An ongoing heatwave in Phoenix, Arizona is so extreme that flights out of the region have been cancelled. But inmates at Tent City, a notorious outdoor jail, are expected to endure conditions too dangerous for jet planes.

The Tent City began as an overflow site for Maricopa County, Arizona’s already-packed jails. The fenced-in facility has housed up to 1,700 inmates outdoors in canvas tents, where temperatures ranged well above and below safe limits, earning the condemnation of human rights organizations. For more than two decades, the lockup’s founder, infamous former Maricopa Sheriff Joe Arpaio appeared to revel in the criticism, at one point publicly joking that Tent City was a “concentration camp”. When Arpaio lost his 2016 reelection bid, his successor pledged to dismantle the facility by the end of 2017.

But while heat wave temperatures soar to 120 degrees Fahrenheit and Phoenix officials warn locals to remain inside, hundreds of Tent City inmates remain confined outdoors.

In April, the sheriff’s office announced a six-month process of closing the facility.

“As of today, there are 380 work furlough inmates remaining in Tent City,” Joaquin Enriquez, a spokesperson for the Maricopa County Sheriff’s Office told The Daily Beast. “Work furlough means they go to their day jobs and return at the end of their workday to sleep in the Tents. Almost all of these inmates are in Tent City only at night. We estimate that approximately 50 [of the 380] will be on site in the daytime – meaning that they work either a second or third shift at their job.”

Even for inmates who leave the facility during the day, overnight temperatures have lingered at dangerous highs throughout the heatwave. On Tuesday, temperatures bottomed out at 90 degrees shortly before sunrise, although the Tent City’s thick canvas structures are notorious for trapping heat even as outside temperatures drop.

Enriquez said the jail implements new policies during extreme heat waves.

“During times like these – high heat warnings – inmates and Detention Officers are given unlimited access to ice water,” he said. “Our Detention Officers pay close attention to the conditions of Officers and inmates. Per standard operating procedures, if an inmate develops a medical condition due to heat or any other factor, the individual is transferred to Correctional Health Services.”

But prison reform activists advise skepticism on the sheriff’s office’s statement.

“I understand that the concession is being made to provide as much ice water as the inmates want,” Donna Leone Hamm, director of the Arizona-based organization Middle Ground Prison Reform told The Daily Beast. “But although the jail advertises that they’re doing that, we don’t know if it’s actually happening, because the demand for ice water might exceed the supply. It also means that the deputies have to constantly refill whatever containers they’re supplying the water in, so it may not happen exactly as advertised.”

Hamm said the extreme conditions could quickly prove dangerous for inmates with health issues, or who required medication.

“The major concern is for anyone with a medical condition where the symptoms may be exacerbated by the heat, she said. “They have to be really, really cautious to exposing someone to those kinds of conditions.”

Arizona officials know what happens when people are forced outside in the state’s dangerous heat. Less than an hour away from Tent City is Perryville, a state prison complex where, in 2009, a 48-year-old woman died after being locked in an outdoor cage for four hours during a 107-degree heat wave.

The woman, Marcia Powell, was isolated in the outdoor enclosure after she requested to see a psychiatrist. Prison policy prohibited inmates from remaining in the cage for more than 30 minutes. But Powell was kept outside for at least four hours, during which time she developed first- and second-degree burns before dying of heat-related complications.

“When her autopsy was performed, her core body temperature was 108. The autopsy stated that the only reason they wrote down 108 was because that’s the highest the thermometer would go,” Hamm said. “We got a tour of that facility after she was killed. I’m not going to say ‘died.’ She was killed. Her cage was 20 feet from an air-conditioned glass room where the guards were standing. There was utterly no plausible excuse to claim, as they did, that they didn’t notice the distress she was in.”

But Arpaio, the founder of Tent City, was openly aware of his inmates’ discomfort during previous heat waves.

During a 2011 heat wave when outside temperatures reached 118, and temperatures inside the tents reached 145, Arpaio displayed callousness toward the inmates. “What am I going to do, take them out of jail because it's too hot?" he asked the Arizona Republic. "Our men and women are working out here in this heat, too. Does anyone feel sorry for them?"

And during a 2003 heat wave, Arpaio told inmates, "It's 120 degrees in Iraq and the soldiers are living in tents and they didn't commit any crimes, so shut your mouths.” Outside temperatures reached 107 degrees that year, and temperatures in the tents were measured at 138 degrees.

Inmates told journalists that the heat had broken the tent city’s fans, and that their shoes were melting.

"It feels like you are in a furnace," James Zanzo't, then a Tent City inmate told the Associated Press in 2003. "It's inhumane."

This week, temperatures in Phoenix are expected to rise 13 degrees above that dangerous 2003 heat wave.