We are having some debate on the safety of 4 castor leg chairs in our organization. There are older reclining wood chairs with 4 castor legs that people do not want to substitute for a chair with 5 castor base, citing that they are sufficiently stable and the legs are fairly long. These are not used at a computer workstation, but rather for short periods of time at a regular table in an industrial setting. Every reference I have indicates an office chair should have a 5 castor base for stability except one that says if 4 legs are present, they should be 15% longer than those of a 5 castor leg base. Short of buying a testing standard and actually testing the chairs, can anyone point me to a reference that indicates that a general occasional use reclining chair with castors requires a 5 arm base?
Chairs with a four-point star base are not safe because they tip when people lean in to them. Five-point bases are much more stable because they prevent that backward tilt. The same as seeing someone tilt back their dining room chair on the rear legs. It’s just not as safe as a five-point star base. No exceptions. You might be able to buy replacement five-point star bases for the chairs and put them on the pre-existing chairs if the people involved are emotionally attached to the chair and there are no other serious ergonomic issues with it. Remember also that caster types differ depending on flooring surface.
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