Heat stress a common cause of fatigue, exhaustion

Heat stress a common cause of fatigue, exhaustion

Workers must be aware of many negative consequences

heat stress worker

Tired stress worker sweat from hot weather in summer working in port goods cargo shipping logistic ground, Black African race people.

Occupational heat stress is the heat load to which someone is exposed in the workplace, which is a function of the environment, physical exertion and clothing.

Heat stress causes increases in both skin and internal body temperatures, leading to dehydration if fluid lost to sweating is not replaced by drinking.

Increases in internal temperature and dehydration have many negative consequences. For instance, the cardiovascular system can become strained, the kidneys are forced to work harder, and cognitive function and decision-making can become impaired.

As a result, occupational heat stress increases the risk of heat illness, elevates the risk of accidents, doubles the risk of injury, and can cause profound decreases in work productivity.

The common denominator underlying these statistics is that heat stress accelerates the development of fatigue, which can ultimately result in exhaustion. This fatigue is caused by a multitude of changes in the body.

By understanding how heat stress promotes the development of fatigue, countermeasures can be put into place to ensure a safe and productive work environment.

Accelerated fatigue

Heat stress accelerates the development of fatigue in two ways — both of which are mostly dependent on how elevated internal temperature becomes.

First, heat stress increases the demand on the cardiovascular system. The goal of the cardiovascular system is to maintain blood pressure so that oxygen-rich blood can be delivered to the active tissues, such as the working muscles and brain.

Heat stress makes this more challenging such that blood pressure is lower during physical work in the heat compared to the same workload when carried out in a cooler environment.

This lower blood pressure during heat stress is accompanied by a higher heart rate to help offset a lower volume of blood ejected from the heart with every beat.

As a result, the demand on the cardiovascular system is greater, which makes physical work in the heat more difficult compared to in cooler conditions.

Importantly, all of this can be made worse by dehydration.

Impaired nervous system

Heat stress can also impair functions of the nervous system.

The nervous system is a way in which signals can be rapidly transmitted throughout the body. For instance, during physical work, nerve signals from the brain tell the muscles to carry out a given task.

Heat stress can alter this process such that to carry out a given task (for example, moving something from one place to another), the nerve signal must be larger during heat stress compared to when the task is carried out in cooler conditions.

As a result, it is more difficult for workers to carry out their normal tasks during heat stress.

Prevention measures

Preventing heat stress-related fatigue and exhaustion involves limiting increases in body temperature and the development of dehydration.

If heat exhaustion (a type of heat illness) is suspected, it is encouraged that the worker be removed from the hot environment and fluids are replenished.

Heat exhaustion is serious, but not life-threatening. However, forcing a worker to continue to work despite being exhausted increases the risk of exertional heat stroke, a life-threatening condition.

This is why it’s important to take steps to minimize increases in core temperature and keep workers hydrated throughout the workday.

When working in a hot environment, it is recommended that workers and their supervisors adhere to recommendations by governing bodies.

Implementing these recommendations will largely prevent sustained increases in body temperature and dehydration.

Such recommendations include provisions for workers taking frequent breaks in cooler environments, giving workers regular access to cool fluids and encouraging them to drink, and having workers participate in heat acclimatization protocols — which can improve the capacity of the body to regulate temperature.

Nicole Moyen is vice-president of research and development at Kenzen, a PPE company in New York. She was assisted with this commentary by Zachary Schlader, an associate kinesiology professor at the School of Public Health – Bloomington at Indiana University, as well as Jessica Freemas, a PhD student studying under Schadler.

This article was featured in OHS Canada, and you can see the original here.

How radiant heat increases injury, illness risk for rooftop solar workers (and four prevention tips)

How radiant heat increases injury, illness risk for rooftop solar workers (and four prevention tips)

by Nicole Moyen

You can see the original article in Solar Builder, here.

Working on a rooftop, closer to the sun and out of the shade, puts workers at increased risk for heat injuries and illnesses. The good news is that heat illnesses are 100 percent preventable if you understand what happens to the body while it’s working on that hot rooftop.

The science

When working in the heat, your heart rate will be higher for the same workload, which makes the work feel harder. Increasing heart rate is the body’s most common response when it is exposed to heat over a period of time during labor. The heart helps the body compensate for several changes that are happening simultaneously to allow the worker to keep pace with his/her activity.

