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Workplace Ergonomics: Understanding and Preventing Musculoskeletal Disorders and Injuries

Workplace Ergonomics: Understanding and Preventing Musculoskeletal Disorders and Injuries. Part III: Prevention of Musculoskeletal Disorders. Developers: Margaret Nuesca and Karen Traicoff (Occupational Therapy Students)

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Workplace Ergonomics: Understanding and Preventing Musculoskeletal Disorders and Injuries

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  1. Workplace Ergonomics: Understanding and Preventing Musculoskeletal Disorders and Injuries Part III: Prevention of Musculoskeletal Disorders Developers: Margaret Nuesca and Karen Traicoff (Occupational Therapy Students) Project Advisors: Tiffany Boggis MBA, OTR/L and Zachery Collins, MOTR/L, CEAS Director, School of Occupational Therapy: John White, Ph.D, OTR/L Spring 2010

  2. Understanding the Body for Injury Prevention • Protecting the body is key to injury prevention in any environment. Neutral positions of joints place the least stress on the body • Non-neutral positions happen in the course of doing work. They become problematic if they: • Happen repetitively over a period of time • Are extreme (at end-range of joint) • Are resisted by force

  3. The Spine • The spine in neutral position has 3 curves: • Cervical • Thoracic • Lumbar • Arranging the work environment and using good body mechanics to maintain these curves optimizes physical strength and reduces pressure on the spine. Image retrieved from www.spinalphysio.co.uk/test%20page%20advice.htm

  4. Prevention of Musculoskeletal Disorders (MSD’s):Levels of Intervention • Engineering Controls • Tools/equipment • Workplace Design • Administrative Controls • Job rotation • Number of workers • Work Practice • Body mechanics • Stretching • Breaks Most Effective Least Effective

  5. Preventing MSDs • First Choice: Engineering Controls Goal: Eliminate or reduce primary risk factors, as well as improve efficiency and productivity • Use proper equipment to reduce difficulty of job • Power-operated hand tools • Rolling carts • Electronic staplers • Adjust work environment to keep body in neutral positions • Use adjustable equipment and furniture • Reposition the work • Raise, lower and/or tilt work surface • Store materials off of floor • Minimize one-sided work • Use specialized tools and equipment, such as angled keyboards • Reduce required force • Provide better grips for hand tools • Create many small loads, rather than one large load Source: Konz & Johnson (2004); U of O and OR OSHA (n.d.)

  6. Preventing MSDs • Second Choice: Administrative Controls • Goal: Reduce employee exposure to primary risk factors • Broaden or vary the job content to reduce repetitive motions and static and awkward postures • Adjust the work pace • Provide recovery time through: • Job rotation: rotate workers through several jobs with different physical demands to reduce stress on limbs and body regions • Scheduling more breaks • Provide proper training when appropriate Source: OR-OSHA 201

  7. Preventing MSDs • Third Choice: Work Practice Controls Goal: Reduce employee exposure to risk factors by using best work methods and encouraging healthy habits • Plan work organization • Avoid awkward postures • Use good body mechanics • Use personal protective equipment • Take frequent breaks • Drink plenty of water

  8. Controlling the Risk Factorsfor Specific Types of Work Select an option to learn more: Return to this screen at any time by selecting the icon. When finished, click here to continue. Office Manual Materials Handling Tool Selection & Use

  9. Reducing Risks in the Office: Computer Monitors • Appropriate monitor selection and placement can reduce exposure to • forceful exertions • awkward postures • overhead glare • Consider the following factors: • Viewing distance • Monitor too close can cause eyes to work harder to focus and may require awkward postures, such as tilting head backward, or moving chair back, resulting in the need to reach for the keyboard • Monitor too far can lead to eye strain and to forward-leaning postures that place excess stress on the torso • Viewing angle (up-down and side-to-side) • Monitor too high requires the user to hold head and neck tilted back, leading to muscle fatigue after prolonged periods • Working to the side for extended periods loads the muscles unevenly and results in muscle fatigue and pain • Viewing time • Monitor use decreases blinking; viewing the monitor for prolonged periods may cause eye fatigue and dryness • Viewing clarity • Lack of image quality can lead to eye strain and awkward postures as the user repositions body to gain focus • Incorrect lighting and glare can lead to eye fatigue Source: http://www.osha.gov/SLTC/etools/computerworkstations/wkstation_enviro.html

