Physiological responses to heat Physiological responses to cold Psychological responses to the thermal environment

139 15 THERMAL ENVIRONMENT: PRINCIPLES, EVALUATION AND CONTROL The human body can be considered as a processing plant, using complex chemical reactions to produce mechanical energy; as a consequence of the inevitable inefficiency of these reactions heat is produced as a by-product. In order to function effectively we need to maintain our bodies at a constant temperature within the range 36.5 - 37.5 o C.

15.1 Human Response to the Thermal Environment

Temperature regulation centres in our brain are sensitive to small changes of blood temperature and also get feed back from sensory nerves at the skin, our brains then use this information to adjust our bodies responses to heat.

15.1.1 Physiological responses to heat

When exposed to heat the blood vessels in our skin expand and our pulse rate increases. This increases blood flow to the surface of the body, thus increasing the potential for heat transfer from body core to skin and surroundings. Sweating also increases heat loss due to latent heat of evaporation. This also has the added effect that it increases our water requirements. In very hot conditions, sweating offers the greatest potential for regulating body temperature. On going from a cool to a predominantly warmer climate it is necessary to allow the body to acclimatise by increasing blood volume and sweat capacity while decreasing salt losses in sweat. It takes about 3 days for this acclimatisation to be about 60 complete and about 10 days for complete acclimatisation. This increased sweat capacity is lost after a few days in a cooler environment. Possible adverse effects of exposure to excessive heat include; fatigue, behavioural modification, including reduced concentration, heat cramps due to salt loss, fainting heat exhaustion and heat stroke. 140

15.1.2 Physiological responses to cold

When exposed to cold the blood vessels in our skin contract and heat flow to the body surface is reduced, thus minimising heat loss from the body. Heat production is increased by physical activity and shivering. There is no physiological acclimatisation to cold. Possible adverse effects to excessive cold include; lassitudelistlessness, chilblains, frost bite and hypothermia.

15.1.3 Psychological responses to the thermal environment

People will often modify the way they work depending on the thermal environment. Often they will try to modify their local work environment e.g. moving to a more comfortable area, changing clothes, increasing or decreasing ventilation etc. Performance and efficiency can also be affected by adverse thermal conditions.

15.2 Heat Transfer from the Body