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Lifting III

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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Lifting III

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  1. Lifting III Rad Zdero, Ph.D. zradovan@uoguelph.ca University of Guelph

  2. Outline • Lifting Limits & Injury • NIOSH Principles • NIOSH Analysis • NIOSH Graphs • NIOSH Examples

  3. Lifting Limits & Injury

  4. FINISH START Lifting

  5. 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

  6. Types of Failure Traumatic Cumulative [McGill, 1997]

  7. 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

  8. NIOSH Principles

  9. 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

  10. 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)

  11. 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).

  12. NIOSH Analysis

  13. FINISH START NIOSH: The Lift

  14. RWL = LCxHMxVMxDMxAMxFMxCM Multipliers Load Constant Recommended Weight Limit NIOSH: The Equation

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

  16. 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

  17. 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 = ___ / ___ = ___

  18. 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

  19. 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

  20. NIOSH Graphs

  21. Horizontal Multiplier (HM) (cm) (in) Horizontal Location

  22. Vertical Multiplier (VM) (cm) (in) Vertical Location

  23. Distance Multiplier (DM) (cm) (in) Lift Distance

  24. Frequency Multiplier (FM) (Below Waist Height, V < 75 cm (30 in) Lifting Frequency (Lifts/min)

  25. Frequency Multiplier (FM) (Above Waist Height, V  75 cm (30 in) Lifting Frequency (Lifts/min)

  26. Asymmetric Multiplier (AM) Asymmetric Angle (degrees)

  27. 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

  28. NIOSH Examples

  29. 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

  30. 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

  31. 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

  32. 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

  33. 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)

  34. 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

  35. 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

  36. 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

  37. 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

  38. 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.

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