  10. Computer MonitorViewing Distance • Need to be able to comfortably read text on screen with back supported by chair and head and neck upright • A good rule of thumb is to keep the front surface of the computer screen at arm’s length, or 20 – 40 inches from the eyes Sources: http://www.osha.gov/SLTC/etools/computerworkstations/wkstation_enviro.html; Dowler (2006)

  11. Computer MonitorViewing Angle • The top of the computer screen should be at or slightly below eye level • Consider the surface on which the monitor is placed; add or remove height to/from this surface to adjust the height of the monitor • Bifocal users who view the monitor through the bottom portion of their lenses may need to lower the computer screen and/or tilt the screen up to avoid the need to tilt head backward • Also consider using single-vision lenses for computer work or trifocal lenses that allow the user to focus on the monitor without the need to tilt the head backward • Adjust the chair height to position eyes correctly with respect to the monitor. A keyboard tray and footrest may be necessary (see upcoming slides) • The computer monitor should be directly in front of the user so that head, neck and torso face forward when viewing the screen Source: http://www.osha.gov/SLTC/etools/computerworkstations/wkstation_enviro.html

  12. Computer MonitorViewing Time • Rest your eyes periodically by focusing on objects that are farther away (for example, look at a clock on a wall 20 feet away for 20 seconds) • Stop, look away, and blink at regular intervals to moisten the eyes • Alternate duties with other non-computer tasks such as filing, phone work, or customer interaction to provide periods of rest for the eyes Source: http://www.osha.gov/SLTC/etools/computerworkstations/wkstation_enviro.html

  13. Computer MonitorViewing Clarity • Use the computer settings to adjust the screen resolution to find an optimum character size • Based on a 20-inch viewing distance the minimum character height should be 1/9 of an inch • Use controls for brightness and contrast so that characters are sharply displayed (no fuzzy edges) and the screen is neither too dark nor too light • Regularly clean the screen of dust to optimize contrast and decrease glare • Tilt the monitor so that it is perpendicular to your line of sight, in order to eliminate character distortion • Use appropriate lighting and decrease glare, as described on following slide…

  14. Lighting and Glare • Use correct lighting for the task; incorrect lighting can lead to eye fatigue and headaches • High illumination washes out images on a computer monitor; the lighting requirement for computer work is less than for paper work • Use light diffusers to limit direct light on computer screen while providing adequate illumination for desk tasks • Remove the middle bulbs of 4-bulb fluorescent light fixtures to reduce brightness for computer tasks if diffuser unavailable • Provide adjustable lamps for supplemental light to read printed documents • Bright light sources behind the display screen create contrast problems • Orient computer monitor perpendicular to windows • Use blinds or drapes on windows • Avoid intense lighting in field of vision; use lamp shades to direct light away from line of sight • Direct light sources cause reflected light to show up on the monitor, making images difficult to see • Position task lighting so it does not reflect on monitor • Use high quality glare filters that do not decrease screen visibility Source: http://www.osha.gov/SLTC/etools/computerworkstations/wkstation_enviro.html; OR-OSHA 207

  15. Reducing Risks in the OfficeDocument Holders • Document holders should be used when printed materials are needed during computer tasks, in order to position documents close to the user and the monitor. The goal is to reduce risk factors such as awkward head and neck postures and frequent movements of head and neck, which lead to muscle fatigue, discomfort, head aches, and eye strain. • Document holders should: • Be at or about the same height as the monitor screen so the user can look from one to the other without moving the head or back • Be at or about the same distance as the monitor screen to avoid frequent changes of focus • Be stable when holding heavier documents • Document holders can be positioned on either side of the monitor or directly beneath the monitor Source: http://www.osha.gov/SLTC/etools/computerworkstations/wkstation_enviro.html; OR-OSHA 207