The muscles that are moving the body during work need energy to keep functioning. This energy comes from the types of food workers eat, but oxygen is needed to metabolize that food to make energy for the working muscles. This necessary oxygen is carried in the blood, and delivered to the muscles. The heart is the organ that pumps the blood throughout the body. The harder you’re working, the faster your muscles need that energy, and therefore oxygen. As a result, the heart must pump the blood faster to the working muscles, leading to an increase in heart rate.

Your heart rate typically goes up in parallel to how hard you’re working under temperate weather conditions on a job site. But in the heat, there is added strain to the system, because the blood not only needs to go to the working muscles, but also the skin to get rid of body heat.

When it’s hot outside, your temperature will start to rise. One of the main ways we get rid of body heat (along with sweating) is by increasing the blood flow to our skin. Blood carries the heat away from the core to the skin. The harder a person works in the heat, the faster his/her body temperature increases, and the stronger the need to get rid of that heat to stay safe. So not only does blood need to go to the muscles to keep working, but also needs to go to the skin to get rid of heat. This is why your heart rate will be higher when working in the heat vs. working in a temperate climate.

Dehydration can exacerbate the effects of heat stress because there is less water (or blood volume) to be sent to the working muscles, and skin, and to be lost through sweat. This means your heart has to work even harder to pump the blood needed at the working muscles and the skin, so heart rates will be even higher when working in the heat dehydrated. When dehydrated, your body also tries to conserve water which means that your sweat rate goes down. With a lower sweat rate, you can’t get rid of body heat as quickly, and so your core body temperature will go up even faster when you’re dehydrated working in the heat (than when you’re well hydrated) putting you at increased risk for heat-related problems.

Prevention actions

Heat injuries and illnesses, including fatalities, happen under these hot conditions which are common in the summer months. But as mentioned, heat illnesses are 100 percent preventable if workers and their supervisors understand what happens to workers in the heat, and take the following 4 actions.

1. Account for radiant heat load.

Solar workers are up on rooftops working directly in the sun, which can pose high risk for heat-related injuries and illnesses. Roofs can range in temperature, but can be upwards of 140°F (60°C) on black roof, for example. Part of this increased risk is due to high radiant heat loads (from the sun). Even on a cool day, if it’s sunny outside, managers should measure the radiant heat load to assess the heat strain on their workers. Radiant heat is measured via black globe temperature, and this measurement should be accounted for when prescribing work/rest schedules for your workers on site. The WBGT (wet bulb globe temperature) accounts for radiant heat, and it should always be factored in at sites where workers are directly exposed to the sun.

2. Stay hydrated.

Start your work day hydrated: you can check your urine color, which should be clear to light lemonade color. Drink 8 oz of water in the morning before heading to work. Throughout the workday make sure to replace the fluids you’re losing through sweat to avoid dehydration. On really hot days, try to drink at least 8 oz (half of a commercial-size water bottle) at least every 30 min if not more often. And after work, minimize the amount of alcohol you drink to avoid dehydration the next day at work.

3. Monitor workers’ heart rates and other vital signs.

It is becoming increasingly easier to monitor the heart rates of every individual on the job through smart PPE worn by the worker that relays warnings to both him/her and the supervisor, and prompts a rest period to avoid dangerously high core body temperatures. If your workers’ heart rates are a lot higher than normal for the same workload (e.g. >15-20 bpm higher), it is likely that they are dehydrated, which exacerbates the effects of heat stress and therefore increases the risk of heat injuries and illnesses.

Avoid high core body temperatures that can lead to heat injuries and illnesses. Monitor core body temperatures and take breaks when necessary to cool the body down, ideally in the shade or an air conditioned space, remove extra clothing layers to help you cool, and rehydrate.

4. Acclimatize to the heat.

Heat acclimatization increases blood volume, which helps to lower heart rate. This means that after acclimatization, your heart rate won’t be as high for the same work in heat, so the body is less strained. Acclimatizing means adapting to hot conditions to minimize the risk of heat illness and death. Heat acclimatization can be accomplished by exercising in the heat, taking saunas or hot water baths after a workout, or simply by working in hot conditions on a daily basis. The biggest changes to the body during the acclimatization process happen in the first 4-5 days of these preparations, but full acclimatization can take up to 2 weeks or longer. After acclimatization, sweat rate will be higher, while heart rate and core body temperature at rest will both be lower. These changes improve the body’s ability to get rid of heat, which helps a person work longer and harder in hot environments without lower risk of heat maladies.

