Presented by: MTM Inc'

1
Chapter 18
Manual Material Handling

• Presented by MTM Inc.

2
Background

• MMH accounts for
• 27 of industrial injuries
• 670,000 injuries/yr in US
• 60 of all money spent on industrial injury
• 93 million work days/yr of industrial injury
• Trauma typically occurs to skeletomuscular system
• Acute- due to one-time event
• Chronic- result of cumulative events

3
Criteria

• Biomechanical
• Focus on force/torque to body during MMH
• Measure force/torque, body dimensions/strengths,
  compute effect
• Concentrate on the back the weak link
• Intra-abdominal pressure test
• Physiological
• Focus on energy requirements, effect on
  cardiovascular system
• Limiting when task done gt 4x minute
• Keep metabolic rate lt 5kcal min
• Psychophysical
• Measure while workers actually perform MMH task
• Combines biomechanical and physiological
  approaches

4
MMH Variables

• Goals
• Increase strength of worker
• Decrease stress due to task
• 3 variable categories
• Individual
• Unique to individual
• Ex gender, age, back strength, arm strength,
  etc.
• Technique
• Come with training
• Ex body posture, hand/foot orientation,
  acceleration, lifting technique
• Task
• Ergonomic variables
• Ex object, weight, clothing, ease of handling,
  angle of rotation

5
Pushing and Pulling

• Pushing/Pulling is better than lifting/lowering
• Use carts in all areas, not just production areas
• Force Limits
• Horizontal
• Vertical
• Task Modification

6
Horizontal Push and Pull

• Amount of force is influenced by force
  direction
• Can push harder than can pull
• Can push left harder than right
• Can lift more than can press down
• Perpendicular vs. parallel to shoulders
• Operators at workstations may move objects
  parallel to shoulders
• Most exertions are perpendicular to shoulder line

7
Force Perpendicular to Shoulders

• Recommended force limits (Tables 18.1-18.4)
• Conclusions
• 2 hands are better than 1
• Ability to apply force increases as frequency of
  application decreases
• Females are weaker than males (???)
• Push at waist level rather than shoulder or knee
  level
• Pull at knee level rather than at waist or
  shoulder level
• Tools can increase efficiency rails and
  rickshaws
• Arms/shoulders are limiting for repetitive tasks
• Lack of solid support also causes problems (Table
  18.5)

8
Vertical Push and Pull

• Recommended force limits (Table 18.6)
• Task Modifications
• Wheel maintenance
• Avoid muscle-powered pushing/pulling for ramps,
  long distances, or high frequency moves USE
  FORKLIFTS !
• More modifications for proper material handling
  (Figures 18.1-18.5)

9
Holding

• Gives a static load
• Involves
• Load from body weight
• Load from object weight
• Problem
• Working on an object 0.5 m away from the spine
  centerline vs. working on an object .6 m away
• Additional torque ? lower back pain
• Solutions
• Reduce torque
• Reduce duration of torque (Figure 18.6)

10
Carrying

• 2 main categories
• Back and shoulders (long distance)
• Hand carrying (short distance)
• Poor job design! (Table 18.7)
• Push or pull instead ? less strain on body

11
Carrying Back Shoulders (Long Distance)

• Use mechanical aids
• Human beast of burden last resort
• Key guidelines
• Minimize the moment arm of the load vs. the spine
• Carry large loads occasionally rather than light
  loads often
• Carrying ladders
• Have a short and a long ladder
• Have a shoulder pad
• Have the upper rail on the shoulder and the arm
  through the rungs
• Teamwork for loading/unloading

12
Hand Carrying(Short Distance)

• Harder to mechanize
• Try balancers, manipulators, robots, or conveyors
• Use of different grips (Figure 18.10)
• Continuous carrying limited by the cardiovascular
  system
• Handles on boxes and bags
• Dont forget non-production activities
• Dont take the stairs
• Move loads between levels with hoists

13
Revised NIOSH Lifting Guidelines
Lifting

• National Institute of Occupational safety and
  Health (NIOSH)
• Primary purpose is to rank alternatives, not give
  absolute risks

14
Basic Formula
RWL LCHMVMDMFMAMCM

• RWL Recommended weight limit, lb
• LC Load constant
• HM Horizontal multiplier
• VM Vertical multiplier
• DM Distance multiplier
• FM Frequency multiplier
• AM Asymmetry multiplier
• CM Coupling multiplier