  16. Reducing Risks in the Office:Keyboard & Mouse • Proper selection and arrangement of the computer keyboard and pointing device helps reduce exposure to: • Awkward postures • Repetition • Forceful exertions • Contact stress • Consider the following factors: • Keyboard & mouse height • Keyboard too low can require bent wrists for typing • Keyboard & mouse too high can lead to raised shoulders, bent elbows, and wrist deviations in order to elevate arms and orient hands to keyboard • Keyboard & mouse distance from body and from each other • Keyboard and mouse too far away may require reaching with the arms or leaning forward with the torso, placing stress on the shoulder and arm • Keyboard too close may lead to extreme elbow angles Image 1* Image 2* * Image 1 retrieved from http://wisha-training.lni.wa.gov/Training/flash/ComputerWorkstation/ErgoOfficeLauncher.htm * Image 2 retrieved from http://www.osha.gov/SLTC/etools/computerworkstations/components_pointers.html

  17. Reducing Risks in the Office:Keyboard & Mouse • More factors to consider: • Tilt angle • Keyboard tilted up by extending back legs of keyboard can cause wrist to bend upward • Wrist rest • Typists tend to rest heel of hand on nearest surface, which can result in contact stresses and awkward angles of wrist • Keyboard & mouse design • Key placement on many keyboards, particularly smaller keyboards, may require sideways wrist deviation in order to reach all of the keys • Keyboards with a 10-key number keypad permanently affixed to the right side of the keyboard can be limiting to left-handed users and require extended reaching for mouse use if mouse is placed to the right of the keyboard • A pointing device that is too big or too small may require increased finger force and awkward wrist positions Source: http://www.osha.gov/SLTC/etools/computerworkstations/wkstation_enviro.html; OR-OSHA 207

  18. Keyboard & Mouse Positioning • Position the keyboard and mouse to maintain a neutral body posture during use: • Elbows should be about the same height as the keyboard and hang comfortably to the side of the body • Forearms should be approximately parallel to floor • Shoulders should be relaxed • Wrists should not bend up or down or to either side • Accomplish appropriate positioning through the following: • Adjust chair height • Adjust work surface height • Work surface should be not more than 2 inches thick. Remove central pencil drawer if blocking thighs. • Use a keyboard tray adjustable in height and tilt • Consider a negative sloping keyboard with 15 degrees of tilt • Adjust keyboard tilt to maintain straight, neutral wrist postures while accommodating changes in arm angles • Have adequate space for positioning keyboard and mouse in the same plane to limit reaching. If the keyboard tray/surface is not large enough to accommodate both the keyboard and mouse: • Use a mouse platform positioned over the keyboard. This design allows the mouse to be used above the 10-key pad. • Install a mouse tray next to the keyboard tray

  19. Keyboard and Mouse Selection and Use • Options to reduce reaching • Use a keyboard that has an incorporated pointing device, such as a touchpad • Use a keyboard without a ten-key number pad, or a detachable keypad, which leaves more room for the pointer/mouse. • Reduce pointing device use by substituting keystrokes for mousing tasks, such as Page Down to scroll, Ctrl+S to save, Ctrl+P to print, and Alt+Tab to alternate between windows. • Options to support forearm and wrist and reduce contact stresses: • Use a padded wrist rest with the keyboard to support heels of hands. Height of wrist pad should not exceed height of first row of keys • Use a mouse pad with a wrist/palm rest to promote neutral wrist posture • Use an arm board to provide support with less localized contact stresses • Options to reduce awkward postures • Consider alternative keyboards Image retrieved from http://medicine.com.my

  20. Reducing Risks in the Office:The Office Chair • “A good chair provides necessary support to the back, legs, buttocks, and arms, while reducing exposures to awkward postures, contact stress, and forceful exertions.” http://www.osha.gov/SLTC/etools/computerworkstations/wkstation_enviro.html • Features of the Office Chair • Seat pan • Backrest • Armrests • Base • Related factors for correct seating • Work table • Footrest Image retrieved from http://pressf14help.wordpress.com/2008/10/13/all-about-repetitive-strain-injury-rsi/

