2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
In contrast to the dry hot environment, the model predicts limited performance in the hot
humid environment. There is danger of heat stress and excessive water losses.
The effect of clothing can be simulated by altering the insulative and evaporative
characteristics of the textiles. The model allows composing different clothing layers from
available the database of textiles. Thermal responses were simulated for the same
environmental condition, but using two conditions: 1) person wearing full cotton ensemble; 2)
person wearing combined cotton clothing, comprising an impermeable textile on the trunk [4].
The results of the simulation revealed that that any local limitation in sweat evaporation
reduces the safe exposure time in a hot environment. Even partly impermeable clothing
decreases heat tolerance significantly. It reduces the time the person performs in a hot
environment since the core temperature increas
Different levels of physical activity can be simulated by adjusting the metabolic rate and
blood flow in different skeletal muscles.
Figure 4. Dynamics of sweat rate and heart rate in hot environment, physical activity 300W.
The model was validated by simulating physical performance in hot environment. The
duration of performance depends on the quantity of water in the body. The model warns the
user when 2% and 4% weight water losses are encountered during an experiment. Fig.3
depicts the simulation of an individual working at a rate of 300W in a hot environment
(Ta=40°C, RH=50%, v=01 m/s). As can be observed, intense sweat rate commences at minute
10 of exposure and steady state is achieved at minute 18. The predicted heart rate is 84 beats
per min. The model predicts no danger for an individual performing at such a rate in this
environment, but warns of possible excessive water losses and recommends compensation of
these losses.
The microclimate cooling (MCS) effect can be predicted through a change of ventilation,
temperature and humidity of the inlet air.
Computer simulations were performed accounting for different combinations of MCS
characteristics. In reality, the cooling effect depends on many parameters and it is not easy to
predict all physiological consequences. A modeling approach in evaluating MCS is interesting
as it can account for many factors and make it possible to obtain preliminary data of the effect
of an MCS under given combinations of environment, clothin and physical activity. MCS
simulations are performed considering either total body cooling, or regional cooling. For such
470
g/h
sweat rate
beats/min
heart rate