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Manual Material Handling


60% of overexertion injuries are due to lifting and lowering ... AL lifting conditions would create tolerable compressive force on the L5/S1 disc ... – PowerPoint PPT presentation

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Title: Manual Material Handling

Manual Material Handling
  • Effects
  • 25 of accidents reported are due to manual
    material handling
  • 60 of overexertion injuries are due to lifting
    and lowering
  • 25-44 year olds have the highest incidence of
    back pain
  • Four avenues of research
  • Epidemiological approach approach characterizes
    the job and workplace along with other factors to
    derive significant trends that may lead to
  • Biomechanical approach interested in
    characterizing the forces and moments on the
    various body elements in order to estimate task
    and load characteristics that may lead to injury
  • Psychophysical methods subjects adjust the load
    in order to arrive at a load that is acceptable
    to them
  • Physiological approach measure physiological
    measures to determine the level of stress imposed
    (heart rate, blood pressure, etc.)

Occupational Biomechanics
  • Biomechanics concerned with the mechanical
    elements of living organisms
  • Occupational Biomechanics
  • Deals with the mechanical and motion
    characteristics of the human body and its
  • The studies of the interrelationships between
    workers and their tools, workplaces, and so on.
  • Inputs include
  • Engineering sciences
  • Physical sciences
  • Biological sciences

Occupational Biomechanics
  • Multidisciplinary work entailing modeling with
  • Modeling allows us to develop smaller-scale,
    simplistic representations of the real life
    events to solve the problem at hand
  • Anthropometry provides the human body and
    segment dimensions including masses and centers
    of gravity
  • Kinesiology covers the area of human motion.
    Body segment motions and triggering muscular
    actions can be described.
  • Bioinstrumentation deals with the data
    acquisition and analysis such as force plates,
    electromyography, goniometry, and linear
    measuring devices.

Occupational Biomechanics
  • What does Biomechanics affect (better matching
    worker with the environment)
  • Tool design
  • Workplace design
  • Job design
  • Worker/task matching
  • Material handling
  • Newtons laws are a basic ingredient of
    biomechanical analysis
  • A mass will remain at rest or in uniform motion
    unless an unbalanced external force acts on it.
  • Force is proportional to the acceleration of a
  • Any action will be opposed by reaction of an
    equal magnitude.
  • Newtons laws are used to describe the state of a
    body (e.g., a body not in motion-sum of all
    forces and moments acting are zero ---state of

Occupational Biomechanics
  • From Lecture 2 In standard anatomical posture
    (standing erect, face forward, holding arms down
    at the side with palms facing forward with thumbs
    away from the body), there are three planes
  • Sagittal plane splits body into left and right
    in a forward and backward direction
  • Coronal plane passes in a left-to-right
    direction and splits the body into front and back
  • Transverse plane passes perpendicular to each
    of sagittal and coronal planes at the abdominal
    area splitting the body into the top(head) and
  • From Lecture 2 Kinesiology helps us describe
    human motion
  • Flexion decreasing the angle between the body
  • Extension increasing the angle between the body
  • Adduction movement toward the middle of the
  • Pronation face down or palm down position
  • Supination face-up or palm up position

Biomechanical Models
  • Single-segment static model
  • A single-segment model analyzes the isolated body
    segment with the laws of mechanics to identify
    the physical stress on the joints and muscles
  • Two-segment static model
  • A two-segment model allows one to to treat each
    body segment as element in kinetic chain and work
    back to affected joints (e.g., determine forces
    working on vertebrae).
  • Back models
  • Back-models allow for the assessment of the lower
    back which is most distant from the load handled
    by hands. However, it is said to be the most
    vulnerable link of the muscular-skeletal system
    in material handling. Low-back pain is perhaps
    most costly and prevalent work-related
    muscular-skeletal disorder in industry. It is
    estimated that low back pain may affect 50-70
    percent of the general population due to
    occupational and other unknown factors.

Equilibrium Laws
Single-segment Models
  • Single Segment Model (http//
  • Problem
  • Solve for the external moment and reactive force
    acting at the elbow for an average female (see
    attached anthropometric data) holding 20 N with
    one hand. Note Assume that WForearmHand
  • Anthropometric Data

Two-Segment Model
  • Two Segment Model
  • (http//
  • Problem Extend the analysis in problem on
    previous slide to include the shoulder moment and
    reactive force with the arm extended
    horizontally. Note Assume that WForearmHand
    15.8N, WUpperArm 20.6 N.
  • Homework Problem Recompute the external moment
    and reactive force if the arm is positioned 30
    degrees below the horizontal. Note Assume that
    WForearmHand 15.8N, WUpperArm 20.6 N.