  21. The Office Chair • Seat pan should be: • Height adjustable, especially when shared by a number of users. Appropriate chair height allows entire sole of the foot to rest flat on the floor to minimize pressure on the thighs. • Wide enough to accommodate the user, leaving no soft tissue unsupported. Chairs with oversize seat pans should be provided for larger users. • Between 13 and 17 inches deep, providing support for most of the thigh while allowing 2 to 4 finger widths space between the chair edge and the back of the knees. The seat must not be so deep that it cuts off circulation to lower legs or hits the back of the lower leg at the knee, requiring the user to sit forward and lose contact with the backrest. • Tilt adjustable, to allow for a variety of seat slopes. A backward seat pan slope of 1°-5° encourages use of backrest without placing excessive stress on thighs. A forward seat pan slope will maintain the anatomically neutral lumbar curve of the spine, reducing the load on the spinal joints and thus preventing back pain. • Firmly padded, and have a rounded, "waterfall" edge to minimize compression of thigh tissues and blood flow restriction. • Covered with a porous, breathable material that is not slippery. Without adequate friction, the user may slide away from backrest, resulting in uncomfortable tissue shearing forces, minimal back support, and fatigue of the muscles used to resist the sliding.

  22. The Office Chair • Backrest should • Provide adequate lumbar support to maintain natural S-shape curvature of spine and take the load off of the back. • Be vertically adjustable to match the lumbar region of the user. • Be adjustable forward and backward to ensure contact with the back • Have an adjustable inclination with ability to lock in desired position. • Have a 15 to 20 inch high support surface • Armrests should be • Adjustable up and down and in and out to match the individual user and the task being performed. Armrests that are not properly adjusted can lead to awkward postures: • Armrests too wide require reaching with the elbow, fatiguing the shoulders and neck. • Armrests too close can restrict movement in and out of the chair. • Removable • Armrests too high elevate shoulders, causing muscle tension, stiffness, pain and fatigue. Also can prevent chair from fitting under work surface, keeping user far from task and/or preventing user from using backrest of chair. • Armrests too low promote slumping or leaning to one side, fatiguing the neck, shoulders and back.

  23. The Office Chair • The Base of the chair should • Swivel to reduce need to twist torso and ease entrance and exit from the chair. The exception to this is for users operating a foot pedal. • Be sturdy, with 5 legs arranged in a circle at least the diameter of the seat itself, in order to prevent tipping. • Have appropriate feet: • Casters, available for both carpet and hard flooring, allow easy movement of chair across surface of floor and decrease reaching and bending. • If movement around workstation is not required, consider not using casters, as they require use of leg muscles to keep chair still. • Optimal chair adjustment happens in relation to other elements of workstation, including monitor, keyboard, and desk • Adjust height of work surface if necessary to maintain neutral body positions while keeping feet flat on floor • If chair cannot be lowered due to height of work surface, use a footrest to provide stable support for feet

  24. Reducing Risks in the Office • The following graph illustrates the force on the lumbar region of the spine in various sitting and standing positions: Data converted and calculated from Sato, K. MD; Kikuchi, S. MD; Yonezawa, T. MD. (1999) • Forces on spine are least when standing upright. Maintaining an upright posture while sitting decreases the force on the spine. Important to avoid slouching. • Sitting flattens the lower back, removing lumbar curve. Keeping hips at >90 degrees can maintain the lumbar curve and reduce forces to spine. Open up the hips while in sitting by: • Reclining the backrest, or • Tilting seat pan forward

  25. Other General Tips to Stay Healthy in the Office • Change positions frequently and avoid prolonged sitting and prolonged standing: • “Postural fatigue and absence due to sickness decrease when there is an opportunity to change one’s work posture.” (Chafin, Andersson, & Martin, 2006, pp. 211-212) • Take advantage of chair’s adjustable features to vary your work posture • Take frequent breaks • Taking a “micro-break” every 15 minutes has been shown to result in reduced neck, lower back, chest, elbow and arm discomfort; lower eyestrain and blurred vision; and higher speed, accuracy and performance of work tasks. (Balci & Aghazadeh, 2003) • Drink plenty of water, which facilitates micro-breaks, and results in the need to get up • Exercise regularly!

