Phoenix Fire Department already runs the most studied prehospital cold water immersion (CWI) program in the country. Less discussed is what happens when the patient is not on a city sidewalk but two miles up a mountain trail. Through the first five months of 2026, Phoenix crews responded to 74 mountain rescues, compared with 49 over the same period the previous year, an increase of more than 50%, according to ABC15 Arizona. Many of those patients present with heat exhaustion or heat stroke, with some arriving at internal temperatures as high as 109°F.

The wilderness cooling problem is not the same as the urban one

Phoenix's urban CWI protocol relies on immersion bags carried on ambulances, filled with bagged ice at the point of care. That works when a truck can reach the patient. On a mountain trail, rescue crews are often carrying gear on foot, sometimes for a considerable distance, with no vehicle access and no water source at the scene. Every pound and every extra step of setup time matters more here than almost anywhere else in fire-based EMS.

What Phoenix's existing program already proved

The department's urban CWI protocol, launched in 2024, has already been validated in peer-reviewed literature: a March 2026 study in Prehospital Emergency Care documented improved neurologic outcomes across more than 300 patients treated with prehospital immersion during one of Phoenix's hottest summers on record. That study, and the full mechanics of the urban protocol, are covered in depth in our earlier feature on the Phoenix program, linked below. The open question the wilderness numbers raise is whether the same cooling standard can be delivered when the truck can't get there.

Why portability decides outcomes in terrain rescue

The IOC/BJSM 2021 consensus on exertional heat illness makes clear that time-to-immersion, not just eventual immersion, drives outcomes. A cooling solution that requires a vehicle, a water main, or two rescuers to set up loses exactly the minutes that matter most when a rescue starts with a hike in. Rescue teams operating in these conditions need equipment that a single responder can carry and deploy without any of those dependencies.

Where Kollder fits

Kollder One™ packs to 85×10×10 cm and 11.1 kg, light enough to carry on a wilderness rescue pack-in, and deploys in under 2 minutes by one person on any surface, without a water source beyond what the crew brings in. Its stainless steel frame and open design also give rescuers full access to monitor airway and vitals throughout cooling, which matters as much on a mountainside as it does in an ambulance bay. For technical rescue and wildland-adjacent teams evaluating portable immersion equipment, specifications and quotes are available at kollder.com/#contact.

Pour aller plus loin / Further Reading

Sources: ABC15 Arizona, "Phoenix firefighters use blue bag and ice to save hikers from deadly heat stroke on Arizona mountain trails"; Comp G et al., Prehospital Emergency Care, 2026; IOC, Hosokawa Y, Racinais S et al., BJSM 2021.

Kollder is the emergency cooling tub that deploys in under 2 minutes, anywhere.

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