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A worker was towing janitorial supplies at a car parts factory. She lost control of the trailer she was driving and it jackknifed, causing her to hit her head on a piece of equipment.
While stacking cans on a skid at a pet food facility, a worker lost consciousness, sliding to the floor.
A worker collapsed on the roof of a golf course clubhouse where he was sweeping pine needles. He was taken to the hospital, where he was pronounced dead.
These incidents occurred in different workplaces and in different parts of Ontario.
But they all have one thing in common: they happened during a sweltering heat wave in July 2020, a month that broke historical records and hinted at the future.
A ÎÚÑ»´«Ã½ Star investigation has found that critical workplace injuries spike on the hottest days of the year. The provincial government knows that heat is a growing and potentially lethal threat to workers, but new protections it once proposed have never materialized.
Heat can also kill. Yet the way Ontario tracks worker deaths overlooks fatalities that could be heat-related, even when provincial officials find evidence of heat exposure on the job.
As climate change multiplies the number of extremely hot days we endure, failing to address this threat is leaving workers vulnerable to potentially life-altering injuries. A Star analysis shows heat is linked to more than 100 extra critical injuries over the past 13 years.
Without action, hundreds more preventable workplace injuries could happen in Ontario over the coming decades.
Workers of any age, gender and industry are at risk, including in workplaces the public might not expect.
“It can happen to all of us. It can happen to me. It can happen to you,” said Glen Kenny, who studies heat stress as the director of the Human and Environmental Physiology Research Unit at the University of Ottawa.
“You don't need to be 90 years old to die in heat. And it doesn't take much.”
Rising risk
Hot days are making Ontario’s workplaces more dangerous — and the problem will only get worse.
Injuries on the job happen every day. But some, from losing consciousness to major burns to fractured limbs, are considered so serious that most Ontario employers are required by law to immediately notify the Ministry of Labour.
More than 3,100 of these “critical injuries” were reported to the province last year. Any of them “could easily have been a fatality,” said Peter Smith, senior scientist and president of the Institute for Work & Health, an independent research organization in ÎÚÑ»´«Ã½.
“If one of these critical incidents happened to you or a family member, it would change your life.”
The head injury at the car parts factory, the loss of consciousness at the pet food facility and the death at the golf course were all reported to the ministry’s 24-hour health and safety contact centre.
The Star obtained dozens of these contact centre reports through access-to-information laws. The Ministry of Labour also provided 13 years' worth of critical injury data at the Star’s request.
Analyses of this data show a persistent pattern.
As temperatures rise, so do injuries
On days when the temperature in ÎÚÑ»´«Ã½ is mild, an average of five critical injuries are reported provincewide. But as the temperature rises, so do reports to the ministry.
On days when the temperature rose above 32 C, an average of six workers suffered a critical injury.
On days when temperatures spiked even hotter, above 35 C, an average of seven workers suffered a critical injury.
(To see our methodology, including why we used the temperature in ÎÚÑ»´«Ã½, click here.)
Because humans are polluting the atmosphere by burning fossil fuels, heat waves are becoming more frequent and intense across Canada. The number of extremely hot days varies from year to year, but climate change is, over time, driving those numbers up.
In a world where we emit high levels of greenhouse gases, climate models predict ÎÚÑ»´«Ã½ will see an average of 22 extremely hot days by the middle of the century. In a world where we curtail emissions, the number stays closer to 14 — more than a week fewer.
In ÎÚÑ»´«Ã½, a 32 C day usually triggers a heat alert, a warning system designed to protect public health. But it doesn’t have to be as hot as that for problems to appear.
Smith analyzed the same data set at the Star’s request, using a statistical method that examines risk: not just whether injuries happened, but whether heat made it more likely for them to happen. His approach accounts for fluctuations in the workforce between years, months, days of the week and on public holidays.
Smith found that risk creeps up before temperatures hit 32 C: On days that are 29 C or hotter, the risk of a critical injury is seven per cent higher than on a mild day in the low 20s. After two days in a row at 29 C or above, the risk jumps 12 per cent. After three days, it jumps 18 per cent.
A 29 C day often doesn’t trigger a heat alert in ÎÚÑ»´«Ã½.
How heat stresses the body
The contact centre reports from the summer of 2020 offer a snapshot of the kinds of critical injuries that are occurring on very hot days.
While it’s difficult to establish with certainty which injuries happened because of high temperatures, in some of the cases, the reports link the incidents to heat exposure.
“At the time of the incident the workplace was pretty warm due to the heat wave,” said the report of the worker who jackknifed the trailer at the car parts factory and hit her head.
"The temperature in the workplace may have contributed to what happened," reads the report of the worker who lost consciousness stacking cans at the pet food factory.
Many of the injuries in the records are not what we would typically recognize as heat stroke. Experts say heat stress manifests in a multitude of health problems.
The body responds to heat stress in two primary ways: by shunting blood toward the skin, which helps transfer heat into the surrounding air, and by sweating, which cools the body as sweat evaporates.
These responses protect the body’s core temperature but come at a cost to other organs. The heart pumps harder and faster, raising the risk of heart attacks and other cardiovascular events. Blood pressure drops, causing fainting.
Dehydration strains the kidneys, leading to acute kidney injuries and worsening kidney disease.
Being under such physical stress also affects cognition and perception, said Kenny, who has observed workers labouring in extreme heat in both his lab and in real work settings.