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Horizontal MultiplierHM BIL/H

• HM Horizontal multiplier, proportion
• H Horizontal distance from the large
• knuckle at the end of the third
  finger
• to the ankle midpoint
• BIL Body interference limit
• 10 for inches
• 25 for cm

16
Vertical MultiplierVM 1 - VC V - KH

• VM Vertical multiplier, proportional
• V Initial vertical height of knuckles
• KH Knuckle height of typical lifter
• VC Vertical constant
• 0.0075 for inches
• 0.003 for cm

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Distance MultiplierDM 0.82 DC/D

• DMDistance multiplier, proporiton
• .82Multiplier atmaximum hand height of 70 inches
  (175 cm)
• DDistance moved vertically
• DCDistance constant
• 1.8 for inches
• 4.5 for cm

18
Frequency Multiplier (FM)

• Can range from less than 1 in 5 minutes to 15
  lifts/min
• Mean number of lifts in a 15 minute period
• Varies depending on lifting duration/session and
  whether the initial vertical location of the
  hands is above or below typical knuckle height

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Asymmetry multiplierAM 1 - 0.0032A

• AM Asymmetry multiplier, proportion
• A Angular deviation of the midpoint of
• the two hands from straight ahead

20
Coupling Multiplier

• Depends on the height of the initial and final
  hand-container coupling and whether the coupling
  is good, fair, or poor

21
Recovery Time

• The person is resting or has light work (such as
  sitting, standing, walking, monitoring)
• If a person does not meet the recovery criterion,
  omit the recovery time and add the work times
  together

22
Control Over the Object

• Input Information depends on whether control over
  the object is needed, and where
• 1) Only at the origin of the movement
• 2) At both origin and destination

23
Control at Destination is Implied by

• A regrasp near the destination
• A momentary hold near destination
• A need to carefully position or guide the load
  near the destination

24
Control Only at the Origin

• Initial horizontal location of the hands from the
  ankle midpoint
• Initial vertical location of the hands
• Initial angle of asymmetry of object center
• Vertical travel distance between the lift origin
  and destination
• Frequency of lifts per minute
• Hand-container coupling classification

25
Control at Both Origin and Destination

• Final horizontal location of the hands
• Final vertical location of the hands
• Final angle of asymmetry of object center

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Force LimitsFL A F DIST

• FLForce limit, kg
• AAge factor
• FFrequency factor
• DISTDistance factor

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Manual Material Handling

• Guidelines for Manual Material Handling

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Guidelines for MMH

• Selecting an individual
• Teaching technique
• Designing the job

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Guidelines for Occasional Lifting

• Select the Individual
• Select strong people based on tests
• Teach Technique
• Bend the knees
• Dont slip or jerk
• Dont twist during the move
• Design the Job
• Use machines
• Move small weights often
• Get a good grip
• Put a compact load in a convenient container
• Keep the load close to the body
• Work at knuckle height

30
Select Strong People Based on Tests

• JSI f (weight/capacity)
• Where,
• JSI Job severity index
• Weight weight lifted or moved
• Capacity capacity of worker for specific task

31
Select Strong People Based on Tests

• What is Capacity?
• A function of fat-free body weight
• Though females have more, worker selections
  should be made through tests

32
Select Strong People Based on Tests

• What types of tests?
• Fat-free weight
• Isometric strengths of specific muscle groups
• Previous back injury
• Uneven leg length

33
Select Strong People Based on Tests

• Benefits to analyzing the task requirements
• Permits a larger proportion
• of the population to do the job
• It reduces the stress on everyone doing the job

34
Bend the Knees

• This concept should work, but
• no one practices
  it !
• Requires too much energy to lower the torso
• Also called squat lifting

35
Bend the Knees

• For bulky loads use straddle stance to keep load
  closer to the spine
• One-hand lift
• When the worker grabs on the one side of the
  container with the hand not in use, to support
  the back

36
Dont Slip or Jerk

• Problem with slipping is the
• unexpected load on the back
• To reduce the chance, have a high coefficient of
  friction between shoes and the floor

37
Dont Slip or Jerk

• Clean and jerk movements
• Practiced by professionals
• Within standardized situations
• Have worker recognition of load type and weight

