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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.

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.

A combustion products analyzer (CPA) was built for use on the Shuttle in response to several thermodegradation incidents during early flights. When the Toxicology Laboratory at Johnson Space Center (JSC) began to assess the air quality monitoring needs for the International Space Station (ISS), the CPA was the starting point for the design of a thermodegradation event monitor. The final product was significantly different from the CPA and was named the “compound specific analyzer-combustion products” (CSA-CP). One major change from the CPA was the replacement of the hydrogen fluoride sensor with an oxygen sensor. The focus of this paper will be the CSA-CP oxygen sensor’s ground testing, performance on ISS, and reduced pressure testing in response to a need on ISS.

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.

For long duration space flights, wastewater from humidity condensate, urine, and used hygiene water will be recycled to provide an adequate supply of potable quality water for the crew. Due to the diverse nature and multiple sources of contaminants entering the recycling system, it is a challenge to maintain the quality of product water such that no adverse health effects occur. NASA Johnson Space Center in cooperation with the Committee on Toxicology of the National Research Council (NRCCOT) has developed a science-based approach, taking into consideration space flight induced factors, to derive Spacecraft Water Exposure Guidelines (SWEG) for 1, 10, 100, 1000 days of consumption. This paper will discuss the ongoing process of setting SWEGs, how candidate chemicals were chosen for risk assessment, and how various toxicological data are collected and interpreted. Our goal is to help environmental engineers understand how the SWEGs they use for hardware design are developed.

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.

The development of innovative technologies leading to flight hardware requires substantially more funding than typical commercial development efforts. Therefore, given the current resource constraints at NASA, funding must be invested wisely in new technologies having a high probability of meeting requirements established by NASA. The Toxicology Laboratory at Johnson Space Center (JSC) was faced with such a choice in selecting technology for a second-generation volatile organic analyzer to be used for monitoring spacecraft air quality in the later phases of the International Space Station (ISS). A method was needed that could fairly and accurately evaluate technologies and ultimately lead to the selection of the best technology. A systematic approach to identifying, reviewing, and rating advanced technologies was developed. Results from the second-generation VOA activities will be used to illustrate this unique technology selection process.

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.

The complexity of the atmosphere aboard the International Space Station (ISS) will require a multifaceted monitoring strategy for both nominal and emergency conditions to protect the health and safety of the crew. Samples to be collected for air-quality assessment will include both archival sampling for ground analysis and on-board automatic analyses. Archival samples will be analyzed after return by standard gas chromatography/mass spectrometry; a separate formaldehyde analysis will be conducted as well. On-orbit analyses are planned for specific combustion products and for specific volatile organic compounds of toxicological significance. The air-lock will be monitored after EVAs to ensure that no propellants are introduced into the cabin atmosphere. Additional remote samples can be collected in sample bags from other ISS elements and brought to the Volatile Organic Analyzer (VOA) for analysis.

The monitoring of trace pollutants in spacecraft air is essential to protect the crew from harmful exposures. Monitoring requirements are focused on those sources of pollutants that pose the highest risk to crew health. Deciding which sources pose the greatest risk is done based on years of experience with the Space Shuttle, and more recently with the Russian Mir space station. Combustion of nonmetallic materials associated with electric circuits or heat-generating devices poses the greatest risk to crew health. Major leaks of fluids from systems or payloads also pose a significant risk. Other potential risks include accumulation of metabolites, entry of propellants, and excess offgassing, especially in modules that have been sealed for long periods.

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.

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.