  26. End of Office SectionClick here to return home…

  27. Manual Material Handling • Involves 5 types of activities • Lifting/Lowering • Lifting is to raise from a lower to a higher level. The range of a lift can be from the ground to as high as you can reach your hands. • Lowering is the opposite activity from lifting • Pushing/Pulling • Pushing is to press against with force in order to move the object. • The opposite is to pull. • Twisting • In this context, twisting is the act of moving the upper body to one side or the other while the lower body remains in a relatively fixed position. • Can take place while entire body is in a state of motion • Carrying • Having an object in ones grasp or attached while in the act of moving. The weight of the object becomes a part of the total weight of the person doing the work. • Holding • Having an object in ones grasp while in a static body position Source: OR-OSHA 206

  28. Lifting and Lowering Limits • The Maximum weight that is safe for 1 person to manually lift with two hands is 50 pounds* (* as determined for nearly all healthy workers who are free of adverse health conditions that would increase their risk for musculoskeletal injury) • The recommended weight limit is less than 50 pounds if any of the following factors are present: • The lifting or lowering occurs farther than 10 inches from the body • The object is lifted or lowered from a height other than waist high • The object is lifted or lowered more than 10 inches • The object is lifted to or from the side of the body • The object is lifted or lowered frequently • The lifting or lowering is done continuously for over an hour, without sufficient recovery time • The object lacks optimal handles or comfortable grip • Manual handling activities other than lifting (holding, pushing, pulling, carrying, walking, climbing) are regularly performed in addition to the lifting. Source: National Institute for Occupational Safety and Health, 1991

  29. Lifting and Lowering Limits The farther away, the less it should weigh! The NIOSH Lifting Equation calculator can be used to calculate the Recommended Weight Limit in specific scenarios.

  30. Safe Lifting Guidelines • Plan the lift • Assess the weight of the load (by observing or pushing) • Mentally review lifting technique • Make sure your footing is stable and the path is clear. • Avoid heavy loads • Never exceed maximum acceptable load • Lighten the load if possible • Get help with heavy loads • Bend at the knees, not at the hips • Squat and stoop lifting are both acceptable for jobs requiring repetitive lifting • Keep the back straight • Hug the load (keep the load as close to the body as possible) • Avoid twisting. Turn with the feet rather than twisting the trunk Images retrieved from http://www.lni.wa.gov

  31. Reducing Risks of Lifting • Reduce the weight • Increase the weight (so people truly can’t lift the item) • Use mechanical assistance • Slide instead of lift • Team lift • Avoid unnecessary lifting • Use mobile storage • Rotate between tasks • Bring loads as close to the body as possible before lifting them • Remove obstacles • Place objects at a good working height

  32. Pushing and Pulling • Pushing and pulling is better than lifting and lowering • Two hands are typically better than one for pushing and pulling • Arm strength decreases when pushing above the shoulders or below the hip • A secure, easy-to-grasp handle is necessary for pulling. Pushing may just require a flat surface • Generally better to push loads than pull them • Exception is in the case of transporting a rolling cart over an obstruction, in which it is better to pull load up and over obstruction, rather than push load downward into obstruction • Pushing while standing • Lean toward the load • Rear foot behind the body’s center of mass • Best to push at waist level • Pulling while standing • Lean away from the load • Front foot ahead of body’s center of mass • Best to pull at thigh level

  33. Force Limits for Pushing and Pulling • Limits exist for safe amounts of push and pull force (which is the force required to push or pull the object; NOT the weight of the object). If your department owns a strain gauge, like the one pictured here, this force can be measured. Upper force limits for two-handed horizontal pushing and pulling perpendicular to shoulder are as follows (Snook & Ciriello, 1991):  • Standing - whole body involved: 50.7 lbs • Standing - primarily arms & shoulders: 24.69 lbs • Kneeling: 42.3 lbs • Seated: 29.3 lbs • Force capability goes down as it is exerted more often – muscles will fatigue over repeated motions; take a break. • Initial force capability is higher than sustained capability - it takes more force to start. • Pushing capability is higher than pulling • Friction coefficients affect difficulty of push or pull • Slippery surfaces can require less push or pull force, but may be more difficult to gain necessary traction with feet

