Recognizing Workstation Risk Factors
Most job-related injuries in the office environment are caused by repetitive movements, awkward postures, or applying pressure or force. According to OSHA, the following are recognized as risk factors that can lead to musculoskeletal disorders (MSDs) such as carpal tunnel syndrome, tendinitis and back injuries:
- Awkward postures. This occurs when the employee’s body is misaligned with workstation components and accessories. If the employee’s monitor is positioned too high, he or she may tilt the head back and fatigue the neck and shoulder muscles. Careless alignment can cause muscles to compress or be stretched; bone-tendon-muscle connections can be strained; and tendons, blood vessels and nerves can be pinched and restricted. When this happens over time, serious health problems can occur.
- Contact stress. Repeated or continuous contact with hard or sharp objects such as desk edges may create pressure that can inhibit nerve function and blood flow.
- Force. Injuries caused by the force of using equipment can be overlooked in an office setting. Office work tools may seem harmless, but the amount of concentrated effort coupled with repetitive movements can seriously damage smaller, localized muscles. Something as simple as having to tightly grasp a mouse to move the pointer around the screen can have serious consequences.
- Repetitive motions. If motions are repeated frequently (e.g., every few seconds) and for prolonged periods (such as an eight-hour shift), fatigue and muscle-tendon strain can result.
- Repletion rate. Understanding the risks of MSDs also includes the number of hand manipulations an employee completes in an eight-hour work shift. These manipulations fall under the category of task-cycle time. Task-cycle times of 30 seconds or less are defined as high repetition; cycle times greater than 30 seconds are rated as low repetition.
- Duration. Duration refers to the amount of time an employee is continually exposed to a risk factor. Tasks that require use of the same muscles or motions for a prolonged time increase the likelihood of both localized and general fatigue. The longer the period of continuous work, the longer the recovery or rest time required.
- Other conditions. Additional workplace conditions that can influence the presence and severity of risk factors for MSDs include cold temperatures, insufficient pauses and rest breaks, and unfamiliar work.
Signs and symptoms of MSDs and other injuries
OSHA recommends checking for these health problems associated with computer use:
- Numbness or a burning sensation in the hand
- Reduced grip strength in the hand
- Swelling or stiffness in the joints
- Pain in wrists, forearms, elbows, neck or back
- Reduced range of motion in the shoulder, neck or back
- Dry, itchy or sore eyes
- Blurred or double vision
- Aching or tingling
- Loss of color in affected regions
Although these symptoms may not necessarily lead to an MSD, they should prompt employees and their managers to conduct an evaluation of their working positions and the workstation layout. If symptoms are not treated, they can lead to loss of strength in the affected area, chronic pain or permanent disability.
Evaluating an Employee’s Workstation
Office ergonomics focuses on an employee’s workstation arrangement – the placement of equipment such as a desk, computer monitor, chair, computer keyboard, mouse and telephone.
An ergonomic evaluation examines:
- An employee’s workstation setup relative to his/her posture, length of time in a position or doing a particular task, types of movements, or repetition of movements
- An employee’s job tools, including any device used to perform job duties, such as a computer mouse or keyboard
- An employee’s job surroundings, including the work surface, lighting, noise level, temperature and humidity
- Top of monitor at or just below eye level
- Head and neck balanced and in-line with torso
- Shoulders relaxed
- Elbows close to body and supported
- Lower back supported
- Wrists and hands in-line with forearms
- Adequate room for keyboard and mouse
- Feet flat on the floor
Each employee is an individual. Therefore, no single, correct workstation setup exists.
However, OSHA guidelines provide a foundation for appropriate working conditions and employee-specific adjustments. Adjustments can be as basic as ensuring each employee has adequate work space to perform the required job tasks – or as sensitive as individual body size. In general, workstations should provide as many customizable features as possible.
Custom-Fitting a Computer Workstation
When making decisions about placement of components, accessories or where the employee should sit, here are the workstation components to evaluate:
- Desktops/work surfaces
- Wrist/palm supports
- Document holders
Here is some additional direction on each component:
- Desktops/work surfaces
- The desk is the cornerstone of a comfortable workstation. Its height, width and work surface help determine the location of workstation components.
The desk’s size should be based on the functions the employee must complete – and the employee’s own size. Typically, a desktop that is approximately 30 inches deep is appropriate for workstation components. Employees should have adequate room for legs, thighs and changes in working postures.
