FARMINGTON HILLS, Mich. — It’s hot and getting hotter for workers and everyone else outdoors as the first significant heat wave of the year makes its way east 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.

But 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

On Monday afternoon, Jose Orozco and about a dozen other workers rested beneath a tree near their water main project in Farmington Hills, a suburb of Detroit. The temperature was already above 80 degrees and rising.

The work of maintaining the public water supply in a heat wave is crucial. But it needs to be done as safely as possible. That means watching for signs of heat exhaustion, or worse.

“All we do is just drink water and take breaks of 15 minutes,” Orozco said. “You can see somebody slow down and it’s time to take a break.”

Do what you need early

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,” Sander said. Workers can also go to an air-conditioned camper.

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. 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, spokesman Craig Bryson said.

Greg Brooks, director of safety and compliance for the Michigan Infrastructure and Transportation Association, said the state requires construction companies to take necessary precautions. Beyond providing drinking water and extra breaks, many companies rotate workers so no one person stays exposed to the heat all day long.

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.