  34. Long Distance Carrying • Carrying objects in hand uses 50% more energy than a load on the back • For loads on the back: • Use pads to protect shoulders • Transverse loads are better than front-to-back loads in which the trunk is bent to the side on which the load is carried • Mechanical aids should be used for: • Transporting loads farther than 10 meters • Repetitive carrying Mechanical aids include: • Lift trucks • Conveyors • Carts • Consider teamwork for loading and unloading • A loads B, who carries to C • Periodically switch jobs Source: Konz & Johnson, 2004 • Chutes • Jib • Cranes "Everything on wheels"

  35. Hand Carrying – Short Distance • Problems: • Places stress on back due to associated twisting and bending • Places stress on arms and shoulders due to load • Asymmetrical carrying (more weight in one hand than the other) uses 10% more energy • Increased danger carrying objects up and down stairs and ladders • Guidelines and Solutions: • Use larger muscles like arms and trunk, rather than smaller distal muscles like wrists and forearms • Carry load closer to body • Reduce required energy by raising initial location of object • Use hoists, platforms and elevators to move loads between levels Source: Konz & Johnson, 2004

  36. Guidelines for Manual Materials Handling • Bend the Knees • Use a straddle stance for lifting bulky loads, so load can be kept closer to spine • Don't Slip or Jerk • Wear shoes with high coefficient of friction • Don't Twist During the Move • Twisting while bending is particularly hazardous • Position materials and work surfaces to reduce bending and twisting • Move feet instead of twisting torso • Use Machines • Best solution is to eliminate or reduce need for manual handling • Move Small Weights Often • Reduce heavy loads • Reduce size of loads • Consider the weight of the container • Slide instead of lift • Keep the Load Close to the Body • Use smaller work surfaces to reduce need to reach • Orient pallets and bins to reduce reach distance • Work at Knuckle Height • Store materials at knuckle height to eliminate reaching to floor or above shoulders • Avoid rounded backs

  37. End of Manual Material Handling SectionClick here to return home…

  38. Preventing Injury During Tool Use The following slides have been adapted from Online Safety Courses developed by the Washington State Department of Labor and Industries. The original training courses are available athttp://www.lni.wa.gov/Safety/TrainTools/Online/Courses/default.asp

  39. Reduce Repetitions and Automate • Reduce the number of repetitions per shift • For example, improve the layout of the work station • Try to semi or fully automate Material on this slide courtesy of Washington State Department of Labor and Industries

  40. Reduce Flexion or Deviation of Wrist Design tasks and select tools to reduce extreme flexion or deviation of the wrist Material on this slide courtesy of Washington State Department of Labor and Industries

  41. Neutral Wrist Bad Good Bad Good Material on this slide courtesy of Washington State Department of Labor and Industries

  42. Bend the tool, not the wrist Bent Handled Tool Examples Material on this slide courtesy of Washington State Department of Labor and Industries

  43. Avoid Forearm Rotation Avoid inward or outward rotation of the forearm when the wrist is bent to minimize elbow disorders Material on this slide courtesy of Washington State Department of Labor and Industries

  44. Reduce Weight of Tools One way to reduce weight is to use an articulating arm or counter-balance. Material on this slide courtesy of Washington State Department of Labor and Industries

  45. Don’t Raise or Extend Elbows with Heavy Tools Material on this slide courtesy of Washington State Department of Labor and Industries

  46. Avoid Pounding and Pressing Avoid repeated pounding with the base of the hand Avoid repetitive, forceful pressing with the finger tips Material on this slide courtesy of Washington State Department of Labor and Industries

  47. Avoid Stress on Soft Tissues Stress concentrations result from poorly designed tools that exert pressure on the palms or fingers. Material on this slide courtesy of Washington State Department of Labor and Industries

  48. Reduce Grip Force Requirements • Optimum grip spans for pliers, scissors, or tongs, measured from the fingers to the base of the thumb, range from 2.3 to 3.5 inches. Material on this slide courtesy of Washington State Department of Labor and Industries

  49. Evaluate Gripping Surface A compressible or larger gripping surface may reduce grip force requirements. Material on this slide courtesy of Washington State Department of Labor and Industries

  50. Optimal Grip Span • Optimum grip spans for pliers, scissors, or tongs, measured from the fingers to the base of the thumb, range from 2.3 to 3.5 inches. Material on this slide courtesy of Washington State Department of Labor and Industries

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