Employing these four action items at your worksite will minimize heat-related injuries and illnesses, and help keep your workers safe in these challenging work conditions.

Nicole Moyen is VP of Research and Development at Kenzen and a heat stress blogger, currently finishing her PhD in Biology from Stanford University. Kenzen is a smart PPE innovator focused on physiological monitoring and the prevention of heat injury and death among workers. Kenzen’s real-time heat monitoring system is used by companies to keep workers safe from heat. 

What “industrial athletes” can learn from professional athletes when it comes to working in heat

What “industrial athletes” can learn from professional athletes when it comes to working in heat

by Nicole Moyen

You can see the original article in Canadian Occupation Safety, here.

Industrial workers can learn a lot about how to maximize their performance and productivity at work by watching how athletes train, eat, sleep, and care for their bodies. Elite athletes are constantly trying to find ways to gain a slight edge over their competition by controlling every possible variable that they can. They must perform in various environmental conditions, including heat, which can lead to a suboptimal performance. Many of the ways athletes prepare for competition in the heat to maximize their performance are practices that can be adopted in the workforce to maximize productivity. Below are tips for commercial workers:

Heat Acclimatization:

Most heat-related injuries and illnesses occur during the first 1-2 weeks of working in the heat, so by acclimatizing (i.e., adapting) to the heat, you minimize the risk of heat illness and death. Acclimatization to the heat can occur via exercise in the heat, sauna or hot water bath, or working in the heat. The largest changes to your body (during the acclimatization process) happen in the first 4-5 days, but full acclimatization can take up to 2 weeks or longer.

After you have acclimatized to the heat, your sweat rate will be higher, your heart rate will be lower, and your core temperature at rest will be lower as well. These changes improve your body’s ability to get rid of heat, which helps you work longer and harder in the heat.

Before competitions in the heat, athletes will acclimatize to the heat either by exercising in the heat for 60+ min per day, or by sitting in a hot water bath (or sauna) after a workout for at least 60-90 minutes per day, for 1-2 weeks.

Note that when initially acclimatizing to the heat, you will likely need to reduce your workload and/or wear less protective gear to help facilitate cooling. Each day, you can gradually work longer or harder, and add on more protective clothing. For example, football players acclimatizing to the heat do not wear their full gear until day 6 of acclimatization, and they minimize practice time to 3-5 hours per day with frequent breaks, to allow their bodies ample time to acclimatize. Athletes also slowly increase their exercise intensity (i.e. workload) and/or duration during the first week of heat acclimatization. These same rules can be applied at the jobsite.

Lastly, you will need to maintain your heat acclimatization by exposing yourself to the heat (either via working in the heat or sitting in a hot water bath/sauna) at least once every 5 days. If this is not possible, then doing a hard workout outdoors or wearing extra clothing (to increase your body temperature) while exercising can help to maintain some of these adaptations.


Another important component of staying safe in the heat is staying hydrated before, during, and after your work in the heat. Athletes are very vigilant of their hydration because they know how much it can affect their performance. The easiest way to make sure that you are staying hydrated is to check your urine color in the toilet bowl. If it is a lemonade color or lighter, you are hydrated. Or if you are urinating at least every 2 hours, you are probably doing a good job staying hydrated as well. Hydration is crucial to keeping your body temperature down, which allows you to stay productive and focused on the job.

Dehydration not only increases the strain on your heart, but leads to a higher core body temperature, which can decrease your performance, mood, and cognition.

Some simple ways to improve your hydration are:

Carry a water bottle with you throughout the day, and make sure that you are drinking at least 8 oz. (half of a standard-sized water bottle) every hour, if not more.
Drink fluids with electrolytes (especially sodium), as it will help to absorb the water you drink. Just watch the sugars in your drinks- you do not need them!
Pace yourself when drinking water- do not chug it! Your body can only absorb water at a certain rate- you can’t just “chug” a bunch of water at the end of the workday— you will just urinate it out. The rule of thumb is that your body can only absorb ~8 oz. (half of a water bottle) every 15 minutes, so try to pace your water drinking to that rate.
You can lightly salt your foods- especially in the first few days of working in the heat. This will help you to replenish the salts you are losing in your sweat and help keep you hydrated.

