Anthony Soto, a 22-year-old baggage claim employee at the Dallas Fort Worth International Airport, crumpled to the floor near gate C15 after a seizure last October that he attributed to hot indoor conditions and strenuous lifting. In record-setting heat in Texas this past summer, Mr. Soto, who has epilepsy, had four more seizures that left him speechless, his body unresponsive, he said.

His blue button-down shirt was streaked with sweat on a recent sweltering day as the temperature again neared 105 degrees. Working in such heat “makes us feel unwanted, unhelpful and unworthy,” he said. “The only thing that matters is how long it takes to scan bags.”

Scientists say the record heat this summer was fueled by climate change and that heat waves are likely to grow more intense. But there are few safeguards for tens of millions of workers increasingly exposed to rising temperatures on the job.

The Biden administration is taking steps to create new rules for employers, with two key steps expected in the coming months. A handful of states have put in place standards for work in extreme heat, including California, which requires employers to allow outdoor workers to rest in the shade in temperatures above 80 degrees.

But in other states, workers like Mr. Soto, who makes $15 an hour, continue to suffer as extreme heat spans the summer months and the early fall. Dallas endured a record number of September days with triple-digit temperatures.

“The worst-performing states are just not going to do it on their own,” said Dr. Rosemary Sokas, an occupational health expert at Georgetown University who co-wrote a recent article in The New England Journal of Medicine on the dangers now faced by workers in absence of a federal regulations.

Prodded in 2021 by President Biden, the Occupational Safety and Health Administration is drafting guidelines for indoor and outdoor work in heat, which could allow the federal government to fine employers that violate its recommendations.

But OSHA is still plodding through a labyrinthine rule-making process. The agency is required to go through nearly 50 steps, most of which are mandated by executive orders or by congressional legislation.

By the end of October, officials expect to complete a consultation with small businesses that would be affected by the standards. Business groups have opposed the possible rule, saying it could be onerous and expensive. By early next year, the agency could lay out a timeline for a rule proposal.

“That’s really a major milestone, because that’s the spot where the agency formally alerts the public that we are proposing a rule,” Andrew Levinson, OSHA’s director of standards, said in an interview.

Mr. Levinson said that the agency was planning to publish indoor and outdoor standards together, since workers “may be shuffling between outdoor work environments and then going into a warehouse, or into some other equipment processing area.” He added that OSHA had to consider different varieties of hot weather, like dry and moist, and how they affect the body.

The agency’s current guidance for employers, with little enforcement muscle, may offer clues to its formal heat standard. Among the guidelines, experts say, could be acclimatization — the practice of gradually easing workers into schedules that expose them to extreme heat. Many workers who have died from heat-related causes succumbed as they began a job.

The agency could also require employers to offer workers access to breaks, shade and cold water. In a statement to The Times, Mr. Soto’s employer, Prospect Airport Services, said that he had been stationed in a cooler work area and that it had offered additional breaks to employees working in a baggage-handling space where the air-conditioning had been unreliable.

Federal lawmakers introduced legislation over the summer that would require OSHA to publish an emergency rule within a year after the bill passes, a measure seen as unlikely to pass because of opposition in the Republican-controlled House.

One of its chief backers, Representative Greg Casar, Democrat of Texas, held a “thirst strike” over the summer to urge the fast-tracking of an OSHA rule. “It’s critical a rule is laid out over the next year,” he said, adding, “If we want to make it permanent, we need to pass legislation.”

David Michaels, an epidemiologist at George Washington University who led OSHA during the Obama administration, said that the agency’s current timeline suggested that new standards might not come by next year. Whenever it arrives, the rule “would be a game changer,” he said, adding: “There’s no question. And it will save lives.”

Extreme heat especially afflicts low-wage earners like Mr. Soto. In higher temperatures, workers in poor counties lose more of their pay, researchers have found. And low-income Americans disproportionately suffer from chronic health conditions that make them more vulnerable to heat-related injuries.

People with epilepsy are more prone to seizures in extreme heat. so Mr. Soto received permission from his supervisors to work in cooler baggage claim areas. The daily medication he takes has steadied him.

Yet he is still anxious as he navigates the sun-drenched and unreliably air-conditioned airport five days a week, including the long walk to a staff room for lunch that he said eats up much of his break time. The airport’s heat, he said, “feels like you’re in the gym, in the sauna.”

