Occupant evaluation of 7-hour exposures in a simulated aircraft cabin - Part 1: Optimum balance between fresh air supply and humidity

Low humidity in the aircraft cabin environment has been identified as a possible cause of symptoms experienced during long flights. A mock-up of a 21-seat section of an aircraft cabin with realistic pollution sources was built inside a climate chamber, capable of providing fresh outside air at very low humidity. Experiments simulating 7-hour transatlantic flights were car-ried out at four outside air supply rates - 1.4, 3.3, 4.7 and 9.4 L/s per person (3, 7, 10 and 20 cfm/p) - yielding average humidity levels of 28%, 16%, 11% and 7% RH, respectively. Four groups of 16-18 subjects were exposed to the four conditions. The subjects completed ques-tionnaires to provide subjective assessments of symptoms commonly experienced during flights. Increasing humidity to 28% RH by reducing outside air supply rate did not reduce the intensity of the symptoms typical of the aircraft cabin environment, and intensified headache, dizziness and claustrophobia.