Validity of Humidity Ramp Protocols for Identifying Limits of Survivability in Heat-exposed Persons

Participants are exposed to 42°C and 28% relative humidity for 70 minutes. Thereafter, humidity is increased 3% until an ambient humidity of 70% is achieved. The humidity at which esophageal temperature (and rectal temperature and heart rate) inflect is subsequently determined.

After a 1 hour equilibrium at 42°C and 28% relative humidity, humidity will be increased 3% every 10 min until it is \~5% higher than the participants' individual esophageal temperature inflection point identified in the humidity ramp protocol. These conditions will be held constant for the remainder of the 9-hour exposure period (starting from the beginning of equilibrium). Tap water will be provided at regular intervals to limit dehydration.

After a 1 hour equilibrium at 42°C and 28% relative humidity, humidity will be increased 3% every 10 min until it is \~5% lower than the participants' individual esophageal temperature inflection point identified in the humidity ramp protocol. These conditions will be held constant for the remainder of the 9-hour exposure period (starting from the beginning of equilibrium). Tap water will be provided at regular intervals to limit dehydration.

Participants are exposed for 9-hours to 28°C with 35% relative humidity. Participant will be allowed to drink tap water ad libitum.