DEA 651 Graduate Project: Fall 1999
The recommendations listed below are intended to educate the Department of Planning and Development on general guidelines for a good ergonomic workstation arrangement.† The recommendations are based on the problems that were identified through the three data collection methods. These guidelines alone will not be able to capture all the interactions and complexities of their work environment, but they will be a good start in providing a base of knowledge about general ergonomic problems and their solutions.
As the following information is reviewed, there are two points to keep in mind. One point is to understand that all body parts are linked together, and consequently a modification in one area may have significant effects in another. For example, lowering the seat height so that someone may comfortably rest his feet on the floor may force a stressful upper body posture if the monitor position or the keyboard height is not adjusted in concert. Also, it is important to note that there is no ďperfect posture for all timeĒ, and that a dynamic posture (frequent changes in posture) is a good way to reduce stress and redistribute pressure related to long duration static posture.
The implementation of these recommendations will help improve the comfort, productivity and quality, as well as the health and safety of the employees of the Department of Planning and Development.
Poor sitting posture can result in lower back injuries and contribute to the poor positioning of other parts of the body, such as the arms, wrists, and legs.† In a seated position, the trunk of the body should form an angle with the base of the chair that is between 100 and 130 degrees.† Both lumbar disc pressure and back muscle activity are lowest at this angle of recline.†
In many of the workstations, this angle was less than 90 degrees and the upper back was not in contact with the back of the chair.† The back should be in contact with the chair so that the weight of the body is evenly distributed throughout the chair. Also, the seat pan of the chair should be angled slightly downward.† This allows the user to sit comfortably and relieve stress on the ischial tuberosities located at the base of the spine.
In some instances, a new chair should be provided for the user. There are many features that constitute an ergonomic chair. Some of the most important of these are upper body and lumbar support; adjustable recline angle between 100 and 130 degrees; adjustable seat height;† and adjustable seat pan angle.† In other cases, the workstation configuration should be changed so that the user can perform his tasks while leaning against the back of the chair.†
Many of the employees were observed leaning forward and bending the neck. The weight of the head was not properly supported which could cause discomfort and injury to the neck and shoulders. This poor neck posture is often caused by improper monitor placement.† If the monitor is placed to low, the user will have to tilt his head downward to view the computer screen.††
Neck discomfort can also be a result of the employee constantly turning the neck and head to read documents while entering data on the computer.† This constant repetition of movements can place severe stress on the neck and shoulder muscles.
The neck and head position can be corrected by adjusting the height of the computer monitor.† The monitor should be in a position so that the userís line of sight is one to two inches below the top of the screen (not the top of the monitor).† This will reduce the userís need to lean forward and tilt his head down thus reducing the stress placed on the muscles in the neck and shoulders.
Neck posture can also be improved through the addition of a freestanding document holder.† This device will allow the user to position documents close to the computer monitor and reduce the movement of the head and neck while working on the computer.† Although some workstations in the facility were equipped with document holders, they only allowed the user to view one sheet of paper at a time.† The employees should be provided with document holders capable of supporting larger documents.
Some employees were observed sitting with their legs not touching the floor or crossed beneath the chair.† This position can place a high amount of stress on the popliteal arch that runs through the underside of the thigh and knee and can result in serious discomfort and injury.†
There should also be room under the desk to extend the legs and feet comfortably.† Many workstations used the space beneath the desk for storage of files, printer paper and other office supplies.† This has caused the employees to tuck their legs and feet under the chair, which could eventually lead to the problems mentioned above.
The userís chair should be height adjustable so that the feet are firmly on the floor in a position slightly in front of the knees.† This posture will ensure that the feet and chair are comfortably supporting the weight of the legs.
It is also important to remove all stored items from beneath the desk to allow for sufficient room for the userís legs.† Proper leg position will also help correct poor upper body posture.
The keyboards at many of the workstations were at the incorrect height for the user.† The result was ulnar deviation and flexion of the wrists.† The use of the hands and wrists in these deviated postures places a large amount of stress on the tendons and nerves in the hands and wrists.†
Improper keyboard position can lead to such cumulative trauma disorders as tendonitis and carpal tunnel syndrome. These disorders are caused by injury to the tendons and the median nerve at the point where they pass through the carpel tunnel of the wrist.
In all of the workstations, the mouse was placed too far to the right of the user.† This caused a large amount of stress on the arm, shoulder and neck. As the user reached to the side to grasp the mouse, the arm became abducted, placing significant strain on the shoulders and neck.†
Most of the problems associated with the keyboard and mouse use can be solved with the installation of an articulating keyboard and mouse tray at each workstation. This system should be height adjustable, allow the user to slightly tilt the keyboard tray away from the body for better wrist posture (negative tilt), and allow the user to use the mouse with his upper arms relaxed and as close to his body as possible.
Use of this system will ensure that the user can reach the keyboard and the mouse with his wrists as flat as possible (not bent up or down) and straight (not bent to the left or right) and with his arm and shoulders in a more neutral position.† Additionally, this system will help facilitate the creation of an elbow angle (the angle between the inner surface of the upper arm and the forearm) that is at or greater than 90 degrees to avoid nerve compression at the elbow.
If an alphanumeric keyboard is used, the user should make sure that the he is centered on the keyboard. Most modern keyboards are asymmetrical in design (the alpha numeric keyboard is to the left and a numeric keyboard to the right). If the outer edges of the keyboard are used as landmarks for centering the keyboard and monitor, the userís hands will de deviated because the alphanumeric keys will be to the left of the userís midline. Therefore, the keyboard should be moved so that the alphanumeric keys are centered with the midline of the user.
It is also possible to use a keyboard without a numeric keypad in order to position the mouse closer to the user.† This is only recommended if the user does not need the numeric keypad for daily tasks.
Incorrect desk height was a problem found at many of the workstations.† Desk height refers to the desk that the computer is on as well as any desk used for writing and other activities.† The desk should be at the correct height to allow the user to position his hands, wrists and arms in a neutral position.† Improper desk height can cause arm abduction and flexion or extension of the wrists.† It is also important that all work surfaces used by the employee are the same height.† This will allow the chair to be adjusted at a height that will promote proper sitting posture at both desks.
The recommended height for a desk used in a computer workstation setting is 28 inches.† This height will allow the user to comfortably perform activities such as reading and writing on the worksurface.† This height is also appropriate for a computer workstation with an articulating keyboard and mouse tray.
Screen glare was a significant problem for many of the users in this facility.† This glare can cause eyestrain and headaches.† To reduce glare, the monitor should be placed so that the screen is flat (not tilted) and directly in front of the user.† Tilting the screen up or down can increase the glare on the screen and can also contribute to improper head and neck posture.
Placing an optical glass filter over the monitor can reduce screen glare.† This type of filter will reduce reflections from nearby windows and overhead lights.† However, it is important to note that the brightness of the monitor must be increased when a filter is used.
Glare can also be reduced by keeping the monitor flat and facing the user.† If the monitor is tilted up or down, it will reflect light from surrounding windows and lights and increase the amount of glare on the screen.