If new chairs are to be purchased, be sure to take the time to make an informed decision. The individual(s) who will be using the chair(s) should be involved in the decision process and should be offered some choice. Also, it is important to have a trial period of about one week for any chairs which are being considered. Try the chair at the work station(s) where it would be used if purchased. A chair is an important investment and it should not be selected based on sitting in it for a couple of minutes. Contact the Office of Environmental Health and Safety for further information and recommendations.
Important Chair Features
How to Adjust the Chair Properly
Important Chair Features
- Selecting an office chair may appear to be overwhelming at first since there are many different types and models of chairs available, each having different features and claiming to be "ergonomic". To assist in the selection/assessment process and to help put all of the features in perspective, this section discusses desirable chair features.
- In evaluating the appropriateness of any chair, the single most important consideration is that as long as the individual is comfortable and able to sit and work properly at his/her workstation, the chair is considered "ergonomic" for that individual.
Features of a Good Chair
- Chair users need to know what features are present on a chair and how to adjust and use these features to maximize comfort. If you are not familiar with the features of your chair, take some time to figure out the levers and knobs on your chair. It is time well spent and you could find yourself sitting much more comfortably.
1. Backrest Adjustment
Backrest adjustments can help prevent or alleviate discomfort associated with sitting for extended periods of time.
Backrest Height - Allows the user to find the backrest height which provides maximum support for the lumbar portion of the lower back (the inward curved portion). This height will vary from person to person -- for example, a person who is six feet tall would tend to position the backrest higher than a person who is five feet tall.
Backrest Tilt (incline/recline)- This feature allows an individual to adopt different postures while still maintaining good support for the lower back - many people find a slight reclining posture is comfortable for longterm sitting and keyboarding. This feature should be adjusted throughout the day.
Horizontal Backrest Movement (i.e. move backrest forward or backward) - This feature is not the same as the tilt feature above. If, for example, the chair user found that the seat pan on the chair is too deep (i.e. there is no space between the back of the knee and the front of the seat pan), then moving the whole backrest forward may help to alleviate discomfort without compromising back support. Conversely, if someone needs an extra deep seatpan, some manufacturers offer a "slider" mechanism to allow the seatpan to move forward (and provide a few extra inches) but maintain back support.
2. Chair Height Adjustment
All office chairs must have height adjustment. The most common height adjustment mechanism is a pneumatic lever that permits the user to readily adjust the height from a sitting position. Older office chairs require the user to place a foot on the base of the chair and spin the seat to raise or lower the height
3. Seat Pan Characteristics
Look for the following characteristics in a chair's seat pan:
Rounded or "Waterfall" Edge at the front of the seat pan - This helps prevent uncomfortable pressure at the back of the legs and behind the knees.
Adequate Seat Pan Depth - There should be a space, about the width of a clenched fist, between the back of the knee and the front of the chair. This helps maintain proper circulation for the legs.
Adequate Seat Pan Width - For optimal comfort, the seat should extend at least 1" from the hips, on either side.
Seat Pan Tilt - This allows posture changes and can alleviate pressure on the back of the thighs.
Seat Cushion Padding and Design - Look for minimal contouring and avoid coverings with buttons and prominent seams since these can create uncomfortable, localized pressure points.
Fabric - Look for durable, permeable material that "breathes" and dissipates moisture and heat.
Armrests should not interfere with the task and should not impede someone trying to get close to the work surface - if a wide range of arm movement is required, armrests are not recommended. Generally, armrests are not needed for "active" keyboarding but armrests can provide support for the arms when performing other tasks such as reading, editing or proofing material on a desk or VDT. If armrests are desired, look for adjustable height, adjustable width, adequate padding and, as mentioned above, the length does not impede the user's approach to the work surface.5. Stability
For stability and mobility, an office chair should have a five-pronged base with appropriate casters (hard casters for surfaces such as carpeting, soft casters for hard surfaces). Four-pronged chair bases are less stable and prone to tipping backwards or sideways when the user leans back or to the side.
How to Adjust the Chair CorrectlyHeight Adjustment
- Adjust the height of the chair such that the feet are able to rest comfortably on the floor and the thighs are roughly horizontal. The angle between the thighs and calves should be greater than 90o. If the angle is less than 90o, the user tends to tuck the lower legs and feet back to rest on the chair base and this can impede blood circulation. If the feet cannot rest flat on the floor, a footrest is required.
- If the chair has a pneumatic lever, height adjustment can be done from a seated position. For older-style office chairs, in order to raise or lower the chair height, the user stands in front of the chair and rotates the seat clockwise or counterclockwise. A general rule-of-thumb for finding the appropriate height for an individual's chair is that the height of the seat pan is just below the height of the user's knee-caps.
- Avoid situations where the feet "dangle" as this compresses the tissue on the back of the thighs and behind the knees and can lead to aches and discomfort in the lower legs. There should be a space, about the width of a clenched fist, between the back of the knees and the front of the chair. If not, lower the chair slightly or, if the chair has the ability, tilt the seat pan forward slightly to alleviate the pressure. A footrest may be required. The waterfall edge on most office chairs today also helps prevent uncomfortable pressure behind the knees.
- At the workstation, the chair should be adjusted to accommodate the work surface. For example, if an individual "hunches" or raises the shoulders in order to work at a desk or keyboard, the chair height should be raised, even it means that a footrest is required.
- Adjust the backrest so that it supports the lumbar area of the lower back (the inward curved portion). This is probably the most important contact point.
- For most situations, but particularly where an individual's job task(s) require extended periods of sitting, the backrest needs to have adjustable height so that the user can get maximum support for the lower back. Some backrests can also be tilted or moved forward or backwards. These features can be especially useful if the seat pan of the chair is a bit deep for the individual using it. For example, moving the backrest forward can provide more space between the front of the chair and the back of the knees and provide support for the lower back at the same time. Do not sit for extended periods of time without back support! Adjust the chair or the workstation instead -- this is the concept of accommodating the person, not the task.