Preventing Exertional Heat Stroke: a field guide for medical teams and EHS managers

Most deaths from exertional heat stroke are preventable. Dr Douglas Casa (Korey Stringer Institute, University of Connecticut) documented across more than 401 cases a 100% survival rate when cooling was initiated within the first 30 minutes. That result is not automatic. It depends on preparation, trained teams, and the right equipment.

Who Is at Risk

Exertional heat stroke does not only affect elite athletes. The at-risk population is broader than commonly assumed.

Endurance athletes — Marathon, trail running, triathlon, Hyrox. Summer races expose large numbers of participants to hyperthermia, including those with strong fitness levels. Insufficient heat acclimatisation and dehydration are the two primary aggravating factors.

Firefighters — Intense physical effort in thermal protective equipment under high ambient temperatures is one of the highest-risk situations for exertional heat stroke. Multiple fire and rescue services have documented cases during summer wildfire operations.

Military personnel — The French Army's medical service has tracked exertional heat stroke cases since 1989. Incidence was 19.8 per 100,000 in 2010, with mortality brought below 1% — down from 30% in the 1980s — through improved protocols.

Outdoor workers — Construction, metallurgy, agriculture, oil and gas. Regulatory frameworks in several countries are tightening employer obligations around heat illness prevention. EHS managers are directly accountable.

Aggravating Factors to Monitor

Beyond ambient heat and exertion intensity, several factors multiply risk:

Dehydration, even mild
Lack of heat acclimatisation (the first 10 days in a hot environment are the most dangerous)
High humidity, which reduces evaporative cooling efficiency
Use of diuretics, beta-blockers, or antipsychotic medications
Prior history of heat stroke (victims show increased susceptibility)
Obesity and pre-existing cardiovascular conditions

Before the Event: the Planning Phase

This is where most critical situations are won or lost. ACSM (2023) and IOC (Hosokawa, Racinais et al., BJSM 2021) recommendations converge on several points.

Monitor WBGT indices. The Wet Bulb Globe Temperature combines temperature, humidity, and solar radiation. The ACSM recommends programme modifications above 28°C WBGT and cancellation or postponement above 32°C for endurance events.

Train the teams. First responders, volunteers, and race officials must recognise early warning signs: confusion, unsteady gait, abnormal behaviour during exertion. The victim is often the last to realise what is happening.

Equip medical posts before the start. A forward medical post with cold water immersion equipment must be operational before the first competitor starts — not during the event.

Define the emergency action plan. Who initiates cooling? Who monitors core temperature? Who calls emergency services? These questions must be answered before any incident occurs.

During Exertion: Early Detection

Exertional heat stroke progresses quickly. Early manifestations can resemble normal signs of fatigue.

Signs that cannot wait:

Confusion or disorientation, even mild
Abnormal behaviour: unexplained aggressiveness, incoherent speech
Unsteady gait, reduced coordination
Sudden cessation of sweating with intense flushing
Collapse

When any of these signs appears, exertion must stop immediately. Definitive diagnosis relies on rectal temperature measurement — the only reliable method in prehospital settings according to international consensus. Any temperature above 40°C (104°F) with neurological signs confirms exertional heat stroke.

The Most Common Field Mistakes

Transporting before cooling. The most dangerous error. During transport, core temperature continues to rise. The Cool first, transport second protocol applies without exception.

Relying on insufficient methods. Wet towels (0.03°C/min), ice packs (0.03°C/min), misting (0.10°C/min): these methods cannot meet the 30-minute therapeutic window from a starting temperature of 42°C (107.6°F). Only whole-body immersion (0.35°C/min or 0.63°F/min) achieves this reliably.

Waiting for diagnostic certainty. When in doubt, cool. The risk of unnecessarily cooling someone without exertional heat stroke is incomparably lower than the risk of not cooling someone who has it.

Not monitoring core temperature. Cooling should stop at 38.6°C (101.5°F) rectal temperature to avoid iatrogenic hypothermia. Without a rectal thermometer, this control is impossible.

Operational Checklist

30 days before

WBGT reference consultation and definition of action thresholds
Medical team training on the immersion protocol
Identification and equipment of forward medical posts

7 days before

Weather forecast review and device adjustment if necessary
Full team briefing on warning signs
Cooling equipment test

Event day

Cooling equipment in place before the start
Ice stock calculated (target: maintain water below 15°C / 59°F)
Rectal thermometers available at the medical post
Communication protocol with emergency services confirmed

The Equipment That Conditions Everything

Prevention reduces risk. It does not eliminate it. When a case occurs despite preventive measures, everything depends on the immediate availability of immersion equipment.

Kollder is designed for teams that cannot afford to wait. Deployable in under 30 seconds by one person, on any terrain, it allows the Cool first, transport second protocol to be applied without any prior infrastructure.

Fire and rescue services, event medical teams, military medical units, and EHS managers who want to evaluate Kollder can contact our team: kollder.com/#contact