During exercise and work in the heat, your body utilizes more carbohydrates than normal. This means that adding more carbohydrates to your diet can improve your performance in the heat. However, not all carbohydrates are created equal. Make sure that you are eating more complex carbohydrates like whole grains, beans, fruits, and vegetables that are high in carbohydrates and in fiber, and that you are not eating a lot of simple carbohydrates like fruit juices, sodas, and baked goods that are filled with sugars.

Athletes know that the foods they put into their body are essential to their performance: it is their fuel. This means that you have to pay attention to the fuel you are giving your body and make sure that you are giving your body foods that will improve your performance and productivity on the job. Make sure that you are eating healthy, balanced meals that contain minimal sugars and alcohol, as these two items can leave you feeling lethargic, dehydrated, and sluggish.

As an industrial athlete, you are working your body hard every day, just like athletes in sport. Make sure you train, eat, sleep, and hydrate like an elite athlete so that you can perform well at your job and minimize your risk for heat-related injuries and illnesses. Take a note from the athletes and get your body in tip-top shape so that it is ready for the heat!

To learn more about heat stress, follow my blog on the topic at https://www.kenzen.com/news-blog/.

Protecting Field Workers in the Summertime Heat

Protecting Field Workers in the Summertime Heat

by Nicole Moyen

You can see the original article in T&D World, here.

Utilities’ and contractors’ field crews must often work in extreme heat during the summer months. Here is how to recognize symptoms of heat stress.

You’ve likely experienced a hot day working in the heat. You’re hot, thirsty, tired, and sweaty, and the work that you’re used to doing feels even harder. But why?

Your body wants to maintain a really tight temperature range: ~3-4°F or 2-3°C. But even increasing your body temperature by 1-2°F can have a big impact on your body’s physiological responses. Your body temperature goes up when you are accumulating heat faster than you can get rid of it.

You can accumulate heat from the environment, like when it’s really hot and humid outside, or when you’re exercising or working really hard in the heat. When you’re working or exercising, your muscles produce heat as a byproduct of the movements you’re doing. In response to this increase in heat production, we increase blood flow to the skin (to move heat from the body core to the skin) and start sweating to get rid of body heat.

However, if you’re producing heat faster than you can get rid of it, your body temperature will go up. As your body temperature gets higher, you will sweat more too in order to try to get rid of more heat. The hitch is that the sweat must be evaporating off of you to cool you down and reduce your core body temperature (i.e. dripping sweat doesn’t cool you down). As you’re sweating more, you’re losing more body water.

Your blood is made up of ~50% water, and so when you lose this water through sweating, your blood volume goes down. This is a problem because you need blood to go to the working muscles in your body for energy. Your blood carries oxygen, which is essential for your muscles to create the energy they need to keep working. This also means that you have less blood going to the skin to get rid of heat. As a result, your heart (which pumps the blood) has to work even harder to get the same amount of blood to your working muscles and to the skin. This means that your heart rate will be higher when working in the heat vs. working in a comfortable environment.

The loss of water (and therefore blood volume) through sweating is one of the reasons staying hydrated is so important. By replacing the fluids you’re losing through sweating, you can help your heart rate to stay lower during your work in the heat. In turn, this will allow you to work harder in the heat–simply by staying hydrated.

If you’re not staying hydrated on the job, not only will you have a higher heart rate, but you will feel more fatigued, and are more likely to be in a bad mood (frustrated, angry, etc), and you might also experience some “fogginess” in your thinking. So make sure that you’re taking frequent breaks, drinking plenty of fluids, avoiding alcohol, and eating healthy foods.

Most importantly, if you start to experience any of the signs and symptoms of heat injury or illness, be sure to stop working right away and take a break. These are early warning signs that your temperature is getting too high and you need to slow down and take a break. Remember that heat illness can lead to exertional heat stroke and even death. Take any signs and symptoms seriously.