Ensure that the employee has a comfortable sitting position sufficiently flexible to reach, use and observe the display screen, keyboard and document holder.
The keyboard should be approximately one to two inches above the thighs. The work surface should be no more than two inches thick. If the employee is using a traditional desk, you may need to remove the central drawer to allow legroom.
- An ergonomically adjustable chair is essential to employee safety and productivity. Overall, a chair should support the back, legs, buttocks and arms to facilitate the employee’s need for neutral posture.
The human body dimension that provides a starting point for determining correct chair height is the “popliteal” height. This is the height from the floor to the point at the crease behind the knee. The chair height is correct when the entire sole of the foot can rest on the floor or footrest and the back of the knee is slightly higher than the seat of the chair. This allows blood to circulate freely.
Carefully observe the design of the chair’s backrest, seat, arms and base. The backrest should fit the natural S-curve of the back and be adjustable to ensure it fits the height of the employee. A lumbar cushion placed correctly behind the small of the back can help to accentuate lumbar support.
The backrest also should have angle, in/out and height adjustments to promote proper alignment of the spine. The angle adjustment allows the employee to change the angle of the backrest relative to the seat pan, as opposed to the tilt mechanism, which moves the seat pan with the backrest. When employees change the tilt, the angle between the seat pan and the backrest should remain the same.
The chair’s seat should be comfortable and sized for the employee. If the seat is too small, it can restrict movement, provide inadequate support, restrict blood flow to the legs, and create irritation and pain. It should have a height adjustment to ensure the employee is aligned appropriately with the keyboard and monitor.
Armrests. If the chairs your employees are using have armrests, OSHA recommends you carefully consider several factors, including the amount of time the employee works at the computer, whether the employee is experiencing or has experienced a MSD or symptoms, and the employee’s design preference. In general, armrests should be adjustable, soft, and positioned to allow the shoulders to relax and the elbows to stay close to the body. If the armrests are made of hard materials or have sharp edges, the employee can irritate the nerves and blood vessels in the forearm, resulting in pain or tingling in the fingers, hand and arm. Armrests work well when employees are completing intensive or long-duration keying jobs.
- Computer monitors and video display terminals
- Correctly positioning the computer monitor (also in some guidelines described as a video display terminal or VDT) is essential to avoid excessive fatigue, eyestrain, neck and back pain, awkward postures and lighting glare.
To begin, consider the monitor’s placement in relation to the space on the desktop, location of the keyboard and position of the chair. Check to ensure there is enough desk space between the employee and the monitor. You’ll want to closely assess the viewing distance, angle and clarity. In addition, if the employee works frequently and refers to printed materials, place the monitor slightly to the side and keep the printed materials as close as possible.
Screens should have user controls for character brightness. Monitors that swivel horizontally and tilt or elevate vertically enable the employee to select the optimum viewing angle.
Viewing distance and legibility. The preferred viewing distance for monitors ranges between 18 and 24 inches. When measuring the distance, add the depth of the display itself. Some monitors are as much as 20 inches deep. Rather than increasing table depth, the easy way to make adjustments is to install a keyboard extender or tray underneath the desk. The cord that plugs into the monitor should be long enough to allow the employee to place the keyboard and monitor in a variety of positions.
Legibility is also a primary consideration in selecting a display screen. Legibility factors to be considered include symbol size and design, contrast and sharpness. Generally, a 15- to 20-inch monitor screen is sufficient.
Overall, the monitor should be:
- Placed at least 18 to 20 inches away – directly in front of the employee
- With the top line of the monitor’s screen at or below eye level
- Placed perpendicular to window
- No farther than 35 degrees to the left or right of the viewing line
Corrective lenses. If an employee uses bifocals, the monitor will be viewed through the bottom portion of the lenses. This can cause the employee to tilt the head, and muscles can become fatigued. In this case, the monitor can be lowered or tilted toward the employee, or the height of the chair can be raised at the same time adjustments are made to the position of the keyboard. After the adjustments are complete, be sure the employee’s feet still can reach the proper position on the floor. If not, you will need to provide a footrest.
Eye fatigue.When employees are concentrating on completing tasks, their eyes can become strained and tired. Long periods of time spent viewing the monitor can result in fatigue and dryness. To prevent these problems, employees should take occasional breaks, rest their eyes and/or blink several times.
