In response to the increasing number of workers relying on back belts to prevent injury during lifting, the National Institute for Occupational Safety and Health (NIOSH) decided to evaluate the evidence of their effectiveness. After an extensive review of the scientific literature completed in 1994, NIOSH concluded at that time that insufficient evidence existed to prove the effectiveness of back belts in preventing back injuries related to manual handling job tasks. An epidemiological study published in 1996 (Kraus et al., Reduction of Acute Lower Back Injuries by Use of Back Supports, International Journal of Occupational and Environmental Health 2:264-273) credits mandatory use of back belts in a chain of large retail hardware stores with substantially reducing the rate of low back injuries. Although NIOSH believes this study provides limited evidence that back belts may be effective in some settings for preventing back injuries, NIOSH still believes that evidence for the effectiveness of back belts is inconclusive. This area is being researched, and the questions about the effectiveness of back belts remain open.

NIOSH believes that well-designed studies to assess the potential benefits and disadvantages of using back belts are still needed. Because of design flaws, the limited studies that have analyzed workplace use of back belts cannot be used to either support or refute the effectiveness of back belts in injury reduction. Moreover, many of the earlier studies did not evaluate the type of industrial back belt most widely in use today. Also, because workers think they are protected, they may attempt to lift even more with a back belt than they would have without it, subjecting them to even greater risk. If employers or workers are currently relying on back belts as protective equipment against back injury, NIOSH believes they should be aware of the questions about their effectiveness.

Rather than relying solely on back belts, the Institute recommends that employers and workers minimize their risk of back injury by developing and implementing a comprehensive ergonomics program. A program of this nature would focus on prevention and:

1. include an assessment of all work activities to ensure that tasks can be accomplished without exceeding the physical capabilities of the worker;
2. incorporate on-going, comprehensive training for all workers on lifting mechanics and techniques;
3. provide a surveillance program to identify potential work-related musculoskeletal problems; and
4. include a medical management program.

Additional information is available in two NIOSH Publications: Workplace Use of Backbelts, Review and Recommendations (DHHS [NIOSH] Publication No. 94-122) and Back Belts - Do They Prevent Injury?(DHHS [NIOSH] Publication No. 94-127). Copies are available free-of-charge from the NIOSH Publications Office while supplies last:

• Accident investigation
• Early return to work program
• Incentive program (that rewards NOT reporting)
• Emergency first aid

• Hazard/Near-miss investigation
• Incentive program (that reward compliance, reporting injuries/hazards, suggesting, and involvement)
• Wellness program

Design strategies try to target the causes of potential musculoskeletal problems. For this reason, engineering approaches are preferred over administrative ones because they eliminate the risk factors as opposed to simply reducing exposure to them. For example, having machines do monotonous, repetitive, forceful work is better than subjecting workers to these risk factors. Administrative controls (such as worker rotation or allowing more rest breaks) remain stop-gap measures. They are not permanent solutions.

A plumbing-ware manufacturing company asked NIOSH to assist in an ergonomics evaluation of their production operations after an OSHA inspection found a high number of back injuries at the facility relative to the rates at other manufacturing plants in the same industrial classification. This industry as a whole had the tenth highest OSHA reportable incidence rate in the United States for 1986. The work areas where most back injuries had occurred were identified by the plant's safety director, and the jobs believed most stressful to the workers' backs became the main targets of the evaluation that ensued [HETA 88–237–L1960].

The owner and employees of a preschool day care center asked NIOSH to identify possible causes of musculoskeletal problems, chiefly back pain and lower extremity (knee) pain and discomfort, reported by the teachers and aides at the school. Subsequent data collected on symptomatic complaints and observations and analyses of work activities indicated that factors such as frequent lifting of infants and sustained periods of kneeling, stooping, squatting, and trunk bending were responsible for the problems [HETA 93–0995–242].

                           Symptoms Survey

Name _______________________   Date _________________
	                 
Work Location __________________  Job _______________
Shift __________  Supervisor ________________________
		                 

Time on this job:
   
____  Less than 3 months   ____  3 months to 1 year   
____  1 year to 5 years    ____  5 years to 10 years     
____  Over 10 years

Have you had any pain or discomfort during the 
last year?  ____  Yes  ____  No 

If you answered “Yes” to the above question, carefully shade 
in the area of the drawings below which indicate the 
location of the pain which bothers you the most.

