FARMINGTON HILLS, Mich. (AP) — It’s hot and getting hotter for workers and everyone else outdoors as the first significant heat wave of the year makes its way eastward across the United States. More than 70 million people were under extreme heat alerts Monday.

What’s more, the heat will move in and sit. Excessive humidity will make it feel even more oppressive. “The duration of this heat wave is notable and potentially the longest experienced in decades for some locations,” the National Weather Service said over the weekend.

That’s dangerous. Emergency medical services across the U.S. already deployed for heat-related emergencies more than 2,400 times between June 1 and June 14, according to a government data tracker.

From gardeners to builders, not everyone can stay indoors. Here’s some advice on how to cope from some of the people who will be working outside this week.

Watch yourselves, and others 

Last year the U.S. had the most heat waves — abnormally hot weather lasting more than two days — since 1936.

Now, “we are going to be looking at some record high temperatures on a daily basis in some locations,” said Andrew Orrison, a meteorologist with the National Weather Service. Temperatures will be near 100 degrees in the Boston, New York and Philadelphia corridor.

Do what you need early

From Southern California to parts of New England and from the Canadian border south to the Florida Keys, temperatures this week are expected to top 90 degrees and even over 100 in some places, according to the National Weather Service.

Chris Sander operates Powder Monkey Fireworks, which is already preparing for the Fourth of July in Missouri. Sales begin this week, and workers have started setting out the merchandise.

Sander said his employees do the hardest physical work early in the morning, before the heat grows. The tents are vented but not air-conditioned.

“We have a bunch of fans, so you’ll pour bottled water on your head and stand in front of a 30-inch fan every five or 10 minutes, take a lot of breaks,” Sander said. Workers can also go to an air-conditioned camper. Sander encourages lunch at a restaurant to help them cool off.

If needed, he’ll send them home.

“If you see somebody a little lethargic or not with it, tell them, ‘You’re done for the day. Come back tomorrow,’” he said.

Know your limits

Urban areas are going to sizzle. Chicago is expected to reach 95 degrees Monday. The Detroit area could see 97 degrees on Thursday. Knoxville, Tennessee, could have 96 degrees by Friday.

Work supervisors with the Oakland County Road Commission in southeastern Michigan try to restrict workers’ hours in the direct sun, said spokesman Craig Bryson.

On some jobs, shifts are staggered. Crews work during the cooler mornings and resume in the evening to avoid the hottest part of the day.

It’s also important to teach workers how to recognize there’s an issue in each other, Brooks said: “Generally, people who are experiencing heat exhaustion aren’t going to recognize it as heat exhaustion because they get tunnel vision.”