When the going gets hot, the hot get nocturnal. Here, NPR reports on a construction site in Phoenix, where both the parameters of pouring and setting concrete mix with concerns over worker safety to make a significant change in work schedules.

A team of construction workers is pouring concrete onto the frame of a structure that will eventually become a wastewater treatment plant. It's 1 a.m. on a clear night in the suburbs of Phoenix. The temperature is still in the high 80s. But that's way down from the area's recent record high temperatures, up to 118 degrees.

Around here, it never really gets cool in the summer. That's partly because Phoenix is such a big city that it traps the heat — a heat island. But now in the middle of the night, it's finally cool enough to start work.

"We try to pour and place and finish concrete when it's below 90 degrees," says Daniel Ward, the construction company's project director. From inside an air-conditioned trailer, he says there are things you can do to modify the concrete, like adding ice to cool it down. But it's just best to work when it's not as hot.

There are two reasons for working such strange hours. One is the concrete itself.

"It sets up too quick in the day with the sun on it," says general superintendent Mike Wigness. "Here it's a little bit slower and manageable."

The other reason is making sure the workers don't overheat.

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