexor tendons directly under skin of palm.
 Hand tool weight - Effects of tool weight can aggravate muscle actions necessary to
precisely position and stabilize the tool during operation. Tool balancers which
counterbalance a tool may be effective depending on how the tool is to be used, how
often and how long. Use of rests, supports, two hand grips, etc. can all help to decrease
the effort required to use heavy tools.
 Right vs Left-handed Tools - Try to design tools for operation with both hands. When
only right-handed users are considered, left-handers may be at an increased risk of injury.
Left-handed people are 5 times more likely to suffer injuries trying to cope with right
handed products.
15. Musculoskeletal Disorders (MSDs)
MSDs are the major work place injury. There are many different names for these injuries:
CTD - Cumulative Trauma Disorders
OOD - Occupational Overuse Disorder
RMI - Repetitive Motion Injury
RMD - Repetitive Motion Disorder
RSI - Repetitive Strain Injury
UECTD - Upper Extremity Cumulative Trauma Disorder
15.1. Etiology of MSDs
Four risk factors increase the likelihood of an MSD:

43. 39
 Posture of hand and body - Posture deviated from "neutral position" increases the
likelihood of injury. This can include hand deviations, wrist extensions, or poor seated
posture.
 Number of Repetitions - High frequency of performing a motion can increase the
likelihood of injury. Insufficient micro breaks between motions (such as keystrokes) and
the resulting muscle fatigue contribute t
15.2. Human vibration
Human vibration is defined as the effect of mechanical vibration of the environment on the
human body. During our normal daily life, we are exposed to various sources of vibration, for
example, in buses, trains, cars. Many people are also exposed to other vibrations during their
working day. Those vibrations have to be monitored and are defined by standards.
15.3. Human vibration and why we need to measure it
Human vibration is defined as the effect of mechanical vibration of the environment on the
human body. During our normal daily life, we are exposed to various sources of vibration, for
example, in buses, trains, cars. Many people are also exposed to other vibrations during their
working day, for example, vibrations produced by hand tools, machinery or heavy vehicles.
Human vibration can be pleasant, unpleasant or harmful. Gentle vibrations, such as that
experienced when sitting in a rocking chair, dancing or running are pleasant. More violent
vibrations, for example, those experienced when traveling in a car down a bumpy road or when
operating a power tool, are unpleasant or harmful. The harmfulness of vibration depends on its
intensity and frequency content and the time of exposure.
Especially at workplaces exposed to vibrations, there is a big likelihood of permanent damage to
some parts of the human body. One effect is known as Reynaud’s disease or the effect of white
fingers where the fingers change color to white and become painful. Another typical effect of
working with heavy machinery or vehicles (a typical example is a helicopter) is the problems
with the lumbar region.

44. 40
Harmful effects of vibration on human health are a serious problem. Mechanical vibrations
transmitted from power tools and other vibrating devices to the human body may have a negative
impact directly on individual tissues and blood vessels, can cause excitation of vibration of the
internal organs or body parts, and even cellular structures.
In practice, the most dangerous is hand-arm vibration transmitted to the upper parts of the body,
which can cause pathological changes in the nervous system, vascular (cardiovascular) and
osteoarticular. Changes in the human body resulting from the contact with the mechanical
vibrations are recognized as an occupational disease, called the vibration syndrome. The three
forms of vibration disease are identified: neurovascular, osteoarticular, and mixed. According to
data, in 2008 the percentage of vibration syndrome in all occupational diseases was: 2.9% in
forestry, 5.6% in mining, 4.3% in the production of metals and as much as 8.7% in construction.
The human vibration module provides measurements to be able to judge the risk of such damage.
It is based on an ISO 2631-1 (dated in 1997) standard that defines basic procedures, ISO 8041
(dated 2005), which defines exact procedures for measurements and ISO 2631-5 (dated 2005)
which defines calculations of lumbar spine response to the vibrations.
There are two main types of measurements:
 whole body measurements (are measured with the help of the so-called seat sensor, where
we need to install the triaxial sensor in the rubber adapter on which we sit on)
 hand-arm measurements (is a measurement of hand-arm where the sensors are installed on
special adapters for holding them on the handle or between fingers)
Both measurements are performed with triaxial accelerometers (it is very common to use 50 g
sensors) and using special adapters. For workplaces with high vibrations (for example impact
hammers), it is necessary to use high g sensors (500 g or more). This sensor should also survive
the high shock.
For the measurement, we need several ICP channels with a 24 bit sigma-delta AD card
(Sirius or Dewe-43, for example).
In theory, we would need to measure a full working day with all the significant loads. Often the
measurement interval is shorter, but we need to ensure that all the significant vibration patterns
are covered correctly in the obtained measurements.

