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.
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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.
— Solar Builder magazine
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