GEOFF BENNETT: It has been a deadly summer.

Extreme heat from across the country has killed dozens of people.

The Biden administration recently announced new rules to protect workers in communities from extreme weather, but it may not come soon enough.

In Maricopa County, Arizona, which includes Phoenix, there have been nearly 450 suspected heat-related deaths this summer.

Stephanie Sy has this report from the Valley of the Sun.

STEPHANIE SY: Summer steamrolled into Phoenix fast and furious, NOAA concluding it's been one of the hottest summers on record, and heat has been suspected in hundreds of deaths, including that of a 10-year-old boy on a hike.

The outdoors can be dangerous at this time of year.

Living outdoors is even more so.

At any given time each summer, some 9,500 people are unhoused in Maricopa County; 49-year-old Jerome Lee is one of them.

JEROME LEE, Unhoused: I mean, my head was -- I was dizzy.

I had a headache.

This heat is hot over here in Phoenix.

STEPHANIE SY: Lee got a saline I.V.

to rehydrate him.

He'd been drinking.

Alcohol can increase the risk of heat illness.

PERLA PUEBLA, Associate Medical Director, Circle the City: We're hoping we can help save some lives with the I.V.

Hydration.

STEPHANIE SY: Perla Puebla works with the nonprofit organization Circle the City, which this summer is trying to meet the most vulnerable where they are.

PERLA PUEBLA: We did encounter a lot of patients last year that needed I.V.

hydration, but they didn't want to go to the emergency room.

They didn't want to leave other belongings behind.

STEPHANIE SY: Last year, 645 people died in Maricopa County from the heat, the most ever recorded.

Almost half the victims were homeless, and over 60 percent had alcohol or drugs in their system.

DR. JOHN BALBUS, Director, Office of Climate Change and Health Equity: Heat is the most readily observable and most attributable adverse health effect of a warming planet.

STEPHANIE SY: Physician John Balbus is the director of the Biden administration's new Office of Climate Change and Health Equity.

How bad are things?

Has there been like a sea change in the risk here?

DR. JOHN BALBUS: The really disturbingly high death tolls that we were talking about in places like Maricopa County are saying that the outdoor spaces are becoming uninhabitable now in places like the Desert Southwest, where the temperatures are getting so high and the heat waves are lasting so long and those minimum temperatures are so high, that people who are suffering in our society, suffering from poverty, suffering from mental illness are at highest risk.

STEPHANIE SY: Another high-risk group, outdoor workers.

Filiberto Lares' job involves ferrying food to planes around the tarmac of Phoenix's main airport, where temperatures can run three to five degrees hotter than surrounding areas.

His truck doesn't have air conditioning.

FILIBERTO LARES, Driver, LSG Sky Chefs: We have to stay there in our cabin.

I think that, when you go to the shopping, when you go to the parking, how is your car, how hot it is.

STEPHANIE SY: He's done this job for 11 years, but now, at 56, he's working mostly at night to avoid the worst of the heat.

FILIBERTO LARES: I got problems with my feet on the summer.

I feel like my feet are burning.

So, as soon as I finish my shift, I got to take my shoes off.

STEPHANIE SY: A new ordinance in Phoenix requires employers to provide access to water, rest and shade.

The new rule also ensures access to air conditioning in vehicles, but won't go into effect until next May, which mean Lares has several more weeks of extreme temperatures to sweat through.

FILIBERTO LARES: I was thinking if I'm going to make it this year.

Now we are on July, so I said half of the season, I can make it.

So, I'm fighting.

I'm fighting to do it.

STEPHANIE SY: It's an occupational hazard that is getting worse every year.

For some, the risks aren't on the job, but at home; 73-year-old DeAnna Mireau divides her time between playing piano in retirement communities and serving as president of the Arizona Association of Manufactured Homeowners.

She says she's an advocate for residents.

DEANNA MIREAU, President, Arizona Association of Manufactured Homeowners: Forty percent of all indoor heat-related deaths occur in mobile homes in Arizona.

STEPHANIE SY: In her home, she added window treatments to block out the sun.

Outside, she's installed awnings and planted large bushes for shade.

DEANNA MIREAU: I said from the minute we moved to Arizona, if people took the measures to keep the -- keep your house warm and keep the cold out like they do in Michigan, all right, they don't seem to do that here in Arizona.

STEPHANIE SY: And older mobile homes are heat magnets because they're not as well insulated, she says.

DEANNA MIREAU: They don't have the dual-pane windows.

They're not necessarily designed to keep the heat out as well as a site-built home.

STEPHANIE SY: Just down the road, Trahnel and Brian Mays' mobile home was built in 1973.

TRAHNEL MAYS, Mobile Home Owner: Our last electricity bill was over $350 for this small trailer.

BRIAN MAYS, Mobile Home Owner: Like when it's this hot, I have got it set at 78 and it's running 82, 83, sometimes all the way up 85 in here, which isn't the end of the world.

But when you have got -- you know your air conditioner is running that long, you know it's going to hurt at the end of the month.

STEPHANIE SY: Trying to stay safe from heat while conserving their limited finances is a challenge.

TRAHNEL MAYS: We just -- we don't go out to eat.

I try to buy everything on sale.

We don't buy a lot of extra stuff.

We don't treat ourselves.

STEPHANIE SY: And to make matters worse, Trahnel is on disability and Brian was unable to work until recently because of a kidney transplant.

Their preexisting conditions raised their risk for heat-related health problems.

TRAHNEL MAYS: I have type 1 diabetes, and if I get to a point where I start getting nauseated, I know that it's gone too far and I'm just going to be dehydrated.

And then, once I start throwing up, I have to go right to the hospital.

STEPHANIE SY: But making places like Phoenix safer outdoors and indoors in a warming climate is possible, says Dr. John Balbus.

DR. JOHN BALBUS: There's a difference between saying the temperature is increasing and saying that there's nothing we can do to help people and that the deaths we're seeing are all because of climate change.

It's that balance of the warming of the planet and our effectiveness of our measures to protect people.

STEPHANIE SY: In an already deadly summer, that protection can't come soon enough.

For the PBS "News Hour," I'm Stephanie Sy in Phoenix.