Human Heat Tolerance

heattol.gifAs military aircraft became more complex after World War II and into the jet age, increasing attention was paid to environmental factors affecting the health and performance of pilots and crew. One of these factors concerned high cockpit temperatures that could occur both on the ground and during flight operations – temperatures sometimes exceeding 200 degrees Fahrenheit, either from high friction flight environments or when preparing aircraft that have been sitting out in the high heat of the summer desert.

Very little data was available on the response of humans to such high heat environments, so this type of research attracted the attention of U.S. Army Air Force Captain Craig L. Taylor while he was assigned duties at the environmental laboratory at Wright Field in Dayton, Ohio. He had started preliminary work on the problem before Dean Boelter recruited him to be a faculty member at UCLA’s new College of Engineering. Research concerning the relationship between engineered systems and their human users, a life-behavioral studies area, was a major goal of Boelter’s educational plan as part of his Unified Engineering Curriculum.

With research equipment constructed largely of war surplus materials, Taylor and his assistant W. Vincent Blockley prepare a range of tests in the late 1940s. The heat chamber or “hot box” is a five-feet long and wide steel cylinder shaped much like a beer keg; heated air is pumped into the chamber at 70 cubic feet per minute; it is sheathed inside with sheet metal, and insulated with rock wool; and it is entered by a heavy, circular door. The chamber was acquired through the War Assets Administration from Ryan Aircraft Company in San Diego, where it was used during the war to test instruments. A harness of nine thermocouples to measure skin and flight suit temperatures is worn by the subject.

The test subject is conditioned in a smaller hot box covered by a canvas hood before entering the pre-heated steel vessel. A series of experiments are undertaken in the range of temperatures between 160 and 235 degrees Fahrenheit. Measurements of skin and rectal temperatures, sweat loss and heart status (EKG) provide pioneering systematic data. Experimental subjects are volunteer students, faculty, and military reserve aircraft pilots. Variations in the temperature of air as it is breathed in and out are measured by thermocouples inserted in the nose and mouth using a plastic mouthpiece. As the experiments take place, the volunteer is observed closely through a glass window in the hot box vessel. The special thermometers reveal that the human body acts as a refrigerator, remaining more than 100 degrees cooler than the temperature in the hot box. When graduate student John Lyman joins the project he quickly devises a series of arithmetic tests using pencil and pad, to be administered in three minute cycles, to test the subjects’ thinking processes while exposed to high heat environments. Lyman goes on to head a project in which fully functional cockpit controls consisting of instrument panel, stick, rudder, pedals and throttle are installed in the heat chamber. “Flights” are made in repetitive four minute cycles as heat exposure increases, accompanied by the same physiological and temperature measurements as in the other tests.

Both experimental and theoretical human heat tolerance studies, covering environments ranging from wet suits to space suits, were continued in the biotechnology laboratory until 1973 when, with the available equipment near obsolescence and funding no longer available, the projects were terminated. Others involved in the hot box projects included engineer R.H. Holloway, and student assistants Philip Elliot, Sidney Friedlander and Lloyd Barnes.

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