The oxygen must be available at a positive pressure to force the oxygen into the lungs, thus a pressure-demand type of mask is necessary. Dehydration is a very subtle physiological problem which is easily brought on by the activities associated with sailplane flying. The best conditions for soaring are in the heat of the summer with air temperatures near 100 degrees. The physical activity associated with assembly of the sailplane often occurs in the late morning when the sun and temperatures are quite warm. Unless the pilot drinks fluids, there is a likelihood that heat exhaustion or a heat stroke may occur as a result of dehydration.
Most pilots are aware of the danger and carry a thermos of water with easy access in the cockpit.
Wide brim hats and sun shades are also used by pilots to keep their heads out of the direct sun. At first glance, fatigue would not appear to be a problem for the sailplane pilot since there is little physical activity associated with controlling the airplane. Soaring is a highly mental sport requiring a continual assessment of weather conditions, current landing sites, flight strategy, current location, etc. In addition there is a physical coordination skill required to achieve the maximum altitude possible from each thermal. Over a flight time of 5 hours or more these demands are quite taxing and can lead to a deterioration in concentration by the pilot.