38
Dont Twist During the Move

• Twisting especially when bent is very bad
• Instead focus on moving feet around

39
Dont Twist During the Move

• To reduce lifting and lowering loads (which
  therefore reduce twisting)
• Have the two surfaces at the same height

40
Use Machines

• Helps to eliminate and reduce
• manual material handling

41
Use Machines

• Common machines
• Balancer or manipulator
• Lift trucks
• Conveyor
• Lever arm
• Carts

42
Move Small Weights Often

• Small weights are better than large
• Weights must be reduced or loads moved more
  frequently
• 15 kg or less is an ideal load

43
Move Small Weights Often

• Things to pay attention to
• If there is added resistance to the load
• Size of the package
• Use shipping personnel

44
Move Small Weights Often

• Ways to reduce a weight
• Let gravity do the work
• Lift with a partner
• Can the job be changed to be done by one person ?

45
Get a Good Grip !

• Cardboard boxes with gripping holes are bad
  because
• Hand cant rotate as object
• is lifted from the knee to
• above the waist
• Small surface area and puts too much pressure on
  the hands

46
Get a Good Grip !

• Best way to get a grip
• Boxes without handles with one had on the upper
  outer corner and the other on the opposite lower
  inner corner
• Gives more stability

47
Put a Compact Load in a Convenient Container

• Keep load close to the spine
• Spinal torque
• SPINET OBJWT OBMARM DISTO DISTCG
• SPINET spinal torque person exerts, kg-m
• OBJWT object weight, kg
• OBMARM Moment arm of the object, m
• DISTO distance between spine and object, m
• DISTCG distance from closest portion of the
  object to
• center of gravity

48
Keep the Load Close to the Body

• Revised equation should read
• SPINET OBJWT OBMARM UBWT BMARM)
• UBWT upper body weight, kg
• BMARM upper body moment arm, m

49
Keep the Load Close to the Body

• Reduce reach distance by
• Moving object closer to person
• Moving person closer to the object
• Modifying vertical distance of conveyors
• Consider food position when turning with the load
• Consider railing on containers

50
Keep the Load Close to the Body

• MISBCK 0.4WT sin(a / LTSLPR)
• MISBCK max isometric back muscles strength
  needed to avoid back pain while working standing
  stooped at angle a, kg
• WT body weight, kg
• a acute angle between the back and the line of
  gravity, degrees
• LTSLPR max long term static load proportion of
  max isometric strength (10-15)

51
Work at Knuckle Height

• Knuckle height
• Change machine height, dont use it just because
  it comes that way from the vendor
• Dont put a load on the floor
• Use racks or trays when applicable
• Strains the back
• Only light items should be about shoulders

52
Work at Knuckle Height

• Dont lift above shoulder
• High lifting is bad for two reasons
• Muscular strength is poor above the shoulder due
  to small muscle groups
• Dangerous to remove an object from top shelf
  because it may be dropped and damaged

53
The Birth of a Paradigm

• A group of scientists placed 5 monkeys in a cage.
  They also placed a ladder with bananas in the
  top. When a monkey went up to have a banana, the
  scientists sprayed the rest of the monkeys with
  cold water. Later on, when a monkey wanted a
  banana the others started to beat him.
• After a day, and despite the temptation, no
  monkey went upstairs for a banana.
• Then the scientists exchange one monkey for a new
  one. Of course the first thing the new monkey did
  was to get into the ladder to get a banana, but
  the other monkeys very quickly get him down and
  beat him. After a short wild the new monkey
  give-up for the bananas.
• A second of the initial monkeys was then
  replaced. The same thing happened, but this time
  the first fresh monkey participated on beating
  the new monkey.
• Then a third of the old monkeys was replaced, and
  then a fourth, and finally the fifth initial
  monkey was replaced. The story still was the same
• Finally the scientists were left with a new set
  of 5 monkeys that, although none of them got a
  cold water bath, they still continue beating any
  other monkey that even tried to get a banana
• If we could Ask them why are you beating every
  one of you that tries to get a banana ?
• The Answer most probably would be I dont know,
  things have always been done like this here !
• Sounds familiar ? Why do we do things in a
  certain way, even if we can change them ?
• It is easier to disintegrate an atom than a
  pre-conception - Albert Einstein.

54
Your Assignment

• From the book in Ch.18
• Problems 2, 6, 8, 12