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Low Back Injuries. TM 655 Summer 2008 Carter J. Kerk , PhD, PE, CSP, CPE. Outline. Concepts A Systems Approach Risk Factor Model ID, Evaluation, Control Identification: Checklists Evaluation Force Posture Repetition. Stover Snook.
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Low Back Injuries TM 655 Summer 2008 Carter J. Kerk, PhD, PE, CSP, CPE
Outline • Concepts • A Systems Approach • Risk Factor Model • ID, Evaluation, Control • Identification: Checklists • Evaluation • Force • Posture • Repetition
Stover Snook At any time, 15 to 20% of adults, evenly split between men and women, experience low back symptoms.
Stover Snook 35% of adults say they’ve had low back pain in the past month, 50% in the last year.
Stover Snook About two-thirds of all back pain develops gradually without any trauma or precipitating event.
US Bureau of Labor Statistics For employees who miss work time due to back problems, the median time away from the job is between 6 and 7 days.
National Research Council In the US, employers in private industry report around 7 million cases of work-related musculoskeletal injuries each year, with 25% of these leading to lost working days and restricted activities. It is estimated that 5 to 6 million of these cases are work-related back pain leading to 100 million working days lost.
Risk Factor Model for Potential Development of Cumulative Trauma Disorders,Including Low Back Pain Lack of Rest Work/Rest Ratio Shift Length Environment Sustained Repetition Occupational Vibration Non-Occupational Temperature Posture Physical & Temporal Risk Factors Force Personal Psychosocial Compounding Risk Factors
Attacking Hazards • Identification • Evaluation • Control
Control of Hazards • Engineering Controls • Administrative Controls • Personal Protective Equipment
Identification • Body Part Discomfort Survey • Quick Exposure Checklist (QEC) • Pareto Analysis
Body Part Discomfort Survey • Ask employee to shade in areas of discomfort • Rate each shaded area on a scale
Quick Exposure Checklist (QEC) Quickly assess the exposure to risks for work-related musculoskeletal disorders See http://www.geocities.com/qecuk
Quick Exposure Checklist (QEC) Steps • Self-Training • Observer’s Assessment Checklist • Worker’s Assessment Checklist • Calculation of Exposure Scores • Consideration of Actions
Quick Exposure Checklist (QEC) A1 A2 A3
Quick Exposure Checklist QEC Observer Assessment Worker Assessment
Quick Exposure Checklist QEC E(%) = X/Xmax x 100%
Use of Checklists • Preliminary screening • Before and after analysis • Relative comparison among tasks
Pareto Analysis • The Powerful Few - Group A – 10% of the tasks produce 70% of injuries – focus on these • The Insignificant Many - Group C – 65% of tasks produce <10% of injuries
Evaluation of Force • Direct force measurement • Force gauge, scale • NIOSH Lifting Guide • Psychophysical Tables
NIOSH Lifting Equation • Recommended Weight Limit • Load that nearly all healthy workers could perform over a substantial period of time without an increased risk of developing lifting-related low back pain • RWL = LC x HM x VM x DM x AM x FM x CM • Lifting Index • Estimate of physical stress • LI = Load Weight / RWL
NIOSH Lifting Equation RWL = LC x HM x VM x DM x AM x FM x CM • LC = 51 lb = 23 kg • HM = Horizontal Multiplier • VM = Vertical Multiplier • DM = Distance Multiplier • AM = Asymmetric Multiplier • FM = Frequency Multiplier • CM = Coupling Multiplier • Each multiplier ranges from 0 to 1
NIOSH Lifting Equation Determination of H and V
NIOSH Lifting Equation Determination of Asymmetry (A)
NIOSH Lifting Equation Does Not Apply When Lifting or Lowering • One hand • Over 8 hours • While seated or kneeling • In a restricted work space • Unstable objects • While carrying, pushing, pulling • Wheelbarrows, shovels • High speed (>30 inches / sec) • Slippery floors
NIOSH Lifting Equation • Horizontal Multiplier • Metric • HM = 25/H • US Customary Units • HM = 10/H • Or Use Table 1
Evaluation of Force • Direct force measurement • Force gauge, scale • NIOSH Lifting Guide • Psychophysical Tables
Psychophysical Tables • How much should a worker be required to lift or lower or push or pull or carry? • How much is too much? • These tables are the culmination of 25 years of experiments at the Liberty Mutual Research Center
Evaluation of Posture • Photography / Videotaping • RULA • Rapid Upper Limb Assessment • REBA • Rapid Entire Body Assessment
Photography / Videotaping • Capture and evaluate entire work cycles • Freeze frame postures • Measure body angles • Protractor / Goniometer • Combine with force measurement • Combine with frequency evaluation
RULA • Rapid Upper Limb Assessment • Used to assess the posture, force, and movement associated with sedentary tasks • Including computer workstation tasks, manufacturing and retail tasks where the worker is seated or standing without moving about
REBA • Rapid Entire Body Assessment • Whole body • Posture is static or dynamic • Frequent or infrequent load handling
REBA • Steps • Observe the task • Select the postures for assessment • Score the postures • Process the scores • Establish the REBA score • Confirm action level and urgency
REBA • Selecting postures for assessment • Most frequently repeated postures • Longest maintained postures • Posture requiring greatest forces • Posture known to cause discomfort • Extreme, unstable, or awkward postures
Evaluation of Repetition • Tools: Stopwatch, Videotape • Methods: Work Measurement Skills • Calculate repetitions: e.g., lifts per minute • Document the work cycles
Biomechanics • Advanced Technique • Uses elements of analysis from • Force and Posture • Requires knowledge of • Anatomy, Anthropometry, Statics, Dynamics
Gender and Posture Differences • Strength testing shows there are significant differences in lifting capability due to gender and posture • These concepts are critical in job analysis and job design
Squat Lift vs. Stoop Lift • Normally a squat lift is recommended over a stoop lift - “Lift with your legs, not your back” • But, if you cannot fit the load between your knees then a stoop lift becomes less stressful than a squat lift
Lifting Analysis • This type of analysis helps to understand the strength required throughout the lift at the elbow, shoulder, and hip. • The most stressful points can be identified.