The main criteria for office chairs is that they should be easily adjustable. A pneumatic adjustment lever or button is the most standard way of operating the gas cylinder to adjust the height of the seat through a distance of approx 480mm – 630mm which should accommodate most users. With the office chair passing through these heights this should allow for the user to have their feet flat on the floor, thighs horizontal and their arms level with the desktop.
Seat width & depth
The width for an office chair varies but is usually around 520mm. The depth should be sufficient to allow the users back to be in contact with the backrest, whilst leaving approx 50mm – 100mm gap between the back of the knees and the front edge of the seat. The front of the seat should also have a pronounced curve which is sometimes called a waterfall edge to relieve pressure from behind the knees. Some office chairs can also be specified with a seat depth adjustment to allow for users with longer legs.
The lower part of our spine has an inward curve that should be supported when sitting for long periods of time. Most office chairs have some form of basic lumbar support for this region of the back, even if it is just shaped foam beneath the upholstery. Some chairs have a pump-up lumbar bag inserted behind the upholstery which is easily adjustable. Mesh back chairs tend to have a lumbar bar (A shaped piece of rubber or plastic) that can be adjusted in height and depth. Sitting for long periods of time without any kind of lumbar support leads to slouching and bad posture.
The backrest of the office chair should ideally be separate to the seat to allow the back to be adjusted independently. This gives the user a fully adjustable chair where the back height can be changed to position the lumbar support in the correct area and the angle to be changed in relation to the seat. The back width can vary depending on design but is generally a similar width to the seat.
If the office chair has the back attached to the seat then the chair should have a tilting mechanism that can be locked when the ideal position has been reached. This style of mechanism should also be accompanied by a tension control to adjust the speed that the back tilts with.
The seat and back of an office chair can be upholstered in a number of different ways, each having benefits over the other. Some users will prefer a fabric upholstered foam seat & back, others a nylon mesh seat & back or a combination between the two.
The fabric upholstered foam is the more traditional approach and allows the user to choose from a vast multitude of fabric colours and styles. The mesh is extremely flexible, moulds to the users shape and allows the users body heat to disperse out through the material. The mesh chairs are usually available in a choice of colours. Some more contemporary chairs have moulded plastic backs that offer a more rigid support.
Ideally the arm rests on an office chair should be adjustable, not only in height but in width and depth also. These adjustments will allow the users arms to rest lightly at a comfortable height. The arms should be adjusted so that the users elbows can rest on them whilst typing or using a mouse.
All office chairs that are to be used for any period of time should be on a swivel mechanism to allow the user to rotate and reach different areas of their workspace without straining.