Heat Stress
Recognize, Prevent, and Respond
- 70+ workers die from heat exposure annually in the U.S.
- Thousands hospitalized each year for heat-related illness
- Most deaths occur in the first week of working in hot conditions
- New and returning workers are at highest risk
- 70% of outdoor worker deaths occur during June-August
- Indoor workers also at risk in hot environments (kitchens, foundries, warehouses)
Learning Objectives:
- Understand how heat affects the body and why it's dangerous
- Recognize three types of heat illness and their symptoms
- Identify risk factors that increase vulnerability to heat stress
- Apply prevention strategies: hydration, rest, acclimatization
- Know how to respond when someone shows heat illness symptoms
- Understand your rights and employer responsibilities
How Your Body Cools Itself
Understanding heat stress
Your body works constantly to maintain a core temperature around 98.6°F (37°C). When you work in heat or exert yourself, your body produces extra heat that must be released.
Sweating (Primary Cooling Mechanism)
When your body gets hot, you sweat. As sweat evaporates from your skin, it cools you down. This is your body's most effective cooling method. However, sweating only works if: (1) you're properly hydrated, (2) humidity isn't too high (sweat can't evaporate in very humid conditions), and (3) you're not wearing clothing that prevents evaporation.
Heat Stress Occurs When Cooling Fails
Heat stress happens when your body can't cool itself fast enough. Heat builds up faster than you can release it. This occurs when: ambient temperature is very high, humidity prevents sweat evaporation, you're doing heavy physical work (generating lots of heat), you're dehydrated (can't produce enough sweat), or you're not acclimatized to heat.
Warning: Internal Temperature Rises
When cooling mechanisms fail, your core body temperature begins to rise. Even a small increase (to 100-101°F) causes symptoms. At 104°F+, organs begin to fail. At 106°F+, death is likely without immediate medical intervention. Heat stroke can kill in as little as 10-15 minutes.
The heat index combines temperature and humidity to show what it "feels like." High humidity prevents sweat from evaporating, making it harder to cool down. A 90°F day with 70% humidity feels like 106°F!
Other factors: Direct sun exposure, lack of air movement/breeze, heavy or non-breathable clothing (PPE, protective gear), physical exertion level, individual health conditions.
Three Types of Heat Illness
From mild to life-threatening
Heat illness occurs in stages of increasing severity. Recognizing early symptoms can prevent progression to more dangerous conditions.
- Painful muscle cramps or spasms
- Usually in legs, arms, or abdomen
- Heavy sweating during activity
- Caused by loss of salt/electrolytes
- Heavy sweating
- Weakness, dizziness, headache
- Nausea or vomiting
- Cool, pale, clammy skin
- Fast, weak pulse
- Fainting or near-fainting
- Body temperature 104°F or higher
- Hot, DRY skin (usually no sweating)
- Confusion, altered mental state
- Slurred speech
- Loss of consciousness
- Seizures
- Rapid, strong pulse OR weak pulse
- Confusion, strange behavior, or doesn't know where they are
- Stops sweating (skin becomes hot and dry)
- Loses consciousness or can't stand/walk
- Seizures or convulsions
Heat Stroke: Emergency Response
Every second counts
Heat stroke is the most dangerous heat illness. It kills quickly if not treated immediately. Body temperature can rise to 106°F or higher in 10-15 minutes, causing brain damage, organ failure, and death.
1. CALL 911 IMMEDIATELY
- Tell dispatcher: "Heat stroke emergency"
- Give exact location
- State person's condition clearly
- Don't hang up until told to do so
2. MOVE TO COOL AREA
- Get person out of heat immediately
- Move to shade, air conditioning, or coolest available location
- If indoors, use fans
3. COOL THE PERSON RAPIDLY
- Remove excess clothing
- Apply ice packs to neck, armpits, and groin (major blood vessels)
- Spray or sponge with cold water
- Cover with wet sheets and use fan to increase evaporation
- If available, immerse in cold water (most effective)
- Goal: Cool body temperature as fast as possible
4. MONITOR AND ASSIST
- Stay with the person until help arrives
- If conscious and able to swallow, give small sips of water
- If unconscious, place in recovery position (on side)
- Be prepared to perform CPR if needed
- Continue cooling efforts until EMS arrives
- Don't wait to see if symptoms improve—heat stroke worsens rapidly
- Don't give fluids if person is unconscious, confused, or vomiting
- Don't give alcohol or caffeinated beverages
- Don't use ice-cold water immersion if person is unconscious (risk of drowning)
- Don't leave them alone—heat stroke can cause seizures or cardiac arrest
Remember: Heat stroke is 100% survivable with rapid treatment. The faster you cool the person, the better their chances. Don't hesitate—CALL 911 and start cooling immediately!
