Lifting III

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Lifting III
Rad Zdero, Ph.D. zradovan_at_uoguelph.ca University
of Guelph
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Outline

• Lifting Limits Injury
• NIOSH Principles
• NIOSH Analysis
• NIOSH Graphs
• NIOSH Examples

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Lifting Limits Injury
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Lifting
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Some Low Back Injury Stats

• Overexertion claimed to be cause of low back pain
  (LBP) by over 60 of sufferers less than 1/3 of
  these return to work
• 2/3 overexertion injuries involve lifting
• 1/5 overexertion injuries involve pushing or
  pulling
• 30 of WCB claims relate to LBP
• Lost wages, medical treatment, lost
  productivity
• 72 billion/yr (U.S.) and 5.7 billion/yr
  (Canada)
• need for scientific research to understand the
  mechanics of LBP to highlight its predisposing
  factors

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Lifting Limits
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NIOSH Principles
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What is NIOSH?

• National Institute for Occupational Safety
  Health (U.S. government agency)
• Standard guidebooks
• Work Practices Guide to Manual Lifting (NIOSH,
  1981)
• Applications Manual for the Revised NIOSH Lifting
  Equation (Waters et al., 1993 and 1994)
• Developed an occupational lifting formula to
  compute Recommended Weight Limit
• Big influence on worker safety and health issues

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NIOSH Recommendations

• Smooth Lifting no sudden jerky motions
• Objects Size moderate width with hand separation
  lt 75 cm
• Posture unrestricted with no torso bracing
• Coupling secure handles low shoe-floor
  slippage
• Temperature favourable for lifting
• Horizontal Location Center-of-Mass of
  object/handles to Ankles
• Vertical Location Center-of-Mass of
  object/handles to Floor
• Vertical Travel distance traveled by hands from
  start to finish of lift
• Frequency of lifting average lifts / minute
  during the time period
• Asymmetry angle from center-of-mass to bodys
  midline from start to finish of lift
• Coupling of load three types of object
  grasping (good, fair, poor)

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Basis for NIOSH

• NIOSH analysis was developed for 3 different
  population norms that would protect 90 of
  workers
• Biomechanically L5/S1 forces should be lt 3400 N.
• Physiologically metabolic energy expenditures
  should be below predicted levels (e.g. lt 4.7
  Kcal/min for lift that has duration lt 1 hour and
  object height lt 75 cm from ground).
• Psychophysically subjective worker estimates
  would accommodate 75 of women and 99 of men (or
  90 of a mix of men and women performing a
  lifting task).

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NIOSH Analysis
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NIOSH The Lift
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NIOSH The Equation
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NIOSH The Factors
Note 0 lt all multiplier values lt 1. If
calculated value gt1.0, then use 1.0
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Lifting Index

• After RWL is computed, it is compared with the
  actual weight W of the object being lifted.
• Comparison is made at the origin and destination
  of a lift
• Larger of the two values is considered the
  stress level of a lift
• LI lt 1.0 . protective of most workers
• LI gt 3.0 . poses significant risk to most
  workers
• 1.0 lt LI lt 3.0 . many jobs fall in this region
• Jobs need to be either redesigned to minimize
  LI, otherwise need increased job screening, more
  careful training, and medical monitoring

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NIOSH Pros

• combination of data from 4 disciplines
  epidemiology, biomechanics, physiology, and
  ergonomics
• comprehensive review of the literature
• multiplicative nature of equation makes estimates
  conservative
• easily measured parameters
• each factor can be measured independently
• useful tool in industry
• good starting point for more complex cases

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NIOSH Cons

• single equation for all populations
• suitable for most, but too high for some subjects
  (advanced age, weaker spines)
• does not consider gender differences
• focus only on lumbar spine
• speed of lifting duration neglected
• frequency multiplier is a physiological limit
• only for two handed lifting technique

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NIOSH Graphs
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Vertical Multiplier (VM)
(cm)
(in)
Vertical Location
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Coupling Multiplier (CM)
Good fingers wrap completely around object or
handles Fair only a few fingers grasp around
the object firmly Poor only a few fingers or
fingertips are partially under or around object
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NIOSH Examples
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Sources

• Chaffin et al., Occupational Biomechanics, 1999.
• NIOSH, Work Practices Guide to Manual Lifting,
  1981.
• McGill, The biomechanics of low back injury
  implications on current practice in industry and
  the clinic, J.Biomechanics, 39(5)465-475, 1997.
• Waters et al., Revised NIOSH equation for the
  design and evaluation of manual lifting tasks,
  Ergonomics, 36(7)749-776, 1993.
• Waters et al., Applications Manual for the
  Revised NIOSH Lifting Equation, 1994.