Contractor Safety Council Awareness Material TOPIC: HEAT STRESS For more information on the CSC and other awareness topics, see

Heat Stress THE BASICS OF WORKING AND SURVIVING IN THE HEAT Note: Heat is not defined by temperature alone. Heat related problems may appear at various temperatures due to variations in clothing, work conditions, work load, individual fitness and environmental factors.

Body Temperature THE BODY IS MADE UP OF TWO REGIONS: A central core which must be maintained at 37°C (98.6°F): heart, kidney, brain. If the temperature goes above 98.6°F => DANGER! A peripheral envelope where temperature can vary greatly without ill effect: skin, muscles, fat, bones – Heat transfer between core and envelope is performed by the blood. – This transfer of heat allows the body to regulate its core temperature.

Body Temperature TWO MAJOR FACTORS AFFECT THE BODY’S TEMPERATURE: Metabolic factors: – Heat generated by the body increases with the work load. Environmental factors: – Air temperature – Radiant temperature (heat radiating from the sun) – Air speed – Humidity If the human body did not have methods of heat control the core temperature would rapidly attain that of the outside temperature.

Apparent Temperature Humidity has effect of increasing apparent temperature to human body:

Heat Loss Convection: Transfer of heat by movement of air next to the skin. Greater cooling effect as air speed rises (ex: fan, wind). – When air temperature is hotter than body temperature, convection does not work well. Radiation: Transfer of heat to cooler surrounding objects which are not in direct contact. It – Cools the body if the surrounding objects are cooler than the skin. Conduction: Transfer of heat between objects that are in contact with each other. – Body loses heat times faster in water than in air. Evaporation: Sweat which evaporates from the skin ’s surface cools the body. – Heat is brought to the skin by the blood. Blood vessels are dilated to increase heat loss.

Heat Production & Loss Heat ProductionHeat Loss Muscular WorkEvaporation FoodRadiation ShiveringConvection Conduction

Body Temperature The brain cannot survive when its temperature exceeds 113°F (44-45°C) Body heat control mechanisms come into action when the blood ’s temperature rises above 98.6°F. When air temperature is as warm as skin temperature, evaporation remains the only effective way to cool the body.

Sweat Sweat consists mainly of water. The more one sweats the more one must drink. Sweating only cools the body if the sweat can evaporate from the skin. This is the case when air is dry, humidity is low and there is air movement. In a very humid climate, evaporation is difficult since the surrounding air is already highly saturated in water.  Alcohol reduces a person ’s resistance to the heat.

Acclimatation HEAT WITHOUT ACCLIMATION => high body temperature high pulse rate profuse sweating important loss of salt HEAT WITH ACCLIMATION => THE BODY ADJUSTS TO THE HEAT WITHIN 7-10 DAYS, WORKING IN THE HEAT BECOMES EASIER – decrease in body temperature – d ecrease in pulse rate – sweating may increase but salt content decreases

Water LACK OF WATER IS THE MAJOR FACTOR IN MOST HEAT DISORDERS In normal conditions the body loses => 84 ounces of fluids/day Heat + strenuous work => Loss of up to 50 ounces of sweat per HOUR!!!! – Drink enough water to replace the water that is lost. – Ideally, fluids should be taken every 20 minutes throughout the day. – Thirst is a poor indicator in preventing dehydration. Drink regularly even if not thirsty!

Food & Salt EAT WELL BALANCED MEALS AT REGULAR INTERVALS DO NOT EAT IF YOU DO NOT HAVE WATER TO DRINK – A person can live for weeks without eating but only a few days without water DO NOT USE SALT TABLETS & DO NOT ADD SALT TO WATER – Salt tablets cause stomach irritation and provoke nausea and vomiting THE NORMAL DIET WILL PROVIDE ALL THE SALT REQUIRED

Requirements for Heat 1.BE MEDICALLY FIT 2.RECEIVE SPECIFIC FIRST AID TRAINING 3.KNOW WEATHER FORECAST INFORMATION 4.BE EQUIPPED (Water, food, etc.) 5.WEAR PROPER CLOTHING/PROTECTION

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