45. 41
There are several parameters, that needs to be calculated:
 RMS - the "root means square" value is a statistical measure of the magnitude of a weighted
signal,
 Peak is the maximum deviation of the signal from the zero line,
 Crest factor is the ratio between the peak and RMS,
 VDV is the fourth power vibration dose value,
 MSDV is the motion sickness dose value,
 MTVV is the maximum transient vibration value, calculated at a one-second interval.
15.4. Measuring human vibration
Vibrations can be desired and perceived as pleasant or give useful feedback over ongoing
processes. However, just as often they are undesired, irritating, cause stress, induce panic and
can lead to physical reactions such as sweating, nausea and vomiting. While these can be
extremely unpleasant experiences and strongly influence a person's life and mental state, for
most people the effect of vibrations will only be temporary or, once the exposure to the
vibrations is stopped, the physical effects will disappear over time.
The physical effect of vibrations on the human body may also be permanent. The risk for
irreparable injuries is especially high for human vibration occurring in context with work, where
the vibration magnitudes can be substantial, the exposure times long and the vibration exposure
may occur regularly or even daily. Typical risk groups are drivers of lorries, trucks,
agricultural/farming, construction site and forest machinery, pilots of certain helicopters, and
workers operating hand-fed machines, hand-guided machines or hand-held power tools and who
need to hold work pieces. During their work, a worker's entire body or parts of it, especially the
hand-arm region may be exposed to excessive vibrations.
Unfortunately, the relation between vibration exposure and health damage is often not that
obvious. Injuries may develop over a long period of time and other activities, such as lifting
heavy loads, could be the reason for the injury (e.g., lower back pain). A worker may feel
numbness or fatigue after a working day while exposed to intensive vibrations, but initially these
effects will only be temporary and the next day everything will seem fine. However, once these

46. 42
effects are permanent (such as cold fingers, lower back pain, etc.) it is often too late. Many of
these injuries are irreversible.
It is therefore of the utmost importance to prevent excessive vibration exposure. In Europe, the
Vibration Directive (Directive 2002/44/EC) has been introduced in order to set minimum
standards for controlling the risks, both from hand-arm and whole-body vibration. The directive
sets action values, above which it requires employers to control the vibration risks, and limit
values, above which workers must not be exposed.
For hand-arm vibrations these values are:
 A daily exposure action value of 2.5 m/s2
 A daily exposure limit value of 5 m/s2
For whole-body vibrations these values are:
 A daily exposure action value of 0.5 m/s2
(or, at the choice of the individual EU Member
State, a vibration dose value of 9.1 m/s)
 A daily exposure limit value of 1.15 m/s2
(or, at the choice of the individual EU Member
State, a vibration dose value of 21 m/s)
Employers are obliged to determine and assess the risk resulting from both hand-arm and whole-
body vibrations and ensure that the exposure values are not exceeded. If analysis suggests that
workers are at risk, employers should set a management program into action to keep the
exposure to vibration at a minimum and prevent the development and progression of injury.
At the first stage, the analysis can be based on emission values, i.e., data of vibration magnitudes
that occur when operating or working with a particular tool, vehicle or machinery. Today such
data is often provided by manufacturers of machines and vehicles but can also be found in
databases maintained by independent organizations and institutes. However, employers must be
aware that these data have been determined following harmonized codes. Emission data
determined according to such standards are primarily meant to allow the customer direct
comparison of similar products. In practice, however, the emission values occurring under real
conditions may be significantly greater.
The reason for this can be wear, overly rough road surfaces, operating vehicles or mobile
machinery on sloped surfaces, and other factors of real, everyday usage. Therefore,