The Dangers of Heat

August 15, 2025

We are well into the heat of summer, with many areas experiencing extreme temperatures that continue to produce headlines that include injured hikers, service workers, and even first responders. The hazards produced by extreme heat and humidity cannot be overstated. There is a fine line between the condition called “heat exhaustion” and the one called “heat stroke”, and the later is a medical emergency that frequently results in death. Do you know the difference? Do you know the signs and symptoms along with the first aid and steps to be taken when you or a colleague fall victim to the heat?

Recognize the Hazard

Step One is to recognize the hazard. The human body produces heat internally. To prevent this heat from building up to the point of damaging internal organs, the body has mechanisms that move the heat away from the core and towards the skin, where the heat can dissipate. Under non-extreme ambient temperatures, the heat dissipates through radiation; in other words, internally produced heat is moved (carried by the blood moving through your body) to the skin where it radiates away from the body keeping your core temperature from rising to the point of causing harm.

Under extreme conditions, the body has to work harder to dissipate this internal heat. Physical exertion increases the rate the body produces internal heat. As that internal heat begins to build up, the body has to work harder to dissipate it. The blood vessels in your skin dilate to accommodate more blood. The heart works harder to pump more blood away from your core and towards the skin, transporting that internal heat to the surface of your body where it can radiate away. As the ambient (outside) temperatures rises above your body’s temperature, radiation becomes a less effective method of heat dissipation. The body is working harder to move the heat away from the core, but it stops leaving the skin.

The body then employs another mechanism to attempt to cool the skin so heat can dissipate. Perspiration begins. Air moving across the skin evaporates the moisture being produced by the body resulting in a cooling effect from evaporation. As outside humidity increases, this evaporative cooling effect also becomes less effective because there is so much moisture in the air. You continue to perspire, but there is little evaporation occurring.

As the body attempts to move a higher volume of blood to carry more heat, and it continues to perspire to encourage evaporative cooling, the demand for hydration increases. Your body needs more water, and it needs that water to be absorbed into the blood stream. As perspiration increases and the body’s demand for a higher volume of blood increases, it is using up fluid resulting in an increased demand for hydration…more water. However, when we drink water it enters the body’s digestive system where it takes time to be absorbed into the blood stream where it’s needed.

Heat, exertion, humidity, and lack of hydration all pose a hazard. As these factors combine, the hazard increases significantly. The heart pumps faster and fluids are rapidly consumed, restricting the ability to move heat out of the core. When the body cannot move heat away from the core fast enough, your core temperature rises. When the body’s core temperature goes too high, it causes damage (often irreversible) to internal organs.

We Can’t Control the Weather Outdoors

Indoors, we have more options available to protect us from the heat and humidity. Air conditioning can be used to control both. But what options do we have when we are outdoors?

First, remember the lesson from last month’s newsletter and apply the hierarchy of hazard controls.

Ask yourself, “Can I eliminate the hazard?”

Some activities should just be avoided. Don’t go hike in the heat of the day. If the trails are closed, it’s for a reason. Move your activity to the cooler parts of the day. Schedule work that requires higher physical exertion for the early morning hours before the temperatures rise. Consider whether activities or portions of the work can be moved in-doors.

Remember engineering and work practice controls

Some work activities can’t be avoided and can’t be shifted to cooler areas or parts of the day, but there are options for “engineering controls” that can help reduce the risk. Fans help move air across the skin to promote evaporative cooling. Misters can also be used (when humidity is not too high) to improve the effects of evaporative cooling. Shade structures are another alternative that can be easily put up to shade and reduce temperatures in the work area or to at least provide a shaded area for breaks.

Speaking of breaks, don’t forget the “work practice controls”. Taking breaks lowers physical exertion and lets the body catch up. Taking breaks in the shade or a cooled area like a job site trailer improves the body’s ability to reduce core temperatures and prevent heat related injuries. Taking off any added layers of clothing such as a PPE also helps the body radiate heat away from the skin. Taking off your hi-vis vest, gloves, and hard hat during breaks can make a big difference. Take breaks more frequently as exertion levels, temperature, and humidity increase. Drink smaller amounts of water more frequently (the CDC recommends drinking 8 ounces of water every 15-20 minutes). It takes time for the water to be absorbed. When you consume a large amount of water all at once, most of it is going to just sit in your stomach and will not provide the immediate relief needed to help with hydration.

Can I turn to PPE?

We are beginning to see some PPE available that promises to help with cooling. Cooling vests, headbands and helmet liners, and even personal fans and cooling devices are becoming available and these are all things you can explore to protect yourself.