Monitoring your heart rate with smart PPE or a chest strap can help you to know if you might be dehydrated, because your heart rate will be higher than normal for the same workload. Make sure that you are staying aware of how you’re feeling throughout the day, and have a buddy to check in with and talk to so that you can make sure you are both doing okay on really hot, humid days.

Drink plenty of fluids, stay cool, and pay attention to your body and any warning signs it might be giving you to stay safe in the heat.

Get Ready for a Safe Summer of Working in the Heat

Get Ready for a Safe Summer of Working in the Heat

by Nicole Moyen

You can see the original article in EHS Daily Advisor, here.

Heat is the invisible factor that affects your workforce. This summer and in the summers to come, temperatures are only projected to get hotter and more variable, so it’s increasingly important to know how to keep your employees safe while they work in the heat.

Aside from outfitting your workforce in smart personal protective equipment (PPE) that allows you to monitor them on a real-time, daily basis and keep them safe in extreme environments, there are several things you can do that are also effective.

Setting up the Worksite

Make sure there are easily accessible cooling stations for your team members that are less than a 5-minute walk from where they’re working. Here are some key considerations for creating your worksite cooling stations.

  • The cooling stations should have an ample supply of potable water that is kept cool and is near the workers’ rest stations.
  • These stations should also be under shade or in an air-conditioned area.
  • There should be a means to reach emergency services at each station in case a worker needs to undergo extreme and immediate cooling.
  • At least one chair or cot should be available at the cooling station in case a worker needs to sit or, if he or she is feeling light-headed, to lay down with his or her legs propped up on the chair to help return blood flow to the heart and brain.
  • There should be an emergency ice bath or cooling system available, such as an ice chest that contains cold compresses, kept within a short (i.e., less than 10 minutes) walk from all highly populated worksites. If the distance from worksites is greater, a mode of transportation should be provided for workers to get to these ice baths quickly if needed. Ice water baths are the number one way to save lives and prevent exertional heatstroke and death. You can also use a tarp (cradled around the individual) filled with ice and water in place of a tub.
  • Along with the ice bath, you will need to fill a chest of ice each day and make sure there is an ample supply of water present near the ice bath to quickly fill or refill the tub. If this is not possible, make sure cold compresses, an ice chest, and a cooler of water are placed near the highly populated worksites each day in case of emergency.

Educating Your Workforce

Make sure you educate yourself and your workers about the signs and symptoms of heat injury and illness, and encourage your workers to be honest when they’re not feeling well. Ensure they take breaks when needed to allow them to stay hydrated and at normal body temperatures throughout the workday. Educate your workers on the dangers of ignoring their signs and symptoms, as well; ignoring changes in their bodies could result in a serious heat injury or illness that will prevent them from working for days or even weeks.

If you don’t have individualized monitoring, you should employ work-rest schedules at your site, which are calculated based on workers’ clothing, the air temperature in the work environment, the humidity, sun exposure, and workload. You should check these work-rest tables each day to assess how long workers should be resting vs. working every hour. But be aware that these work-rest schedules are not specific to each individual, so there will be some individuals who need to rest earlier and some who can keep working despite the prescribed work schedules.

Workers should be made aware that these work-rest schedules are not “one-size-fits-all” and that they may need to stop sooner, or be able to work longer, than what’s prescribed. Many factors unique to each individual (e.g., age, sex, medications) will change how well a worker can tolerate the heat, which will affect how well he or she can work in the heat.

Let Workers Take Breaks When Needed

Letting your workers take breaks when needed—ideally resting for 10 to 15 minutes each hour when it’s very hot and humid—will help them keep their core body temperature lower and allow them to stay hydrated. This, in turn, allows them to work harder and longer while ensuring they stay alert and focused on the job.

If you push your workers too far, you can put them at risk of heat injuries and illnesses. Depending on which injuries or illnesses your workers obtain and the severity of the incident, they could be out of work for a day or up to several weeks. When in doubt, listen to your workers when they need to rest, and err on the side of caution by giving them a 10- to 15-minute break each hour to cool down. This will ensure your workforce stays safe and productive instead of risking long-term absences from work due to heat illness.

By making a commitment to stay informed and share your knowledge of heat safety with your workforce, your entire team will stay healthy, safe, and productive.