Heat stress makes workers more likely to forget safety training, commit uncharacteristic mistakes or react slowly to danger, increasing the risk of traumatic injuries.
“When you do become heat stressed, your focus is so narrow. All you’re thinking about is survival, because your body is under stress,” said Kenny.
One of the reports to the contact centre was for a worker hit by a dump truck while paving a road.
“The Site Supervisor had indicated that the worker/victim was standing on the wrong side of the road from where he was supposed to when he was struck,” according to the report.
That day reached 38 C with the humidex in the area, and was the sixth day in a row of punishing temperatures. The heat wave helped push July 2020 toward a dubious award: hottest month on record at Pearson airport.
Deaths on the job
Scientists call heat the “silent killer” because it masquerades as so many other health problems.
Studies from all over the world, including Canada, find spikes in mortality during heat waves. Many of those extra deaths are from cardiac events such as heart attacks and from respiratory diseases, the research shows. Deaths from diabetes, psychiatric illnesses and other underlying conditions also rise. Heat is the deadliest form of extreme weather, according to the World Health Organization, killing more people than floods, hurricanes or wildfires.
The Ministry of Labour said it is aware of two heat-related workplace fatalities in Ontario since 2010. Missing from this count are at least three more deaths the Star has identified where provincial officials found evidence of heat exposure on the job.
A worker at a construction site suffered a heart attack after helping move concrete on a July 2017 day that reached 34 C with the humidex. The worker’s widow could not believe her husband had died, according to a workplace compensation tribunal decision: he did not drink or smoke, was always “on the go,” and was the “picture of health.”
The coroner listed coronary artery disease as the worker’s primary cause of death, and “heat and humidity” as a “significant condition” contributing to the death. The tribunal ultimately agreed that his death was work-related, and awarded his family survivor benefits.
A spokesperson did not respond to questions about whether the Ministry of Labour could be missing some heat-related workplace fatalities in its tally, including this one.
At the time the worker died, deaths at construction sites were investigated through a mandatory inquest. Inquests are intended to generate recommendations that improve public safety and prevent similar deaths in the future.
No inquest was held into this worker’s death. A spokesperson for the coroner’s office, Stephanie Rea, said that for an inquest to be mandatory, the manner of death had to be an accident that occurred in the course of employment. In most situations, a heart attack after strenuous activity or during a hot day wouldn’t be considered an accident, but a natural death, Rea said.
The government’s count is also missing cases where Ministry of Labour officials inspected a workplace following a death and found the employer had violated safety laws by not providing training on heat stress.
The worker who died at the golf course in July 2020 collapsed while sweeping pine needles off the roof of the clubhouse. That day reached 40 with the humidex. A workplace insurance document provided by the employer states that the worker died of a heart attack. The employer said he had only been on the roof for 15 minutes, and that his duties that day weren’t strenuous.
A maintenance worker died in August 2010 while moving picnic tables at a college campus. The morning the worker died felt like 33 C with the humidex. The worker could be seen on surveillance video wiping his face and neck with a towel, a tribunal heard. The employer claimed his duties that day had not been particularly taxing.
The coroner found he had died from sudden cardiac death due to coronary artery disease, and that “exertion in hot and humid environment” was a “possible contributing factor” to his death.
In the wake of these deaths, the employers were found to have violated the Occupational Health and Safety Act by failing to provide training on the hazards of working in a hot environment and on protective measures for heat-related illness, records show. They complied with orders to train their employees soon after.
Those violations alone do not establish that the workers died from heat. To better understand how heat is helping kill Ontarians, the province would have to investigate and track deaths in a systematic way. Advocacy groups have been calling on the government to do this for years.
Ontario ‘data blind’ on heat deaths
In July 2021, the Canadian Environmental Law Association and other legal clinics wrote to the Ontario coroner to ask for better tracking of all heat-related deaths. The association has written that these are dramatically undercounted in Ontario, calling the province’s approach “data-blind.”
Four years later, “we remain in the same spot, where we're stuck with data that's really not capturing the scope of the problem,” said Jacqueline Wilson, counsel at the association.
Deaths directly caused by heat — such as heat stroke — would be recorded as such. But if heat worsens a condition like heart or lung disease, the coroner would not track it, and would classify the death as natural, rather than accidental.
The coroner does investigate deaths in workplaces, including ones that happen suddenly or unexpectedly. If a worker dies on the job of a heart attack, and if heat is determined to play an indirect role in contributing to the cause of death, that death would be classified as natural. The Ministry of Labour excludes deaths from natural causes in its workplace fatality tracking, a spokesperson said.
“We're stuck with data that's really not capturing the scope of the problem,”
Jacqueline WilsonDr. Dirk Huyer, Ontario’s chief coroner, told the Star that his office had carefully considered the request to track heat-related deaths, but concluded that doing so “is logistically not doable.”
“And if it was doable, then what would we learn from this? We know that heat causes people to die.”
Huyer said that tracking would be inaccurate, because “there is no scientific way” to answer the question of whether heat led to someone’s death from an underlying condition.
Other jurisdictions, including British Columbia, have taken extra effort to determine who is dying from heat and how. During the West Coast heat dome in 2021, the B.C. coroner issued instructions that if heat was in any way suspected to be a contributing factor to a person’s death, the death must be reported to the B.C. Coroner’s Service, which would review each case before issuing a death certificate.
That precedent continues. Over the past two summers, more than two dozen other suspected heat-related deaths were reported by the coroner. In B.C., these deaths are considered accidental, not natural.
