Alternatives to Sitting
Tensioning and relaxation of muscle tissue improves blood circulation, helping
to reduce fatigue. Operators should
look for opportunities to periodically stand up and move around.
Consider Advanced Task Seating
A number of manufacturers offer more advanced chairs that may be preferable to a traditional task chair. Consult
Environmental Health and Safety for further information.
Recommended Features
The task chair should have an adjustable seat pan height, an adjustable backrest angle, an adjustable lumbar
support, an adjustable seat pan tilt, and a forward-tilting seat pan. This will support
the operator in the different sitting postures, and it will allow them to frequently change their posture
throughout the day, helping them to avoid fatigue, discomfort, and back pain. Additional recommended features that
are found on most modern task chairs include a waterfall front and a five star base.
Task Chair Mechanisms
"Traditional task seating," as discussed throughout this site, generally refers to task chairs that have a multi function
control. This is a good staring point because it is a common design that supports the features listed above. It is
important to recognize that a number of manufacturers have incorporated significantly different designs which also
provide effective support.
Proper Fit
To ensure that the task chair is a good fit for an operator, it should include the recommended features and
have the following characteristics:
- An effective of lumbar support. The contour of the backrest should fit the curvature of the lower back to help
prevent flattening of the lumbar spine. The backrest should be adjustable to allow the proper placement of the
lumbar support
- The seat pan height range of the chair should be sufficient to support the operator in the declined, reclined,
and upright postures.
- The seat pan depth should not exceed, nor be more than two inches shorter than the popliteal-buttock
length of the operator. If the seat pan is too deep, the chair may increase pressure behind the knee
and decrease the effectiveness of the back support. If the seat pan is too shallow, it will increase pressure
on the operator's legs.
Seat Pan Height Range
Fig. 1. Task Chair Seat Pan Height Range
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When selecting a traditional task chair, the standing knee height is often used
to determine the seat pan height range of the chair. The standing knee height is the distance from the floor
to the upper edge of the operator's knee cap. This measurement is taken with the operator wearing their shoes.
With the chair in the forward tilt configuration, the center of the seat pan should reach the standing
knee height of the operator. It is important that the chair will support the operator at this height, so
one should take compression of the pneumatic cylinder and the seat cushion into account. If the upper seat pan
height range supports the operator in the declined posture, the chair should be sufficient to support the
operator in the upright and reclined postures as well.
For individuals with a standing knee height of less than twenty-one inches, in this respect, many of the
standard task chairs will work. If the standing knee height is greater than twenty-one inches, more care is
usually needed for task chair selection; a chair with a larger pneumatic cylinder may be needed to increase
the seat pan height.
For chairs that tilt at the center of the seat pan, such as ones with synchro, multi function, and tri-action
controls, the seat pan height range should generally come up to the standing knee height of the operator. If the
chair tilts from the front of the seat pan, or the chair does not rely on the full declined posture to keep the
operator comfortable, the seat pan may not need to raise as high.
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Armrests
The armrests of a task chair should be taken into consideration as they can significantly help or
hinder the operator. The armrests should be adjustable and provide support with the operator comfortably
relaxed at the shoulder. If the armrests
lead to awkward postures or interfere with positioning the chair with respect to the video display
terminal, It may be preferable to remove the armrests altogether.
Flexibility and Additional Features
Adjustable armrests and seat pan sliders will increase the flexibility of a chair, allowing it to accommodate
a greater number of people. More advanced features, such as
memory foams, inflatable lumbar support, bisynchronous tilt, special arm options, and hip abduction are
available; they aren't recommended by Environmental Health & Safety unless they are deemed necessary on
a case by case level. Selecting an appropriate task chair can be complex; if you have questions, you are
welcome to contact Environmental Health & Safety for assistance.