Who Is at Higher Risk?
Recognizing vulnerability factors
While anyone can get heat illness, certain factors increase your risk. Knowing your risk helps you take extra precautions.
- Tell your supervisor about risk factors
- Take more frequent breaks
- Drink more water than others
- Work during cooler parts of day if possible
- Have a buddy watch for symptoms
- Know where cooling areas and water are located
Prevention: Water is Critical
Hydration strategies
Proper hydration is the single most important heat illness prevention strategy. When you sweat, you lose water and electrolytes. Without replacement, your body can't cool itself.
How Much Water Do You Need?
OSHA/NIOSH Recommendation: Drink 1 cup (8 oz) of water every 15-20 minutes when working in heat—that's about 24-32 oz per hour! Don't wait until you're thirsty. By the time you feel thirsty, you're already dehydrated. Drink on a schedule, not based on thirst.
What to Drink
Best: Cool water (50-60°F). Good: Sports drinks with electrolytes (especially for extended work or heavy sweating). Avoid: Caffeine (coffee, energy drinks, soda)—acts as diuretic. Alcohol—dehydrates you and impairs judgment. Very cold/ice water—can cause stomach cramps.
Access to Water
Employer requirement: Fresh, cool drinking water must be readily accessible at all times. "Readily accessible" means located as close as practical to work area. If working in remote areas, water must be provided on-site. There's no excuse for not having water available.
- Dark yellow urine (should be pale yellow or clear)
- Decreased urination or not urinating at all
- Dry mouth, lips, or tongue
- Headache or dizziness
- Fatigue or weakness
- Muscle cramps
- Start work well-hydrated—drink 2-3 cups of water 2-3 hours before work
- Keep water bottle with you at all times
- Drink during breaks AND while working
- Set a timer or reminder to drink every 15-20 minutes
- Drink more if sweating heavily
- Continue hydrating after work to replace lost fluids
Prevention: Rest Breaks & Shade
Cool down to stay safe
Regular rest breaks in cool or shaded areas allow your body to cool down and prevent heat buildup.
Rest Break Frequency
As temperature and workload increase, you need more frequent breaks. Recommended: At minimum, 10-15 minute break every hour in hot conditions. For very hot conditions (heat index >103°F) or heavy work, breaks should be more frequent—every 30-45 minutes. Don't skip breaks to "get more done"—heat illness will cost you more time.
Shade Requirements
Employer must provide: Shaded area large enough to accommodate workers during breaks. Shade can be natural (trees) or man-made (canopies, tents, buildings). Must block direct sunlight. Indoor rest areas should have fans or air conditioning. Temperature in shade should be cooler than work area.
How to Cool Down During Breaks
Remove heavy clothing or PPE if possible. Sit or lie down in shade. Drink cool water. Wet a cloth or bandana and place on neck, forehead, or wrists. Use fans if available. If you have access, wet your shirt or hat. Take enough time to feel cooled before returning to work.
Prevention: Acclimatization
Your body needs time to adapt
Acclimatization is the process of your body adapting to work in heat. This adaptation takes time and cannot be rushed. Most heat deaths occur in new workers during their first week.
- Sweating starts sooner and at a lower temperature
- Sweat becomes more dilute (conserves electrolytes)
- Heart rate decreases during same work
- Core temperature stays lower
- Blood flow to skin increases (better cooling)
Acclimatization Schedule for New Workers
NIOSH/OSHA recommend the 20% rule:
• Day 1: 20% of normal work duration in heat
• Day 2: 40% of normal work duration
• Day 3: 60% of normal work duration
• Day 4: 80% of normal work duration
• Day 5+: 100% of normal work duration (still monitor closely)
Example: If a full day is 8 hours, new worker should work 1.6 hours in heat on day 1, gradually increasing.
Who Needs Acclimatization?
Anyone who: Is new to the job or hasn't worked in heat before, is returning after a week or more away (vacation, illness, time off), is starting to work in hotter conditions than before (heat wave, new location), or has been working indoors and is now working outdoors. Even experienced workers need time to re-acclimatize after time away.
- After 1 week away from heat: Partial loss
- After 2-3 weeks away: Complete loss—need to re-acclimatize
Know Your Body's Warning Signs
Early recognition saves lives
You are the first person to know when something is wrong. Don't ignore symptoms or "tough it out." Heat illness progresses quickly—what starts as mild symptoms can become life-threatening in minutes.
