OBJECTIVES:
Prior to the Skylab program, there was an increased concern by scientists that a closed-loop environment in a space station would facilitate the build up of poisonous gases. More and more newly developed nonmetallic materials, such as fluorinated polymers, were being used in the spacecraft materials during the Apollo Program. This required special attention to test for outgassing products from these materials. In addition, none of the environmental control life support systems in previous spacecraft or in the Skylab were designed to provide carbon monoxide (CO) removal. In order to provide a quality environment, the Skylab program adopted several layers of atmospheric protection which included:
1. A nonmetallic material screening program which was designed to eliminate those materials that could cause problems as a result of their outgassed products.
2. Establishment of acceptance levels for both carbon monoxide and total organics based on the spacecraft habitable volume, the trace gas removal rate, the environmental control life support systems, and the cabin leak rate.
3. Eetermination of lethal dosages for pyrolysis products from polymers which were considered for use as electrical components.
4. Identification of pyrolysis products by gas chromatography and mass spectrometry.
During the launch of the Skylab Orbital Workshop on the Saturn V rocket, the micrometeoroid shield was ripped away from the outer surface of the spacecraft, leaving Skylab exposed to the intense heat of the Sun. This resulted in the overheating of the Orbital Workshop interior wall insulation material. Temperature sensors indicated that the interior walls had attained a projected temperature of a scorching 350 degrees Fahrenheit on the skin side of the insulation and 160 degrees Fahrenheit on the interior volume side of the spacecraft insulation. Since the protective insulation was made up of rigid polyurethane foam, a potential toxicological hazard could develop as a result of the thermal decomposition of the polymer, to produce an isocyanate derivative.
The objectives for making a toxicological assessment of Skylab were to measure both carbon monoxide and toluene diisocyanate, and to identify possible nonmetallic toxicants in the Skylab Orbital Workshop.
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APPROACH:
Before the entry of the Skylab 2 crewmembers into the workshop, a series of pressurization-depressurization cycles of the Skylab Orbital Workshop atmosphere were done to discharge and dilute any contaminating gases of potentially toxic levels. Secondly, the crew sampled the air for carbon monoxide and toluene diisocyanate first in the Multiple Docking Adapter and then in the orbital workshop, using the supplied analyzer tubes.
Two types of gas analysis detector tubes and two activated charcoal and hopcalite filtered masks were put aboard the Command and Service Module to protect the unsuited crewmen upon their initial entry into the orbital workshop to sample the atmosphere. One set of gas detector tubes were used for carbon monoxide detection and the other set was used for toluene diisocyanate detection. The tubes used to detect toluene diisocyanate were only used during the Skylab 2 mission. Air samples were taken by using a syringe-type pump to force air into the gas detector tubes. Each tube contained a colorimetric compound that reacted with carbon monoxide (sensitivity of 11 mg/m3) or toluene diisocyanate (sensitivity of 0.14 mg/m3). After the air samples were collected, the crew used a color scale to compare the sample color to determine the concentrations. The remainder of the Skylab 2 mission, and Skylab missions 3 and 4, were accomplished without any other atmospheric trace gas problems.
Concerns of a coolant leak in the Skylab workshop during Skylab 2 prompted the collection of additional air samples on subsequent missions; samples were collected on Skylab 3 on mission days 11, 46 and 77. These samples were collected for the identification of atmospheric gases with a specialized device called the Atmospheric Analyzer. It consisted of double-barrel glass tubes filled with a gas chromatographic absorbent material that trapped atmospheric compounds in the glass tubes for analysis. Airflow was allowed to flow through the glass barrels for 15 hours, making for a total of 60 liters that passed through the Atmospheric Analyzer.
RESULTS:
The analysis of the samples collected from the Atmospheric Analyzer indicated the presence of more than 300 compounds in the Skylab atmosphere during the occupancy of the Skylab 3 crew. Of this number, 107 were identified by mass spectral methods. The molecular weights of the identified compounds ranged from 60 to 584. These data revealed that there was no coolant fluid leaking into the interior of the Orbital Workshop. When the three atmospheric samples taken on mission days 11, 46, and 77 were compared, the results indicated only minor differences in the levels of atmospheric contamination. This indicated that the Environment Control Life Support System had attained a state of equilibrium earlier between the gas generation rates of the contaminant sources and the removal rate. The results from the other samples indicated no detectable toluene diisocyanate and an extrapolated 5 mg/m3 level of carbon monoxide.
Rippstein WJ, Schneider HJ. Chapter 10: toxicological aspects of the Skylab program. In: Johnson RS, Dietlein L, eds. Biomedical Results from Skylab. Washington, DC: NASA Headquarters; 1977:70-2. NASA SP-377.
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Rippstein WJ, Schneider HJ. Toxicological aspects of the Skylab program. In: Johnston RS, Dietlein LF, eds.
The Proceedings of the Skylab Life Sciences Symposium; Houston, TX; 27-29 August 1974. Houston, TX: NASA Lyndon B. Johnson Space Center; 1974;1:157-68. NASA TM X-58154.
[NTRS]
Skylab mission report, second visit. Postflight analysis of engineering, experimentation, and medical aspects. NASA Johnson Space Center; Houston, TX, United States. January 01, 1974. NASA TM-X-69996.
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