The coroner’s instructions are the reason we know the specific death toll of the heat dome — 619 people — and allowed the province to understand who was most at risk. Some of those findings were surprising even to health professionals, including that almost all deaths happened indoors, and that schizophrenia was associated with a higher risk of death than any other chronic disease.
“This was brand new information,” said Dr. Samantha Green, a family doctor and a volunteer with the Canadian Association of Physicians for the Environment, which has also asked the Ontario coroner to track heat deaths.
“There was no one who was broadly aware of this, even people working with schizophrenia. Absolutely, that was a key finding.”
Green added that Ontario might discover different risk factors than British Columbia.
“We don’t know what we don’t know. We're a completely different province. We have different geography, different populations.”
Huyer said that since we already know heat kills, people should focus on prevention.
Proposed protections never appeared
Two summers ago, the Ministry of Labour proposed new heat stress protections that would, for the first time, create specific requirements for employers related to heat exposure.
“Heat stress is a significant cause of occupational illnesses that may lead to death,“ states a paper the ministry published explaining why it was proposing the change. “Due to changes in our climate, extreme heat events are a growing health risk to workers in Ontario.”
When the proposal was opened for consultation, however, it attracted criticism from legal, labour and agricultural groups. Critics said it would require cumbersome and expensive equipment when easy-to-use alternatives were available; that it neglected some of Ontario’s most vulnerable workers, including migrant farm workers; and that it set exposure limits unacceptably high.
The ministry does not appear to have advanced the regulation since, and a spokesperson did not answer a question about the status of the proposal.
Last May, the NDP opposition critics on environment and labour, MPPs Peter Tabuns and Jamie West, challenged Labour Minister David Piccini in the Legislative Assembly about the consultations, and why the government had not subsequently strengthened heat protections.
Piccini responded that any worker has a legal right to refuse unsafe working conditions, and that there were “robust protections” in the existing health and safety laws, which he said had been strengthened under Premier Doug Ford and his Progressive Conservative government.
“We work with our prevention council. We work with labour groups across Ontario. There’s also an element of common sense,” Piccini said.
In late May, Tabuns announced he was re-tabling a private member’s bill that would create enforceable heat stress protections for workers. He was joined at the press conference by workers' advocates, including Ontario Federation of Labour president Laura Walton, who urged the government to take action.
“Leaving something up to ‘common sense’ is killing people, and the right to refuse often comes with a price of losing your job or being reprimanded for actually exercising your rights,” Walton said.
Piccini did not respond to the Star’s request for an interview for this story. A spokesperson, Michel Figueredo, said that “Ontario leads North America on safety in the workplace,” and that the government continues to take action to protect workers.
He cited proposed requirements to require defibrillators at some construction sites and recently introduced legislation that, if passed, would create new financial penalties to better enforce health and safety compliance.
“Employers are legally required to take every reasonable precaution to protect workers — including implementing measures to reduce the risk of heat-related illness. Ontario’s laws are backed by the strongest workplace safety fines in Canada,” Figueredo said.
The Ontario government has also invested $250,000 in the development of a heat stress prevention tool kit that was launched in 2024 and provides resources to help workplaces assess risk, implement control measures and respond to heat stress concerns, a spokesperson said.
Smith, of the Institute for Work & Health, noted that all critical injury reports to the province have risen significantly over the past decade.
“Whatever we're doing to prevent them is not currently working,” Smith said.
No one deserves to be injured at work, Smith added.
“The number of critical injuries is going to increase over time, unless we do something about it. And each one of these injuries is catastrophic for the worker, catastrophic for the workplace and catastrophic for the family and the community around that worker.”
Kate Allen can be reached at kallen@thestar.ca
METHODOLOGY
Data: The analyses in this story are based on two data sets. One data set contains information on workplace critical injuries and fatalities in Ontario, and one data set contains information on temperature and precipitation in ÎÚÑ»´«Ã½.
The injury data set is a daily count of critical injuries and fatalities reported to the Ontario Ministry of Labour between 2012 and 2024. The data set was provided by the Ministry at the Star’s request.
The definition of a critical injury can be found . All employers covered by Ontario’s Occupational Health and Safety Act (OHSA) are required to immediately report critical injuries and fatalities to the Ministry’s 24/7 health and safety contact centre. Almost every worker, employer and workplace in the province is covered by OHSA; the few exceptions include federally regulated workplaces like banks, servants in private residences, and some farms. The data may include injuries of nonworkers, which are required to be reported in very limited circumstances, such as when there is a “reasonable connection” between the hazard that caused the incident and a realistic risk to worker health and safety.
The temperature data set is from Environment and Climate Change Canada’s “ÎÚÑ»´«Ã½ City” weather station (ID 6158355) in downtown ÎÚÑ»´«Ã½. It contains the daily maximum temperature, daily minimum temperature and total rainfall amounts for each day between 2012 and 2024. That data set can be downloaded .
Limitations: The critical injury data set provided by the Ministry does not include geographic, demographic or industry information — in other words, it does not say where in the province the injury happened, who it happened to or what type of work they were doing.
We chose to use the temperature in ÎÚÑ»´«Ã½ for a few reasons. The first is the density of the workforce in the ÎÚÑ»´«Ã½ region. Almost half of the province’s workers are in the immediate ÎÚÑ»´«Ã½ region, and 71 per cent are in the Greater Golden Horseshoe.
