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After several decades of human spaceflight, the community of space-faring nations has accumulated a diverse and sometimes harrowing history of toxicological events that have plagued human space endeavors almost from the very beginning. Some lessons have been learned in ground-based test beds and others were discovered the hard way - when human lives were at stake in space. From such lessons one can build a risk-management framework for toxicological events to minimize the probability of a harmful exposure, while recognizing that we cannot predict all possible events. Space toxicologists have learned that relatively harmless compounds can be converted by air revitalization systems into compounds that cause serious harm to the crew.

As mission length and the number and complexity of payload experiments increase, so does the probability of thermodegradation contingencies (e.g. fire, chemical release and/or smoke from overheated components or burning materials), which could affect mission success. When a thermodegradation event occurs on board a spacecraft, potentially hazardous levels of toxic gases could be released into the internal atmosphere. Experiences on board the Space Shuttle have clearly demonstrated the possibility of small thermodegradation events occurring during even relatively short missions. This paper will describe the Combustion Products Analyzer (CPA), which is being developed under the direction of the Toxicology Laboratory at Johnson Space Center to provide necessary data on air quality in the Shuttle following a thermodegradation incident.

Carbon dioxide (CO2), a natural product of human metabolism, accumulates quickly in sealed environments when humans are present, and can induce headaches, among other symptoms. Major resources are expended to control CO2 levels to concentrations that are tolerable to the crews of spacecraft and submersible craft. It is not practical to control CO2 levels to those found in the ambient environment on earth. As NASA looks ahead to long-duration missions conducted far from earth, difficult issues arise related to the management and effects of human exposure to CO2. One is the problem of “pockets” of CO2 in the habitat caused by excess generation of the gas in one location without a mechanism to purge the area with fresh air. This results in the crew rebreathing CO2 from their exhaled breath, exposing them to a much higher concentration of CO2 than whole-module measurements would suggest. Another issue is the potential increased sensitivity to CO2 in microgravity.

A volatile organic analyzer (VOA), developed by Graseby Dynamics, Ltd. under contract to the Johnson Space Center Toxicology Laboratory, is the core instrument for trace contaminant monitoring on the International Space Station (ISS). The VOA will allow trace amounts of target compounds to be analyzed in real time so that ISS air quality can be assessed in nominal and contingency situations. Recent events on Mir have underscored the need for real-time analysis of air quality so that the crew can respond promptly during off-nominal conditions. The VOA, which is based on gas chromatography/ion mobility spectrometry, is the first spacecraft instrument to be used for such a complex task. Consequently, a risk mitigation experiment (VOA/RME) was flown to assess the performance and engineering aspects of the VOA. This paper is a review of VOA/RME results from the STS-81 and STS-89 flights and their implications for the ISS VOA design and operations.

NASA has unique requirements for the development and application of air quality standards for human space flight. Such standards must take into account the continuous nature of exposures, the possibility of increased susceptibility of crewmembers to the adverse effects of air pollutants because of the stresses of space flight, and the recognition that rescue options may be severely limited in remote habitats. NASA has worked with the National Research Council Committee on Toxicology (NRCCOT) since the early 1990s to set and document appropriate standards. The process has evolved through 2 rounds. The first was to set standards for the space station era, and the second was to set standards for longer stays in space and update the original space station standards. The update was to be driven by new toxicological data and by new methods of risk assessment for predicting safe levels from available data. The last phase of this effort has been completed.

The Toxicology Laboratory at Johnson Space Center (JSC) had provided the combustion products analyzer (CPA) since the early 1990s to monitor the spacecraft atmosphere in real time if a thermodegradation event occurred aboard the Shuttle. However, as the operation of the International Space Station (ISS) grew near, an improved CPA was sought that would include a carbon monoxide sensor that did not have a cross-sensitivity to hydrogen. The Compound Specific Analyzer-Combustion Products (CSA-CP) was developed for use on the International Space Station (ISS). The CSA-CP measures three hazardous gases, carbon monoxide, hydrogen cyanide, and hydrogen chloride, as well as oxygen. The levels of these compounds in the atmosphere following a thermodegradation event serve as markers to determine air quality. The first permanent ISS crew performed the CSA-CP checkout operations and collected baseline data shortly after arrival aboard the ISS in December 2000.

Since the early years of the manned space program, NASA has developed and used exposure limits called Spacecraft Maximum Allowable Concentrations (SMACs) to help protect astronauts from airborne toxicants. Most of these SMACS are based on an exposure duration of 7 days, since this is the duration of a “typical” mission. A set of “contingency SMACs” is also being developed for scenarios involving brief (1-hour or 24- hour) exposures to relatively high levels of airborne toxicants from event-related “contingency” releases of contaminants. The emergency nature of contingency exposures dictates the use of different criteria for setting exposure limits. The NASA JSC Toxicology Group recently began a program to document the rationales used to set new SMACs and plans to review the older, 7-day SMACs. In cooperation with the National Research Council's Committee on Toxicology, a standard procedure has been developed for researching, setting, and documenting SMAC values.

Airborne dust, suspended inside a space vehicle or in future celestial habitats, can present a serious threat to crew health if it is not controlled. During some Apollo missions to the moon, lunar dust brought inside the capsule caused eye irritation and breathing difficulty to the crew when they launched from the moon and reacquired “microgravity.” During Shuttle flights reactive and toxic dusts such as lithium hydroxide have created a risk to crew health, and fine particles from combustion events can be especially worrisome. Under nominal spaceflight conditions, airborne dusts and particles tend to be larger than on earth because of the absence of gravity settling. Aboard the ISS, dusts are effectively managed by high efficiency filters, although floating dust in newly-arrived modules can be a nuisance.

NASA issued a Request For Information (RFI) to identify technologies that might be available to monitor a list of air pollutants in the ISS atmosphere. After NASA received responses to the RFI, an expert panel was assembled to hear presentations from 9 technology proponents. The goal of the panel was to identify technologies that might be suitable for replacement of the current Volatile Organics Analyzer (VOA) within several years. The panelists consisted of 8 experts in analytical chemistry without any links to NASA and 7 people with specific expertise because of their roles in NASA programs. Each technology was scored using a tool that enabled rating of many specific aspects of the technology on a 4-point system. The maturity of the technologies ranged from well-tested instrument packages that had been designed for space applications and were nearly ready for flight to technologies that were untested and speculative in nature.

The crew of flight 2A.1 that manned the International Space Station (ISS) assembly mission (STS-96) in May 1999 experienced symptoms that they attributed to poor air quality while working in the ISS modules. Some of these symptoms suggested that an accumulation of carbon dioxide (CO2) in the work area could have contributed to temporary health impacts on the crew. Currently, a fixed-position CO2 monitor in the FGB is the only means of measuring this air contaminant aboard ISS. As a result of this incident, NASA directed the Toxicology Laboratory at Johnson Space Center (JSC) to deliver a portable CO2 monitor for the next ISS assembly mission (STS-101). The Toxicology Laboratory developed performance requirements for a CO2 monitor and surveyed available CO2 monitoring technologies. The selected portable CO2 monitor uses nondispersive infrared spectroscopy for detection. This paper describes this instrument, its operation, and presents the results from ground-based performance testing.