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Concepts in Human Factors Engineering (Part 9 of 11)

Concepts in Human Factors Engineering (9): A Hot Workplace

by Dennis R Andrews PhD, PSP, CECD

By Dennis R Andrews PhD, PSP, CECD (ExpertPages member profile page)

The physical environment of the worker of is an important part of the workplace. The body attempts to cool itself by perspiring and exhaling. Clothing is an important part of a comfortable work environment but the environment must be controlled regardless of the outside climate. The law of thermodynamics states that heat flows from warmer to colder matter, which accounts for heat loss around doorways and windows. If the body deviates from the core temperature of approximately 99 degrees Fahrenheit/37 degrees Celsius, the safety and productivity of the work may suffer.

Concepts in Human Factors Engineering is a series containing eleven articles:
  1. An Overview of Anthropomorphic Data Gathering
  2. The Fragile Skeletal System
  3. The Energy Force of Our Frame
  4. The Message Delivery System
  5. The Body as a Machine
  6. The Oxygen Machine
  7. The Body’s Transportation System
  8. Human Body Energy
  9. A Hot Workplace
  10. The Rhythm of Working
  11. The Bionic Worker of the Future
While it is dangerous for the core body temperature to rise above 99 degrees it is also unsafe and dangerous to drop below this temperature. The body can be kept warm through heating the workplace as well as by proper clothing. The type of clothing chosen should take into consideration the task to be performed especially if it involves working with heavy machinery. Loose clothing or clothing with strings or tassels should be avoided when working under these circumstances. The body must be in balance with the work done, rate of heat gain or loss and the rate of energy storage with the energy intake.

Heat is either lost or gained through radiation where two surfaces have a temperature difference. As stated earlier heat tends to move towards cold, which is, why home heat is lost through doors and windows in the wintertime. Radiated heat in terms of gain or loss can be calculated knowing the area of the body surface, coefficient of absorption, opposing surface temperature, coefficient of emission and body surface temperature. This formula can be used to determine a comfortable workplace.

Heat exchange is also accomplished by convection and conduction wherein the heat transfer is proportional to the area of the subjected human skin and temperature difference between the skin and the adjacent layer. Conduction occurs when the skin contacts a solid object and the heat flows to the colder object. Conduction requires the skin to be in contact with the transferring object while convection simply requires the skin to be in an atmosphere with a different temperature. Convection would take place when the human skin is in a medium such as water. Hypothermia can even occur in water temperatures of 75 degrees if the person remains in the water for a length of time. Survival suits serve the purpose of controlling and limiting heat loss when a person is in the water such as the sinking of a commercial fishing boat. Hypothermia can be delayed for a person fully clothed as opposed to a naked body. While the water permeates clothing heat loss is reduced compared with no clothing.

Heat exchange is also accomplished by evaporation, which is another term for perspiration. In hypothermia if the body cannot conserve heat it begins to shake violently in order to create heat. While this may help to postpone the inevitable this shaking uses valuable energy. Consequently suffering heat stroke the body will feel cold and usually will not perspire. The human body has mechanisms to react on its own but it is insufficient in extreme conditions. Air or water temperature, humidity, air or water movement and the temperature of your body surface determine our environment. All of these factors increase or decrease the comfortability of our environment and consequently our body. In a cold environment the body will attempt to shut down unnecessary parts and pump warm blood to the critical parts.

Clothing also determines the surface area of the exposed body. Obviously the more surface area exposed the faster the body will retain heat or lose heat depending upon the environment. Dehydration is an important concern when working strenuously in high temperatures and humidity. Dehydration in moderate or cool climates is not a great concern as compared with higher temperatures. As the body tries to regulate heat it does so by evaporation of perspiration on the surface of the skin. This perspiration causes loss of valuable water in the body. Dehydration can be quickly counteracted by drinking water. In very strenuous conditions adding salt may assist the body from excess salt loss and adding sugar may avoid or postpone fatigue. Either one of these losses can be hazardous if concentration is mandatory in a task such as working with machinery, serious or fatal injuries can occur. Plain water is usually best to drink since it would be relatively close in temperature with the body. Overheating of the body not only can cause stroke but can cause other problems before reaching this acute level. Overheating of the muscle tissue can cause fatigue and increase the metabolic rate, which would increase other functions of the body. Mental acuity is important and can suffer along with dexterity depending upon the environmental temperature and the body temperature.

Adjustments to create a comfortable and healthy work environment can be made if one knows what to do. To adjust radiated heat the adjacent surface or surfaces must be either cooled or warmed. If convection heat can be controlled through the movement of air such as air conditioning or forced hot air heating system. Adjusting the solids, such as walls etc., that come in contact with the skin of the worker controls conductive heat and evaporation is controlled through humidity or air movement. Much is talked about pertaining to wind chill factors basically this is a calculation to theoretically determine energy loss through the exposed skin from the environmental temperature and the velocity of the wind on the skin. Some think that wind chill is only important in bitterly cold climates. The body can lose heat through exposed skin in climates that are hot, warm or pleasant. Of course much less energy is lost through the exposed skin on a hot day compared to a bitterly cold day i.e. 200 kilojoules per meter squared per hour as opposed to 4900 kilojoules per meter squared per hour. The higher the heat loss the quicker the body can freeze. It should be said at this point that comfortable temperatures are as individual as the persons themselves. Some people are cold in winter even if the temperature is warmer than in the summer simply because of the lack of humidity.

In summary it is crucial to maintain the core body temperature at approximately 99 degrees. Any change up or down to the core temperature can result in injury or fatalities depending upon the work & task environment at the time. Heat is gained or lost through various methods such as radiation, convection, conduction and evaporation. All of these can be modified to make the work environment more pleasant, efficient and safe. The tolerance levels for individuals can be as varied as the individuals themselves consequently the health and stamina of the individual is an important function directly correlating to a productive and safe work environment. The environment is a combination of humidity, temperature, and air movement as well as the structures or walls.

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