Engineering topics
Publications and source records attributed to James, John T..
The toxicological assessment of 6 GSCs from the ISS is shown. The average recoveries of the 3 surrogate standards from the grab sample containers were as follows: C-13-acetone, 115%; fluorobenzene, 108%; and chlorobenzene, 93%.
Carbon dioxide (CO2) is released in large quantities from humans while they live and work in spacecraft or work outside the spacecraft during extravehicular activity (EVA). Removal of this anthropogenic pollutant requires major resources, and these resources increase dramatically as the levels of CO2 set to protect human health and performance are reduced. The current Spacecraft Maximum Allowable Concentration of CO2 aboard the ISS is 0.7% or 5.3 mmHg; however, according to Chits (mission action requests), NASA and its international partners have agreed to control CO2 levels to less than 4 mmHg. In the meantime, retrospective investigations attempting to associate crew symptoms with elevated CO2 levels over the life if the International Space Station (ISS) are underway to determine if this level is sufficient to protect against health and performance decrements. Anecdotal reports suggest that crewmembers are not able to perform complex tasks as readily in spaceflight as they were able during ground-based training. While physiological effects of CO2 have been studied for many decades, it is only recently that the effects of CO2 on higher reasoning capabilities have been studied. The initial results are shocking. For example, one study published in the respected journal Environmental Health Perspectives showed obvious adverse effects of CO2 exposures on higher reasoning at 1.9 mmHg. The implications and limitations of this study are paramount in determining future CO2 SMACs for human spaceflight, both aboard the ISS and in exploration-class missions. Key Words: carbon dioxide, spacecraft, air quality, toxic effects
One mini-grab sample container (m-GSC) was returned aboard Space X1 because of the importance of quickly knowing first-entry conditions in this new commercial module. This sample was analyzed alongside samples of the portable clean room (PCR) used in the Space X complex at KSC. The recoveries of C-13-acetone, fluorobenzene, and chlorobenzene from the GSCs averaged 130, 129, and 132 %, respectively.
As the lunar dust toxicity project winds down, our attention is drawn to the potential toxicity of dust present at the surface of more distant celestial objects. Lunar dust has proven to be surprisingly toxic to the respiratory systems of test animals, so one might expect dust from other celestial bodies to hold toxicological surprises for us. At this point all one can do is consider what should be known about these dusts to characterize their toxicity, and then ask to what extent that information is known. In an ideal world it might be possible to suggest an exposure standard based on the known properties of a celestial dust without direct testing of the dust in laboratory animals. Factors known to affect the toxicity of mineral dusts under some conditions include the following: particle size distribution, particle shape/porosity, mineralogical properties (crystalline vs. amorphous), chemical properties and composition, and surface reactivity. Data from a recent Japanese mission to the S-type asteroid Itokawa revealed some surprises about the dust found there, given that there is only a very week gravitational field to hold the dust on the surface. On Mars the reddish-brown dust is widely distributed by global dust storms and by local clusters of dust devils. Past surface probes have revealed some of the properties of dust found there. Contemporary data from Curiosity and other surface probes will be weighed against the data needed to set a defensible safe exposure limit. Gaps will emerge.
