ERGONOMICS UNIT

AN ASSESSMENT OF

Liberty pedestal armchair

manufactured by

Humanscale

for compliance with BS EN ISO 9241: Part 5 (1999)

Date 6th June 2007 Ref 0107/HUMA/01E/GS Reported by Gina Sands FIRA International Ltd Maxwell Road Stevenage SG1 2EW

0107/HUMA/01E/GS

3 of 14

DIMENSIONAL FIT/ADJUSTABILITY The dimensions of the Liberty chair were checked against the BS EN 1335 Part 1. Full details are given in a separate report (ref 0107/HUMA/01/GS). All of the users found that there was enough adjustment in the seat depth so that they could sit back in the seat without the front edge of the seat digging into the back of their knees. However one user felt the seat depth was too short. This was the tall (96th percentile) male user. The users also reported that the width of the seat pad was acceptable, with larger users finding that it was wide enough for them. The height of the seat could be adjusted over a large range, meaning that users could easily adjust it to suit both their height, and the height of the desk at which the worked. There was no provision to adjust the angle of the seat pad independently of the backrest, and some of the users reported that the seat tilted down too far at the front, however most users had no problems in this area. The tilt of the backrest could not be locked and was left to move freely, therefore this did not cater for users who preferred to have the backrest fixed. Most of the users liked the free-floating backrest and found that the tension adjusted well for their body weight. However two users commented that the tilt of the backrest was slightly too far back. The height of the backrest could not be changed, yet most users found that the height of the lumbar support suited them. They felt that the backrest deformed sufficiently to support their lumbar area. This was supported by the separate investigation of users spine when standing, when sitting upright and reclined on the Liberty chair. It was found that the shape of spine of all users was in lordosis and in some cases it was better when sitting on the Liberty chair than standing. For further details refer to the Appendix to this report. The height of the armrests above the seat pad could be adjusted and there was enough range to suit users of different statures. However, a couple of users with curved desks commented that the armrests sometimes prevented them from getting close to their desks, as they are too high or too far forward. However, they said by lowering the arms they were able to get close to their desk and used the desk surface for supporting their arms. CONTROLS / REACH The controls were located in areas that allowed the user to easily reach and adjust the chair whilst sitting on the chair. The users did not find any aspects of the chair that could have caused injury and the controls were not operated accidentally or inadvertently.

0107/HUMA/01E/GS

4 of 14

EASE OF USE Each of the controls was located in the place the users most associated with each function, this helped new users along with the text on the controls to adjust the chair to suit them correctly. This was also a very easy chair to adjust, as there were only two adjustments, this chair would be particularly useful in hot-desking situations where users are changing chairs a lot. INSTRUCTION LEAFLET There were no instructions supplied with this chair. However, users had no difficulty in understanding how to adjust the chair once it was explained to them. COMFORT Nearly all the users found this chair comfortable, with most reporting no aches and pain and most feeling increased comfort during the user trial. However one user found the Liberty chair uncomfortable and reported some discomfort in her neck, back and thighs. This user does have a long-term chronic back problem and so her comments were not consistent with other users in the trials. The Liberty chair achieved an average score of 7.44 out of 10, with most users giving very high scores and one user (chronic back pain sufferer) giving it 3 out of 10. CONCLUSIONS In conclusion most users found this chair comfortable to sit on for long periods of time. The Liberty chair has only two adjustments, yet most of the users found that the chair fitted them very well. Tall users may find the seat depth not to be as deep as they wish. The armrests were suitable for most users, but for some users they did restrict getting close to curved and L-shaped desks. However as the armrest can be lowered so far down that the armrests go under the desk overcomes this eventuality. The tension of the chair automatically adjusts very well to suit different weight users and the small amounts of adjustment needed when changing user makes this chair particularly desirable for hot-desking. The Liberty chair achieved an average score of 7.44 out of 10, and therefore was very much liked by most of the users.

0107/HUMA/01E/GS

5 of 14

APPENDIX Virtual Lumbar support of Liberty chair

0107/HUMA/01E/GS

6 of 14

Virtual Lumbar support of Liberty chair It is clear that the Liberty chair does not have a physically moving lumbar support. The back is shaped s that there is a lumbar point. Its height can be measured as described in the BS EN 1335 Part 1. This would appear to make the chair to have a fixed height lumbar support. In real life use the chair behaves as if it has a moving height adjustable lumbar support. During the user trials carried out at FIRA most users found that the chair provided sufficient support for their lower back and they felt no aches or pain. They found the chair to be very comfortable. Users varied from 1st percentile female to 96th percentile male. It is understood that the information Humanscale has about the experiences of users of Liberty chairs support this finding. So how is this possible? As the users lean against the backrest, semi loose mesh which is sewn in three vertical patches deforms and at the same time becomes somewhat firm to replicate the users back. The shape of the backrest and the design of the patches together with the characteristics of the mesh do not appear to allow users to slouch but maintain a good lordosis. This happens at the appropriate height for each individual, so it does not appear to be human size specific. It is not possible to measure the virtually moving lumbar support and lordosis of the back y using the traditional methods prescribed in standards such as BS EN 1335 Part 1. So it was decided to trace the shape of users spines when they are standing (Posture 1) when sitting in the Liberty chair in an upright posture (Posture 2) and finally when reclining in the Liberty chair (Posture 3). The comparison of such traces would show if the spine was in lordosis around the lumbar area or users were slouching. A spinal mouse was use to trace users spines. As the back rest of the Liberty chair was mesh it was very easy to trace from the back without having to cut the central section of the chair. The following pages show the traces of spines of 8 users. Trace 1 is for the standing posture which should show the most natural lordosis of the back at the lumbar. Trace 2 is the shape of the spine in an upright sitting posture and the Trace 3 is the shape of the spine when sitting in a reclined posture. As can be seen from these charts, for most people shape of the spine improves as they go from standing to sitting and then reclining. They also show that the chair does not permit users to slouch (ie having C shaped spines when sitting and reclining). No subject appears to sit in a slouched posture. Therefore given the results of the spine traces and feedback from the users during the user trials, it can be concluded that the backrest of the Liberty chair automatically deforms to provide a self adjusting lumbar support for a very wide range of users. Levent Çaglar, Senior Consultant Ergonomist

0107/HUMA/01E/GS

7 of 14

0107/HUMA/01E/GS

8 of 14

0107/HUMA/01E/GS

9 of 14

0107/HUMA/01E/GS

10 of 14

0107/HUMA/01E/GS

11 of 14

0107/HUMA/01E/GS

12 of 14

0107/HUMA/01E/GS

13 of 14

0107/HUMA/01E/GS

14 of 14