Manual Materials

1
Chapter 8

• Manual Materials
• Handling Limits

2
Introduction

• Robotics has decreased manual labor
• repetitive and structured jobs
• mostly successful industries
• CATCH 22 capital investment for robots, need to
  be successful to get investment
• Unstructured jobs still manual labor
• construction, assembly, equipment repair, fire
  fighting, police, nursing

3
Results of 1981 NIOSH Study

• Overexertion claimed cause 60 of low back
  pain.
• If significant lost time, less than 1/3 with back
  pain return to previous work.
• Overexertion injuries account for 1/4 of all
  reported occupational injuries in the US (some
  industries 1/2)
• 2/3 of overexertion claims involved lifting
  loads, 20 pushing or pulling

4
Factors affecting manual material handling system

• Worker characteristics (Individual)
• Physical age, anthropometrics, posture
• Sensory visual, audit, tactile, proprio etc
• Motor strength, ROM, endurance
• Psychomotor coordination, RT
• Personality job satisfaction, SES
• Training/experience education
• Health status previous, drug use
• Leisure time activities 2nd job, sedentary

5
Factors affecting manual material handling system

• Material/container characteristics (Task
  Environment).
• Load.
• Dimensions.
• Distribution of load
• 1 vs 2 hand, Moment Arm about back
• Couplings (handles).
• Stability of load (liquids bulks).

6
Factors affecting manual material handling system

• Task workplace characteristics (environment)
• Workplace geometry
• Frequency/duration/pace.
• Complexity
• environment temperature, noise

7
Factors affecting manual material handling system

• Work practice characteristics
• individual speed and accuracy
• Organization teamwork, safety functions, medical
  staff
• Administrative safety incentives, work shift
  length, rotation, personal protective devices

8
3 strategies to preventoverexertion injury

• 1) design the task for all workers
• 2) select workers believed to be at low risk
• 3) train workers to reduce personal risk levels

Often determined by socio-legal-economic
considerations
9
Lifting Limits in Manual Handling

• Setting safe limits for employees
• gold standard for workplace
• Needs to consider
• Epidemiology of MS injury
• Biomechanical concepts
• Physiological principles
• Psychophysical lifting limits

10
Lifting Limits in Manual Handling
Note different limiting factors
11
1981 NIOSH equation to evaluate sagittal plane
lifting

• objective method to determine safe load
• Recommendations
• lifting smooth, with no sudden acceleration
• objects of moderate width (hand separation of
  less than 75 cm (29.5 inches)
• Good couplings (secure handholds and low foot
  slippage potential)
• Favourable temperatures for lifting

12
1981 NIOSH equation to evaluate sagittal plane
lifting

• objective method to determine safe load
• Need to define 4 job attributes
• location of CofM (or handgrip center) of the
  object in horizontal direction (H)
• horizontally from midpoint of ankles

13
1981 NIOSH equation to evaluate sagittal plane
lifting

• objective method to determine safe load
• Need to define 4 job attributes
• location of CofM (or handgrip center) of the
  object in horizontal direction(H)
• location of CofM(or handgrip center) in vertical
  direction at start of lift (V)
• from floor to CofM or handle

14
1981 NIOSH equation to evaluate sagittal plane
lifting

• objective method to determine safe load
• Need to define 4 job attributes
• location of CofM (or handgrip center) of the
  object in horizontal direction(H)
• location of CofM(or handgrip center) in vertical
  direction at start of lift (V)
• vertical travel distance of the hands (D)
• from origin to destination

15
1981 NIOSH equation to evaluate sagittal plane
lifting

• objective method to determine safe load
• Need to define 4 job attributes
• location of CofM (or handgrip center) of the
  object in horizontal direction(H)
• location of CofM(or handgrip center) in vertical
  direction at start of lift (V)
• vertical travel distance of the hands (D)
• Frequency of lifting (lifts / minute) averaged
  over a period (F)

16
1981 NIOSH equation to evaluate sagittal plane
lifting

• objective method to determine safe load
• BUT
• limited to sagittal plane
• did not consider asymmetry
• needs more consideration of width (H)
• needed consideration of quality of coupling
• needed revision of weight limits based on
  frequency

