Mitigating the Hazards of Working in the Heat

Words: Jim Rogers

Words: Jim Rogers
Photos: GregorBister

Construction is a labor-intensive industry. We rely on people to get things built, and those people need to be safe and healthy to do their jobs. Much of this work is done outside, and extreme weather conditions are something that cannot be controlled. In areas where extreme heat can be expected throughout the summer, it is important to understand the risks and hazards presented by these environments, as well as understanding the signs and symptoms of heat-related illnesses in order to keep people safe. It is also prudent to develop objective criteria for categorizing the risks each day so that managers and those working in the field can take appropriate precautions.

The human body is in a constant state of fluctuating between generating heat and losing heat. Under normal non-working conditions, the body can be exposed to a wide range of temperatures and still maintain its core temperature within a degree or two of normal. However, when a person is working, exercising, or conducting any increased physical activity, the body generates more internal heat. The body attempts to move that heat away from its core and out to the skin by increasing the size of the blood vessels near the surface of the skin so they can carry more blood, causing the heart to work harder to push the blood to the surface and fill these enlarged vessels. In extreme conditions, when the body is unable to get rid of heat fast enough, its core temperature will begin to rise. As body temperature increases, heat-related illnesses can occur. As body temperature continues to increase and approaches 104 degrees, internal organs can begin to shut down and the condition can be fatal. 

The body uses different mechanisms to rid itself of internal heat:

  • Conduction is the direct contact of a body part to a cooler object that causes the heat to transfer away from the body – this is why devices like the “cool bands” work when they are worn on the neck, they not only feel cool, they help draw away some of the excess heat.
  • Evaporation is another important mechanism the body uses to cool itself. Skin becomes wet with sweat and the evaporation of that moisture from your skin causes the body to lose heat. During intense physical activity, the body loses 85% of its heat through sweating; however, this effect decreases as the humidity in the air goes up, which is why high humidity can increase the chances of a heat-related illness, even in lower to moderate temperature ranges. 
  • Radiation is like heat leaving a fireplace. This is the normal process of heat moving away from the body. In cooler weather, this is how the body loses most of its heat, but as the temperature outside rises above your body temperature, this becomes less effective.
  • The body can also lose some heat through Convection, which occurs when the wind blows across the skin, carrying away additional heat

While the outside temperature and humidity cannot be controlled, there are other factors that can increase a person’s risk for heat-related illnesses that can be controlled. 

Working outside in direct sunlight creates more exposure than what is measured on a thermometer. Besides measured ambient heat, there is exposure to additional radiant heat from that direct sunlight. This effect increases on days with no clouds, or when working on a very reflective surface such as a radiant roofing membrane, or near a radiant heat source like welding. 

Published weather reports that include the Heat Index, or a “feels like” temperature that takes both heat and humidity into account do not account for this radiant heat. It assumes light activity in a shaded area. In the direct sun, doing physically demanding work, the Heat Stress Index can be as much as 15 degrees higher than the published Heat Index. In the field, consider controlling this by using shade that can be created with inexpensive pop-up shade structures. 

Limited air movement when there is no breeze outside increases the risk of heat illness because the body cannot lose any heat through convection. This is when fans can be used to help the cooling effect.

Low fluid consumption is a big factor in heat-related illnesses. It is important to avoid caffeinated drinks because caffeine causes the body to lose moisture faster. High caffeine energy drinks should be discouraged or even banned from the job site. The body can only absorb liquids so fast, which means that a person needs to start hydrating by drinking plenty of water the night before work and avoid alcohol. Then, throughout the work shift, it is important to drink frequent small amounts of water throughout the day, about 1 cup every 15 to 20 minutes under moderate conditions. This water should be kept cool and placed in convenient locations around the job site to facilitate frequent use. 

Physical exertion is a factor that increases risk. This makes the need for frequent breaks important in the heat of the summer. As the risk of heat exposure increases, productivity expectations need to be adjusted down, especially for very physically demanding tasks. 

Heavy personal protective clothing can make that effect worse, so look for loose cotton clothing and reduce the number of layers by doing things like wearing a high visibility shirt, rather than a vest over a shirt. 

Poor physical conditions or health problems can increase a person’s risk. As can some medications, pregnancy, advanced age, or a previous episode of heat illness. People that fit into any of these categories need to consult with their health care professionals for personal recommendations. 

Many studies show a lack of recent exposure to hot working conditions is a risk factor. New workers, anyone that is not accustomed to working in the heat, or people that have not worked in the heat for more than a week, should be acclimatized to build up their ability to work in the heat by gradually increasing the workload and allowing for more frequent breaks during the first two weeks of exposure.

Heat illness includes a group of health-related conditions that can occur when the body is unable to effectively rid itself of heat buildup. This can range from heat rash and heat cramps, which can be dealt with on the job site, to heatstroke, which is a life-threatening medical emergency that will result in death if not treated in a medical facility. 

In order to prevent these heat-related illnesses, workers and supervisors should be trained about the hazards of heat illness, the factors that increase those hazards, how to recognize the symptoms of heat illness, and the first aid measures that need to be taken in the field. Train and encourage workers to immediately report heat illness symptoms in themselves and others and encourage them to watch out for their co-workers. 

One of the common questions from the field is, “how can we make prevention less subjective, and how can we come up with a mandatory set of actions based on the heat risk factors.” 

The Centers for Disease Control (CDC) and the National Institute for Occupational Safety and Health (NIOSH) answered this question in a lengthy research report titled NIOSH Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments. The research draws on success using systems and criteria utilized by the military and professional athletes in training. It recognizes the deficiencies in using the published heat index and accounts for both temperature and relative humidity. The optimal way to do this involves using an instrument to determine the Wet Bulb Globe Temperature (WBGT), which is the only way to accurately account for radiant heat. This is not always practical on job sites, so a simplified set of criteria is also provided that is quick and easy to deploy on any project. 

The simplified criteria utilizes the published heat index but establishes modified cut off points to create heat hazard categories that account for typical job site conditions of more strenuous work being conducted in direct sunlight. Very specific work practice recommendations are given for each of the established heat hazard categories. 

A screenshot of a cell phone

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The simplified criteria is also supported by a smartphone app published as the OSHA-NIOSH Heat App, that is available for both Android and iPhones. This application is location-enabled and allows anyone on-site with a smartphone to quickly determine the heat hazard category for their location. Clicking a button in the app opens the specific criteria that needs to be followed for each category, and it also includes signs, symptoms, and first aid for heat-related illness. 

Don’t forget the basic heat stress solutions of water, rest, and shade! Learn the signs and symptoms of heat illness. Treat the extreme heat with respect and realize that it is no different than snow and ice and extreme cold, in that sometimes the only thing we can do to stay safe is reschedule the work. 

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