Simplified Back Model
  • Simplified Back Model (http//

NIOSH Lifting Guide-1981
  • Most comprehensive approach to controlling
    adverse effect of lifting (front of body)
  • AL (action limit) is the lower level threshold,
    compression force of 770 LB on the lumbar spine
  • This is based on psychophysical studies of
    acceptable loads in lifting tasks
  • Based on 4 assumptions
  • Musculoskeletal injury incidence and severity of
    injury rates increase moderately in populations
    exposed to AL lifting conditions
  • AL lifting conditions would create tolerable
    compressive force on the L5/S1 disc of most young
    and healthy workers
  • Metabolic rate would not exceed 3.5 kcal/min
    under AL conditions
  • Over 75 of women and over 99 of men could lift
    loads described by the AL

NIOSH Lifting Guide-1981
  • MPL (maximum permissible limit) is based on
    primarily biomechanical studies and is 1430 lb.
  • Attempts to meet the following criteria
  • Significant increases occur in musculoskeletal
    injury and severity rates in populations exposed
    to lifting conditions above MPL
  • Lifting conditions above the MPL produce
    intolerable compressive forces on the L5/S1 disc
    in most workers
  • Metabolic rates exceed 5 kcal/min under
    conditions above MPL
  • Only 25 of men and less than 1 of women can
    perform above MPL

NIOSH Lifting Guide-1981
  • AL 40(15/H)(1-0.004V-75)(0.7
    7.5/D)(1-F/Fmax) metric
  • AL 90(6/H)(1-0.01V-30)(0.7 3/D)(1-F/Fmax)
  • MPL 3 AL
  • H horizontal distance (cm or in) from the load
    center of mass at the origin of the vertical lift
    to the midpoint between the ankles (lumbar spine)
  • V vertical distance (cm or in) of the hands to
    the floor at the origin of the lift (no minimum,
    max of 70 inches)
  • D vertical travel distance of the object
    measured by the difference between the final and
    initial locations of the hands (minimum of 10 in
    and a maximum value of 80-V are assumed)
  • F average frequency of lifting (lifts/min) with
    a minimum value of 0.2 and a maximum value as
    defined by Table 3.8.

Example Problem
  • Assume a compact object 6 x 8 with handles
    (with the 8 parallel to the shoulders) is lifted
    from the floor to the table 36 above the floor.
    The lift should be done less than once per hour.
    Compute the AL, MPL, and assess the guidance.
  • A task has been evaluated using the 1981 NIOSH
    guide. A female operator must lift a box weighing
    15 kg. The action limit (AL) has been computed to
    be 11.75 kg. The horizontal distance from the
    center of gravity of the box to the center of the
    lifters ankles is 40 cm. What is the maximum
    permissible limit and what guidance would you
    provide management on the task.

Revised NIOSH-1991
  • Revised NIOSH (1991) resulted in Recommended
    weight limit
  • (RWL) 51(10/H)(1-0.0075V-30)(0.821.8/D)(FM)(1
    -0.0032A) (CM)
  • No MPL, any load above the RWL is considered
  • H horizontal location of hands from midpoint
    between the ankles (min 10 in, max 25 in, set HM
    to 0 for Hgt25in
  • V vertical height of hands from the floor (max
  • D vertical travel distance between the origin
    and the destination (min 10 in, max 70 in)
  • A angle of asymmetry refers to a lift that
    begins or ends outside the sagittal plane
    angular displacement of the load from the
    sagittal plane (range 0-135 degrees)
  • F lifting frequency, average number of lifts
    per minute as measured over a 15 minute interval
  • FM - set using Table 3.15, p. 69
  • CM coupling multiplier is an index evaluating
    effectiveness of the hand container interface.
    (Table 3.16, Table 3.17)

Revised NIOSH-1991
  • Revised NIOSH
  • Epidemiological support still lacking
  • Based on research findings since 1981
  • Stress for engineering controls over
    administrative controls
  • Revised NIOSH Speadsheet
  • International Occupational Safety and Health
    Center estimates
  • 55 LB max for males 25-35 and 33 LB for females
  • Other Manual Handling Activities
  • Research
  • One-handed has had less research done but 48.4 LB
    weight can be lifted occasionally
  • If in seated position, 8.8 LB max
  • Much less work has been done in pulling, pushing,
    carrying, but Pulat on pg. 61 offers some

Job Severity Index
  • Job Severity Index
  • JSI job demand/operator capacity
  • Premise severity of the job in terms of its
    injury potential is a function of job demands and
    job capacity
  • Through validation studies, it has been found
    that a JSI greater than 1.5 is unacceptable

Job Severity Index Formula
JSI Procedure
  • Table 3.9 provides range assignments for lift
  • Initial capacity is determined using lifting
    range, frequency of lift and gender Table 3.10.
  • Initial capacity is adjusted by the size of the
    box or load, Table 3.11.
  • Second adjustment is made for the percentage of
    population to be accommodated (Tables 3.12 and
  • Final adjustment is due to possible twisting (5
    reduction in capacity) and handles (7.2
    reduction for absence).

JSI problem
A male worker receives packages from a conveyor
at a rate of four per minute. The conveyor height
is 24 inches and the stacking height is 45 inches
above the ground. The probability distribution
for the receipt of packages is as follows along
with the package characteristics
For 7 hours a day, the packages received are
listed here
For 1 hour a day, the packages received are
listed here