17
1991 committee to revise1994 published revision

• considered new research findings
• biomechanical criteria
• physiological criteria
• psychophysical criteria
• added
• angle of asymmetry from sag plane (A)
• quality of coupling (C) in 3 classes
• still many unknowns and controversies

18
Biomechanical criteria

• Site of greatest stress L5/S1
• Compressive force critical determinant
• 3.4 kN (3400 Newtons)
• safe for most but not all employees
• cadaver study biomechanical models

19
Spinal Motion Segment Failure
Traditional Model
Revised Model (McGill, 1997)
20
Physiological criteria

• energy expenditure related to repetitive lifting
• large energy expenditures required to lift the
  body and the load
• if lifting energy requirements exceed energy
  producing capacitygtfatigue

21
Psychophysical criteria

• how much an individual will choose to lift if
  given the choice when lifting for an extended
  period of time
• Guidelines set to meet acceptable lifting
  capacity of 75 of females (99 males)

22
Quantifies risk increase when

• 1. Heavy objects are lifted.
• 2. The object is bulky.
• 3. The object is lifted from the floor.
• 4. Objects are frequently lifted.
• 5. Poor grips are provided

23
Revised (1994) NIOSH lifting equation
RWL LC x HM x VM x DM x AM x FM x CM
RWL Recommended weight limit Identifies the
MAXIMAL load for the scenario defined in
the equation. Use this value to calculate level
of stress. Lift Index (LI) Task load / RWL
percentage of healthy population at risk???
most healthy population can exceed LI of
1.00?? Compare relative hazard of two tasks/two
environments If LI gt 3 many workers at elevated
risk
24
Revised (1994) NIOSH lifting equation
RWL LC x HM x VM x DM x AM x FM x CM
RWL Recommended weight limit Identifies the
MAXIMAL load for the scenario defined in
the equation.Use this value to calculate level of
stress. Lift Index (LI) Task load / RWL
percentage of healthy population at risk???
most healthy population can exceed LI of
1.00?? Compare relative hazard of two tasks/two
environments If LI lt 1 protective of most workers
25
Revised (1994) NIOSH lifting equation
RWL LC x HM x VM x DM x AM x FM x CM
LC Load constant Maximum recommended weight for
lifting at the standard lifting location
sagittal plane, occasional lift, good
couplings, lt25 cm vertical displacement 23 kg
(230N) or 51 lbs acceptable to 75 of female
population
26
Revised (1994) NIOSH lifting equation
RWL LC x HM x VM x DM x AM x FM x CM
Multipliers used to adjust (reduce) the
recommended load to compensate for less than
optimal lifting conditions
27
Revised (1994) NIOSH lifting equation
RWL LC x HM x VM x DM x AM x FM x CM
Horizontal multiplier increased horizontal
distance from spine increases moment arm and
leads to increased lumbar stress. HM (metric)
25 / H HM (english) 10/ H H horizontal
distance of hands from midpoint between
ankles Note that 25 cm (10 in) is about width of
body. Measured at origin and destination.
28
Revised (1994) NIOSH lifting equation
RWL LC x HM x VM x DM x AM x FM x CM
Vertical multiplier reflects increased lumbar
stress lifting loads near the floor (What is the
cause??) Lifting from near floor requires
greater energy expenditure (Why?) Therefore
reduce RWL by 22.5 if lift begins at floor More
dangerous to lift load to or past shoulder
height Therefore reduce RWL by 22.5 for
shoulder height VM (1-0.003 V-75) V in
cm VM (1-0.0075V-30) V in inches
where V is vertical distance of hands from floor
Measure at origin destination, use worst
case
29
Revised (1994) NIOSH lifting equation
RWL LC x HM x VM x DM x AM x FM x CM
DM Distance multiplier reflects increase in
physiological demand as vertical distance
traveled is increased (? fatigue) DM (0.82
(4.5 / D ) in cm DM (0.82 (1.8/ D)
in inches where D is the total vertical distance
moved between origin and destination
30
Revised (1994) NIOSH lifting equation
RWL LC x HM x VM x DM x AM x FM x CM
Asymmetric multiplier lifting away from
sagittal plane Reduce load by 30 for 90 degrees
of twist AM ( 1 - (0.0032 A)) Where A is
angle of asymmetry (angular displacement from
the sagittal plane) Measure at origin
destination, use worst case
31
Revised (1994) NIOSH lifting equation
RWL LC x HM x VM x DM x AM x FM x CM
FM Frequency Multiplier Table D-5, p 561 from
text Based on work duration (lt1 hr, lt 2hr, lt
8hr) and V (vertical distance of hands from
floor, in cm) and Frequency (rate of
lifting) lifts/min
32
Frequency Multiplier
33
Revised (1994) NIOSH lifting equation
RWL LC x HM x VM x DM x AM x FM x CM
CM Coupling Multiplier Table D-7, p562 from
text Based on V (vertical distance of hands
from floor, in cm) and quality of
coupling Note penalty is not more than 10
decrease in RWL, so rating not that critical.
34
Calculate RWL, then what??

