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Lifting III. Rad Zdero, Ph.D. zradovan@uoguelph.ca University of Guelph. Outline. Lifting Limits & Injury NIOSH Principles NIOSH Analysis NIOSH Graphs NIOSH Examples. Lifting Limits & Injury. FINISH. START. Lifting. Some Low Back Injury Stats.

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slide1

Lifting III

Rad Zdero, Ph.D.

zradovan@uoguelph.ca

University of Guelph

slide2

Outline

  • Lifting Limits & Injury
  • NIOSH Principles
  • NIOSH Analysis
  • NIOSH Graphs
  • NIOSH Examples
slide4

FINISH

START

Lifting

slide5

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
slide6

Types of

Failure

Traumatic

Cumulative

[McGill, 1997]

slide7

Biomechanical (weight & force lift limits), or

Physiological (“calorie” energy expenditure), or

Psychophysical (subjective “I can or cannot lift it”)

Recommended

Weight Lifting

Limit

Frequency (Lifts per minute), or

Time Duration of Lift & Carry, or

Distance of Lift, or

Style of Lift

Lifting Limits

what is niosh
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
niosh recommendations
NIOSH Recommendations
  • Smooth Lifting: no sudden jerky motions
  • Objects Size: moderate width with hand separation < 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 body’s midline from start to finish of lift
  • Coupling of load: three types of object “grasping” (good, fair, poor)
basis for niosh
Basis for NIOSH

NIOSH analysis was developed for 3 different population norms that would protect 90% of workers:

  • Biomechanically: L5/S1 forces should be < 3400 N.
  • Physiologically: metabolic energy expenditures should be below predicted levels (e.g. < 4.7 Kcal/min for lift that has duration < 1 hour and object height < 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).
slide13

FINISH

START

NIOSH: The Lift

slide14

RWL = LCxHMxVMxDMxAMxFMxCM

Multipliers

Load Constant

Recommended Weight Limit

NIOSH: The Equation

niosh the factors
NIOSH: The Factors

Note: 0 < all multiplier values < 1. If calculated value >1.0, then use 1.0

slide16

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 < 1.0 …. protective of most workers
  • LI > 3.0 …. poses significant risk to most workers
  • 1.0 < LI < 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
slide17

Job Analysis Worksheet

Job Description____________

_________________________

_________________________

_________________________

Department________________

Job Title __________________

Analyst’s Name ____________

Date______________________

Step 1. Measure and Record Task Variables

Step 2. Determine Multipliers and Compute RWL

RWL = LC x HM x VM x DM x AM x FM x CM

Origin RWL = ___ x ___ x ___ x ___ x ___ x ___ x ___ = ___

Destination RWL = ___ x ___ x ___ x ___ x ___ x ___ x ___ = ___

Step 3. Compute the Lifting Index

Origin Lifting Index = Weight / RWL = ___ / ___ = ___

Destination Lifting Index = Weight / RWL = ___ / ___ = ___

slide18

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
slide19

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
slide21

Horizontal Multiplier (HM)

(cm)

(in)

Horizontal Location

slide22

Vertical Multiplier (VM)

(cm)

(in)

Vertical Location

slide23

Distance Multiplier (DM)

(cm)

(in)

Lift Distance

slide24

Frequency Multiplier (FM)

(Below Waist Height, V < 75 cm (30 in)

Lifting Frequency (Lifts/min)

slide25

Frequency Multiplier (FM)

(Above Waist Height, V  75 cm (30 in)

Lifting Frequency (Lifts/min)

slide26

Asymmetric Multiplier (AM)

Asymmetric Angle (degrees)

coupling multiplier cm
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

slide29

Example 1

70 cm

END

  • Other Items
  • feet remain fixed
  • 1 lift / 4 hrs
  • 8 hour shift
  • very firm grip
  • no twist motion

160 cm

START

38 cm

20 kg

53 cm

slide30

Job Analysis Worksheet

Job Description____________

_________________________

_________________________

_________________________

Department________________

Job Title __________________

Analyst’s Name ____________

Date______________________

Step 1. Measure and Record Task Variables

20 20 53 38 123 160 122 0 0 0.2 8 Good

Horizontal

Body-to-Hand

Distance (feet

are locked in

place)

