7.1.3 Storage
It is instructive to compare side elevation views of standard kitchen units with ergonomic recommendations for storage zones, (as discussed in the next chapter, see Table 8.4)—as shown in Figure 7.3. Cupboard space in the 800–1100 mm optimum height range being strictly limited, the most accessible storage space in the kitchen becomes the worktop—which disappears under a clutter of food mixers, spaghetti jars and other homeless objects. Clutter expands to fill the available space—Pheasant’s principle of ergonomic decay (see also Section 6.1).
needless volume, requiring filling with expensively heated water. It is also a notoriously hazardous environment for the frail and infirm.
Two principal postures are adopted in the bath: a reclined sitting position and a recumbent position (possibly with the knees flexed) in which the body is submerged to neck level. For comfort in the sitting position the horizontal bottom of the tub must be sufficient to accommodate buttock-heel length (95th %ile man=1160 mm) and the end of the bath should provide a suitable backrest. Kira (1976) recommends a rake of 50–65° from the vertical and contouring to conform to the shape of the back. This seems excessive to me—a rake of 30° and a suitable radius where the base meets the end should be quite adequate—we are not particularly looking for postural support since the buoyancy of the water will both unload the spine and lift it away from the backrest. The more we increase the length of the horizontal base the greater the possibility for total submersion. We may shorten our recumbent bodies by around 100 mm by flexing our knees—given that we wish to keep our heads above water—and that as the 95th %ile male shoulder height is 1535 mm there seems little point in lengthening the horizontal part beyond around 1400 mm.
The width of the bath must at least accommodate the maximum body breadth of a single bather (95th %ile man=580 mm). The ergonomist, who is usually a broad- minded sort of person, should also consider the accommodation of couples. Methods for calculating the combined dimensions of more than one person are discussed in section 4.3. For couples wishing to sit side-by-side the necessary clearance is given by their combined shoulder breadth (920 mm for a 95th %ile couple of the opposite sex). For couples sitting at opposite ends (probably the more common arrangement) the clearance is given by combined breadth of the hips of one person and the feet of the other. This is greatest when the hips are female and the feet are male, in which case the 95th %ile combination is 625 mm. This arrangement does, however, demand that the taps should be in the centre to avoid arguments (Figure 7.4).
Consider a 95th %ile man (sitting shoulder height 645 mm) reclining against the end of the bath. His shoulders will be 645 cos 30=558 mm above the base of the bath. He could not reasonably require more than 400 mm of water. If the backrest was raked further, say to 45°, then 300 mm of water would suffice. (These figures are
Figure 7.4 The economically designed bath.
mere speculation; it would be very interesting to perform a fitting trial to find out what depth of water people really do want.) Assuming a 30° rake, a bath depth of 500 mm would be required for an adequate quantity of water without too much danger of it splashing over the edge. In fact, a typical tub depth at the present is about 380 mm (15 in.), although older models are often deeper. The outside height of the rim (above the floor) is, of course, generally greater than the tub depth (often by as much as 100 mm).
A deep bath or a high rim is generally deemed to make entering and leaving more difficult and hazardous—although Kira (1976) casts some doubt on this, arguing that the manoeuvres people use to enter and leave baths have been insufficiently analysed.
Grandjean (1973) cites evidence that a height of 500 mm is acceptable to most elderly or frail people. Grab rails are usually advocated as an aid to stability. These could reasonably be a little above knuckle height at the point where you climb in (e.g. 800 mm above the bath base), around shoulder height (e.g. 575 mm) at the sitting end and about 40 mm in diameter. Vertical grab rails may well be better for the infirm.
Additional holds along the side of the bath are also desirable and, for the frail, a non- slip mat inside the bath is essential.
7.2.2 The handbasin
This device will be used for washing the hands and face and sometimes the hair. The criteria are relatively simple: it should be possible to wet the hands without water running down the forearms and bending should be minimized. Hence, a basin rim that is at about the elbow height of a short user would be appropriate (5th %ile woman=930 mm unshod). Kira (1976) studied the above activities experimentally by observing subjects first miming the actions without the constraints of an appliance and then using an adjustable rig. On the basis of these fitting trials he concluded that, for washing the hands, the water source should be located some 100 mm above the rim of the basin, which should be set at 915–965 mm. Conventional handbasins are very much too low (commonly less than 800 mm)—except perhaps for use by children. The present practice of placing the taps at or below the level of the rim seems based on the assumption that people will fill the bowl and wash in the water therein. In fact, according to Kira, 94% of people prefer to wash under a running stream of water.
7.2.3 The water closet
There is a strong body of opinion that takes the view that the sitting posture, which in Western society we use when emptying our bowels, is physiologically unsound.
Proponents of this view—most notably Hornibrook (1934)—argue that a squatting position, in which the thighs are pressed against the abdominal wall, encourages an easy and physiologically more efficient bowel movement, which in the long run will help prevent a variety of nasty diseases (to which we are prone as a result of our diet and sedentary habits).
I am not aware of this theory having been tested experimentally. (It would be difficult to do so.) But experience suggests that it is basically correct. The physiology remains unclear. It is not solely a matter of increased intra-abdominal pressure, as has
been suggested—since this is the act of ‘straining at stool’ which is allegedly deleterious.
The plinth of the conventional WC is typically around 380–400 mm in height. For squatting this would have to be halved. One consequence of reducing the height is that the buttocks take a much greater proportion of body weight. So the contouring of the lavatory seat itself becomes much more critical for comfort. But as you would not have to sit there for so long it probably would not matter so much.
For a discussion of the ergonomics of the more conventional sorts of lavatory, see McClelland and Ward (1976, 1982).