Heat Stress Risks for Construction Workers: What the Latest Research Reveals

Heat stress is no longer a seasonal inconvenience. For construction workers, it is a year-round occupational hazard with serious consequences. Recent studies, including groundbreaking work by the University of New Mexico, have shed new light on how heat affects the human body and why existing safety measures are insufficient.

This article examines recent research on heat stress in the construction industry, highlighting the factors that put workers at a greater risk and revealing how current safety measures often fall short. It also explores how these findings can inform more effective workplace policies, equipment choices, hydration practices, and environmental monitoring standards.

The UNM Construction Worker Heat Study

A pioneering study led by Professor Fabiano Amorim from the University of New Mexico has become one of the most detailed investigations into heat stress among U.S. construction workers. The research, conducted in Kansas City with support from Turner Construction, Indiana University, and La Isla Network, focused on real workers in real environments.

One of the most revealing aspects of the study was that many companies attempted to beat the heat by starting shifts earlier, sometimes as early as 3:30 in the morning. While this seems logical on the surface, the data told a different story.

The study found that a significant number of workers reached dangerously high core body temperatures despite the early start times. More than 60 percent of workers arrived on-site already dehydrated. Even with hydration protocols in place, many workers failed to maintain proper fluid levels throughout the shift.

The implications were clear. Early start times and access to water are not enough. Heat stress is not just a matter of the time of day. It is a combination of total heat exposure, clothing, exertion level, and environmental conditions.

First of Its Kind in the United States

What made the UNM study so important is that it was the first to focus on the internal core temperatures of U.S. construction workers while they were on the job. Most prior studies had focused on outdoor agricultural labor or used simulated lab conditions. By using wearable sensors and real-time monitoring, the researchers were able to observe how heat exposure played out hour by hour.

This approach brought forward several findings that could not be dismissed. Core body temperatures regularly exceeded 100.4°F, a level considered dangerous by occupational health experts. Workers who began the day dehydrated were much more likely to reach these thresholds early in their shifts.

Perhaps most concerning, the study found that workers often underestimated their own risk. They reported feeling fine even when sensors showed they were approaching unsafe physiological limits.

Metabolic Load and Hydration: The Overlooked Pair

The research team also evaluated the role of metabolic load. Workers performing high-intensity tasks, such as roofing, concrete work, and demolition, were significantly more likely to overheat, regardless of the ambient temperature. Their rate of exertion pushed their bodies to generate more internal heat, making hydration and rest breaks even more critical.

But hydration was often inadequate. Many workers did not drink regularly or relied on sugary drinks that did not effectively replace fluids and electrolytes. In cases where workers did hydrate, they sometimes did so only after symptoms began. That reactive approach proved insufficient.

The researchers recommended that hydration begin before the shift starts, continue at regular intervals, and include options with electrolytes, not just water. Workers also need to be trained to recognize thirst as a late warning sign, not an early one.

Not Just a U.S. Problem

Studies from around the world have confirmed the findings of the UNM team. In Japan, researchers found that heat exposure among construction workers regularly exceeded thresholds set by occupational health guidelines. Many workers experienced elevated heart rates and signs of dehydration by early afternoon.

In India, a survey of workers in high-heat zones revealed that nearly 60 percent of respondents had experienced heat-related symptoms during the summer months. The conditions included headaches, nausea, muscle cramps, and lightheadedness. Many of these workers had no access to shaded rest areas, cooling equipment, or formal hydration protocols.

Even in developed countries, basic protections are often missing. Portable fans, shaded rest areas, and scheduled hydration breaks are still not standard across all job sites. Employers often rely on workers to self-regulate their breaks, despite clear evidence that this approach can lead to inconsistent and unsafe behavior.

The Problem with PPE and Clothing

Another important variable identified in multiple studies is clothing. Construction workers are often required to wear heavy protective gear, including hard hats, gloves, reflective vests, and boots. While necessary for safety, this gear also limits the body's ability to release heat.

Layered clothing and impermeable materials prevent sweat from evaporating, which is the body's primary cooling mechanism. Workers wearing full protective clothing consistently reached higher core body temperatures compared to those in lighter gear.

Researchers emphasized that protective equipment needs to be designed with both safety and heat mitigation in mind. In some cases, lighter materials or breathable designs can reduce risk without compromising protection.

Why Standard Measures Fall Short

The heat index and air temperature are still commonly used to determine heat risk. Still, these single-metric measurements often overlook critical environmental factors, such as wind, solar radiation, and surface temperature. As a result, they can underestimate actual conditions.

In contrast, multi-factor tools like the Wet Bulb Globe Temperature provide a better estimate of heat stress. Studies have shown that relying solely on temperature or heat index often leads to unsafe work continuation when conditions are actually hazardous.

Monitoring WBGT levels, along with internal body temperature and heart rate when possible, gives a much clearer picture of total heat load.

Cooling Gear and Wearables: Do They Work?

Several recent pilot programs have tested the effectiveness of wearable cooling gear, including vests with built-in fans and moisture-wicking fabrics. In trials, workers who wore these garments experienced lower core body temperatures and were able to stay on task longer without symptoms of heat stress.

Cooling vests and sleeves were particularly effective during rest breaks. Workers who used cooling gear during 15-minute recovery periods experienced faster drops in internal temperature than those who used only shade or cold water.

Wearables that measure body temperature and hydration status are also showing promise. These devices provide real-time data that can alert supervisors before workers reach dangerous thresholds. This allows for proactive intervention rather than emergency response.

Cultural and Behavioral Barriers

One often-overlooked factor in heat safety is the workplace culture surrounding breaks. In some job sites, there is pressure to keep working regardless of conditions. Workers may be reluctant to speak up about discomfort or may feel that taking extra breaks could affect their job security.

Researchers have emphasized the need for improved training and stricter policy enforcement to address this issue. Workers should be encouraged to take rest and hydration breaks without stigma or penalty. Supervisors need to set the tone by modeling safe behaviors and ensuring that rest cycles are not only allowed but expected.

Policy Gaps and What Needs to Change

Despite the risks, many regions still lack enforceable heat safety standards. In the United States, the Occupational Safety and Health Administration (OSHA) provides recommendations, but not all states mandate compliance. Some local governments have implemented heat ordinances, but coverage is inconsistent.

Researchers and occupational health experts are calling for federal regulations that require employers to implement heat safety programs. These programs would include mandatory monitoring, hydration plans, scheduled rest periods, and access to cooling zones.

Until such standards are in place, many companies will continue to rely on internal policies, which vary widely in quality and enforcement.

Toward a More Effective Future

The research is clear. Heat stress is not just a theoretical risk; it is a measurable, preventable hazard with real-world consequences. Core temperature data, dehydration rates, and productivity losses all point to the same conclusion. Construction workers face serious heat-related dangers, even when basic precautions are taken.

The path forward involves enhanced monitoring, more effective hydration strategies, redesigned protective gear, and formal policies that prioritize health and safety. It also requires a cultural shift on job sites, where rest, recovery, and communication are treated as essential parts of the workday.

With global temperatures continuing to rise, these steps are no longer optional. They are essential for maintaining the safety, health, and productivity of workers.