= 53 cm + 70 cm

= 123 cm

Total

Vertical

Lift

= Dest. – Origin

= 160 cm – 38 cm

= 122 cm

Minimum

NIOSH

Value

Reportable

slide31

Origin of Lift

    • LC = 23 kg = fixed factor
    • HM = 25/H = 25/53 = 0.47
    • VM = 1 – (0.003|V-75|) = 1 – (0.003|38-75|) = 0.889
    • DM = 0.82 + (4.5/D) = 0.82 + (4.5/122) = 0.856
    • AM = 1 – 0.0032A = 1 – 0.0032(0) = 1
    • FM = 0.85 (since 1 lift/4 hrs = 0.004 lifts/min = approx. 0 on graph)
    • CM = 1.0, since V  75 cm and “good” grip
  • Destination of Lift
    • LC = 23 kg = fixed factor
    • HM = 25/H = 25/123 = 0.203
    • VM = 1 – (0.003|V-75|) = 1 – (0.003|160-75|) = 0.745
    • DM = 0.82 + (4.5/D) = 0.82 + (4.5/122) = 0.856
    • AM = 1 – 0.0032A = 1 – 0.0032(0) = 1
    • FM = 0.85 (since 1 lift/4 hrs = 0.004 lifts/min = approx. 0 on graph)
    • CM = 1.0, since V  75 cm and “good” grip

Step 2. Determine Multipliers and Compute RWL

RWL = LC x HM x VM x DM x AM x FM x CM

Origin RWL = 23 x 0.47 x 0.889 x 0.856 x 1 x 0.85 x 1= 7.02 kg

Destination RWL = 23 x 0.203 x 0.745 x 0.856 x 1 x 0.85 x 1= 2.53 kg

slide32

Conclusion

  • Origin: the start of the lift is acceptable and safe since LI < 3
  • Destination: the end of the lift is dangerous since LI > 3. The “stress level” is LI = 7.91, the larger of the values. This could be the point where serious low back injury will occur. The task setup must be changed at the destination, or increased job screening, medical monitoring, and training must be introduced.

Step 3. Compute the Lifting Index

Origin Lifting Index = Weight / RWL = 20 / 7.02 = 2.85

Destination Lifting Index = Weight / RWL = 20 / 2.53 = 7.91

slide33

Example 2

60cm

  • Task
  • Moving trays from conveyor belt and putting them on the cart
  • Other Items
  • 10 kg trays
  • 1 lift/min
  • 4 hour shift
  • feet are fixed
  • “fair” grip
  • upper body twist motion at START
  • tray placed straight down onto cart at END

90cm

90cm

(Start)

50cm

45deg

20cm

Sagittal

Body

Midline

(End)

slide34

Job Analysis Worksheet

Job Description____________

_________________________

_________________________

_________________________

Department________________

Job Title __________________

Analyst’s Name ____________

Date______________________

Step 1. Measure and Record Task Variables

10 10 60 90 50 20 70 45 0 1 4 “fair”

Total Vertical

Object Movement

= Start – End

= 90 – 20

= 70 cm

slide35

Origin of Lift

    • LC = 23 kg = fixed factor
    • HM = 25/H = 25/60 = 0.416
    • VM = 1 – (0.003|V-75|) = 1 – (0.003|90-75|) = 0.925
    • DM = 0.82 + (4.5/D) = 0.82 + (4.5/70) = 0.884
    • AM = 1 – 0.0032A = 1 – 0.0032(45) = 0.856
    • FM = 0.77 (from graph, since 4 hr shift and V  75 cm)
    • CM = 1.0 (from table, since V  75 cm and “fair” grip)
  • Destination of Lift
    • LC = 23 kg = fixed factor
    • HM = 25/H = 25/50 = 0.5
    • VM = 1 – (0.003|V-75|) = 1 – (0.003|20-75|) = 0.835
    • DM = 0.82 + (4.5/D) = 0.82 + (4.5/70) = 0.884
    • AM = 1 – 0.0032A = 1 – 0.0032(0) = 1
    • FM = 0.75 (from graph, since 4 hr shift and V < 75 cm)
    • CM = 0.95 (from table, since V < 75 cm and “fair” grip)

Step 2. Determine Multipliers and Compute RWL

RWL = LC x HM x VM x DM x AM x FM x CM

Origin RWL = 23x0.416x0.925x0.884x0.856x0.77x1.0= 5.16 kg

Destination RWL = 23x0.5x0.835x0.884x1.0x0.75x0.95= 6.05 kg

slide36

Conclusion

The stress level is the larger value, LI = 1.94. But, at both origin and destination the lifting index, LI < 3. Thus, most workers will be safe from any potential back injury. The task can remain as is.

Step 3. Compute the Lifting Index

Origin Lifting Index = Weight / RWL = 10/5.16 = 1.94

Destination Lifting Index = Weight / RWL = 10/6.05 = 1.65

slide37

Example 3

  • Task
  • Moving boxes from conveyor belt & placing them onto a cart
  • Other Items
  • 15 kg boxes
  • 3 lifts/min
  • 3 hour shift
  • feet are fixed
  • “poor” grip
  • upper body twist motion at START
  • boxes placed straight down onto cart at END

50cm

100cm

100cm

(Start)

35cm

30 deg

30cm

Sagittal

Body

Midline

(End)

Answers:LI (start) = 3.57, LI (end) = 2.41

sources
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.