What is this and how can it be used to reduce heat-related illnesses? How can they be prevented?

The index, also referred to as “apparent temperature”, is a measure of the contribution humidity makes with high temperature to reduce the body’s ability to cool itself, and is explained in chart 1 below. (A similar chart can be seen at: http://www.usatoday.com/weather/wheat3.htm.)

Chart 1
Temperature, Humidity, and Apparent Temperature (Degrees Fahrenheit)

A  110  *  99 105 112 123  137 150
I  105  *  95 100 105 113  123 135 149
R  100  *  91  95  99 104  110 120 132 144
    95  *  87  90  93  96  101 107 114 124 136
T   90  *  83  85  87  90   93  96 100 106 113 122
e   85  *  78  80  82  84   86  88  90  93  97 102 106 
m   80  *  73  75  77  78   79  81  82  85  86  88  91 
p   75  *  69  70  72  73   74  75  76  77  78  79  80 
    70  *  64  65  66  67   68  69  70  70  71  71  72 
- - - - - - - - - - - - - - - - - - - - - - - - - - - - 
            0  10  20  30   40  50  60  70  80  90 100 
            Relative Humidity (%)

Whenever weather conditions warrant, increased attention must be paid to the prevention of heat illnesses, and appropriate steps should be taken to reduce the effects of heat and humidity.

Learning to identify heat stresses can sometimes mean the difference between life and death. Some of the heat illnesses, symptoms, dangers, and first aid are:

1. Heat Rash, also known as prickly heat, occurs when people are constantly exposed to hot and humid air, causing a rash that can substantially reduce the ability to sweat. Heat rash is not just a nuisance because of discomfort, but by reducing the ability to sweat, the ability to tolerate heat is reduced.
   

   First Aid: Cleanse the affected area thoroughly and dry completely. Calamine or other soothing lotion may help relieve the discomfort.

2. Heat Cramps may occur after prolonged exposure to heat . They are the painful intermittent spasms of the abdomen and other voluntary muscles. Heat Cramps usually occur after heavy sweating and may begin towards the end of the workday.
   First Aid: Rest, drink plenty of water or electrolyte drink.

3. Heat Exhaustion may result form physical exertion in hot environments. Symptoms may include profuse sweating, weakness, pallor, rapid pulse, dizziness, nausea, headache, vomiting, and unconsciousness. The skin is cool and clammy with sweat. Body temperature may be normal or subnormal.
   First Aid: Rest in the shade or cool place. Drink plenty of water or electrolyte drink.

4. Heat stroke is a serious medical condition that urgently requires medical attention. Sweating is diminished or absent, which makes the skin hot and dry. Body temperature is very high (106 degrees Fahrenheit and rising) and if uncontrolled may lead to delirium, convulsions, a coma, and even death. This is a Medical Emergency! Brain damage and death are possible.
   First Aid: Douse the body continuously with a cool liquid and summon medical aid immediately.
   

1. Temperature
   
2. Humidity
   
3. Movement of air
   
4. Radiant temperature of surroundings
   
5. Amount and type of clothing
   
6. Physical activity
   

Prevention of heat-related illnesses can be accomplished in several ways, including acclimatization, conditioning, hydration, air movement many conditions, and the wearing of proper clothing.

Acclimatization means becoming adjusted to work in heat and is essential if work is to be done in hot environments. In a heat-stressful situation acclimatized persons will have lower heart rates, lower body temperatures, and higher sweat rates that consist of a more dilute sweat (with less salt) than persons who are not acclimatized. Maximum sweat rates vary from 0.6 liters per hour in the unacclimatized person to more than 1.5 liters per hour for a fully acclimatized person.

Evaporation of sweat from skin surfaces help provide cooling. Fans may help cool a person in many situations, however fans don’t cool a person at temperatures greater than 90 degrees F. when humidity is greater than 35%. Fans have been associated with increased heat stress when the ambient temperature exceeds approximately 100 degrees F. Air movement when the air temperature is greater than body temperature may increase heat stress. New employees and employees who have been away from work for a few days must be given adequate time to acclimate to the heat. Edwin L. Alpaugh writes in Fundamentals of Industrial Hygiene that “both work and heat stress are required to initiate the body changes that result in acclimatization. Working in the heat for about two hours per day for a week or two will result in essentially complete acclimatization to that work-stress combination. Working more that two hours per day in the heat will not speed acclimatization, nor hinder it”.

Workers in good condition can safely tolerate higher work rates than people not so fit. The more fit a person is, the lower the heart rate and the body temperature, and the more efficient their sweating mechanism as compared to a less fit individual. Obese and stocky individuals are not able to tolerate heat as well as leaner people. Extremely obese individuals are six times more likely to suffer heat stroke that thin people.

Hydration, or having enough body water, is also an essential factor in working safely in elevated temperatures. In order to help prevent dehydration, which is excessive loss of body water, adequate fluids should be consumed before, during, and after the job. Thirst may not be an adequate warning of dehydration, and workers should not be afraid of drinking too much water, since any excess will be eliminated in the urine. Drink at set intervals, rather than only when you feel thirsty.

Physicians recommend against taking salt tablets, since they may cause stomach distress. Salt tablets also take fluid to digest, which means that fluid will be diverted from the blood, which it needs to help cool the body. Recent research has shown that water is an adequate fluid replacement drink for low intensity and short duration activities in low heat environments.

During prolonged heat exposure or a greater intensity workload, a carbohydrate-electrolyte beverage offers a variety of benefits according to Steven Gregg, Ph.D., including:

1. Blood glucose falls and electrolytes are lost in sweat. Electrolytes (sodium, potassium and chloride) are critical elements in maintaining the body’s fluid balance and promoting fluid absorption in the small intestine. Sodium helps maintain blood volume, which is important for counteracting the effects of dehydration and responding to heat stress.

2. Working muscles need the energy found in carbohydrates to avoid fatigue and maintain work levels. In addition, proper amounts of carbohydrates help stimulate fluid absorption in the small intestine. Drinks should be non-alcoholic and non-caffeinated because both alcohol and caffeine increase urine output, which leads to dehydration.

Proper clothing is essential because up to 70 percent of the cooling effect of your body’s sweat evaporation may be lost by improper clothing. Light colored clothing should be worn because in reflects the sun’s radiant heat, whereas dark colors absorb it. Simply putting on a shirt and trousers interferes with the cooling of your body due to heat loss from sweat evaporation. Changing from wet to dry clothing as needed helps reduce heat stress exposure.

Dresser, Richard, “Heat Index Helps Workers Keep Their Cool”, National Safety Council: Public Utilities Newsletter, July-August 1985. National Safety Council, Itasca, IL.

Dresser, Richard and Roy Lee, “Heat Stress In and Out of PPE and Its Effects on Worker Performance: A Nuclear Power Industry Perspective”, presented at the Seventh Annual Environmental Management and Technology Conference Central , and published with other technical papers from that conference, Rosemont, Illinois, April 12-14, 1994, pp. 603-616.

Johnson, Sandra J., “Fluid Loss Can Lead to Heat Stress, Though Replenishment Offsets Effects”, Occupational Health & Safety, June 1993.

Rev 1/31/97