(1) Employer Responsibilities

(c) Every employer must be responsible for providing the health hazard control measures necessary to protect the employees' health from harmful or hazardous conditions and for maintaining such control measures in good working order and in use.

(d) Every employer must inform the employees regarding the known health hazards to which they are exposed, the measures which have been taken for the prevention and control of such hazards, and the proper methods for utilizing such control measures.

(a) Each employer must investigate or cause to be investigated every lost time injury that workers suffer in connection with their employment, to determine the means that should be taken to prevent recurrence. The employer must promptly install any safeguard or take any corrective measure indicated or found advisable.

(c) Any supervisors or persons n charge of work are held to be the agents of the employer in the discharge of their authorized duties, and are at all times responsible for:

(A) The execution in a safe manner of the work under their supervision; and

(B) The safe conduct of their crew while under their supervision; and

(C) The safety of all workers under their supervision.

(4) Intoxicating Liquor and Drugs. The use of intoxicating liquor on the job is strictly prohibited. Anyone whose ability to work safely is impaired by alcohol, drugs, or medication must not be allowed on the job while in that condition.

(5) Horseplay. There must be no horseplay, scuffling, practical jokes, or any other activity of a similar nature.

(6) Extraordinary Hazards. When conditions arise that cause unusual or extraordinary hazards to workers, additional means and precautions must be taken to protect workers or to control hazardous exposure. If the operation cannot be made reasonably safe, regular work must be discontinued while such abnormal conditions exist, or until adequate safety of workers is ensured.

(7) Inspections

(a) All places of employment must be inspected by a qualified person or persons as often as the type of operation or the character of the equipment requires. Defective equipment or unsafe conditions found by these inspections must be replaced or repaired or remedied promptly.

(b) Wherever required by this safety code, a written and dated report, signed by the person or persons making the inspection, must be kept.

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Additional controls for cumulative trauma

This section of the Guidelines introduces common computer-related health problems and provides solutions.

Back problems

Back pain is one of the more common computer user complaints. The back is a very complex structure; back problems can result from several causes.

Problem: A chair that fails to support the lumbar (lower) region of the spine is a common cause of back discomfort, because up to 35 percent more pressure can be placed on the lower back when sitting. The normal alignment of the spine, if viewed from the side, is an S-shaped curve with an inward curve at the neck, an outward curve in the middle of the back, and an inward curve at the lower back, the lumbar region. When a chair does not provide adequate lumbar support, the lower curve of the back flattens (this is called lumbar lordosis). When a person is seating himself, the bottom of the hipbone contacts the chair first. As the sitting process is completed, the hip actually rotates backward, flattening the curve in the lower part of the back. This causes the spinal discs to stretch from the vertebrae, causing back discomfort.

Solution: A chair that provides good low-back support and has the backrest set at the proper height can maintain the normal alignment of the lower spine, relieving fatigue and discomfort.

Problem: A straight-back chair provides little or no support to the lower and upper back. Sitting in this type of chair causes back muscle fatigue as a result of muscular efforts to maintain back posture for a long time.

Solution: A tiltable backrest allows the user to change positions, reducing muscular effort and fatigue from sitting. A slight backward recline also helps to reduce the flattening of the lower spine when sitting.

Problem: When a chair is too soft, the user sinks into the seat pan. This restricts movement and causes thigh, buttock, and lower back fatigue. Conversely, when a chair is too hard, a user may need to change postures frequently to relieve thigh and buttock discomfort.

Solution: People spend much of their time at work sitting. This is especially true of computer operators. A computer user’s chair should be designed to allow free movement while sitting. The chair must be properly designed for comfort, efficiency, and the task. Because computer users’ chairs are very personal items, users must be involved in the selection and purchase of chairs. This will ensure that users are satisfied with their chairs and that the best chair has been selected for each user.

Problem: When a display screen is too low, it causes the operator to lean forward, slouch down, or lower his or her chair to improve screen viewing. This can cause the lower curve of the back to flatten as a result of no lumbar support.

Solution: Raise the monitor to the correct viewing height, so that the topmost active line of the character display on the screen is at or just below the operator’s eye level.

