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inevitable lowering of body temperature. This last state of hypothermia can lead
to loss of life and is a particular concern in relation to elderly people.
Radiation
Radiation heat transfer takes place between the body and its surroundings.
The direction of heat transfer may be either way, but normally a minor part of
the total body heat loss takes place by this method. Radiation between skin and
clothing surfaces and the room depends on the fourth power of the absolute sur-
face temperature, the emissivity, the surface area and the geometric configura-
tion of the emitting and receiving areas. Thus a moving person will experience
changes in comfort level depending on the location of the hot and cold surfaces
in the room, even though air temperature and speed may be constant.
Some source of radiant heat is essential for comfort, particularly for sed-
entary occupations, and hot-water central heating radiators, direct fuel-fired ap-
pliances and most electrical heaters provide this. The elderly find it particularly
difficult in keeping warm when they are relatively immobile, and convective
heating alone is unlikely to be satisfactory. A source of radiant heat provides
rapid heat transfer and a focal point, easy manual control and quick heat-up pe-
riods. Severe cases of underheating can be counteracted by placing aluminium
foil screens in positions where they can reflect radiation onto the rear of the
chair.
Overheating from sunshine can also cause discomfort and glare, and tol-
erance levels for radiant heating systems have been established.
Evaporation
Humid air is exhaled, and further transfer of moisture from the body takes
place by evaporation from the skin and through clothing. Maintenance of a
steady rate of moisture removal from the body is essential, and this is a mass
transfer process depending on air humidity, temperature and speed as well as
variables such as clothing and activity.
Ventilation
The quality of the air in a building depends upon the quantity, type and
dispersal of atmospheric pollutants. Some of these, odorants, can be detected by
the olfactory receptors in the nose. These are the odours, vapours and gases that
ingress from the outdoor environment and are released from humans, animals,
flora, furnishings and the structural components of the building. Solid particles
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