The human body temperature is always constant. The constant temperature that is slightly fluctuate approximately 37^o Celsius in the brain, hearth and stomach defined as core temperature. The opposite of the core temperature defined as shell temperature that obtained in muscles, hands, foot and whole part of our skin that indicates certain variation. So, in order to keep the constant temperature and reduce the negative effects that may occur (such as physical exhausted), there are three actions:

1. Blood supply control, core temperature and shell temperature
2. Body temperature control by perspiration activity
3. Increase the heat production of the body by stretching the muscles. Such as by doing some exercises.

Heat Transfer

In some conditions, over heat may occur in our body, so it released to the domain. The transfer occur continuously depends on physiologic mechanism and it appropriate with heat transfer process in physic.

1. HOT ENVIROMENTAL CONDITIONS (Health Effect/Hyperthermia)

The health of a worker exposed to high levels of radiant or converted heat may be damage in one or both of two ways. First, the skin’s elevated temperature of over 45°C (113°F). These effects, however, are immediately observable and under normal circumstances the pain will cause the operator to remove the exposed body part from danger.

Over the years many studies have been performance to investigate the effect of thermal conditions on performance usually using some type of cognitive task such as memory or vigilance. Unfortunately, however, because of experimental limitations and wide differences between tasks, techniques and conditions, no firm conclusions can be drawn from the combined result.

2. COLD ENVIROMENTAL CONDITIONS (Health Effect/Hypothermia)

In the same way that slight rises in deep body temperature can rapidly lead to hyperthermia, fairly small amounts of deep body cooling is likely to produce a severe risk to health. In this case to condition is known as hypothermia. Accidental hypothermia can result from exposure in bad weather, short-term immersion in very cold water or long-term exposure in slightly cold water or particularly in the elderly; it may be a consequences of illness or accident.

After reviewing much of the work of the effects environmental cold on human performance concluded that cold can affect performance in 5 areas:

a. Tactile sensitivity

b. Manual performance

c. Tracking

d. Reaction time

e. Complex behaviors

These five behaviors can be grouped into two main categories: motor performance and cognitive performance.

A large number of variables contribute to the assessment of thermal comfort. Besides the obvious physical aspect as the environment discussed above, aspect as the room color and size the season of the year, the subject’s age, activity, clothing and duration of exposure.

To these, Fanger (1970) adds national and geographical location, body build, and the condition of a woman during her menstrual cycle, circadian rhythms and ethnic differences. Some of these will be discussed.

The heat transfer may occur with four ways:

1. Conduction

2. Convection

3. Evaporation

4. Radiation