Neck problems

Neck strain is also a common complaint, and causes are often related to the computer monitor height, the absence of a document holder, or improper positioning of the holder.

Problem: The monitor is too high or low, causing the user to bend the neck backward or forward to see the screen.

Solution: Lower or raise the monitor to the correct viewing height, as recom-mended under “Display screens” on page 6.

Problem: Documents placed flat and off to the side of the work surface cause forward bending and twisting of the neck.

Solution: An articulated document holder or a document holder mounted on the monitor, positioned at the same elevation as the monitor screen, should relieve this problem. A document holder should be usable on either side of the monitor, between the keyboard and the computer screen.

Problem: The document holder is too far off to the side, causing repetitive neck rotation.

Solution: The screen and document holder should be the same distance from the eye (to avoid constant changes of focus), and close enough together so that the operator can look from one to the other without excessive neck or back movement.

Shoulder problems

Shoulder strain can occur when the user’s arms are positioned too high or too low. When computer operators’ hands and arms are too high, they tend to pull their shoulders up, straining their shoulder and back muscles. When their hands and arms are too low, they pull their shoulders down, putting pressure on shoulder and back muscles and compressing nerves in the neck and arms.

Problem: The arms are too high or too low when using the keyboard. Solution: Lower the keyboard or raise the chair, and reinforce the principle of keeping the operator’s hands, arms, and forearms parallel to the keyboard.

Problem: The user’s arms are too high or too low when using the chair arm-rests.

Solution: Remove the armrests or replace with adjustable armrests. Forearm and hand problems Problems can occur if the user’s hands don’t form a straight line with the forearms, or if the sharp edge of the work surface presses against the palms, wrists, or forearms.

Problem: The keyboard is too thick, too low, or too high, causing wrist bending.

Solution: Purchase thin keyboards to minimize wrist deviation. Adjustable-height and sloped keyboard trays make proper keyboard height and hand-wrist posture easier to accomplish. A keyboard fitted with a wrist rest will support the heel of the operator’s hand and minimize wrist deviation. The wrist rest thickness should not exceed the height of the first row of keys. Wrists should never rest on the wrist pad when using the keyboard. Wrist rests are to be used between periods of typing.

Problem: The keyboard user supports the wrists on the edge of the work surface while typing or resting. This can cause backward bending of the wrist, numbness of the hand and fingers, or tingling.

Solution: All table surface edges should be rounded, and the keyboard should be retrofitted with a wrist rest.

Leg problems

Leg problems can result from decreased blood circulation. This causes the legs to fall asleep.

Problem: The edge of the seat pan presses against the thighs.

Solutions: A proper seat-pan length allows for a two- to three-finger clearance from the front edge of the chair to the back of the thighs upon properly adjusting the chair height to the workstation. Use a footrest if feet aren’t flat on the floor.

Problem: Using the foot rungs on the chair or chair legs as footrests can pro-duce excessive knee flexing.

Solutions: Properly adjust chairs and provide a footrest, as needed.

Vision problems

There are no conclusive studies that document permanent vision or eye problems associated with computer use; however, the most common complaints are eye strain, burning eyes, blurred vision, irritated eyes, and headaches.

Solutions: Because these complaints are associated with focusing at close range, the minimum eye distance should be 16 inches from the monitor. Recommend a short rest break (3-5 minutes) following each hour of continu-ous Computer work, during which time the operator should get up and stretch, move about, or do other work. Periodically focus on distant objects. This serves to relax eye muscles.

Uncorrected or improperly-corrected vision can aggravate any of these complaints. When getting fitted for glasses, computer operators need to tell their eye care specialists that they perform Computer work regularly. The focal distance for reading (10-12 inches) is less than it is for Computer work (16-29 inches).

People wearing bifocals or trifocals have to tilt their heads back to read through the bottom portion of the lenses. This can cause neck strain. Correct the problem by lowering the computer screen height or using single-focal-length glasses specifically for computer use.

Poor or excessive lighting contributes to vision problems. The illumination level for Computer work should be 30-50 footcandles for screen viewing only and 50-70 footcandles for reading printed documents.

Room glare can be reduced or eliminated by lowering the lighting; having the operator sit facing a matte-finished, dark-colored wall; or adjusting the screen upward, downward, or slightly to the left or right. However, too much screen deviation can cause neck problems.