Heat waves are also caused by big, slow-moving high-pressure atmospheric systems that tend to affect large regions. These systems are part of “synoptic” weather patterns that range in scale from 1,000 kilometres across to even larger. (On a map, a circle that size with ÎÚÑ»´«Ã½ as its bullseye stretches roughly from Michigan to Montreal and from Washington D.C. to Timmins). A that examined three heat waves in southern Ontario between 2010 and 2012 found that the rate of emergency room visits at rural hospitals increased significantly in those periods, suggesting that the health effects of extreme heat events are shared broadly in the region, beyond the major urban centre of ÎÚÑ»´«Ã½.
However, using ÎÚÑ»´«Ã½ temperature as a proxy for the whole province may obscure some of the relationship between temperature and critical injuries. But it is more likely to be masking the true relationship than inflating or creating it. In general, mismeasurement of one variable in this kind of analysis tends to weaken an association, rather than create a false one, which means the true relationship between heat and critical injury may be stronger than what we reported here.
Analyses: To examine the relationship between temperature and injuries, the Star first did a simple descriptive analysis of the data, and then asked the Institute for Work & Health's Peter Smith to do a more rigorous statistical analysis.
The Star’s analysis calculated the average number of injuries in two-degree and four-degree buckets.
Smith’s analysis used what is known as a “case-crossover” design. In this type of study, a day when a critical injury occurred (a case day) is compared to days when the injury did not occur (referent days). Referent days are the same day of the week for all other weeks in that calendar month and year.
The basic question is this: if a worker suffered a critical injury on a Wednesday in May, did the temperature on that Wednesday differ from other Wednesdays in the same month?
Each critical injury is analyzed as a separate event, with case and referent days examined as their own groups and then summarized. Smith’s analysis also adjusted for amount of precipitation and for whether the case or referent day was a public holiday.
The particular value of this study design is that it controls for fluctuations in the workforce: for example, that different days of the week have more people working, that between May and September the size of the labour force changes because of seasonal jobs, and that the number of people in the workforce generally grows every year. Smith has used the same study design in published, peer-reviewed papers on occupational injuries and temperature.
Findings: The analyses show a consistent relationship between very hot days and increased risk of critical injuries. They also show a dose-response relationship: the higher the temperature and the more hot days in a row, the greater the risk of critical injury.
The Star’s analysis shows that there are an average of 6.3 critical injury reports on days above 32 C, and an average of seven critical injury reports on days above 35 C, compared to an average of roughly five on days in the teens and low 20s. It’s worth noting there are few days in the data set above 35 C (eight) compared to ones above 32 C (63).
Smith’s analysis used days between 21 C and 24 C as a reference range. Compared to days with those temperatures, he found that the risk of injury increases 24 per cent on days over 32 C. One day above 29 C, and two or more, or three or more consecutive days above 29 C, also showed an increased risk of critical injuries compared to the reference range, as did higher minimum temperature (e.g., hot nights as compared to cool nights). When examining maximum temperature as a continuous exposure, each one degree rise is associated with a one per cent increase in risk of critical workplace injury. These results were all statistically significant at a conventional threshold (p < 0.05). Given the consistency of these patterns across different analyses, it is unlikely the relationship between heat and critical injuries observed in this analysis happened by random chance alone.
There were too few fatalities in the data set to draw clear conclusions (689, compared to 24,612 critical injuries.) However, Smith’s analysis does show that the risk of a workplace fatality more than doubles after two and three hot nights in a row (20 C or more), a finding that was also statistically significant, but warrants further study.
Extra injuries: the number of excess critical injuries on 32-plus C days over the 13 year data set was calculated by comparing the expected number of critical injuries on those days if the temperatures were mild compared to how many more were actually observed, after removing public holidays and adjusting for month and year. It showed that approximately 116 extra critical injuries were observed in that period compared to what would be expected at lower temperatures.
Climate data: The climate change calculations are based on CMIP6, the most current global climate model data available and the foundation of the United Nations Intergovernmental Panel on Climate Change’s Sixth Assessment Reports. The global CMIP6 model was downscaled to the ÎÚÑ»´«Ã½ census subdivision using , a climate data portal created by Environment and Climate Change Canada and other organizations. We examined four climate change pathways that model different levels of greenhouse gas emissions and global development — SSP126, SSP245, SSP370 and SSP585 — but chose to visualize two of these for the sake of readability, a low-emissions scenario (SSP126) and high-emissions scenario (SSP370).
To calculate how many injuries could occur in the future, we extracted data from on the number of days above 32 C from 2025 to 2065 under the low- and high-emissions scenarios. We multiplied the cumulative number of 32-plus C days for the four decades in each scenario by 1.56. That 1.56 multiplier is the result of an ordinary least squares regression model calculated by Smith, which gives the predicted mean number of critical incidents on days over 32 C compared to days 32 C and under, after adjusting for month, year, day of the week, and amount of precipitation.
Our calculation is simplistic, because it does not account for demographic or workforce changes in Ontario in the coming decades. Even the most conservative estimate, however, shows that hundreds more workplace critical injuries associated with 32-plus C days will occur in the coming decades.
Acknowledgments: The Star would like to thank two external reviewers for their feedback: Kristie L. Ebi of the University of Washington’s Center for Health and the Global Environment, and Dr. Vincent Spilchuk of the University of ÎÚÑ»´«Ã½’s Temerty Faculty of Medicine’s Division of Occupational Medicine.