This is a very limited set of samples on which to perform an air quality assessment. However, based on these samples, we have no reason to believe that nominal ISS air is unsafe to breathe. We must continue to be vigilant when dealing with nominal atmospheres in ISS. New, unmanned modules require special attention when the crew first enters. Carbon Monoxide Accumulation aboard ISS: Beginning in late 2008 the nominal concentrations of CO began increasing gradually (Figure 1). The results from samples returned on this flight indicate that the CO concentrations, after dropping in late 2009, have cycled upward and then settled back to concentrations near 2 mg/m3. In any case, these changes are well below the 180-day SMAC for CO, which is17 mg/m3. There is no threat to crew health. Carbon Dioxide: This anthropogenic compound has drawn much attention recently because of the possibility that it could contribute to the effects of intracranial hypertension experienced because of spaceflight-induced fluid shifts. From now on we will maintain a plot (Figure 2) of carbon dioxide concentrations ( SD) by averaging the values found in the 3-5 mini-GSC samples taken each month in diverse locations of the ISS. This will enable us to estimate the average exposure of crewmembers to carbon dioxide during their stay aboard the ISS. In general, concentrations are being maintained below 3.5 mmHg. Figure 1
Carbon dioxide (CO2) removal is one of the primary functions of the International Space Station (ISS) atmosphere revitalization systems. Primary CO2 removal is via the ISS s two Carbon Dioxide Removal Assemblies (CDRAs) and the Russian carbon dioxide removal assembly (Vozdukh); both of these systems are regenerable, meaning that their CO2 removal capacity theoretically remains constant as long as the system is operating. Contingency CO2 removal capability is provided by lithium hydroxide (LiOH) canisters, which are consumable, meaning that their CO2 removal capability disappears once the resource is used. With the advent of 6 crew ISS operations, experience showing that CDRA failures are not uncommon, and anecdotal association of crew symptoms with CO2 values just above 4 mmHg, the question arises: How much lower do we keep CO2 levels to minimize the risk to crew health and performance, and what will the operational cost to the CDRAs be to do it? The primary crew health concerns center on the interaction of increased intracranial pressure from fluid shifts and the increased intracranial blood flow induced by CO2. Typical acute symptoms include headache, minor visual disturbances, and subtle behavioral changes. The historical database of CO2 exposures since the beginning of ISS operations has been compared to the incidence of crew symptoms reported in private medical conferences. We have used this database in an attempt to establish an association between the CO2 levels and the risk of crew symptoms. This comparison will answer the question of the level needed to protect the crew from acute effects. As for the second part of the question, operation of the ISS s regenerable CO2 removal capability reduces the limited life of constituent parts. It also consumes limited electrical power and thermal control resources. Operation of consumable CO2 removal capability (LiOH) uses finite consumable materials, which must be replenished in the long term. Therefore, increased CO2 removal means increased resource use, with increased logistical capability to maintain necessary resources on board ISS. We must strike a balance between sufficiently low CO2 levels to maintain crew health and CO2 levels which are operationally feasible for the ISS program
Six mini-grab sample containers (m-GSCs) were returned aboard Soyuz 23 because of concerns that new air pollutants had been present in the air and these were getting into the water recovery system. The Total Organic Carbon Analyzer had been giving increasing readings of total organic carbon (TOC) in the potable water, and it was postulated that an increased load into the system was responsible. The TOC began to decline in late October, 2010. The toxicological assessment of 6 m-GSCs from the ISS is shown in Table 1. The recoveries of 13C-acetone, fluorobenzene, and chlorobenzene from the GSCs averaged 73, 82, and 59%, respectively. We are working to understand the sub-optimal recovery of chlorobenzene.
No abstract available
Fifteen mini-grab sample containers (m-GSCs) were returned aboard Soyuz. This is the first time all samples were acquired with the mini-grab samplers. The toxicological assessment of 15 m-GSCs from the ISS is shown. The recoveries of the 3 internal standards, C(13)-acetone, fluorobenzene, and chlorobenzene, from the GSCs averaged 75, 97 and 79%, respectively. Formaldehyde badges were not returned on Soyuz 24
The toxicological assessments of 2 canisters (mini-GSC or GSCs) from the Shuttle are reported. Analytical methods have not changed from earlier reports. The percent recoveries of the 3 surrogates (C-13-acetone, fluorobenzene, and chlorobenzene) from the 2 Shuttle GSCs averaged 86, 100, and 87, respectively. Based on the end-of-mission sample, the Shuttle atmosphere was acceptable for human respiration.
Six mini-grab sample containers (m-GSCs) were returned aboard Soyuz 25. The toxicological assessment of 6 m-GSCs from the ISS is shown. The recoveries of the 3 internal standards, C-13-acetone, fluorobenzene, and chlorobenzene, from the GSCs averaged 76, 108 and 88%, respectively. Formaldehyde badges were not returned aboard Soyuz 25.
