Manual Handling Techniques for Workplace Safety

1. Manual handling is associated with • 27% of all industrial injuries • 670,000 injuries/yr in the United States • 60% of all money spent on industrial injuries • 93,000,000 lost workdays/yr

2. Approaches to recommendations • Biomechanical • emphasizes forces and torques • load limit does not vary with frequency • Physiological • emphasizes energy requirements and cardiovascular demands • important for repetitive lifting • Psychophysical • combination of the above • predicts “real” capability based on performance under controlled conditions

3. Manual handling variables • Individual • Technique • Task • Goals: • increase the strength of the worker • decrease the stress due to technique and task • both

4. Pushing and pulling strength factors • Handles • One hand vs. two hands • Body posture • Application height • Direction

5. Push/pull summary • Two hands are usually better than one. • Force capability goes down as it is exerted more often. • Initial force capability is higher than sustained capability. • Pushing capability is higher than pulling. • Push at waist level; pull at thigh level.

6. Task modifications • Measure the force required to move all wheeled equipment; periodically check the forces. • Install vertical push/pull bars on carts. • Push rather than pull loads. • Avoid muscle-powered pushing and pulling for ramps, long distances, and frequent moves. • Use mechanical aids and momentum. • Reduce force by reducing friction.

7. Holding • Problems • Holding gives a static load combining body weight and object weight. • Low-back pain arises from spine biomechanics. • Solutions • Reduce the magnitude and duration of the torque. • Use balancers. • Limit high loads to short durations.

8. Carrying guidelines • Replace carrying with pushing or pulling. • Minimize the moment arm of the load relative to the spine. • Consider carrying large loads occasionally rather than light loads often. • Use teamwork. • Consider using balancers, manipulators, conveyors, or robots. • Reduce lifting by raising the initial location. • Avoid carrying objects up and down stairs.

9. Lifting guidelines • 51 lbs is the maximum that can be lifted or lowered (load constant). • Recommended weight limit (RWL) is load constant multiplied by various factors. • Lifting index = load weight / RWL

10. NIOSH lifting example • At initiation, • Horizontal location, H1 = 10 in. • Vertical location, V1 = 40 in. • Vertical location, V2 = 51 in. • Angle of asymmetry, A = 0 • Frequency, F = 12 /min. • Load = 14 lbs. • Duration = 2 hr. • What is the RWL? • What is the Lifting Index, LI?

11. Basic NIOSH lifting formula (pg. 253) RWL = LC × HM × VM × DM × FM × AM × CM • RWL = recommended weight limit • LC = load constant (51 lbs.) • HM = horizontal multiplier • VM = vertical multiplier • DM = distance multiplier • FM = frequency multiplier • AM = asymmetry multiplier • CM = coupling multiplier Note: review the conditions under which this will not apply – turned around, they make a good set of criteria for lifting task design!

12. Multiplier formulas Horizontal multiplier HM = BIL / H • BIL = Body interference limit • H = Horizontal location Vertical multiplier VM = 1 – VC × | V – KH | • VC = Vertical constant = 0.0075for inches, 0.003 for cm. • V = Vertical location • KH = Knuckle height (assume 30 in.)

13. Multiplier formulas (cont.) Distance multiplier DM = .82 + DC/D • DC = Distance constant = 1.8 for inches, 4.5 for cm. • D = Vertical travel distance Asymmetry multiplier AM = 1 – .0032A • A = Angle of symmetry

14. Multiplier formulas (cont.) Frequency multiplier See Table 13.9, pg. 255. • Lifting frequency = mean number of lifts in a 15-minute period • Lifting duration /session in hours may be: • Short = .001 h to ≤ 1 h • with recovery time of ≥ 1.2 × duration • Moderate = >1 h ≤ 2 h • with recovery time of ≥ .3 × duration • Long = >2 h but ≤ 8 h

15. Multiplier formulas (cont.) Coupling multiplier See Table 13.10, 13.11, Fig. 13.13 • Depends on: • Height of initial and final hand–container coupling • Whether coupling is good, fair, or poor

16. Solution … • HM = • VM = • DM = • FM = • AM = • CM = • RWL = • LI =

17. Force limits FL = A × F × DIST • A = Age factor • F = Frequency factor • DIST = Distance factor • Differences between force limits and NIOSH guidelines. • Different factors • Different criteria • FL permissible load ~1.8 times that of NIOSH

18. Resources • Manual Handing Guide (Mital et al.) • Biomechanical software • ErgoIntelligence MMH • 2D Static Strength Prediction Program • 3D Static Strength Prediction Program

19. Guidelines for manual handling • Three categories: • Select individual • Select strong people based on tests. • Teach technique • Bend the knees. • Don’t slip or jerk. • Don’t twist during the move. • Design the job • Use machines. • Move small weights often. • Get a good grip. • Put a compact load in a convenient container. • Keep the load close to the body. • Work at knuckle height.

20. Examples to discuss