Heat Casualty Triage on a Training Run
At 0715, 30 cadets begin an 8 km formation run in fatigues. The wet-bulb globe temperature is 31°C, relative humidity is 78%, and wind is 3 km/h. The last meal was 5 hours earlier. Water points are at 3 km and 6 km. Cadet A drank 500 mL before the run and at km 5 reports dizziness, headache, and heavy sweating; skin is cool and clammy. Cadet B drank 1.5 L, has stopped sweating, is confused, and has hot dry skin at km 7. The medic has one cooling station, oral rehydration salts, and no IV fluids. Decide who is treated first and why; explain how humidity changes evaporative cooling; estimate minimum water need for the 30 cadets for the run if each should drink 400 mL per hour and the run lasts 90 minutes.
1. Who should be treated first, Cadet A or Cadet B? Justify using the signs and the likely condition.
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Cadet B first. Cadet B shows confusion, hot dry skin, and cessation of sweating - signs consistent with heat stroke, a medical emergency involving failure of thermoregulation and possible central nervous system dysfunction. Cooling must begin immediately; delay increases risk of organ damage. Cadet A shows dizziness, headache, heavy sweating, and cool clammy skin - more consistent with heat exhaustion, which is serious but generally less immediately life-threatening. Cadet A should be moved to shade, given oral rehydration salts if alert, and cooled, but B needs the cooling station first. The judgement call is not "who feels worse" but "who has the most time-critical physiology."
2. Explain why 78% relative humidity makes the run more dangerous than the same temperature at low humidity.
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Evaporation of sweat is the body's main cooling mechanism during exercise. Evaporation depends on a vapor pressure gradient between skin and air. At 78% relative humidity, the air already holds most of the moisture it can hold at that temperature, so sweat drips off rather than evaporating. Less evaporation means less heat loss, so core temperature rises faster for the same workload. The low wind speed of 3 km/h also reduces convective cooling and limits the removal of saturated air near the skin. Thus the WBGT of 31°C is more dangerous than a dry 31°C because the body cannot dissipate heat effectively.
3. Estimate the minimum water need for the 30 cadets during the 90-minute run at 400 mL per hour each. Is the planned water point schedule enough?
Read the worked answer
Per cadet: 400 mL/h × 1.5 h = 600 mL. For 30 cadets: 30 × 0.6 L = 18 L. That is the minimum drinking need during the run, not counting post-run rehydration or spillage. The two water points can meet this if each cadet actually drinks about 300 mL at each point, but that requires discipline and monitoring. The schedule is adequate only if the water points are stocked with at least 9 L each and cadets are encouraged to drink. Because humidity is high and sweat losses may exceed intake, the medic should also weigh or monitor cadets and provide oral rehydration salts after the run.