• Calculate the Lift Index (LI), as
  Actual Load Lifted / RWL
• Likely that LI gt 3 poses a significant risk to
  many workers (lt1 is protective)
• a comparison value
• multipliers are factors that increase stress
• Which multiplier has greatest potential for
  change?
• what changes will reduce the multipliers?

35
Solve for the overhead

• 200 Newton load
• 38 cm handles above ground
• Ht to press of 160 cm
• Assume steps forward the 53 cm to press
• Work duration 8 hours
• Loads twice during shift
• Good grips on stock
• Calculate

36
Solve for the overhead

• What if poor handles?
• What if unable to step forward, so all is reach?
• What if twists 30 degrees to load?

37
Limitations of equation

• Does not recognize individual risk assessment
• future include age, sex Body weight???
• Not for use with one-handed lifting
• or seated, or kneeling, or constrained, or
  hot/cold/contaminated environment, or shovel use,
  or high-speed lifting
• Physiological criteria relate to whole body
  fatigue, not site specific
• relates more to risk of injury?

38
Summary

• Provides a quantitative starting point for
  comparing tasks.
• Links factors associated with risk of LBP in a
  multiplicative manner
• Starting point for ongoing research and
  validation of assumptions and guidelines

39
Homework
Go to this website by Dr. Peter Keir (York
University, Toronto, Canada) and do the
assignment (skip the Mital calculations)
40
NIOSH recommendations to control lifting hazards

• Identify jobs with high musculo-skeletal injury
  incidence and severity rates by statistical
  analysis of medical data.

41
NIOSH recommendations to control lifting hazards

• Observe suspect jobs and for each lift task
  measure the weight of loads and related H, V,
  and D data, and note whether lifts are occasional
  or performed regularly throughout the shift.

42
NIOSH recommendations to control lifting hazards

• Evaluate the lifting risk levels by computing the
  LI
• Load lifted / RWL

43
NIOSH recommendations to control lifting hazards

• Develop engineering controls such as
• a. Use of manual handling devices.
• b. Repackaging load to reduce weights.
• c. Rearranging workplace / redesign hardware to
  reduce H, V, D factors.

44
NIOSH recommendations to control lifting hazards

• Propose administrative controls
• a.Add personnel to reduce lift frequency
• b. Use or modify job rotation to shorten the
  period of lifting (cross-training)
• rotate workers onto other, less physically
  demanding jobs

45
NIOSH recommendations to control lifting hazards

• Develop formal training programs emphasizing lift
  techniques that minimize H, V, D, F

46
NIOSH recommendations to control lifting hazards

• Develop worker selection placement procedures
  to improve match between worker physical work
  capacities and specific lifting requirements in
  problems jobs.

47
NIOSH recommendations to control lifting hazards

• Implement the most feasible solutions and
  evaluate effectiveness with follow-up medical and
  job surveillance.

48
Load Pushing and Pulling Capabilities

• Approximately 20 of overexertion injuries have
  been associated with pushing and pulling acts.
• One of the leading causes of non-vehicle related
  deaths in industry is slipping and/or falling.

49
Load Pushing and Pulling Capabilities

• Vertical height of the handle is critical
• About hip height is recommended.
• vision
• strength in this position
• allows development of horizontal force without
  compromising friction

50
Material Handling Considerations

• Stand/sit erect
• Eliminate reaches
• Use rollers/conveyors vs. carriers/pivots
• Gravity-fed slides/shelves
• Keep it close to worker
• Tilt bins
• Allow access to all sides