As extreme heat continues to grip large parts of the country, cities like Phoenix are turning to an unlikely — and remarkably effective — lifesaving tool: bags of ice.
Phoenix is no stranger to the deadly impact of high temperatures. In fact, heat kills more people there each year than homicides. Now, the Phoenix Fire Department is taking a low-tech approach that’s setting a national example in combating heat-related illnesses: cold water immersion.
Firefighter Colin Kennedy is all too familiar with the dangers posed by relentless heat.
“So, right now, we’re going to a 50s female outside of a dollar store,” Kennedy said during a recent call. “So it’s 105, 106 degrees. The pavement is hot.”
When firefighters found the woman, she was suffering a stroke on a scorching sidewalk. If her core temperature had reached 104 degrees or higher, the team would have placed her into a large blue plastic bag and filled it with ice water — a new emergency protocol designed to rapidly cool down heatstroke victims on the way to the hospital.
“We have a bag and we have ice and we’re saving lives with it,” said Captain Dave Kirk of the Phoenix Fire Department.
Originally developed by the military, cold water immersion has found its place in urban emergency response as climate change intensifies heat waves across the country. According to Climate Central, Phoenix now experiences 39 more hot summer days than it did in 1970, and dangerous multi-day heat streaks are becoming increasingly common nationwide.
Traditional methods of treating heatstroke — such as placing ice packs on the neck and groin or administering cold IV fluids — are no longer enough. Captain Kirk says the effectiveness of ice immersion is “night and day.”
This method can cool patients three to five times faster than older techniques — a critical difference that can prevent brain damage and organ failure.
In the country’s hottest city, every Phoenix fire station now stocks ice — just like a gas station might.
“We’ve got eight bags at seven pounds inside, essentially a large trash bag right now, and this bag is going to come out and it’s going to come with us on the call,” Kennedy said.
The method is already proving its worth. Last year, during a trial period, Phoenix firefighters used ice immersion more than 300 times. Despite 2024 being one of the hottest summers on record in Phoenix, heat-related deaths actually dropped. This summer, they’ve expanded their efforts by stockpiling ice at popular trailheads to cool off overheated hikers on-site.
“We’re seeing people go from 108, 109, 110 core body temperature to 101 or 100 degrees even by the time they arrive at the hospital,” Kennedy said.
At Valleywise Health Medical Center in Phoenix, Dr. Geoff Comp has been training medical teams on this cold water protocol for several years.
“It’s fast. The thermal conductivity of water is so much faster than air,” Comp explained when asked why full-body immersion is so effective.
He emphasized that cooling patients before they arrive at the ER makes all the difference.
“If we’re able to decrease the amount of time that the patient is impacted by that higher temperature, it’s going to be better. By doing this, we’re decreasing mortality…we’re saving people’s lives,” he said.
In the face of intensifying heatwaves, Phoenix’s ice bag tactic is emerging as a critical — and surprisingly simple — weapon in the fight against heatstroke.
This story was produced in partnership with Climate Central.
