HUMAN FACTORS

WORKSPACE

Physical design of a workspace includes:

working out how much space is needed,

positioning of furniture, tools, equipment and any other items needed to perform the tasks, in respect to posture, access, clearance, reach and vision of the user.

A poorly designed workspace / a bad arrangement of furniture or equipment, may result in:

injuries and strains due to adoption of uncomfortable working postures,

less 'spare' capacity to deal with unexpected events or emergencies,

the increased possibility of errors or accidents, and inefficiency (the dinner takes longer to cook if your kitchen is badly organised!)

Workspace Factors

You should find the answers to the following questions when designing workspaces:

What type of task will be carried out and what specific actions are to be used to complete the task?

Will the potential users of the workspace (your user population) be seated or standing?

What postures will the users have to adopt? What are the relevant body dimensions of the users?

(use of anthropometric tables). Do you need to design using minimum, average or maximum dimensions?

How far can the users reach, horizontally and vertically?

What are the visual aspects of the task?

It may also be necessary to consider factors such as how long the task will take, the environmental conditions that the task is performed under (lighting, temperature, noise levels), and the experience that the users have of performing the task.

Body dimensions Using anthropometric data

People vary both in their body dimensions and proportions. Body size varies with: age, gender, nationality, ethnic origin, occupation (as people of a certain size are often

more suited to certain occupations, for example, truck drivers tend to be larger males),

body type (muscular, thin etc) and disability.

It is critical that when you are designing for a specific group, you must use workspace data that is specific to them. In general, this tends to be a broad spectrum of users.

A workspace may be designed to be used by a restricted group of users, for example, drivers of fire fighting vehicles (mainly male, 30-50 years old),

or be designed to be used by the majority of the adult population, for example, drivers of private cars (both male and female, 17-70+ years old).

Allowances should also be made if special clothing or personal protective equipment, such a hard hats or gloves, needs to be worn. These may restrict motion and reach in certain directions, or require greater clearances, for example, people who need to wear boots will need more foot room.

Designing for the 'average'

It is important to realise that there is no 'average' individual.

You may be 'average' for one or two body dimensions, say arm length and height, but generally that is all.

Designing for the average user is often seen as bad design, as it only accommodates 50% of a population, however, there are a few cases where it is appropriate:

Designing for the extreme or with maximum adjustability may not be practical, and designing for the 50th percentile may be the only way to reach a compromise with other design factors, for example, cost, time and space.

An example is the counter height on a supermarket checkout. This is designed for the 50th% percentile because it is important for it not to be too high OR too low, and because adjustability is not feasible.

Designing for adjustability

Wherever possible, it is best to design adjustability into any workspace. An example is the interior of a car, where the driver's seat has height adjustment, and forwards and backwards adjustment, to comfortably fit as many users as possible.

For an adjustable range, we generally use:- 5th percentile female for the lower limit,- 95th percentile male for the upper limit.

Designing for extreme individuals

In some situations a specific dimension of a workspace layout becomes the limiting factor that may restrict the use of the workspace for some people. This limiting factor can either be designed for the minimum or maximum value for a population, depending upon what is required.

You should design for the minimum population when the minimum value (lowest) of the feature has to accommodate all users. For example, controls should be within reach of the smallest operator.

You should design for the maximum population when the maximum value (highest) of a feature has to accommodate all users. For example, the height of a doorway should allow all users to pass through without stooping or banging their head!

‘Workspace Envelope'

This is a 3-dimensional space within which you carry out physical work activities when you are at a fixed location.

The limits of the envelope are determined by your functional arm reach which, in turn, is influenced by the direction of reach and the nature of the task being performed.

Most of the things that you need to use to carry out your tasks should be arranged within this area.

Workspace envelopes should be designed for the 5th percentile of the user population, which means that 95% of users will be able to reach everything placed within the envelope.

Seated workspace Standing workspace In general, the maximum work area is the area within

comfortable reach of your extended arm, while the normal work area is within the limits of a

comfortable sweeping movement of your arm, with your elbow bent at a right angle or less.

You should also consider any potential restraint caused by clothing that you might have to wear, as well as personal factors such as age, gender

(women have greater

flexibility than men), and

any disabilities.

The type of task being performed also affects the boundary of the workspace envelope. For tasks that require the activation of a switch, it is common to use anthropometric measurements from the fingertip reach of the users to set the envelope boundary.

However, where a grasping action is involved, the reach of the user is reduced as your fist has to be clenched.

The limit of the workspace envelope for a standing user can be seen as the space in which an object can be reached and gripped comfortably, when you are standing up straight.

Your arms and hands are most powerful when your elbows are close to your sides and bent at right angles or more, that is, extended slightly. The work surface should allow this kind of posture for manual work requiring strength.

Some general principles for seated work: Working with relaxed upper arms and elbows at

approximately 90° provides comfort and helps maintain straight wrists, which reduces the strain of repetitive tasks.

Adjustable height work surfaces allow each user to fit the work surface to their own needs. If this is not possible, fix the work surface height to be at a level that places the working item, for example, a keyboard, at elbow height.

Make sure that there is adequate clearance for your thighs under the work surface.

Small users whose feet do not touch the floor when seated should have a footrest.

For fine work, requiring better visibility, the work surface can be raised, but elbow support must be provided.

Some general principles for standing work: For work that requires the application of

force from the shoulder and back muscles, the work surface should be about 100-250mm lower than the level of the elbows.

For normal tasks that do not require much strength, the worktop should be about elbow height or just below.

For precision work, the work surface should be about 50-100mm above elbow height.

For precise, fine work, as well as for writing, drawing and reading, the work surface should be higher so that the elbows can be rested on it. This will also bring the work closer to your eyes.

