Physical Workload and Heat Stress - Human Factors and Ergonomics - page 233

FIGURE 12.5 The globe temperature
T G measures the radiated heat using a
thermometer inside a black painted
copper globe. The more sun, the hotter
the globe, so T G will increase. The
capacity of the air to absorb evaporated
water is measured by the wet bulb
temperature T NW . This uses a
thermometer which is covered by a
cloth wick, the lower part of which is
immersed in a reservoir of water. In
dry air the water will evaporate. This
will draw energy (calories) from the
thermometer, and temperature reading
will decrease. The dry bulb air
temperature T A is measured using an
ordinary thermometer.
TABLE 12.2 Reference Values of the WBGT
Heat Stress Index
Reference Value of WBGT (Celsius)
Workload Metabolism (M) (W/m 2 ) Acclimatized Not Acclimatized
Resting <65 33 32

Low 65-130 30 29

Moderate 130-200 28 26