Oxygen will continue to play a prominent role in man's atmosphere, and it can be assumed that oxidative processes will be occurring continually. Numerous air pollution studies have shown that incomplete oxidation of certain materials produces large amounts of trace contaminants. Since most of man's sub-systems carried aboard will not operate at 100% efficiency, incomplete oxidation may present a significant problem for the astronauts. Certain oxidative processes are hazardous, however, while similar ones are benign. For example, with methyl alcohol, only partial oxidation is achieved with the resultant formation of formaldehyde, whereas with ethyl alcohol, sealed-cabin environmental studies2 indicate that its oxidation is complete, and there is no formation of toxic aldehydes. Thermal degradation presents many inherent difficulties. In some instances, toxicants may be degraded to nontoxic materials, whereas the opposite is also true; probably the latter occurs more frequently. An example in a sealed atmosphere has been shown in the studies aboard nuclear submarines. Freon (CC12F2) has been employed for air conditioning. At slightly elevated temperatures this material was decomposed into hydrogen fluoride, hydrogen chloride, chlorine gas, and fluorine. This is an example of a material which is generally considered to be nontoxic but produces several lethal by-products. At high temperatures Freon is broken down into carbonyl chlorides, known as phosgene in chemical warfare. Such degradation in the submarine has forced surfacing; however, in our space vehicle, one cannot anticipate having the privilege of calling off a mission when the environment becomes adverse. Table 1 indicates the numerous variables which may affect an orbiting laboratory. Almost none of these has been clearly defined in our present ground investigations, as such endeavors must be undertaken in both locales to establish the role each will have in a manned space environment. The interactions of all of the contaminants can show combined synergism and/or antagonism with all of the described factors. This would constitute a profile of combined biophysical and biochemical stressors. Certainly, atmospheric specialists are not overly familiar with any of the reactions just expressed for an orbiting station and the summation of such reactions would be only problematical. However, it must be assumed that the effects would be deleterious and would endanger man's performance and his space vehicle to the extent that they might be noxious, obnoxious, or even lethal with the possible consequence of aborting the mission. References