• Position the Computer workstation at right angles to the window.
• Install the Computer workstation between rows of overhead lighting.
• Install screen glare filters and visor hoods over the monitor screen.

This should be your last resort, because it may reduce image quality. Window glare can be reduced or eliminated by covering the windows with draperies or blinds. Blinds are preferred over drapes, and vertical blinds are preferred over horizontal blinds.

• Install natural-density filter shades over the windows.
• Add outdoor window awnings.

Muscle fatigue problems

Computer work consists of fixed posture and repetitive motions, resulting in local muscle fatigue. Muscles need adequate rest to prevent discomfort, fatigue, and possible injury, or illness. To reduce local muscle fatigue for computer workers the following are recommended:

• Take more frequent breaks of shorter duration (3-5 minutes) every hour on the hour.
• Change job tasks to reduce fatigue and monotony. Allow different sets of muscles to be used with a different posture.
• Exercise to help relax tight muscles, reduce stress, and lessen the sense of general fatigue.

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Computer workstation design considerations

• Chairs should be adjustable. (see seating recommendations)
• Work surfaces should be large enough to support the keyboard, mouse, monitor and documents.
• The top line of the screen should be just below eye level to keep the neck straight.
• Monitors should be placed 18-30 inches away from the worker.
• Keyboards and monitors should be detachable so the angle and position can be adjusted.
• Keyboard and work-surface edges should be rounded.
• Documents should be at the same height and distance from the screen.
• The screen and document should be easily viewed without turning or tilting the worker's head.
• The monitor and keyboard should be placed perpendicular to windows to avoid glare.
• Screen contrast and brightness should be easily adjustable.
• Screen characters should be clearly displayed. No waving or flikering.
• The mouse should be located so that the arm and should are as close as possible to neutral position.

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Effective lifting techniques

• Do not exceed the physical ability of the worker.
• Provide adequate recovery time for tasks that require frequent lifting.
• Provide easy access so the load is in front of the person lifting.
• Eliminate twisting by changing the start or end point of the lift.
• Put items to be lifted between knee and shoulder height.
• Provide handles or cutouts to make grasping easier, permit a closer lift, and allow items to be carried near the body.
• Change an object's shape to make it easier to grasp.
• Decrease the weight of the object.
• Decrease the distance or height over which the object must be moved.
• Distribute a load evenly within a container.
• use hand carts or hand trucks.
• Use a vacuum-assisted hoist or integrated conveyors.
• Use loaders, cranes and motorized material pallets to help move load that are larger or heavier than one or two people can safely handle.

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Lighting

An environment with high illumination washes out images on a video-display screen because a computer produces its own illumination and contrast. For this reason, Computer work areas should have lower light levels than standard office areas. For these areas, illumination ranges should be 30-50 footcandles for screen viewing and 50-70 footcandles for reading printed documents. Adjustable lamps may be needed to provide supplemental light for reading printed documents. To control direct-glare and reflected-glare sources, the walls, furniture, and other equipment located near a computer should not have highly-reflective finishes. To reduce glare, walls can be painted non-reflective, subdued colors.

Windows should have adjustable vertical blinds or drapes, and the Computer work area should be located away from and at right angles to windows. During bright, sunlit periods, the window must be draped, shut, or shaded to prevent screen glare and eye fatigue. Employees must be able to adjust window blinds as needed.

Light fixtures should be equipped with diffusers, cube louvres, or parabolic louvres when located near computers. Recessed or indirect lighting systems can eliminate glare and reflections but are not suitable for all workplaces. To reduce glare and reflection from overhead lights, place the Computer work areas between rows of overhead lights.

Screen glare filters should be used as a last resort, as they can contribute to blurring and poor contrast of screen characters. Using screen filters is a supple-mentary solution and not a substitute for proper lighting as described above. The American Optometric Association has compiled results of screen glare filter tests. If screen filters are used, a supplementary visor hood should be considered.

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Temperature and humidity

Set room temperature controls to maintain thermal comfort (sufficient cooling and ventilation). Avoid overcrowding Computer work areas. Provide a fairly constant relative humidity level (30-70 percent is recommended). Do not direct warm air units from central processing units (CPUs) and disk and diskette drives toward operators.

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