Working in hot conditions may pose special hazards to safety and health. Since 1936, 30,000 people have died from heat related illnesses. On average, 384 people die each year during normal hot temperatures.

How the Body Handles Heat

Four environmental factors affect the amount of stress a worker faces in a hot work area: temperature, humidity, radiant heat (such as from the sun or a furnace) and wind speed. Individuals with high blood pressure or some heart conditions and people who take diuretics (water pills) may be more sensitive to heat exposure.

The body defends itself from heat through three mechanisms: breathing, sweating, and changing the blood flow. The first reaction is to circulate blood to the skin, which increases skin temperature and allows the body to give off some heat. During heavy work, muscles need more blood flow, which reduces the amount of blood available to flow to the skin and release the heat.

Sweating also helps the body to cool off, but only when the humidity levels are low enough to allow the sweat to evaporate and if water and salts lost through sweating is replaced.

At Risk Employees

Some employees are more likely to experience heat disorders than others. Younger employees and those more physically fit are often less likely to experience problems. Employees 65 years of age and older may not compensate for heat stress efficiently and are less likely to sense and respond to change in temperature. Employees with heart, lung or kidney disease, diabetes and those on medications are more likely to experience heat related stress problems. Diet pills, sedatives, tranquilizers, caffeinated drinks and excessive alcohol consumption can all exacerbate heat stress effects.

It often takes two to three weeks for employees to become acclimated to a hot environment. This acclimation can subsequently be lost in only a few days away from the heat. Thus employees should be more cautious about heat stress after coming back from a vacation, when beginning a new job, or after the season’s first heat wave. In short, precautions should be taken anytime there are elevated temperatures (approaching 90 degrees F) and the job is physically demanding.

Other Factors

Other heat stress factors are also very important. In addition to temperature, increased relative humidity, decreased air movement, lack of shading from direct heat (radiant temperature), the type of clothing worn will all affect the potential for heat stress

Heat Stress Disorders

High temperatures and humidity stress the body’s ability to cool itself, and heat illness becomes a special concern during hot and/or humid weather. There are three major forms of heat illness: heat cramps, heat exhaustion, and heat stroke. The following table identifies each condition, the signs and symptoms, and recommended first aid

Heat Stress Prevention

Supervisors

• Allow time for employees to adjust to the summer heat. It often takes two to three weeks for an employee to become acclimated to a hot environment;
• Adjust the work schedule, if possible. Assign heavier work on cooler days or during the cooler part of the day;
• Reduce the workload. Increase the use of equipment on hot days to reduce physical labor. Also, reduce the use of equipment that produces excess heat;
• Establish a schedule for work and rest periods during hot and humid days;
• Inform employees how to recognize signs and symptoms of heat stress disorders and be prepared to give first aid if necessary; and
• Avoid placing "high risk" employees in hot work environments for extended time periods. Realize individual employees vary in their tolerance to heat stress conditions.


Employees

• Use the Heat Stress Disorders table to recognize the signs and symptoms of heat stress;
• Pre-hydrate by drinking plenty of water or electrolyte containing drinks before work in hot environments is started. You should drink at least 8 oz of fluid every 20-30 minutes to stay hydrated. Drink BEFORE you are thirsty;
• Pace the work, taking adequate rest periods. The breaks should take place in an air conditioned environment. If air conditioning is not available, seek shelter in a cool or shady area;
• Keep shaded from direct sunlight or other heat sources where possible, for example, wear a hat and apply sunscreen;
• Work by using the buddy system on hot, humid days; and
• Wear light colored, loose (unless working around equipment with moving parts) clothing.


General Tips

Clothing

Wear loose-fitting, lightweight clothing to allow sweat to evaporate. Light colors absorb less heat than dark colors. Wear a hat with a brim to keep the sun off head and face.

Drinking

Drink plenty of fluids to replace fluids lost during sweating. Drink water and/or electrolyte containing drinks and avoid caffeinated beverages. Drink 16-32 ounces of cool fluids each hour. Drink BEFORE you are thirsty.

Work Schedule

Heavy work should be scheduled during the cooler parts of the day whenever possible. Rather than be exposed to heat for extended periods of time during the course of a day, employees should, wherever possible, be permitted to distribute the workload evenly over the day and incorporate work-rest cycles. Work-rest cycles give the body an opportunity to get rid of excess heat, slow down the production of internal body heat, and provide greater blood flow to the skin. Take more frequent breaks when working in extreme temperatures or at the first sign of heat stress symptoms.

Body Weight

Workers may be at greater risk if they lose more than 1.5% or their body weight in a single day from sweating.

Heat Stress Index

The heat stress index is a measure of how hot it really feels in degrees Fahrenheit when relative humidity is factored with the actual air temperature. This chart has been adapted from the National Weather Service’s “heat index”.

To read the table: find the temperature on the left hand side, and then move to the right until you find the column for the approximate relative humidity. That number will be the temperature that it will "feel" like. Example: A temperature of 95 and relative humidity of 50% will "feel" like 107 degrees. Add up to 15 degrees if in the direct sun.