Rising risk
Hot days are making Ontario’s workplaces more dangerous — and the problem will only get worse.
A worker was towing janitorial supplies at a car parts factory. She lost control of the trailer she was driving and it jackknifed, causing her to hit her head on a piece of equipment.
While stacking cans on a skid at a pet food facility, a worker lost consciousness, sliding to the floor.
A worker collapsed on the roof of a golf course clubhouse where he was sweeping pine needles. He was taken to the hospital, where he was pronounced dead.
These incidents occurred in different workplaces and in different parts of Ontario. But they all have one thing in common: they happened during a sweltering heat wave in July 2020, a month that broke historical records and hinted at the future.
A ÎÚÑ»´«Ã½ Star investigation has found that critical workplace injuries spike on the hottest days of the year. The provincial government knows that heat is a growing and potentially lethal threat to workers, but new protections it once proposed have never materialized.
Heat can also kill. Yet the way Ontario tracks worker deaths overlooks fatalities that could be heat-related, even when provincial officials find evidence of heat exposure on the job.
As climate change multiplies the number of extremely hot days we endure, failing to address this threat is leaving workers vulnerable to potentially life-altering injuries. A Star analysis shows heat is linked to more than 100 extra critical injuries over the past 13 years.
Without action, hundreds more preventable workplace injuries could happen in Ontario over the coming decades.
Workers of any age, gender and industry are at risk, including in workplaces the public might not expect.
“It can happen to all of us. It can happen to me. It can happen to you,” said Glen Kenny, who studies heat stress as the director of the Human and Environmental Physiology Research Unit at the University of Ottawa.
“You don't need to be 90 years old to die in heat. And it doesn't take much.”
Injuries on the job happen every day. But some, from losing consciousness to major burns to fractured limbs, are considered so serious that most Ontario employers are required by law to immediately notify the Ministry of Labour.
More than 3,100 of these “critical injuries” were reported to the province last year. Any of them “could easily have been a fatality,” said Peter Smith, senior scientist and president of the Institute for Work & Health, an independent research organization in ÎÚÑ»´«Ã½.
“If one of these critical incidents happened to you or a family member, it would change your life.”
The head injury at the car parts factory, the loss of consciousness at the pet food facility and the death at the golf course were all reported to the ministry’s 24-hour health and safety contact centre.
The Star obtained dozens of these contact centre reports through access-to-information laws. The Ministry of Labour also provided 13 years' worth of critical injury data at the Star’s request.
Analyses of this data show a persistent pattern.
As temperatures rise, so do injuries
On days when the temperature in ÎÚÑ»´«Ã½ is mild, an average of five critical injuries are reported provincewide. But as the temperature rises, so do reports to the ministry.
On days when the temperature rose above 32 C, an average of six workers suffered a critical injury.
On days when temperatures spiked even hotter, above 35 C, an average of seven workers suffered a critical injury.
(To see our methodology, including why we used the temperature in ÎÚÑ»´«Ã½, click here.)
Because humans are polluting the atmosphere by burning fossil fuels, heat waves are becoming more frequent and intense across Canada. The number of extremely hot days varies from year to year, but climate change is, over time, driving those numbers up.
In a world where we emit high levels of greenhouse gases, climate models predict ÎÚÑ»´«Ã½ will see an average of 22 extremely hot days by the middle of the century. In a world where we curtail emissions, the number stays closer to 14 — more than a week fewer.
In ÎÚÑ»´«Ã½, a 32 C day usually triggers a heat alert, a warning system designed to protect public health. But it doesn’t have to be as hot as that for problems to appear.
Smith analyzed the same data set at the Star’s request, using a statistical method that examines risk: not just whether injuries happened, but whether heat made it more likely for them to happen. His approach accounts for fluctuations in the workforce between years, months, days of the week and on public holidays.
Smith found that risk creeps up before temperatures hit 32 C: On days that are 29 C or hotter, the risk of a critical injury is seven per cent higher than on a mild day in the low 20s. After two days in a row at 29 C or above, the risk jumps 12 per cent. After three days, it jumps 18 per cent.
A 29 C day often doesn’t trigger a heat alert in ÎÚÑ»´«Ã½.
How heat stresses the body
The contact centre reports from the summer of 2020 offer a snapshot of the kinds of critical injuries that are occurring on very hot days.
While it’s difficult to establish with certainty which injuries happened because of high temperatures, in some of the cases, the reports link the incidents to heat exposure.
“At the time of the incident the workplace was pretty warm due to the heat wave,” said the report of the worker who jackknifed the trailer at the car parts factory and hit her head.
"The temperature in the workplace may have contributed to what happened," reads the report of the worker who lost consciousness stacking cans at the pet food factory.
Many of the injuries in the records are not what we would typically recognize as heat stroke. Experts say heat stress manifests in a multitude of health problems.
The body responds to heat stress in two primary ways: by shunting blood toward the skin, which helps transfer heat into the surrounding air, and by sweating, which cools the body as sweat evaporates.
These responses protect the body’s core temperature but come at a cost to other organs. The heart pumps harder and faster, raising the risk of heart attacks and other cardiovascular events. Blood pressure drops, causing fainting. Dehydration strains the kidneys, leading to acute kidney injuries and worsening kidney disease.
Being under such physical stress also affects cognition and perception, said Kenny, who has observed workers labouring in extreme heat in both his lab and in real work settings.
