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, lt33 with back pain
  return to previous work
• Overexertion injuries account for 25 of all
  reported occupational injuries in the US (some
  industries 50)
• 66 of overexertion claims involved lifting
• 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
Pitts, E.H. Speaking up front, Fitness
Management, October 1997.
10
Lifting Limits in Manual Handling

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

11
Lifting Limits in Manual Handling
Note different limiting factors
12
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

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)
• horizontally from midpoint of ankles

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)
• from floor to CofM or handle

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)
• from origin to destination

16
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)

17
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

18
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

19
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

20
Spinal Motion Segment Failure
Traditional Model
Revised Model (McGill, 1997)
21
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

22
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)

23
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

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 gt 3 many workers at elevated
risk
25
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
26
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
27
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
28
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.
29
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
30
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
31
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
32
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
33
Frequency Multiplier
34
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.
35
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.
36
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?

37
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

38
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?

39
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?

40
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

41
Homework
Go to this website by Dr. Peter Keir (York
University, Toronto, Canada) and do the
assignment (skip the Mital calculations)
42
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.

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www.southworthproducts.com
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NIOSH recommendations to control lifting hazards

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

46
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.

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Air-bed tables for sliding
49
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

50
NIOSH recommendations to control lifting hazards

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

51
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.

52
NIOSH recommendations to control lifting hazards

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

53
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.

54
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

55
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

56
Low back pain and Lifting
Study Training Won't Prevent Back Injuries
February 2, 2008 Training showing the correct
way to lift heavy objects does not prevent back
injuries, according to a systematic review
published on the Web site of the BMJ (British
Medical Journal). Back pain is a highly prevalent
complaint and a cause of much suffering. In the
UK, employers have to ensure workers get proper
training on how to handle loads correctly and
this generally includes advising workers on
specific lifting techniques. However this study,
which reviewed all the evidence currently
available, found no evidence that the advice has
any effect. The researchers looked at 11 studies
eight studies dealt with health workers who
manually handled patients, the other three looked
at baggage handlers and postal workers. All the
participants in the studies worked in jobs where
there was strain on the back and where there was
the potential for alleviating any strain through
an intervention such as training. None of the
workers in the studies were actively seeking
treatment for back pain. The researchers found no
difference in back pain in studies where one
group received training and the other didnt.
Training compared to minor advice (a video)
showed no effect on back pain after a
year. Another trial showed no significant
difference in back pain between one group who
received training and another who were given back
belts to wear. Training and physical exercise
were compared in one trial and again no
difference in back pain was found during a follow
up less than a year later. Finally a group
receiving both training and an assistive device
was compared to a group receiving training only
and another control group which received nothing
-- there was no difference in back pain at follow
up. The researchers say either the advocated
techniques do not actually reduce the risk of
back injury, or workers do not significantly
change their habits enough for it to make any
difference. They concluded that what's needed is
a better understanding of the relationship
between exposure to stresses on the back at work
and the subsequent development of back pain in
order to develop new and innovative ways of
preventing back pain because of lifting. In an
accompanying editorial, Associate Professor Niels
Wedderkopp says the current advice for people
with back pain to stay active may not be
appropriate for people whose work involves heavy
lifting. He stated "A change of job and
(prudently) staying active in daily life may be
the best way for these patients to regain command
of their back and their occupation."
http//www.ohsonline.com/articles/58040