You Asked for It
April 2002

"Is there a safety concern with carpet casters on chair mats?"

B.Weir
Occupational Health Nurse

Most chairs come equipped with hard casters that are designed for use with low pile carpeting. Many work places add chair mats to assist workers who must move between areas of the work station (i.e. between the computer and the paperwork areas). This is invaluable for shorter workers who can't propel their bodies with their legs because their feet don't touch the floor. I have only encountered a couple of concerns with this practice.

In one situation, the floor was sloped in the area of the desk, so that the chair tended to drift away easily. Seeing as leveling the floor wasn't an option, removing the chair mat could increase the resistance enough to keep the chair in place. Some European chairs come standard with casters that increase resistance when the chair is unloaded - my old Ikea chair has these, which is fine unless I want to move my chair to another room. If the chair drifted while the person was in it, another option would be to use what I call "weight locking" casters.

The other situation happened when a fellow stood up and the backs of his legs gently bumped the chair. It was enough to move the chair about 12". When he went to sit down, the chair was not where he expected and he landed on the floor. In this situation, there wasn't enough resistance / friction between the casters and the floor because of the chair mat. Removing the chair mat is one choice. The other alternative is to switch to casters intended for hard surfaces. These have a rubber surface that attenuate noise and give a bit more grip on hard surfaces such as hardwood, linoleum and tile.

I often recommend the installation of chair mats when workers have to move between work areas. If the carpet is new or more deep piled than most older industrial carpets, the chair mat is invaluable to reduce resistance. This is particularly important if the workers cannot use their legs and feet to assist their movement. Care should be exercised to ensure that there is still enough friction to keep the chair from sliding away spontaneously.

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