2007, Piran, Slovenia

Occupational Thermal Problems
The heat required to maintain manikin skin temperature at 34 o C was 78 Wm -2 on average
indoors and 37 Wm -2 on average outdoors. It can be concluded that the contribution of the sun
to the thermal load on the manikin is therefore 41Wm -2 .
STUDY THREE: Estimation of the contribution of the sun to thermal stress using theoretical
analyses: A body heat equation was determined for conditions in Study One and Two above
for outdoor conditions where actual radiant temperatures were used in the calculation as well
as conditions that assume radiant temperatures were equal to air temperatures. Assumptions
made and environmental conditions used are presented in Table 3. The body heat equations
are shown in Table 4 (see Parsons 2003).
Table 4: Calculations of the body heat equation
Outdoors(ta = 23ºC, tr = 33ºC) Outdoors(ta = tr = 23ºC)
E = M −W
− C − R − C − E
req
= 284 – 0 – 91 – 10 – 4 – 22
= 157
res
res
E = M −W
− C − R − C − E
req
= 284 – 0 – 91 – 60 – 4 – 22
= 107
It can be concluded that the additional thermal load caused by the sun is 50 Wm -2 .
DISCUSSION AND CONCLUSION
The three methods provided different but comparable estimates of the contribution of solar
load to thermal strain when working in the heat. Naturally this is for the specific conditions
investigated and further studies would be required to account for other factors such as time of
day and season as well as weather conditions and type of clothing. Each method made
different assumptions and it may be regarded as useful to take a three ‘direction’ approach to
this problem. Other studies have found similar results McNeill (1998) and if one is prepared
to accept a ‘rule of thumb’ to this practical problem then working in the full sun may add 80
Wm -2 to the thermal load on the body requiring in the heat for example and additional 0.25
litres of sweat per hour to be produced when wearing normal clothing.
ACKNOWLEDGEMENTS
The authors would like to thank Dr Simon Hodder for his practical support during the
experiments.
REFERENCES
McNeill, M. B. (1998) Ergonomics issues and methodologies in industrially developing
countries. PhD thesis, Loughborough University.
Monteith and Unsworth (1990) Principles of Environmental Physics (Second ed.). London:
Edward Arnold, ISBN 0-7131-2931-X.
Parsons, K. C. (2003) Human Thermal Environments (Second ed.). London: Taylor and
Francis, ISBN 0415237939
res
res
623