Chapter 13: Manual Handling Learning Outcomes: After successful studying this chapter, You should be able to: 1. Define the term manual handling, 2. Know the activities involved in manual handling, 3. Know types of injuries caused by manual handling, 4. Know the risk factors of manual handling that can lead to injuries, 5. Outline ways of minimizing manual handling risk, 6. Calculate the allowable load to be lifted according to NISOH, 7. Identify the hazards and explain the precautions and procedures to ensure safety in the use of lifting and moving equipment with specific reference to fork-lift trucks, manually operated loadmoving equipment (sack trucks, pallet trucks), lifts, hoists, conveyors and cranes. 1
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Wrong way! I m using my back instead of my legs Using a trolley is the way to go! 3
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Manual Handling Manual handling tasks are any activity at the work place that require the use of force by a person. Primarily lifting but includes pushing, pulling, grasping, throwing, striking, restraining, lowering, holding etc. Manual Handling Manual Materials Handling (MMH): The use of human power to move loads by lifting, lowering, pushing, pulling, and/or carrying. Dynamic Effort: The muscle acts as a local pump in the circulatory system. Compression squeezes blood out of the muscle and the subsequent relaxation releases a fresh flow of blood into it several times greater than normal. In fact, the muscle may receive between 10 and 20 times as much blood as when it is resting. ( A muscle performing dynamic work is therefore constantly flushed out with blood and returns the energy-rich sugar and oxygen balance contained in it, while at the same time waste products are removed. ) 5
Manual Handling Static Effort: During static effort the muscle is not allowed to extend, but remains in a state of heightened tension, with force exerted over an extended period. ( During static effort the blood vessels are compressed by the internal pressure of the muscle tissue, so that blood no longer flows through the muscle. ) * Waste Product Accumulation: A muscle that is performing heavy static work is receiving virtually no sugar or oxygen from the blood and must depend upon its own reserves. Moreover - and this is by far the most serious disadvantage - waste products are not being excreted. Quite the reverse, the waste products are accumulating and produce the acute pain of muscular fatigue. Manual handling checklist Is the job repetitive Are the loads handled heavy at times Are awkward postures used Do you feel tired at the end of the shift 6
Risk factors in manual handling Individual physical factors, e.g., Weight Physique Gender Task demand factors, e.g., Horizontal distance to load Posture Repetition Environmental factors, e.g., Workplace design Slippery floors Psychological factors, e.g., Depression Anxiety Common causes of injury Prolonged poor posture Repeated heavy lifting Manual handling in a poor posture, Sudden unexpected movements Work on unstable or slippery surfaces 7
Types of injuries Fractures to limbs, ribs, hands, arms caused by slips, falls and dropped objects, Torn or over- stretched muscles, ligaments, tendons due to unnatural movement, Injuries to the discs due to bending, twisting, Example Statistics on Manual Handling Manual handling is associated with: 27% of all industrial injuries 670,000 injuries/year in the United States 60% of all money spent on industrial injuries 93,000,000 lost workdays/year 8
MH Criteria Categories Biomechanical Emphasizes the forces and torques of manual handling and their effects on the body. (the back is the weakest link) Physiological Emphasizes the energy requirements of the task and the effects on the cardiovascular system. Psychosocial combines biomechanical and physiological Under controlled conditions, individuals perform tasks to determine real rates for workers. Manual Handling Variables Individual Technique People are not machines People forget People make mistakes People fail to learn Task Permanent change by task modification 9
Manual Handling Variables (cont.) Individual What can be done so a small person can do the job? Stronger usually better But don t exclude too many! Technique Posture Hand orientation Foot position Lift training Task Object height Ease of handling (shape, handles, etc.) Initial/final height Lift symmetry Pushing and Pulling Strength Factors Handles (Switches, Grips) One hand vs. two hands Body posture Application height Direction 10
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. Push/Pull Summary (cont.) Application height Push at waist (between elbow and hip) Pull at thigh (between hip and knee) Direction Generally, to the shoulders is best to shoulders 50% - 60% of Table values Overall, pushing & pulling is better than lifting & lowering; generally pushing is better than pulling. 11
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. 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. 12
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. (You should sometimes carry heavy boxes instead of carrying light loads often) Carrying Guidelines (cont.) Use teamwork. Consider using balancers, manipulators, conveyors, or robots. Reduce lifting by raising the initial location. Avoid carrying objects up and down stairs. Students often carry back bags, 10% of the body weight is a recommended maximum (especially for children). (A convenient locker can reduce the load carried) 13
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 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 14
NIOSH lifting example At initiation, Horizontal location, H 1 = 10 in. Vertical location, V 1 = 40 in. Vertical location, V 2 = 51 in. Angle of asymmetry, A = 0 Frequency, F = 12 /min. Load = 14 lbs. Duration = 2 hr. What is the RWL? (Recommended Weight Limit: RWL) What is the Lifting Index, LI? Basic NIOSH Lifting Formula RWL = LC HM VM DM FM AM CM LC = Load constant HM = Horizontal multiplier VM = Vertical multiplier DM = Distance multiplier FM = Frequency multiplier AM = Asymmetry multiplier CM = Coupling multiplier The RWL protects about 85% of women and 95% of men. (Recommended Weight Limit: RWL) 15
