Manual Material Handling

1
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
  accidents
• 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.)

2
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
  elements.
• The studies of the interrelationships between
  workers and their tools, workplaces, and so on.
• Inputs include
• Engineering sciences
• Physical sciences
• Biological sciences

3
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.

4
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
  mass.
• 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
  equilibrium)

5
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
  bottom(feet)
• From Lecture 2 Kinesiology helps us describe
  human motion
• Flexion decreasing the angle between the body
  parts
• Extension increasing the angle between the body
  parts
• Adduction movement toward the middle of the
  body
• Pronation face down or palm down position
• Supination face-up or palm up position

6
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
  involved.
• 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.

7
Equilibrium Laws
8
Single-segment Models

• Single Segment Model (http//www.ecn.ou.edu/cheo07
  71/www/biomodel/index.htm)
• 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
  15.8N.
• Anthropometric Data

9
Two-Segment Model

• Two Segment Model
• (http//www.ecn.ou.edu/cheo0771/www/biomodel/index
  .htm)
• 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.

10
Simplified Back Model

• Simplified Back Model (http//www.ecn.ou.edu/cheo0
  771/www/biomodel/index.htm)

11
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

12
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

13
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)
  English
• 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.

14
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.

15
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
  hazardous
• 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
  70in)
• 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)

16
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
  recommendations

17
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

18
Job Severity Index Formula
19
JSI Procedure

• Table 3.9 provides range assignments for lift
  conditions
• 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
  3.13).
• Final adjustment is due to possible twisting (5
  reduction in capacity) and handles (7.2
  reduction for absence).

20
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