Sketch courtesy from Riekes Material Handling

1. Manual Handling (MH) IE 665 Sketch courtesy from Riekes Material Handling

2. Severity of the problem • Manual handling (lifting) is injury prone & expensive • BLS 2007: 140,330 out of 1,158,870 or 12% of all non fatal injuries and illness cases in US private industries with days away from work occurred from exposure from overexertion in lifting. • Median days away from work per incident was 8 days • 26.8% cases caused 31 or more days off. • Details: http://stats.bls.gov/news.release/osh2.nr0.htm

3. Pain in shoulder, upper back, lower back and knee. It is believed that cumulative trauma of soft tissue over time is the cause of injury and not from an acute trauma due to overload. Lower back pain is a major problem associated with MH. Nature of Injury Courtesy, US Department of Energy, Berkeley Lab

4. Approaches to investigation of cause of MMH injuries • Biomechanical approach • Physiological (or cardiovascular) approach • Psychological approach

5. Biomechanical approach • Computes torque/internal-forces due to body posture and load handled on critical body joints and compares those to joint strength. • Generally applicable for one time loading situation or worst case scenario of a task. • Can predict localized muscle fatigue. • Shortcoming: Does not take into account effect of duration and frequency of MMH task.

6. Physiological (or cardiovascular) approach • Considers metabolic energy requirement of the MMH task and systemic fatigue. • Goal is to keep metabolic rate less than 5 Kcal/min for an eight hrs task • Takes into account rate and duration of MH and dynamic effect of body movement. • However, injury may occur due to localized muscle or joint overload, which this method cannot isolate.

7. Psychological approach • Based on the assumption that human can inherently perceive the stress level and can determine his or her limits of MH. • Skilled handlers perform MH in laboratory settings with varying load and type of activity. Frequency and other MH factors (distance, height , size of the box etc.) are kept constant for a given task. Based on the maximum load acceptable by the handler population, allowable load limits are determined in percentile form. • Supposed to take care of both biomechanical and physiological factors.

8. MH variables • Individual • Selection • strength testing • Technique • training • posture • Task • Most effective way to limit occupational injury is to design the MH task such that everybody can perform it with least risk of injury

9. MH task types • Pulling/pushing • holding • carrying, and • lifting

10. Pulling & pushing • Limits of pull and push forces for many combinations of handle height and frequencies are available for industrial population. Table 13.1 and 13.2. • Force capability goes down as it is exerted more often. • Pushing capability is higher than pulling. Pushing also produces less spine compressive force. • Push at waist level; pull at thigh level

11. Pulling/pushing task design • Use a force gage to measure the force • Reduction of friction coefficient may reduce the force. • Remove obstacles, larger wheels. • A vertical push-pull bar may allow height adjustment for both short and tall person. • Avoid muscle power for long distance, ramps and high frequency moves.

12. Holding • Holding causes static muscle contraction and fatiguing. • Often higher reach requirement causes undue muscle tension at the lumbar spine region. • Reduce the holding torque and reduce the duration of holding.

13. Carrying • Carrying induces internal static muscle tension in hand, arm, shoulder and trunk muscles. • Reduce the load and or reduce the moment arm. Body hugging back-pack design reduces the moment arm. Keep the load as close as possible to the spine. • Box with a handle may induce more lower back stress compared to a box without a handle.

14. Lifting • NIOSH lifting equation (1994) provides a formula to determine the Recommended Weight Limit (RWL) for a specific lifting task. • It starts with a load constant of 51 lbs (23 kg), which is the maximum load for an ideal lifting task situation. • This load constant is then multiplied by various factors (all are equal or less than 1) to obtain the RWL. • RWL= 51 x HM x VM x DM x FM x AM x CM lbs • If control of the load is necessary at the lift initiation and lift destination, then two RWLs are determined, one for the lift initiation and lift destination points. • Lifting Index (LI) = Actual Load weight during lifting / RWL, • if LI is >1, the task is not acceptable and design modification is needed to make the LI = 1 or less • LI < 1 should be acceptable to 75 percent females and 99 percent males.

15. Criteria used to develop niosh lifting equation • NIOSH lifting equation (1994) is based on • Biomechanical criterion of max spine compressive force 3400 N • Physiological (metabolic) criterion of 9.5 kcal/minute (which is VO2 max for 50th percentile female of age 40) multiplied 70% (due to arm work), 50% for one hour, 40% for two hours, and 33% for eight hours. • Psychophysical criterion is based on a 34 cm wide box for a vertical displacement of 76 cm and lifting frequency of 4 lift/min.

16. Scope of NIOSH lifting equation • Applicable for two handed lifting task in free standing posture. Not applicable MH at seated or kneeling posture. Load must not be unstable. • Handling should not include too much carrying, not more than one or two steps. • performed in normal room ambient condition. • Other physical tasks are 10% or less. • For other conditions, specific biomechanical and physiological investigation will be needed to set the limit.

17. Factors in NIOSH Equation (US system of measures inch, lb) • Horizontal multiplier HM =10/H , where H is the projected distance from the handle to body centerline. • Closest to body (H<=10 inch) is optimum HM = 1, If H is more than 25 inch, HM = 0. • Vertical Multiplier VM = 1- .0075|V-30|, where V = objects vertical location (knuckle location) from floor. • Knuckle Height (V=30 inch) is optimum, any height other than this is penalized. • Penalty for both up and down from knuckle height.

18. Factors in NIOSH Equation (continued) • Distance multiplier (DM) = .82 + 1.8/D, where D is the vertical load movement distance. If D is less than 10 inches DM = 1, If D = 70 inches DM = 0. • Asymmetry multiplier AM = 1- 0.0032A, where A is the angle in degrees from mid-sagittal plane. • For lifting in mid-sagittal plane AM = 1. • Ignore positive or negative angle. • Max value of A = 135o.

19. Factors in NIOSH Equation (continued) • Frequency multiplier (FM) is based on lift frequency (lift/min) • (1) over short (< 1hr), moderate (< 2hr), long (< 8hr) duration. • (2) have adequate recovery times after the lifting task • (3) whether below or above knuckle height • Refer to table 13.9 to determine FM. • Max frequency is 15 lifts/min and beyond this FM = 0. • If the job is short term (<1hr) and F < 0.2 lift/min, FM = 1.

20. Factors in NIOSH Equation (continued) • Coupling multiplier (CM) Depends on handle design, and vertical location (V) of load • See table 13.10 and 13.11.