Heat stress makes workers more likely to forget safety training, commit uncharacteristic mistakes or react slowly to danger, increasing the risk of traumatic injuries.
“When you do become heat stressed, your focus is so narrow. All you’re thinking about is survival, because your body is under stress,” said Kenny.
One of the reports to the contact centre was for a worker hit by a dump truck while paving a road.
“The Site Supervisor had indicated that the worker/victim was standing on the wrong side of the road from where he was supposed to when he was struck,” according to the report.
That day reached 38 C with the humidex in the area, and was the sixth day in a row of punishing temperatures. The heat wave helped push July 2020 toward a dubious award: hottest month on record at Pearson airport.
Deaths on the job
Scientists call heat the “silent killer” because it masquerades as so many other health problems.
Studies from all over the world, including Canada, find spikes in mortality during heat waves. Many of those extra deaths are from cardiac events such as heart attacks and from respiratory diseases, the research shows. Deaths from diabetes, psychiatric illnesses and other underlying conditions also rise. Heat is the deadliest form of extreme weather, according to the World Health Organization, killing more people than floods, hurricanes or wildfires.
The Ministry of Labour said it is aware of two heat-related workplace fatalities in Ontario since 2010. Missing from this count are at least three more deaths the Star has identified where provincial officials found evidence of heat exposure on the job.
A worker at a construction site suffered a heart attack after helping move concrete on a July 2017 day that reached 34 C with the humidex. The worker’s widow could not believe her husband had died, according to a workplace compensation tribunal decision: he did not drink or smoke, was always “on the go,” and was the “picture of health.”
The coroner listed coronary artery disease as the worker’s primary cause of death, and “heat and humidity” as a “significant condition” contributing to the death. The tribunal ultimately agreed that his death was work-related, and awarded his family survivor benefits.
A spokesperson did not respond to questions about whether the Ministry of Labour could be missing some heat-related workplace fatalities in its tally, including this one.
At the time the worker died, deaths at construction sites were investigated through a mandatory inquest. Inquests are intended to generate recommendations that improve public safety and prevent similar deaths in the future.
No inquest was held into this worker’s death. A spokesperson for the coroner’s office, Stephanie Rea, said that for an inquest to be mandatory, the manner of death had to be an accident that occurred in the course of employment. In most situations, a heart attack after strenuous activity or during a hot day wouldn’t be considered an accident, but a natural death, Rea said.
The government’s count is also missing cases where Ministry of Labour officials inspected a workplace following a death and found the employer had violated safety laws by not providing training on heat stress.
The worker who died at the golf course in July 2020 collapsed while sweeping pine needles off the roof of the clubhouse. That day reached 40 C with the humidex. A workplace insurance document provided by the employer states that the worker died of a heart attack. The employer said he had only been on the roof for 15 minutes, and that his duties that day weren’t strenuous.
A maintenance worker died in August 2010 while moving picnic tables at a college campus. The morning the worker died felt like 33 C with the humidex. The worker could be seen on surveillance video wiping his face and neck with a towel, a tribunal heard. The employer claimed his duties that day had not been particularly taxing.
The coroner found he had died from sudden cardiac death due to coronary artery disease, and that “exertion in hot and humid environment” was a “possible contributing factor” to his death.
In the wake of these deaths, the employers were found to have violated the Occupational Health and Safety Act by failing to provide training on the hazards of working in a hot environment and on protective measures for heat-related illness, records show. They complied with orders to train their employees soon after.
Those violations alone do not establish that the workers died from heat. To better understand how heat is helping kill Ontarians, the province would have to investigate and track deaths in a systematic way. Advocacy groups have been calling on the government to do this for years.
Ontario ‘data blind’ on heat deaths
In July 2021, the Canadian Environmental Law Association and other legal clinics wrote to the Ontario coroner to ask for better tracking of all heat-related deaths. The association has written that these are dramatically undercounted in Ontario, calling the province’s approach “data-blind.”
Four years later, “we remain in the same spot, where we're stuck with data that's really not capturing the scope of the problem,” said Jacqueline Wilson, counsel at the association.
Deaths directly caused by heat — such as heat stroke — would be recorded as such. But if heat worsens a condition like heart or lung disease, the coroner would not track it, and would classify the death as natural, rather than accidental.
The coroner does investigate deaths in workplaces, including ones that happen suddenly or unexpectedly. If a worker dies on the job of a heart attack, and if heat is determined to play an indirect role in contributing to the cause of death, that death would be classified as natural. The Ministry of Labour excludes deaths from natural causes in its workplace fatality tracking, a spokesperson said.
Dr. Dirk Huyer, Ontario’s chief coroner, told the Star that his office had carefully considered the request to track heat-related deaths, but concluded that doing so “is logistically not doable.”
“And if it was doable, then what would we learn from this? We know that heat causes people to die.”
Huyer said that tracking would be inaccurate, because “there is no scientific way” to answer the question of whether heat led to someone’s death from an underlying condition.
Other jurisdictions, including British Columbia, have taken extra effort to determine who is dying from heat and how. During the West Coast heat dome in 2021, the B.C. coroner issued instructions that if heat was in any way suspected to be a contributing factor to a person’s death, the death must be reported to the B.C. Coroner’s Service, which would review each case before issuing a death certificate.
That precedent continues. Over the past two summers, more than two dozen other suspected heat-related deaths were reported by the coroner. In B.C., these deaths are considered accidental, not natural.