“You fully start sweating. I start looking at my hands and I think, How am I already sweating? I haven’t done anything,” Mr. Soto added. “My uniform, you can literally see the sweat on your back and stomach.”

How heat injures the body

Dangerous heat waves are affecting more of the country, including states with typically milder climates.

The costs to the economy are vast: In 2021, more than 2.5 billion hours of labor in the U.S. agriculture, construction, manufacturing and service sectors were lost to heat exposure, according to data compiled by The Lancet, the London-based medical publication. Productivity dips heavily in hot weather.

Few states offer more vivid examples of these new perils than Texas. More than 40 people have died in Texas from heat-related causes since 2011, including a lineman and letter carrier over the summer.

The risks to workers were apparent on a series of sweltering late summer days at DFW, where temperatures neared 110 degrees.

Over 650,000 Americans worked in commercial airports as of 2022, according to federal data compiled by the Service Employees International Union. Many have jobs that involve full or partial heat exposure, including wheelchair escorts, shuttle drivers and airplane cleaners that can ask for loitering in hot areas without adequate air-conditioning.

Workers on the tarmac, such as baggage handlers, typically face the highest temperatures and most dangerous conditions. While some industries and employers have allowed workers to clock in early in the morning or late at night to avoid the worst of a day’s heat, flight schedules are fixed. Most airport workers cannot choose the time or place for their work.

Travun Watts, a contractor who makes $14 an hour cleaning American Airlines planes at the airport between 2 p.m. and 10 p.m., fainted one afternoon in August as he waited in a jet bridge in scorching weather.

Sitting in a baggage claim area on a recent afternoon before his shift, Mr. Watts, who has diabetes, recalled waking up at a Dallas hospital, uncertain about what had landed him there. “I felt like I was in a loop, incoherent,” he recalled.

To assess the limits of work in extreme heat, scientists point to what is known as the wet-bulb temperature — a measurement of both temperature and humidity. Above 95 degrees, sweat cannot evaporate and the body cannot cool. Hours outdoors can be fatal.

“When you have hot conditions, there’s increased demand on the heart to pump more blood to the largest organ in our body, which is our skin,” said Dr. Jonathan Patz, a scientist at the University of Wisconsin-Madison who has studied the environmental health effects of climate change.

Extreme heat can wreak havoc on the body’s major organs. The heart and the kidneys can become deprived of blood and oxygen, leading to kidney failure. If the brain becomes overheated and oxygen-deprived, it can halt the signals to the body to cool itself, preventing sweat.

Mr. Watts spent more than three days in the hospital, he said. A nurse still visits him at home once a week to check on him. His job had been unrelenting even after he returned, he added, often involving cleaning as many as 14 planes per shift.

“Instead of giving me five to 10 minutes to set my insulin meter, they’d rush me, make me run from one plane to next, even when I told them it’s detrimental to my health,” he said.

Airports are particularly risky settings for work, with concrete structures and tarmac that easily retain heat, Dr. Patz noted.

Extreme heat can reduce the safety of indoor spaces by reducing airflow and raising the temperature of air-conditioned spaces. Terminal C, where Mr. Watts works, is older than others at the airport, with crowded walkways, unreliable air-conditioning and drinking fountains with lukewarm water.

At 5:30 p.m. on a recent day, as the temperature hovered around 100 degrees, baggage employees rested their heads and arms on the ramps that funneled bags out of flights in Terminal A.

“Any strenuous activity like throwing luggage on a conveyor belt takes a lot more out of you,” said Dr. Frank LoVecchio, an emergency physician who treated airport workers over the summer at the Valleywise Health Medical Center in Phoenix.

“I’ve seen people super red. They look like they just jumped in a pool,” said Zach Bodine, who makes around $15 an hour helping passengers in wheelchairs at the Phoenix Sky Harbor International Airport. He recalled co-workers “throwing up in the bathroom nonstop.”

Mr. Soto, the Dallas baggage claim worker, said that he had considered quitting, a move that could protect his health. But he recalled being a boy who was awe-struck watching planes land at DFW with his father — a feeling that led to his dream of becoming a pilot.

Mr. Soto sometimes rides the airport’s outdoor tram system just to glimpse aircraft. “Everyone wishes they could fly,” he said.

Audio produced by Kate Winslett.