Personal Choices

When dealing with the heat, it’s important to recognize that there are many personal choices and factors that you have the power to control. The concept of acclimatization comes into play here. This concepts says that a person’s body can acclimate to the heat. The concept is real, and has been proven in many studies. It says that by gradually increasing exertion and exposure to the heat, a person’s body adapts and becomes better able to regulate its core temperature. While some acclimation regimes may hinge on your employer understanding the concept and implementing work schedules to accommodate it, it’s up to you to choose to comply. Spend a week or two gradually increasing the amount of time you work in the heat. Gradually increase your level of exertion. Take more breaks during this two week acclimation period. It allows your body to adjust and acclimate, and it helps you to gain a better level of understanding of what you can do to avoid heat related injuries.

Hydration is another big personal “choice”. Yes, your employer needs to provide a readily available source of cool drinking water. But it’s up to you to drink it, and to do so regularly, throughout the day. Don’t wait till you are thirsty. That’s your body telling you that you have waited too long and are becoming dehydrated. You also need to work on hydration outside of work hours. You can’t just wake up in the morning and drink a gallon of water. Remember that is just going to sit in your stomach. It needs time to absorb. Start hydrating the night before. Speaking of the night before, drinking alcohol leads to de-hydration. Think about that when planning your evening activities! Coffee, energy drinks, and excessive amounts of caffeine can also lead to dehydration. Consumption of all of these things is your personal choice. Choose wisely.

Understand the Severity

There are many resources for learning more about the effects of heat on the body and the care and treatment of people who are experiencing heat related injuries or illness. Some of these are listed in the next section along with links so you can learn more. However, before ending this discussion on heat related hazards, it’s important for everyone to understand how severe heat related illness can be.

Heat Stress, also referred to as Heat Exhaustion, occurs when a person becomes dehydrated and the body’s internal temperature begins to rise. As the condition worsens, a person can become faint, dizzy, and disoriented. Falls are more likely to occur and mistakes are more likely to be made. The body needs to be cooled and hydrated to prevent the condition from worsening. A person in this condition should never be left alone and may require medical evaluation to properly diagnose and treat their condition. Left unchecked, this condition can rapidly progress to Heat Stroke; a medical emergency that often results in death. At this point the body’s internal temperature rises above 105 degrees F (40.5 C) and organ damage and failure begins. Perspiration may stop because the body has no more moisture to perspire, which also means the volume of blood in the body is too low and blood pressure can drop.

Immediate medical treatment is required for a person to survive this condition. Rapid cooling using chilled intravenous fluids is required to avoid permanent organ damage. While you should administer first aid similar to that used for heat exhaustion (move to a cool area, remove additional layers of clothing, apply cold packs to central vascular points, and get the person to sip water or water with electrolytes or hydration multipliers), a person in Heat Stroke will not recover without immediate medical attention. It can be difficult to tell the difference between the two conditions without medical training and instruments to check core body temperature, blood pressure and heart activity. If in doubt, get help immediately. Don’t wait. Don’t send a person off to get help on their own. It is better to call for emergency responders and not need them, than to wait until it is too late.

All of the things discussed here also makes doing physically demanding activity out in the heat while alone, particularly dangerous. If you fall, or faint and hit your head, you may not get help unless someone finds you. If you are dehydrated and confused, you may not realize you need medical attention.

Additional Resources

Click the links in this article to read the news stories behind some of the statements being made here! These unfortunate emergencies, rescues, and fatalities really happen. If you work or train in the heat, get educated. Take a course to learn to recognize the signs and symptoms of heat related illnesses, and how to administer first aid. Learn about how to assess the hazards based on the conditions, and what you can do to control or reduce hazards.

• Occupational Safety and Health: Working in the Heat - A course on LinkedIn Learning
• NIOSH / OSHA Heat App - A smartphone app that uses weather data to assign a hazard category throughout the day, also includes signs, symptoms, and first-aid
• CDC Guide to Working in the Heat - On on-line resource from the Centers for Disease Control and Prevention with downloadable content
• Working in Outdoor and Indoor Heat Environments - On on-line resource from U.S. Department of Labor that includes employer responsibilities and regulatory requirements
• Working in the Heat - On-line guide with downloadable content, guides, posters, etc. with translations to several other languages from WorkSafeBC
• Sports and Hydration for Athletes - Great discussion by Johns Hopkins Medicine about proper hydration and the use of sports drinks
• Proper Hydration Poster - A downloadable (PDF) document from the CDC that reminds people how to stay hydrated