- Headache: Often the first symptom. Persistent headache during hot work is a warning sign. Stop, rest in shade, drink water.
- Dizziness or lightheadedness: Feeling like you might faint, room spinning, unsteady on your feet. STOP immediately—sit or lie down before you fall.
- Nausea or upset stomach: Feeling sick to your stomach, vomiting, or loss of appetite. Your body is struggling. Stop working and cool down.
- Unusual fatigue or weakness: Feeling much more tired than normal for the amount of work you're doing. Muscles feel weak. This is your body telling you it's stressed.
- Confusion or difficulty concentrating: Can't think clearly, forgetting things, making mistakes. Serious sign—get help immediately.
- Irritability or mood changes: Feeling unusually angry, anxious, or emotional. Heat affects your brain function.
- Excessive sweating or sudden stop in sweating: If you're dripping sweat, you're working too hard in heat. If you STOP sweating but are still hot, this is a medical emergency.
- Rapid heartbeat: Heart pounding or racing while at rest. Sign your body is struggling to cool itself.
- Feel like you might pass out
- Can't think clearly or feel confused
- Severe headache that won't go away
- Persistent nausea or vomiting
- Stop sweating but still feel hot
- Can't catch your breath
- Chest pain or pressure
2. Tell someone—supervisor, coworker, buddy
3. Move to cool, shaded area
4. Drink water if you're able to swallow
5. Remove excess clothing or loosen clothing
6. Cool yourself—wet cloths, fan, ice if available
7. Don't return to work the same day
8. Seek medical attention if symptoms don't improve in 30 minutes or if they worsen
Watch Out for Each Other
The buddy system saves lives
Heat illness victims often don't recognize their own symptoms due to confusion and altered mental state. Having coworkers watch each other can catch heat illness before it becomes critical.
- Check on each other regularly (every 15-30 minutes in extreme heat)
- Watch for signs of heat illness
- Take breaks together
- Speak up if you notice symptoms in your buddy
- Get help if needed—don't leave them alone
What to Watch For in Coworkers
Observable signs: Excessive sweating or no sweating, stumbling or poor coordination, slurred speech, unusual behavior or confusion, irritability or aggression, stopping work and sitting/lying down frequently, pale or flushed skin, rapid breathing or panting. Ask questions: "Are you feeling okay?" "Do you have a headache?" "Are you dizzy?" Don't assume they're fine—check!
How to Intervene
If you notice symptoms in a coworker: 1. Speak up immediately—"Hey, you don't look good. Let's take a break." 2. Help them to shade. 3. Get them water. 4. Tell a supervisor. 5. Stay with them—don't leave them alone. 6. Call 911 if they're confused, won't respond appropriately, or collapse. Don't be afraid to intervene—you might save their life.
Employer Responsibilities
What your employer must provide
Under OSHA's General Duty Clause and specific state regulations, employers have legal obligations to protect workers from heat stress.
- Provide water: Fresh, cool, potable water must be readily accessible to all workers at all times. No exceptions.
- Provide rest and shade: Access to shaded or cool rest areas. Breaks must be allowed as needed based on heat conditions.
- Allow acclimatization: Gradual increase in workload for new and returning workers. Follow 20% rule for first week.
- Training: Train all workers and supervisors on heat illness recognition, prevention, and emergency response. Training must occur before working in hot conditions.
- Emergency procedures: Have plan for responding to heat illness. Ensure communication methods (phone, radio) to call for help. Know location of nearest medical facility.
- Monitoring: Supervisors must monitor workers for heat illness symptoms, especially new workers, during heat waves, and during heavy exertion.
- Modify work when needed: Adjust work schedules to cooler times of day, reduce physical demands during extreme heat, provide additional breaks and staff.
- Never retaliate: Workers cannot be punished for taking water/rest breaks, reporting heat illness, or refusing unsafe work in dangerous heat.
- Access to water and rest breaks
- Work in safe conditions free from recognized hazards (including heat)
- Refuse work if you believe conditions are immediately dangerous
- Report heat illness or unsafe conditions to OSHA without retaliation
- Request an OSHA inspection if heat protections are not provided
- California: Detailed heat illness prevention standards (Cal/OSHA Title 8, Section 3395)
- Washington: Outdoor heat exposure rule
- Oregon: Heat illness prevention for both outdoor and indoor workers
- Minnesota: Indoor heat standards for certain industries
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