Precision work should preferably be done sitting, when the back muscles should be supported and relieved by suitable seating and elbow support. The provision of high stools allow users to alternate between a standing and a 'perched' position.

Adjustable height work surfaces allow each user to fit the work surface to their own needs. If this is not possible, design for the largest user, and supply platforms to those that are smaller.

Maximum vertical and horizontal reach

Vertical reach is limited by how far you can reach and grasp objects above or below your shoulder height without stretching or bending. Measurement of vertical reach is taken from the surface of your shoulder to the centre of your closed hand (or extended middle finger for button operation). Height of reach is used when positioning shelves for storage, handles or controls above head height.

Horizontal reach is measured in the same way, but about the horizontal plane.

Visual workspace

We alter our direction of gaze by moving our eyeballs within their sockets and by moving our head. It is good to have some movement of the head during work in order not to tire the neck muscles. The head is supported by the effort of the muscles in the neck. If you hold your head still, your muscles are doing static work, that is, they are working continuously with no breaks to rest. This is more tiring than if you move your head, when the muscles are doing dynamic work, and muscles groups get a chance to rest as others take over. Therefore, the visual aspects of the workplace should be arranged to cause the lowest level of static work by the neck muscles.

You should aim to position frequently viewed items within a comfortable zone in front of you.

This is normally within 15° above, or 30° below, the horizontal, and 15° to the left and right.

In the normal, relaxed position of the head, neck and eyes, the line of sight is about 10 to 15° below the horizontal, therefore, viewing horizontally straight ahead actually requires a small amount of effort.

Distance is also a factor in visual fatigue. Visual displays are comfortably viewed from 500-750mm or more, depending on the size of the display components. The lens of the eye stiffens as people get older, altering the distance at which they can easily focus, so objects need to be positioned further away for clear viewing. They also take longer to focus on things (it will happen to you one day!).

Access Clearance

When you are designing a workspace, you must remember that you need access to it and to be able to move around within it. For example, you need to allow at least 600mm

width for a person to walk normally down a corridor, and 1200mm for two people to pass side by side. You should allow 1200mm from the front edge of a desk to push a chair back and stand up, with no restrictions.

The space that you need to move around freely in can often be more than you think.

Try standing with your back against a wall and bend forwards. You won't be able to bend far before you start to fall forwards, as your centre of gravity falls outside the area of your feet. You need to move away from the wall to allow yourself to move your bottom backwards to counterbalance the weight of your upper body. How far do you need to stand away from the wall before you can bend over without restriction? Is it further than you thought?

Sometimes people have to work in, move through, or access restricted areas, for example, for maintenance work.

Clearance can be seen as the minimum distance required to allow the desired user group into, or through, an area. This is especially crucial for the design of features such as escape hatches and emergency exits. Some examples are:

The minimum vertical space between the floor and an overhead obstruction must allow for the tallest user plus their footwear and headgear.

The minimum horizontal space between two obstructions must allow for the widest user plus room for movement and equipment.

A hazard must be beyond the reach of the user with the longest arm, if there is no room to bend.

Grille openings in front of a hazard must not allow reach to the hazard by the user with the longest or thinnest finger.

Man Access Space Requirements

These figures illustrate approximate man access requirement.  [The dimensions are only for guidance and are based on USA adult male (95% percentile)].

Minimum Area Entry Widths 0.330m to 0.45m .... Difficult For 1 Man 0.450m to 0.6m .... Reasonable For 1 Man 0.6m to 0.9m .... Good For 1 Man > 0.9m .... Good For 2 Men

Body clearance for prone access

Body clearance for kneeling man

Body clearance for crawling man

Body clearance for squatting man

Maintenance reach levels

Ramp Access

Stairs Step Ladders

Ladders Miscellaneous

Working out how much total space you need Guidance on the Workplace Regulations states that work

rooms should have enough free space to allow people to get to and from workstations and to move within the room easily. The number of people that may work in any particular room at any one time depends not only on the size of the room, but on the space taken up by furniture, fittings, equipment, and on the layout of the room.

The total volume of the room, when empty, divided by the number of people normally working in it should be at least 11 cubic metres. In making this calculation, a room or part of a room which is more than 3.0m high should be counted as 3.0m high.

Guidelines for the design of workspaces Encourage a frequent change in posture

People involved in seated work should be encouraged to change posture and sit in a variety of positions. Most modern office chairs help to promote this sort of

behaviour. For industrial tasks, 'sit-stand' workspaces are advisable, whereby the task is set at a height that is suitable for standing at, but a high stool is also provided for support.

Avoid forward bending of head and trunk. This is common during visual tasks, and where the work

surface is too low. For fine visual work, consider sloping the worksurface towards you.

Avoid causing the arms to be held in a raised position. This is common where the work surface is too high, or the

seating is too low. If, usually for visual reasons, the task should be performed in a raised position, then elbow support should be provided. A lack of support leads to stress on the shoulder muscles, and an extra circulatory burden on the heart.

Avoid twisted and asymmetrical positions These are most common when displays or controls are poorly

located. Frequently used items should be placed centrally between waist and shoulder height to reduce the need to bend or twist to reach.

Avoid postures that require a joint to be used for long periods of time at the limit of its range of motion This is particularly important for the wrist and forearm. Make

sure that items that are often used are within easy reach.

Provide adequate back support for all seats If, due to operational reasons, the user is not using the back

support, it should still be provided in order to give support during rest periods.

Where muscular force must be exerted the limbs should be in a position of greatest strength The muscles and joints work best when they are in the mid-

third of their range. Position items so that the arms can be used in this way.

Test your workspace layouts

Make sure that you have designed the workspace well by trying it out on a range of users performing relevant tasks.