Tilted monitors also can cause fatigue and eyestrain. The monitor should be positioned perpendicular to the employee’s line of sight, or with a tilt that is no more than 10 degrees to 20 degrees.
It’s best to isolate computer workstations from other electrical equipment. Electrostatic fields (equipment with electrostatic potentials in excess of +/- 500 volts) can result in display distortions. Monitors also should be periodically cleaned and dusted to avoid conditions that can reduce contrast and degrade viewing quality.
- Now that you have determined where the employee’s line of vision should be in relation to the monitor, place the keyboard directly in front of the employee and the monitor.
The keyboard, monitor and chair must work together to promote a neutral posture by lowering or raising the keyboard, monitor or chair to reduce the possibility of the wrists’ working at an awkward angle. The employee’s shoulders should be relaxed, with the elbows close to the body and the wrists straight and in line with the forearms. The employee also can elevate the front or back of the keyboard to achieve a neutral posture depending on the height of the keyboard.
Paying attention to these considerations keeps the wrists from being bent at an awkward angle, which can result in hand, wrist and shoulder stress and discomfort.
Left-handed use. Most keyboards have a 10-key keypad permanently attached to the right side of the keyboard. This can be awkward for left-handed employees – or if you want to allow employees to alternate hands while working. Left-handed keyboards are readily available with the10-key keypad affixed to the left side of the keyboard. There are also models with a detached keypad that allows employees to switch positions for either left or right-handed use. Programmable standalone keypads are an option, too.
When seeking the optimum setup for left-handed employees, look for a left-hand pointer/mouse that fits large or small hands. A device designed for either hand is also a good choice, particularly when you encourage employees to rest one hand by switching between hands.
Alternative keyboards. Today you have a choice of keyboards to help achieve neutral wrist postures. Alternative keyboards use different designs to attempt to change the user’s posture. These keyboards have been shown to promote neutral wrist posture; however, research does not provide conclusive evidence that alternative keyboards reduce the risk of discomfort or injury.
It’s important to evaluate whether the keyboard will affect the performance of the user. Some alternative keyboard designs make it difficult to see the keys. This can be particularly disruptive for employees who rely on key visibility (hunt-and-peck typists). Also, check whether the job requires use of the numeric keypad and specialized keys because some alternative keyboards eliminate or reconfigure these keys.
Accessories. Another option is a keyboard that allows the user to place the keypad and mouse on either side of the keyboard. If you have such equipment, ensure there is adequate space for multiple input devices on the keyboard’s resting surface. If the pointer/mouse is too close or too far away, the employee may assume an awkward posture or elbow angle, or lean the torso forward to reach the pointer/mouse. Working outside the ranges of neutral posture may cause musculoskeletal disorders of the elbows, shoulders, hands and wrists.
- Your selection and placement of a pointer/mouse are equally important factors in creating a safe computer workstation. As with keyboards, there are a variety of options beyond the conventional mouse. You’ll find trackballs, touch pads, fingertip joysticks and pucks among your choices.
Assess the placement of the pointer/mouse in relation to the desk, chair, keyboard tray and keyboard to prevent the employee from developing an awkward posture, particularly when working at the keyboard for prolonged periods. Place the pointer/mouse close to the keyboard to allow the employee to maintain a neutral posture. Improper placement of these workstation components increases the risk of the employee’s developing musculoskeletal disorders.
Device calibration. As if there weren’t enough variables to consider, now you must ensure that the device you have selected is set at the correct sensitivity for the employee. Whichever device is selected, it should feel comfortable and not require extra finger force or wrist movement to control how rapidly and where the pointer moves on the screen.
Make adjustments to lessen the risk of musculoskeletal injuries if the mouse:
- Is too sensitive and requires excessive and prolonged finger force
- Is not sensitive enough and requires large wrist movements to get the pointer around the screen
- Must be gripped tightly to maintain control
A trackball should be set so:
- It feels comfortable and adjustable
- It can be controlled with a light touch
- Its exposed surface area is at least 100 degrees and rotates in all directions
- The pointer is able to cover the full screen while the wrist maintains a straight, neutral posture
Check and adjust the sensitivity settings on the computer control panel.
- Wrist/palm supports
- Opinions vary, but in some cases you may be able to increase an employee’s comfort and reduce stress and risk from using a keyboard and mouse by the use of a wrist or palm rest.
