Atmospheric Analyzer, Carbon Monoxide Monitor and Toluene Diisocyanate 

ALBERT V. SHANNON 

The purpose of the atmospheric analyzer and the carbon monoxide and toluene diisocyanate monitors is to analyze the atmospheric volatiles and to monitor carbon monoxide and toluene diisocyanate levels in the cabin atmosphere of Skylab.

The carbon monoxide monitor was used on Skylab 2, 3, and 4 to detect any carbon monoxide levels above 25 ppm. Air samples were taken once each week.

The toluene diisocyanate monitor was used only on Skylab 2. The loss of a micrometeoroid shield following the launch of Skylab 1 resulted in overheating of the interior walls of the Orbital Workshop. A potential hazard existed from outgassing of an isocyanate derivative resulting from heat-decomposition of the rigid polyurethane wall insulation. The toluene diisocyanate monitor was used to detect any polymer decomposition.

The atmospheric analyzer was used on Skylab 4 because of a suspected Coolanol leak in the Skylab cabin. An air sample was taken at the beginning, middle, and the end of the mission. 

Experiment Description 

The Carbon Monoxide Monitor is configured with a color change (from yellow to dark green) indicator tube to detect the level of carbon monoxide in the cabin. One hundred cubic centimeters of air is pulled through each tube by a 100 cm³ hand pump. The flow rate is regulated by an orifice in the pump. After the sample is taken, the color of the indicator tube is matched to a color chart to determine the carbon monoxide level. The Toluene Diisocyanate Monitor is configured with a color change (from light pink to dark pink) indicator tube also. Two thousand cubic centimeters of air is pulled through each tube by repeated pumping of a 100 cm³ hand pump. After the sample is taken the color of the indicator tube is matched to a color chart to determine the toluene diisocyanate level.

The Atmospheric Volatiles Concentrator is a cylindrical container accommodating two tubes filled with a porous polymer absorbent of high temperature stability, which is marketed under the name Tenex GC. It is designed and used for convenient and rapid exchange of atmospheric gases during the space flight. The device is equipped with the appropriate connections to mate with a quick disconnect module (standard equipment onboard the spacecraft). 

Design and Construction 

A carbon monoxide monitoring unit (fig. A.II.c.-1) consists of a sealed glass tube filled with a chemical that changes color from yellow to dark green when exposed to air. The tube is wrapped in clear Teflon tape, housed in an aluminum cylinder and insulated from the sides of the cylinder by Viton washers. The end tips are cut prior to assembly into the aluminum cylinder. A bayonet locking-type end cap is provided on each end of the cylinder to seal that end of the glass tube from the atmosphere until use. A female bayonet locking-type connector is provided on the end of the pump for attaching the sampling tubes.

The toluene diisocyanate monitoring unit (fig. A.II.c.-2) consists of a glass tube filled with a chemical that changes color from light to dark pink when exposed to toluene diisocyanate. The tube is wrapped in clear Teflon tape and housed in an aluminum cylinder which has a bayonet locking-type end cap. It is configured with an adaptor which is attached to the carbon monoxide monitor pump, a short piece of aluminum tubing, a 15.24 cm (6 in.) long hose with 0.4 cm (0.11 in.) inside diameter, a 4 cm (1.5 in.) long flexible hose with 0.6 cm (0.25 in.) inside diameter, and a command module hatch equalization valve adaptor. For sampling, the toluene diisocyanate tube is removed from the cylinder and installed in the sampling apparatus.

Figure A.II.c.-3 represents a technical drawing of the atmospheric sampler. The metallic parts of the devicc body, caps, and jets—are made of aluminum. Other materials machined from Teflon and Viton, are used and act as seals. The sample tubes are made of Pyrex glass, 50 mm X 10 mm o.d. They contain 4.5 ml of absorbent per tube. A single layer of Teflon tape provides the insulation of the tubes from the wall, and three Viton washers are installed for each tube to serve both as seals and as elastic buffers. A groove is provided for the washer at the air inlet which keeps tension on the tubes and thus allows a tight seal to be made between the tube and the jet orifice plate at one end, and the tube and main body at the other end.

The atmospheric analyzer (fig. A.II.c.-3) consists of a cylindrical housing about 2.5 cm (1 in.) in diameter and 12.7 cm (5 in.) long with end caps. It contains two glass tubes filled with Tenex GC absorbent. The air flow through each tube is regulated by a fixed orifice with a flow rate of approximately 200 cm³ per minute. The air flow rate is obtained by attaching the atmospheric analyzer to the spacecraft vacuum system and collecting a total air sample of about 30 liters. 

Conclusions 

Each equipment item, Carbon Monoxide Monitor, Toluene Diisocyanate Monitor, and the Atmospheric Analyzer performed as required during the Skylab missions.

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