This article originally appeared in the blog of the Harvard T.H. Chan School of Public Health on July 31, 2025. Written by Carly Stearnbourne.
A new article published Tuesday in Nature Cities finds that heat stress is responsible for productivity losses between 29.0% to 41.3% on construction job sites. As demand for new construction grows, and extreme heat affects cities across the globe, understanding the effects of heat and humidity on outdoor workers is key to protecting both worker health, as well as project timelines and costs.
“If unmitigated, heat can lead to acute fatal outcomes (for example, heat stroke), long-term health effects or increase the risk of workplace injuries,” the study authors write. “However, even before reaching dangerous levels, physically demanding work in hot-humid conditions is associated with discomfort, irritability, loss of concentration and fatigue.”
For businesses and employers, there is mounting evidence that shows that heat exposure leads to significant reductions in worker productivity, resulting in longer project timelines, development delays and, subsequently, substantial economic losses.
“The conditions for construction workers can actually be a lot worse than other occupational settings, because — in addition to working outside in the elements — constructions workers often use heat-generating tools as part of the job, such as welding torches, power tools, etc. In addition, heat reflects off of concrete structures and steel, making it even hotter for the workers,” says Barrak Alahmad, study co-author, and researcher at the Harvard T.H. Chan School of Public Health. “To account for those scenarios, we measured the exact temperatures and humidity and conditions for workers at an individual level; each worker wore a small sensor around their waist that continuously, minute by minute, collected the data.”
Research like this highlights the cost of doing nothing to mitigate heat stress among workers, and lays the groundwork for future research to investigate what types of strategies can protect workers while also boosting productivity and reducing costs for construction companies and builders.
There are workers that are doing a lot of strenuous and difficult jobs in the hot weather,” says Dr. Alahmad. “And right now, globally, there is lack of protection for these workers.
This research also comes at a time when OSHA is in the middle of the regulatory process to establish a federal heat rule. Right now in the US, there is no federal heat rule, heat is instead governed by the general duty clause. “Creating a federal heat rule would mean that OSHA could regulate things like rest, water, and shade, and also improve planning for construction companies to try to mitigate the effects of heat ,” says Dr. Alahmad.
This is important not only to protect workers, but also to protect the bottom line for construction projects, where loss of productivity leads to delays, missed deadlines, and cost overruns.
The research was conducted in Taiwan where a growing demand for housing has led to a construction boom in the hot, humid climate. Co-author Shih-Chun Candice Lung from the Research Center for Environmental Changes at Academia Sinica in Taipei, Taiwan, collaborated with Dr. Alahmad on the findings. Dr. Lung is an alumnus of Harvard T.H. Chan School of Public Health, who previously studied under Dr. Jack Spengler.
This investigation was made possible by grant no. T42 OH008416 from the National Institute for Occupational Safety and Health (NIOSH) through Harvard–NIOSH Education and Research Center (ERC) grant. In addition, this research was supported by the Institute of Labor, Occupational Safety and Health, Ministry of Labor, Executive Yuan, Taiwan, under project nos. 1050004 and 1060047.
First published by Department of Environmental Health – Harvard TH CHAN. Reposted with permission. Text by Carly Stearnbourne
