heat stress

Overview

Understanding heat stress can 

help you to stay safe while 

working in hot environments.

Things you need to know:

• Heat exposure can cause a range of effects on

your body, from irritating rashes to heat stroke,

which is often fatal.

• Heat exposure can cause confusion and poor 

judgment—use the buddy system to monitor

coworkers for heat illness. 

• Drinking enough water is critical to preventing

heat illness. Stay hydrated.

• Cooling is the treatment for all heat illness.

Factors that Increase Heat Illness Risk

• High humidity

• Lack of wind or breeze to cool the body1

• Dehydration

• Lack of acclimatization

• Age over 60 years

• Protective gear, including non-breathable

or minimally breathable clothing, respirators,

and chemical-resistant apparel

• History of heat illness

• History of recent illness unrelated to heat

(especially involving vomiting or diarrhea)

• Certain health conditions2

• Certain medications2

• Physically demanding work

• Recent alcohol use (within previous 24 hours)

1

When ambient conditions are higher than body 

temperature, warm airflow can actually increase heat gain.

2

Refer to the Heat Stress: Risk Factors fact sheet [(DHHS) 

NIOSH No. 2017-125] or consult a healthcare provider.

Workers need to look out for each other! 

Use a buddy system!

Often it is a coworker who first 

notices signs of heat stress in 

another employee.

OFTEN FATAL Severe Less Severe

Types of Heat Illness

Heat rash/“prickly heat”

• Red cluster of pimples or small blisters,

usually on neck, upper chest, groin, under 

breasts, and in elbow creases

Heat cramps

• Muscle cramps, pain, or spasms in the

abdomen, arms, or legs

Heat syncope (fainting)

• Fainting, dizziness, or light-headedness,

after prolonged standing or suddenly 

rising from a sitting or lying position

Heat exhaustion

• Headache

• Nausea

• Dizziness, weakness

• Irritability

• Thirst

• Heavy sweating

• Elevated body temperature, decreased

urine output

Heat stroke

• Confusion, altered mental status, slurred

speech, loss of consciousness

• Hot, dry skin or profuse sweating

• Seizures

• Very high body temperature

• Fatal if treatment is delayed

Photo by ©Thinkstock
heat stress Overview

Points to Remember

Hot environments can be hazardous! 

• Heat exhaustion is treatable, but can turn into heat 

stroke quickly if not recognized and treated.

• Heat stress can affect alertness and judgment, 

which can lead to accidents and injuries.

• Heat illness does not always happen on the hottest 

days. It can happen in moderate conditions, or 

even in cool conditions when performing heavy 

physical work. 

• Get emergency medical aid immediately if heat 

stroke is suspected. The risk of death is higher 

without rapid treatment.

Stay hydrated! 

• Drinking enough fluids is one of the most important 

ways to avoid heat illness.

• Don’t rely on thirst to tell you when you are 

dehydrated—thirst lags behind dehydration by 

several hours.

• Drink 1 cup (8 ounces) of water every 15–20 

minutes while working in the heat.

• Electrolytes can be replaced by eating regular meals.

• Sports drinks can also replace electrolytes, but 

are not usually necessary unless heavy sweating 

continues for more than 2 hours and eating meals 

or snacks is not an option.

Acclimatization is critical, and may need 

to be repeated!

• Heat acclimatization is the improvement in heat 

tolerance that comes from gradually increasing 

the duration or intensity of work performed in a 

hot setting.

• Acclimatization is most effective if it takes place 

gradually over a period of 7 to 14 days.

• You begin to lose your acclimatization after about 

one week away from work in the heat.

• After 1 month away from work in the heat, most 

people will have lost nearly all heat acclimatization.

Give your body time to cool off. 

Pay attention to work/rest schedules!

• You must take rest breaks periodically to allow your 

body to cool down.

• Work/rest schedules can increase productivity and 

reduce risk of heat illness by guiding workers on 

how often to take cooling breaks.

• Know your personal limits and options for cooling 

at your worksite. Let a buddy know if you need to 

take a break to cool down.

Case Study: Heat Illness and Heavy Machinery*

A 48-year-old employee was running a loader at an open pit

mine in Arizona in mid-August when another employee noticed

he was just sitting in the cab and not moving. A supervisor

called the employee on the radio three times with no response.

The supervisor went to the employee and discovered him to be

confused and unresponsive. 

More than just a health issue!

What might have happened if the employee had been 

driving or operating the loader when he became unresponsive?

*MSHA Accident and Injury Report

Photo by ©Fotolia 

DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

DHHS (NIOSH) Publication No. 2017-123