Overheating or inadequate heating of the body are two aspects of the same problem. The body maintains a deep body temperature of about 36 – 39° C. The system for maintaining the equilibrium of body temperature is called the homeostatic mechanism. It is remarkably effective and over a period of one day, irrespective of the variations in temperature in the surroundings, the body temperature will remain very stable.
It is possible to throw a strain on the homeostatic mechanism, resulting in its breakdown. To understand how this happens, it is necessary to look at how the mechanism works. Its operation is a function of the interaction of;
• Metabolism ;
• Evaporation ;
• Convection ;
• Conduction ;
• Radiation ;
• Storage ;
Metabolic heat is generated by the digestive activity of the body, producing energy from food and, in fuelling the physical activity of the body, more heat is generated from the movement and exercise of the muscles in the course of that physical activity.
Perspiration is produced in the course of strenuous physical activity, thus wetting the skin. Wet skin gives off heat to the air much more efficiently than dry skin, which is the reason we feel chilly on stepping out of a shower and is also the reason we like to run in and out of the sea on a hot summer’s day. The loss of heat through perspiration is called evaporation.
The effectiveness of evaporation will depend on the temperature of the air immediately adjacent to our skin. If the transfer of heat to that air from the body raises its temperature relative to the rest of the body of air, of which it forms part, the heated air will rise or otherwise move, and be replaced by cooler air. This air movement is called convection.
Convection will not function in conditions where the temperature of the air is generally higher than the body.
The body can lose heat directly into solid or liquid surfaces in immediate contact with the body. This is known as conduction.
Radiation is analogous to metabolic heat in that it is a source of heat and increased temperature to the body as opposed to reducing agents like convection, conduction and evaporation. Radiation may have other effects than raising the deep body temperature and these will be referred to later.
Lastly, the body has a capacity to store heat and retain it. Body fat is particularly important in this regard. When it was in fashion, female swimmers of the English Channel tended to be chubby women, a valuable attribute when long periods immersed in cold water are in prospect.
The interaction of all these factors determines the deep body heat of the human person. Of course the need for clothing is clear. Clothing is used around the world to maintain proper body temperature. In the deserts of the Middle East and North Africa the people wear long loose fitting gowns. These protect against the radiant heat of the sun and permit access of air flows to the body to facilitate convection. In Ireland we rely on cosy clothing to protect against cold.
The Symptoms of Heat Exposure
In the case of a temperature rise, sweating and dilation of the peripheral blood vessels, resulting in skin reddening and more rapid transportation of excess heat to the skin, through the blood circulation system, will occur. Thirst will be experienced with loss of fluid. If the temperature rise continues the worker may feel weak or dizzy.
The Effects of Heat Exposure
Efficiency of workers will begin to fall. Levels of confusion will increase accompanied by an increase in mistakes in the work in hand. Any of these mistakes can result in injury to the worker or his/her companions or members of the public. Loss of time off work can be reasonably anticipated.
Heat cramps will very likely ensue caused by a loss of salt through perspiration. Continued lack of attention to the problem can lead to heat collapse . There are variations of tolerance between individuals but heat collapse will ensue in more than two thirds of cases where body heat reaches 40-43° C. The worker will abruptly lapse into a coma. He/she will require immediate hospitalisation and immediate attempts to lower the body temperature. If the worker is to survive, his/her deep body temperature must be reduced to at least 40° C.
Radiant heat, apart from raising deep body temperature will damage skin, with skin reddening as the symptom, resulting in soreness and dryness. Cataracts may form in the eyes leading to permanent loss of function.
Dermatitis can arise due to excess temperature or humidity.
People at Risk
Workers at or in foundries or other hot working conditions generally are at obvious risk. Laundry workers can be exposed to considerable temperatures although without the element of radiant heat from the hot metal of a foundry.
Shielding of the worker from radiant heat is an obvious remedy to be adopted. Protective clothing may suffice for this purpose although the eyes will need a face mask or goggles. Frequent periods of rest from physical effort will assist the worker in keeping down the generation of metabolic heat. Retreat from the source of the heat and exposure to cooler air will assist in heat reduction through convection. A supply of salt drink will replace the salt lost in perspiration and avoid the onset of heat cramps. Proper organisation of work with planned lowered work rates or lowered periods of work are a necessary step to be taken by the employer.