Water intake for moderate heat stress conditions

BACKGROUND

Heatstroke is a condition caused by any inability of the body to control its temperature, and its onset may be recognized by the symptoms of dehydration or, in some cases, only upon complete collapse. To prevent it, an ample supply of water should be carried and used at frequent intervals whether the pilot feels thirsty or not. The recommended drinking rates are one quart per hour for severe heat stress conditions and one pint per hour for moderate stress conditions; for reference, the body normally absorbs water at a rate of 1.2 to 1.5 quarts per hour. Thirst is a poor guide, because most people do not become thirsty until they carry a 1.5 quart deficit or have lost 2 percent of total body weight, and a small amount of fluid in the mouth shuts the thirst mechanism off again. Flying a small unmanned aircraft (UA) for long periods in hot summer temperatures increases the rate of water loss, and the first noticeable effect of dehydration is fatigue.

STUDY TIP

Practice converting between the FAA's liquid measures before test day, since the figures are given in both quarts and pints: 1 quart equals 2 pints, and the eight-glasses-a-day guide of 64 ounces equals 2 quarts. Read the stem carefully for whether the heat stress described is severe or moderate, because that word alone changes the answer.

KEY POINTS

• Drink one quart per hour in severe heat stress conditions and one pint per hour in moderate conditions.
• Over a 4-hour operation in moderate conditions that works out to 4 pints, or 2 quarts.
• Drink on a schedule rather than waiting for thirst, which only appears after a 1.5 quart deficit.

SOURCES

• remote_pilot_study_guide.txt ch9 "Heatstroke"
• remote_pilot_study_guide.txt ch9 "Dehydration"