Multiplier Formulas Horizontal multiplier HM = BIL / H BIL = Body interference limit H = Horizontal location (BIL = 10 inches = 25 cm) HM = BIL / H = 10 / 10 = 1) Vertical multiplier VM = 1 VC V KH VC = Vertical constant = 0.0075 for inches, 0.003 for cm. V = Vertical location KH = Knuckle height (assume 30 in.) Multiplier Formulas (cont.) Distance multiplier DM =.82 + DC D DC = Distance constant D = Vertical travel distance Asymmetry multiplier AM = 1.0032 A A = Angle of symmetry (D = V 2 V 1 = 51 40 = 11 DM = 0.82 + (1.8/11) = 0.9836) 16
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 Multiplier Formulas (cont.) Frequency multiplier (See Table 13.9) Frequency multiplier 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 (F = 12/min > 1 but < 2 hrs (in this case, 2 hrs.) V> 30 in. FM = 0.21) 17
Multiplier Formulas (cont.) Coupling multiplier (See Table 13.10) Depends on: Height of initial and final hand container coupling Whether coupling is good, fair, or poor Lift Index (LI) The equation provides a recommended weight limit (RWL) which is compared with the weight of the object lifted, producing a Lift Index (LI). The Lift Index is the ratio of the weight of the load to the recommended weight limit. If LI > 1, some workers may be at risk of developing low-back injuries. If LI > 3, most workers may be at risk of developing low-back injuries. 18
NIOSH Lifting Guidelines A closer examination of the equation reveals certain task modifications that can be made to reduce the risk of developing lowback injuries from lifting: Reducing the frequency of lifting Eliminating awkward postures such as twisting Reducing how far the object is lifted Keeping the object as close to the body as possible. Beginning the lift at least 30 inches/75 cm above the ground. NIOSH Calculation 1. Determine each component of the equation such as horizontal and vertical distance 2. Use the tables from NIOSH to obtain multipliers for each component (http://www.ccohs.ca/oshanswers/ergonomics/niosh/calculating_ rwl.html) 3. Calculate recommended weight limit 4. Compare it with the load weight. In the next few slides, we will see examples using the NIOSH calculation. 19
NIOSH Examples Horizontal Distance In this example, the worker lifts a 15kg box to the shelf. He lifts five times an hour (12 minutes per lift). There is a barrier between the person and the table. Load constant: 23 kg Horizontal distance: 50 cm Vertical distance: 75 cm Travel/lifting distance: 40 cm Angle: 0 (torso twist) Frequency: 5 lifts/minute Coupling: Fair (easy to grab/hold) RWL = 23 Kg x 0.50 x 1.00 x 0.95 x 1.00 x 1.00 x 1.00 = 10.9 kg The weight of the load (15 kg) is higher than the recommended weight limit (10.9 kg). This task is poses a risk of injury. NIOSH Examples Vertical Distance In this example, the worker lifts an 15 kg box from a pile of metal pieces from the floor to the shelf. He lifts five times an hour (12 minutes per lift). Load constant: 23 kg Horizontal distance: 30 cm Vertical distance: 0 cm Travel/lifting distance: 115 cm Angle: 0 (torso twist) Frequency: 5 lifts/minute Coupling: Poor (difficult to grab the box) RWL = 23 Kg x 0.80 x 0.80 x 0.86 x 1.00 x 1.00 x 0.90 = 11.4 kg The weight of the load (15 kg) is higher than the recommended weight limit (11.4 kg). This task is poses a risk of injury. 20
NIOSH Examples Vertical Distance In the previous example, the critical component was the vertical distance (V). This task can be redesigned by raising the starting height and reducing travel/lifting distance. Load constant: 23 kg Horizontal distance: 30 cm Vertical distance: 75 cm Travel/lifting distance: 40 cm Angle: 0 (torso twist) Frequency: 5 lifts/minute Coupling: Poor (difficult to grab the box) RWL = 23 Kg x 0.80 x 1.00 x 0.95 x 1.00 x 1.00 x 0.90 = 15.7 kg The weight of the load (15 kg) is lower than the recommended weight limit (15.7 kg). Most people can safely perform the task. Guidelines for Manual Handling Select strong people based on tests. Bend the knees. Don t slip or jerk. Don t twist during the move. 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. 21
Guidelines for Manual Handling (cont.) Three categories: Select individual 1. Select strong people based on tests. Teach technique 2. Bend the knees. 3. Don t slip or jerk. 4. Don t twist during the move. Design the job 5. Use machines. 6. Move small weights often. 7. Get a good grip. 8. Put a compact load in a convenient container. 9. Keep the load close to the body. 10. Work at knuckle height. Examples to discuss 22
Resources Manual Handing Guide (Mital et al.) Biomechanical software 2D Static Strength Prediction Program 3D Static Strength Prediction Program End of Chapter 13 23
Example Cartons weighing 30 lbs are to be picked up from the floor and placed on a roller conveyor 24" above floor level. Hand holds are located 18" above the floor and 12" forward of the midpoint of the worker's ankles. The average frequency of lifting is.2 lifts per minute and the task duration is more than an hour. Note: The table value for Fmax for this task is 12. AL (lb) = 90(6/H)(1-.01 V-30 )(.7+3/D)(1-/Fmax) MPL (lb) = 3(AL) (AL: Action Limit, MPL: Maximum Permissible Limit) Discuss with class CM = 1, 0.95, 0.9? (looking at fig 13.13, I estimate fair, so since V=40 in., CM = 1) Then RWL = LC HM VM DM FM AM CM = 51*1*0.925*0.9836*0.21*1*1 = 9.7443 LI = LW / RWL = 14/ 9.7443 = 1.44 24
Example AL (lb) = 90(6/H)(1-.01 V-30 )(.7+3/D)(1-F/Fmax) H Factor = (6/H) = (6/12) =.50 V Factor = (1-.01 V-30 ) = (1-.01 18-30 ) =.88 D Factor = (.7+3/D) = (.7+3/24) =.825 F Factor = (1-F/Fmax) = (1-.2/12) =.983 AL = 90(.50)(.88)(.825)(.983) = 32 lbs MPL = 3(AL) = 3(32) = 96 lbs Conclusion: The weight lifted is below the AL. This task represents an acceptable risk for most workers. 25