The coroner’s instructions are the reason we know the specific death toll of the heat dome — 619 people — and allowed the province to understand who was most at risk. Some of those findings were surprising even to health professionals, including that almost all deaths happened indoors, and that schizophrenia was associated with a higher risk of death than any other chronic disease.
“This was brand new information,” said Dr. Samantha Green, a family doctor and a volunteer with the Canadian Association of Physicians for the Environment, which has also asked the Ontario coroner to track heat deaths.
“There was no one who was broadly aware of this, even people working with schizophrenia. Absolutely, that was a key finding.”
Green added that Ontario might discover different risk factors than British Columbia.
“We don’t know what we don’t know. We're a completely different province. We have different geography, different populations.”
Huyer said that since we already know heat kills, people should focus on prevention.
Proposed protections never appeared
Two summers ago, the Ministry of Labour proposed new heat stress protections that would, for the first time, create specific requirements for employers related to heat exposure.
“Heat stress is a significant cause of occupational illnesses that may lead to death,“ states a paper the ministry published explaining why it was proposing the change. “Due to changes in our climate, extreme heat events are a growing health risk to workers in Ontario.”
When the proposal was opened for consultation, however, it attracted criticism from legal, labour and agricultural groups. Critics said it would require cumbersome and expensive equipment when easy-to-use alternatives were available; that it neglected some of Ontario’s most vulnerable workers, including migrant farm workers; and that it set exposure limits unacceptably high.
The ministry does not appear to have advanced the regulation since, and a spokesperson did not answer a question about the status of the proposal.
Last May, the NDP opposition critics on environment and labour, MPPs Peter Tabuns and Jamie West, challenged Labour Minister David Piccini in the Legislative Assembly about the consultations, and why the government had not subsequently strengthened heat protections.
Piccini responded that any worker has a legal right to refuse unsafe working conditions, and that there were “robust protections” in the existing health and safety laws, which he said had been strengthened under Premier Doug Ford and his Progressive Conservative government.
“We work with our prevention council. We work with labour groups across Ontario. There’s also an element of common sense,” Piccini said.
In late May, Tabuns announced he was re-tabling a private member’s bill that would create enforceable heat stress protections for workers. He was joined at the press conference by workers' advocates, including Ontario Federation of Labour president Laura Walton, who urged the government to take action.
“Leaving something up to ‘common sense’ is killing people, and the right to refuse often comes with a price of losing your job or being reprimanded for actually exercising your rights,” Walton said.
Piccini did not respond to the Star’s request for an interview for this story. A spokesperson, Michel Figueredo, said that “Ontario leads North America on safety in the workplace,” and that the government continues to take action to protect workers.
He cited proposed requirements to require defibrillators at some construction sites and recently introduced legislation that, if passed, would create new financial penalties to better enforce health and safety compliance.
“Employers are legally required to take every reasonable precaution to protect workers — including implementing measures to reduce the risk of heat-related illness. Ontario’s laws are backed by the strongest workplace safety fines in Canada,” Figueredo said.
The Ontario government has also invested $250,000 in the development of a heat stress prevention tool kit that was launched in 2024 and provides resources to help workplaces assess risk, implement control measures and respond to heat stress concerns, a spokesperson said.
Smith, of the Institute for Work & Health, noted that all critical injury reports to the province have risen significantly over the past decade.
“Whatever we're doing to prevent them is not currently working,” Smith said.
No one deserves to be injured at work, Smith added.
“The number of critical injuries is going to increase over time, unless we do something about it. And each one of these injuries is catastrophic for the worker, catastrophic for the workplace and catastrophic for the family and the community around that worker.”
METHODOLOGY
Data: The analyses in this story are based on two data sets. One data set contains information on workplace critical injuries and fatalities in Ontario, and one data set contains information on temperature and precipitation in ÎÚÑ»´«Ã½.
The injury data set is a daily count of critical injuries and fatalities reported to the Ontario Ministry of Labour between 2012 and 2024. The data set was provided by the Ministry at the Star’s request.
The definition of a critical injury can be found . All employers covered by Ontario’s Occupational Health and Safety Act (OHSA) are required to immediately report critical injuries and fatalities to the Ministry’s 24/7 health and safety contact centre. Almost every worker, employer and workplace in the province is covered by OHSA; the few exceptions include federally regulated workplaces like banks, servants in private residences, and some farms. The data may include injuries of nonworkers, which are required to be reported in very limited circumstances, such as when there is a “reasonable connection” between the hazard that caused the incident and a realistic risk to worker health and safety.
The temperature data set is from Environment and Climate Change Canada’s “ÎÚÑ»´«Ã½ City” weather station (ID 6158355) in downtown ÎÚÑ»´«Ã½. It contains the daily maximum temperature, daily minimum temperature and total rainfall amounts for each day between 2012 and 2024. That data set can be downloaded .
Limitations: The critical injury data set provided by the Ministry does not include geographic, demographic or industry information — in other words, it does not say where in the province the injury happened, who it happened to or what type of work they were doing.
We chose to use the temperature in ÎÚÑ»´«Ã½ for a few reasons. The first is the density of the workforce in the ÎÚÑ»´«Ã½ region. Almost half of the province’s workers are in the immediate ÎÚÑ»´«Ã½ region, and 71 per cent are in the Greater Golden Horseshoe.
