Summer 2025 has come to an end but the work to protect workers from heat stress and significant health consequences continues in earnest.
 
Over the past decade, numerous studies have provided clear evidence that heat stress in the workplace poses a direct threat to workers' health. Heat stress is the body’s response to extreme heat coming from hot work environments or from the body itself. A newly released technical report entitled Climate change and workplace heat stress: technical report and guidance from the World Health Organization (WHO) and the World Meteorological Organization (WMO) provides advice on addressing workplace heat stress as caused by the climate crisis, including health impacts, assessment methods and prevention strategies.
 
Although heat stress affects vulnerable populations like children and older adults it has especially negative effects on manual workers exposed daily – particularly those working in the agriculture, construction and fishing sectors. However, it is important to recognize that heat-related hazards are not limited to outdoor jobs. Individuals working in hot or humid indoor environments such as bakeries, commercial kitchens, laundries, factories and warehouses are also vulnerable. Even spaces like schools are not immune. With increasing heat waves, it is not uncommon for aging schools without air conditioning to reach indoor temperatures of 40°celcius. Add forest fires to the mix and even windows can’t be opened.

Report summary and recommendations

The WHO and WMO report that workers exposed to high heat whether outdoors or indoors face serious health risks, including dehydration, kidney damage, heatstroke, and neurological issues. They advise general heat-health warnings and public prevention programs often don’t meet the needs of workers required to stay productive despite extreme heat. To protect them, tailored occupational heat action plans are essential.
 
They further advise workplace heat stress assessments should consider job-specific and personal factors, including accounting for return-to-work situations after heat-related illness. Accordingly, public health officials, employers, workers, their representatives, supervisors and health and weather services can take key actions to manage workplace heat stress and reduce its impact on health and productivity.
 
These include:

• Developing heat-health policies tailored to local conditions, job types, and worker needs.
• Prioritizing protection for vulnerable groups, including older adults, those with poor fitness, and people with chronic illnesses.
• Training responders, employers, and workers to recognize and manage heat-related health issues.
• Involving key stakeholders—including employers, workers, unions, and health experts—in designing heat-health strategies.
• Ensuring policies are practical, cost-effective, and environmentally sustainable.
• Using technology to enhance safety and productivity.
• Supporting research to evaluate and improve heat-health policies and advisories.

Read the full Climate change and workplace heat stress report.
 
Train workplace joint health and safety committees and supervisors for prevention.

Home-grown research and the law

Canadian scientist Glenn Kenny from the University of Ottawa, also a contributor to the international report, studies how the human body responds to extreme heat (heat stress) specifically in workers. Kenny explains that heat protection strategies should be tailored to each individual worker, particularly those who are older, have chronic health conditions, or are not physically fit. As people age, their ability to release excess body heat decreases. He notes that while heat waves and climate change intensify, Ontario’s plan to protect workers has not.
 
Exposure to extreme heat can also cause serious health issues such as heart attacks, as it raises the body’s core temperature above 38 degrees and heart rate to unsafe levels. A study published in the Lancet Planetary Health concluded an estimated 220 Canadian workers die annually from occupational heat stress. In addition to the health effects noted in the latest international report, other effects include heat exhaustion, heat cramps, fainting, heat rash and transient heat fatigue. Heat stress can also create safety hazards from fogging of safety glasses, sweaty palms, and dizziness. Mental alertness and physical capacity also may suffer as temperatures rise.
 
Under the Occupational Health and Safety Act (OHSA), Ontario does not have specific regulations governing heat exposure and heat stress, rather it relies on the general duty provision (s.25 (2)(h), which requires employers to take every precaution reasonable to protect workers’ health and safety. This includes implementing policies and procedures to protect employees who work in hot environments, such as near hot equipment, radiant heat sources, or in hot weather conditions.
 
To help bridge this gap, the Ontario Federation of Labour (OFL) is working with the Ontario New Democratic Party (NDP) to actively advocate for heat stress safeguards in OHSA, similar to existing provisions for workplace violence and harassment. Bill 36, an NDP private members bill introduced last May proposes the Ministry develop a Worker Heat Protection Standard, requiring employers to implement a heat stress prevention policy in consultation with joint health and safety committees and workplace health and safety representatives. The bill mandates limits on heat exposure using the hierarchy of controls, compensation for rest breaks, protective measures, and training for all.
 
OHS training shouldn’t be ‘one and done’. Continue building your knowledge and skills.

United for workplace protections and change

Meantime, Ontario workers and their representatives are working to address the issue one workplace at a time. To this end the OFL also partnered with the Workers Health & Safety Centre, (WHSC) and the Occupational Health Clinics for Ontario Workers (OHCOW) to equip them with training, information and tools to document, measure and control heat stress exposures at work while critically assessing workplace interventions or lack thereof as part of their ongoing heat stress campaign. Participants were provided with hygrometers to monitor heat and humidity levels in their workplaces. These devices offer a practical alternative to more complex instruments, which are often costly, time-consuming, and difficult to operate. The data collected from the hygrometers will help to inform the next phase in the OFL’s heat stress campaign as well as to aid in developing action plans in individual participants’ workplaces.

On-site training

The weather may be cooling for now, but clearly the climate crisis isn’t going away. Development of requisite knowledge, skills, policies and plans to combat heat stress takes time and effort. Will you be ready for summer 2026? WHSC can bring heat stress prevention training to your workplace. To learn more contact a WHSC training services representative near you.
 
JHSC Certification and supervisor training can help too. Among other things these foundational, mandatory programs train learners in health and safety law, workplace health and safety policy and programs, and strategies for hazard identification, assessment and control.
 
Check out our complete schedule of instructor-led in-person and virtual training today.
 
Related resources and reading
WHO and WMO report Climate change and workplace heat stress: technical report and guidance
WHSC hazard bulletin Heat Stress: Cool Solutions
OFL Heat Stress Campaign
Bill 36, Heat Stress Act, 2025
Heat stress toolkit, WHSC training help combat growing hazard
Heat Stress Toolkit and related OHCOW resources
Sunsafetyatwork.ca
MLITSD Guideline No. 33: Working In extreme temperature conditions