• Occupational health
• International Health Regulations
• Public health
• Environment

2023 was the hottest year on record; 2024 is set to be even hotter. The rise in climate change-driven occupational heat stress is putting the health and livelihoods of workers at grave risk.1 2 The number of workers suffering the consequences of excessive heat is alarming. An International Labor Organization (ILO) report in 2024 has shown that at least 71% of the global working population are exposed to excessive heat leading to almost 23 million injuries and 19 000 deaths every year.3 Another 2024 ILO report has shown that workers in Africa (92.9%), the Middle East (83.6%) and Asia and the Pacific (74.7%) were the most exposed to excessive heat.4 Meanwhile, the Americas and Europe have experienced the steepest increases in heat-related workplace injuries since 2000 with a rise of 33.3% and 16.4%, respectively.4 Recent reports of regulatory violations5 and media stories6 7 have highlighted the preventable loss of life due to hazardous heat exposure while at work across various regions previously unaccustomed to this level of heat.

In response to this escalating global crisis, the US occupational health regulatory agency, the Occupational Health and Safety Administration (OSHA), has taken the lead by issuing a newly proposed comprehensive rule addressing heat-related occupational hazards in the USA (https://www.osha.gov/heat-exposure/rulemaking). Under this new rule, OSHA would apply two heat index thresholds nationally factoring in temperature and humidity. At 80°F (26.7°C), employers would be required to provide drinking water and break areas. More protections would kick in at 90°F (32.2°C) including monitoring for signs of heat illness and mandatory 15-min rest breaks every 2 hours. The rule offers an option for employers to use thresholds previously developed by the US federal occupational health research arm, the National Institute for Occupational Safety and Health (NIOSH). This option would use the wet bulb globe temperature (WBGT) and the metabolic work rate of the job. This optional approach aligns WBGT thresholds with the work intensity of physical labour to establish appropriate work–rest schedules.8

Previously, heat protection in the USA was largely left to the goodwill of employers or workers taking their own precautions. To date, only a handful of states have protections and some unionised workplaces and programmes such as the Fair Food Programme (https://fairfoodprogram.org/) bargained for heat-related accommodations like frequent breaks and earlier start times. Meanwhile, some states actively opposed such protections. Florida passed legislation to block local heat protections and Texas eliminated minimal protections like mandated water breaks. The proposed federal rule would cover most workers, including the non-unionised and those who need it most, addressing a critical gap that exists not only in the USA but in many other countries facing similar challenges.

While OSHA’s proposed rule is commendable, it represents only a first step: A universal mandate of fundamental protections for all workers including access to water, shade, mandatory rest breaks, sanitation, education about heat stress and emergency heat response plans as well as theoretically assuring that workers who seek respite are not punished for doing so. These measures are essential for immediate protection. However, the chosen triggers (80°F and 90°F heat index) do not capture the full spectrum of heat-related risks such as high solar radiation, metabolic heat load and physiological strain thus underestimating risk to worker health and making the rule unlikely to be effective for the most strenuous jobs in the most extreme environments. While the rule gives an option to account for workload and more specific environmental conditions, this choice will require employers to measure and record WBGT. Given the easy option of using off-the-shelf heat index values taken from the National Weather Service website, it is likely that employers will choose this option despite the limitation of not accounting for the solar heat load.

Nevertheless, this rule should be viewed as part of a broader-phased approach to address heat-related risks in the workplace. Following this initial rule, there must be subsequent phases to inform future rulemaking. A second phase should involve building enhanced guidelines with data-driven measures. With that comes the development of appropriate work–rest schedules through continuous monitoring of environmental and metabolic heat production. While NIOSH’s non-mandatory work–rest schedules are theoretically effective,9 they are often impractical in real-world settings. For example, in the tropics or during the summer in much of the US South following NIOSH’s guidance could regularly reduce work to 15 min per hour for much of the day or possibly lead to work being called off altogether. We need to replace these static curves with context-specific ones that are informed by research that is physiologically relevant and that meets the operational viability challenge. Eventually moving to dynamic risk assessment models that consider age/sex and individual health conditions, clothing, work environment and acclimatisation levels. While most technology for accurate physiological and environmental exposures is expensive, such an effort should motivate more scalable systems. The third phase would leverage these data-driven work–rest schedules and focus on supporting implementation.

Building this evidence and the will to put it into practice requires a multisite, multi-industry initiative developed through a multistakeholder process to create effective and practical interventions. This is not a pipe dream and has precedent. Federal institutions in the USA and EU have pursued and funded similar initiatives in the Global South to improve heat stress protections in industries long resistant to such changes. The US Department of Labor10 and institutions from Germany11 funded successful efforts in the Mesoamerican sugar industry. With similar vision, these institutions could establish comparable initiatives in the USA and EU. Notably, some companies such as Turner Construction12 and governments such as Greece and Cyprus13 have already begun investing in such efforts. Still, other parts of the world still lag behind.4

While it is clear that regulatory efforts often encounter resistance, particularly from industry, we emphasise that the role of occupational health professionals is to protect workers’ safety and well-being even if this stance may at times conflict with production imperatives. However, in the extensively studied cohort of sugarcane agricultural workers in Nicaragua, implementing more rigorous heat standards not only resulted in a 70% reduction in incident kidney injury14 but also a 9–19% increase in productivity15 and a 22% positive return on investment for employers.11 These outcomes demonstrate that, in some contexts, robust worker protection can not only improve workers’ health outcomes but they can also coincide with productivity gains and positive economic returns.16 While economic arguments can sometimes help build support for occupational safety and health measures, they should not overshadow the ethical imperative to protect workers from harm. If a rule effectively safeguards health but is deemed unviable by employers and workers, it risks inconsistent implementation leaving millions vulnerable. No regulatory body can enforce rules comprehensively across all at-risk populations; therefore, it is necessary to address biases and entrenched resistance through continuous practice and evaluation.

Globally, overcoming science and regulatory challenges requires a foundation of interventional and implementation evidence that engages workers and employers from the outset to build effective and attainable protections against heat-related risks. In the face of climate change, we call for a big tent and a process that addresses outdated biases particularly the notion that protecting workers is merely a cost without benefit. Our phased-approach roadmap will ensure that the next generation of standards is based on the latest climate science, precise occupational health research and real-world data on heat-related illnesses while being inclusive of employers and safeguarding workers globally.