Heat waves are also caused by big, slow-moving high-pressure atmospheric systems that tend to affect large regions. These systems are part of “synoptic” weather patterns that range in scale from 1,000 kilometres across to even larger. (On a map, a circle that size with ÎÚÑ»´«Ã½ as its bullseye stretches roughly from Michigan to Montreal and from Washington D.C. to Timmins). A that examined three heat waves in southern Ontario between 2010 and 2012 found that the rate of emergency room visits at rural hospitals increased significantly in those periods, suggesting that the health effects of extreme heat events are shared broadly in the region, beyond the major urban centre of ÎÚÑ»´«Ã½.
However, using ÎÚÑ»´«Ã½ temperature as a proxy for the whole province may obscure some of the relationship between temperature and critical injuries. But it is more likely to be masking the true relationship than inflating or creating it. In general, mismeasurement of one variable in this kind of analysis tends to weaken an association, rather than create a false one, which means the true relationship between heat and critical injury may be stronger than what we reported here.
Analyses: To examine the relationship between temperature and injuries, the Star first did a simple descriptive analysis of the data, and then asked the Institute for Work & Health's Peter Smith to do a more rigorous statistical analysis.
The Star’s analysis calculated the average number of injuries in two-degree and four-degree buckets.
Smith’s analysis used what is known as a “case-crossover” design. In this type of study, a day when a critical injury occurred (a case day) is compared to days when the injury did not occur (referent days). Referent days are the same day of the week for all other weeks in that calendar month and year.
The basic question is this: if a worker suffered a critical injury on a Wednesday in May, did the temperature on that Wednesday differ from other Wednesdays in the same month?
Each critical injury is analyzed as a separate event, with case and referent days examined as their own groups and then summarized. Smith’s analysis also adjusted for amount of precipitation and for whether the case or referent day was a public holiday.
The particular value of this study design is that it controls for fluctuations in the workforce: for example, that different days of the week have more people working, that between May and September the size of the labour force changes because of seasonal jobs, and that the number of people in the workforce generally grows every year. Smith has used the same study design in published, peer-reviewed papers on occupational injuries and temperature.
Findings: The analyses show a consistent relationship between very hot days and increased risk of critical injuries. They also show a dose-response relationship: the higher the temperature and the more hot days in a row, the greater the risk of critical injury.
The Star’s analysis shows that there are an average of 6.3 critical injury reports on days above 32 C, and an average of seven critical injury reports on days above 35 C, compared to an average of roughly five on days in the teens and low 20s. It’s worth noting there are few days in the data set above 35 C (eight) compared to ones above 32 C (63).
Smith’s analysis used days between 21 C and 24 C as a reference range. Compared to days with those temperatures, he found that the risk of injury increases 24 per cent on days over 32 C. One day above 29 C, and two or more, or three or more consecutive days above 29 C, also showed an increased risk of critical injuries compared to the reference range, as did higher minimum temperature (e.g., hot nights as compared to cool nights). When examining maximum temperature as a continuous exposure, each one degree rise is associated with a one per cent increase in risk of critical workplace injury. These results were all statistically significant at a conventional threshold (p < 0.05). Given the consistency of these patterns across different analyses, it is unlikely the relationship between heat and critical injuries observed in this analysis happened by random chance alone.
There were too few fatalities in the data set to draw clear conclusions (689, compared to 24,612 critical injuries.) However, Smith’s analysis does show that the risk of a workplace fatality more than doubles after two and three hot nights in a row (20 C or more), a finding that was also statistically significant, but warrants further study.
Extra injuries: the number of excess critical injuries on 32-plus C days over the 13 year data set was calculated by comparing the expected number of critical injuries on those days if the temperatures were mild compared to how many more were actually observed, after removing public holidays and adjusting for month and year. It showed that approximately 116 extra critical injuries were observed in that period compared to what would be expected at lower temperatures.
Climate data: The climate change calculations are based on CMIP6, the most current global climate model data available and the foundation of the United Nations Intergovernmental Panel on Climate Change’s Sixth Assessment Reports. The global CMIP6 model was downscaled to the ÎÚÑ»´«Ã½ census subdivision using , a climate data portal created by Environment and Climate Change Canada and other organizations. We examined four climate change pathways that model different levels of greenhouse gas emissions and global development — SSP126, SSP245, SSP370 and SSP585 — but chose to visualize two of these for the sake of readability, a low-emissions scenario (SSP126) and high-emissions scenario (SSP370).
To calculate how many injuries could occur in the future, we extracted data from on the number of days above 32 C from 2025 to 2065 under the low- and high-emissions scenarios. We multiplied the cumulative number of 32-plus C days for the four decades in each scenario by 1.56. That 1.56 multiplier is the result of an ordinary least squares regression model calculated by Smith, which gives the predicted mean number of critical incidents on days over 32 C compared to days 32 C and under, after adjusting for month, year, day of the week, and amount of precipitation.
Our calculation is simplistic, because it does not account for demographic or workforce changes in Ontario in the coming decades. Even the most conservative estimate, however, shows that hundreds more workplace critical injuries associated with 32-plus C days will occur in the coming decades.
Acknowledgments: The Star would like to thank two external reviewers for their feedback: Kristie L. Ebi of the University of Washington’s Center for Health and the Global Environment, and Dr. Vincent Spilchuk of the University of ÎÚÑ»´«Ã½’s Temerty Faculty of Medicine’s Division of Occupational Medicine.
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