Built-in Fire Fighter

The specter of fire in a man-carrying spacecraft has long haunted NASA scientists. In the pure-oxygen cabin atmospheres of U.S. craft, it seemed all too probable that a random spark from electrical equipment or insulation overheated by a short circuit might touch off fires that would blaze with explosive fury.

That fear now seems to have been exaggerated. Recent NASA tests at Wright-Patterson Air Force Base showed that all orbiting spacecraft carry a built-in fire fighter: weightlessness.

To simulate fires in orbit, the scientists loaded test chambers containing high concentrations of oxygen into KC-135 jet transports and flew them through parabolic arcs, creating 30 seconds of zero gravity during each maneuver. In the brief period of weightlessness, they ignited a variety of materials within the test chambers and took color movies of the results. Though the fires lit up promptly, the flames began to die down within 1 1/2 seconds; they simply smoldered or went out completely during the remaining period of weightlessness. Scientists estimated that the burning rates of test materials were reduced by as much as 90% .

It was weightlessness that made the difference. On earth, light, hot combustion products rise from a fire while cool air moves in to take their place, setting up convection currents that feed the blaze. In the weightlessness of space flight, the scientists discovered, there is no reason for the combustion products to rise. Unless they are disturbed by an artificial draft they hover around the burning object, quickly forming a blanket that excludes oxygen and suffocates the flames.

This file is automatically generated by a robot program, so reader's discretion is required.