Again, neutral posture is the goal. The employee should be able to perform keyboard tasks without increasing the angle at which the wrists are bent.
First, check to see if the employee’s wrists are in contact with a hard or sharp workstation component. If you decide a wrist or palm rest is needed, make sure it does not inhibit the motion of the wrist. The employee’s hands should be able to move freely and be elevated above the wrist or palm rest while entering data. When the hands are at rest, the pad should be in contact with the heel or palm of the hand instead of the wrist.
The wrist rest should be rather soft and rounded, and match the width, height and slope of the front edge of the keyboard. OSHA recommends it be at least 1.5 inches (3.8 cm) deep.
In all cases, you want to avoid increasing the angle of the wrist. This can increase contact stress and irritation of tendons, particularly when the employee’s tasks are highly repetitive or prolonged.
- Document holders
- While easy to overlook, the document holder plays a part in an ergonomic workstation. The position of the document holder must work in harmony with the position of the monitor, keyboard, pointer/mouse and chair. Minimizing the strain on the eyes, head, neck and shoulders will reduce the risk of headache, fatigue and eyestrain.
Position the documents in a holder as close to the employee and monitor as possible – and at the same height and distance – as the monitor. Task lighting is also important, because it ensures that the document does not create a glare on the monitor. The holder should be sturdy and stable.
- Placement of the phone and the kinds of devices connected to the phone are essential elements of a comfortable workstation.
Telephones should be positioned close enough to the monitor and keyboard to keep the employee from reaching repeatedly. The cord should be out of the way and untangled, and if a headset is used, it should have volume adjustments.
A Proactive Approach to Preventing Office Injuries
It’s important that you and your employees take a proactive approach to maintaining everyone’s physical health – on a daily basis. OSHA recommends that all employees receive general training on ergonomic issues.
Specific training can be built into initial safety and health training. In general, this training should include:
- The procedures for reporting work-related injuries and illnesses as required by OSHA
- The company’s ergonomics process
- How to identify ergonomic risk factors
- The policies and procedures for avoiding injury, including proper work practices and use of equipment
- How to recognize MSDs and their early indications
- The advantages of addressing early indications of MSDs before serious injury has developed
Because back injuries are so common, training programs should also cover the following:
- Health risks of improper lifting
- Body strengths and weaknesses – determining lifting capacity
- Physical factors that contribute to an accident and how to avoid the unexpected
- Safe postures and timing for smooth, easy lifting
- Lifting aids
- Recognizing body responses – warning signs – when lifting
You can more effectively address ergonomics at the initial stages of:
- Job transfer or task reallocation
- Development of new job descriptions
- Work processes reengineering
- Workstation layout and design
- Purchase of workstation components
- Purchase of new software
- Development of new software systems
To better manage the ergonomics process and ensure that all employees are following safe work practices, supervisors should receive the same training as the employees at risk of injury.
OSHA recommends that supervisors receive additional training on how to recognize hazardous work practices, correct such practices, ensure the ergonomics process is properly implemented and track ergonomic corrections.
Supervisors should also be instructed on how to determine if employees need additional training in safe work practices, and how to monitor workers on restricted duty.
Apply engineering controls whenever you make changes. For example, if you are redesigning your software system, evaluate how the changes will affect the employee at the keyboard. New systems may require additional work, such as using a mouse on drop-down menus and other navigation tools. That can put an extra strain on tendons and muscles. Work with your software developer to imbed keyboard shortcuts that eliminate the extra use of the mouse. It is less costly to build in good design than it is to redesign later.
Also look at the smart use of administrative controls. Here are a few actions you and your employees can take to minimize the risk of injury:
- Rotate tasks, whenever possible
- Minimize prolonged, uninterrupted data entry
- Take short pauses every hour (OSHA recommends taking a five-minute break from computer tasks every hour)
- Look away from the computer screen
- Stand up, stretch or walk
- Change working posture by adjusting chairs, for example, to another seating position to allow different muscle groups to provide support
- Ensure that there is enough space on the desktop so employees can use each hand alternately to perform mouse tasks, allowing the tendons and muscles of the free hand to rest
You can also work with your healthcare provider to identify management strategies and policies that support your proactive ergonomics program. Doing so will help you create an environment that encourages early intervention and sensible habits.