Workstation Ergonomics Part 2
By Don Williams
When setting up the seated work station correct chair and desk choice is critical
When selecting a chair and desk, there are a number of essential features which should be addressed.
Seat base - stable 5 star base which swivels and is on wheels or castors (most modern chairs will have this).
Seat pan - height adjustable with a range suited to the desk. Optimally, the seat pan should be tilt adjustable.
Back rest - should be stable and independently adjustable for height and angle
Lumbar support - integrated into the backrest. Should be adjustable so that it sits in the small of your back.
Armrests - not recommended as they are likely to interfere with the ability to move the chair close enough to the desk. Some chairs will have armrests which drop down to leg height. These are uncommon and expensive.
(Diagram located on the bottom right of this page.)
The goal of the chair adjustment and height is to have you sitting comfortably in front of your desk with the shoulders and elbows relaxed, not to much pressure on the backs of the legs, looking straight ahead at the screen. To get a good rough chair height, stand in front and facing chair, adjust the height so that the front of the seat pan is just below your knee.
Next, sit on the chair and keep your feet flat on the floor. The hips should be slightly higher than the knees.
Push your hips as far back as they can go in the chair Grasp the back of your legs between the seat-pan and the back of your knee. Wiggle back or forward until you can just fit your hand comfortably between the seat - pan and the back of your knee.
THE BACKREST IS THERE TO SUPPORT YOUR BACK, MAKE SURE YOU USE IT!
Adjust the backrest so that the lumbar support fits into the small of your back. The centre of the lumbar lordosis must be supported to ensure good posture and alignment of the neck and shoulder. Lean against the backrest until your back is at least 90° reclined angle to your legs, although a slightly more open posture is better, up to 110° maximum. If your armrests are in the way, remove them. Tilting the seat-pan a fraction downward helps give your body a slightly more open posture and relieves any pressure you might have under your legs.The end result should see a straight line through the ears, shoulders and hips, with little pressure on the neck and shoulders.
Height adjustable desks are the preferred option. Height to the top of the work surface should be between 580mm and 730 mm above floor level.
For a fixed height desk, between 680mm and 720mm.
Minimum work surface area - 1500mm X 900mm with maximum bench thickness of 25mm.
The leg space should be 800mm wide X 550mm deep X 580mm high minimum.
No sharp edges, rough surfaces or protrusions.
Desk surface should be continuous, mouse and keyboard at the same level for effective use.
The viewing distance to work and monitor should be between 350mm and 780 mm. As a rough guide, with monitors, when viewing videos/movies a comfortable range is that the viewing distance should be approximately twice the dimension of a screen, so a 23 inch monitor should be around 46 inches away, however, with focused work, the effective distance is usually around 150% (so in the example of a 23 inch monitor, the eyes/face should be somewhere around 35 inches from the screen).
How to Sit at Your Desk
It is important to remember that the majority of the time, you should be looking and working straight in front of your body and head, looking directly at your monitor, rather than having it off to the side, causing you to turn your head all day. It is best to have soft light behind the monitor and no hard lights shining directly on the screen.
Approach your desk and place the keyboard directly in front of you, but give yourself enough space between the keyboard and the edge of the desk so that you can rest the pad of your thumb lightly on the desk for a moment when you are not typing. Never rest your wrist on the on the desk. ( The mouse should be to the side of the keyboard, rather than out in front which will cause you to stretch and reach out, this commonly causes slouching posture as the day progresses).
Keeping your wrists straight, observe the angle of your forearm. If it is parallel to the floor, or slightly more open, up to a 100° angle at the elbow joint, then move on to Step 4. If not, then proceed to 3b.
Chin slightly tucked in and looking straight at the middle to top of the screen (as if nodding yes).Try to ensure that the ears, shoulders and hips are in a straight, vertical line.
Taller people may find that the drop keyboard mechanism interferes with the top of their legs. If this is the case, arrange to have the mechanism removed and the keyboard fixed, but make sure that the mechanism remains readily accessible because the next person to use the desk after you may need to have it refitted.
If you find that your elbow joint is open more than 100° call us for further assistance. If your elbow joint is less than 90°, then follow the flow chart below.