Safe breathing air for space faring crews is essential whether they are inside an Extravehicular Mobility Suit (EMU), a small capsule such as Soyuz, or the expansive International Space Station (ISS). Sources of air pollution can include entry of propellants, excess offgassing from polymeric materials, leakage of systems compounds, escape of payload compounds, over-use of utility compounds, microbial metabolism, and human metabolism. The toxicological risk posed by a compound is comprised of the probability of escaping to cause air pollution and the magnitude of adverse effects on human health if escape occurs. The risk from highly toxic compounds is controlled by requiring multiple levels of containment to greatly reduce the probability of escape; whereas compounds that are virtually non-toxic may require little or no containment. The potential for toxicity is determined by the inherent toxicity of the compound and the amount that could potentially escape into the breathing air.
Space toxicology greatly matured as a result of research and operations associated with the Shuttle. Materials offgassing had been a manageable concern since the Apollo days, but we learned to pay careful attention to compounds that could escape containment, to combustion events, to toxic propellants, to overuse of utility compounds, and to microbial and human metabolites. We also learned that flying real-time hardware to monitor air pollutants was a pathway with unanticipated speed bumps. Each new orbiter was tested for any excess offgassing products that could pollute the air during flight. In the late 1990s toxicologists and safety experts developed a 5-level toxicity rating system to guide containment of toxic compounds. This system is now in use aboard the International Space Station (ISS). Several combustion events during Shuttle Mir and also during Shuttle free-flight impelled toxicologists to identify hardware capable of monitoring toxic products; however, rapid adaptation of the hardware for the unique conditions of spaceflight caused unexpected missteps. Current and planned combustion analyzers would be useful to commercial partners that wish to manage the risk of health effects from thermal events. Propellants received special attention during the Shuttle program because of the possibility of bringing them into the habitable volume on extravehicular activity suits. Monitors for the airlocks were developed to mitigate this risk. Utility materials, such as lubricants, posed limited toxicological problems because water was not recovered. One clearly documented case of microbial metabolites polluting the Shuttle atmosphere was noted, and this has implications for commercial flights and control of microbes. Finally, carbon dioxide, the major human metabolite, episodically presented air quality problems aboard Shuttle, especially when nominal air flows were obstructed. Commercial vehicles must maintain robust air circulation given the anticipated high density of human occupants.
The primary reason for monitoring air quality aboard the International Space Station (ISS) is to determine whether air pollutants have collectively reached a concentration where the crew could experience adverse health effects. These effects could be near-real-time (e.g. headache, respiratory irritation) or occur late in the mission or even years later (e.g. cancer, liver toxicity). Secondary purposes for monitoring include discovery that a potentially harmful compound has leaked into the atmosphere or that air revitalization system performance has diminished. Typical ISS atmospheric trace pollutants consist of alcohols, aldehydes, aromatic compounds, halo-carbons, siloxanes, and silanols. Rarely, sulfur-containing compounds and alkanes are found at trace levels. Spacecraft Maximum Allowable Concentrations (SMACs) have been set in cooperation with a subcommittee of the National Research Council Committee on Toxicology. For each compound and time of exposure, the limiting adverse effect(s) has been identified. By factoring the analytical data from the Air Quality Monitor (AQM), which is in use as a prototype instrument aboard the ISS, through the array of compounds and SMACs, the risk of 16 specific adverse effects can be estimated. Within each adverse-effect group, we have used an additive model proportioned to each applicable 180-day SMAC to estimate risk. In the recent past this conversion has been performed using archival data, which can be delayed for months after an air sample is taken because it must be returned to earth for analysis. But with the AQM gathering in situ data each week, NASA is in a position to follow toxic-effect groups and correlate these with any reported crew symptoms. The AQM data are supplemented with data from real-time CO2 instruments aboard the ISS and from archival measurements of formaldehyde, which the AQM cannot detect.
Within the decade one or more space-faring nations intend to return humans to the moon for more in depth exploration of the lunar surface and subsurface than was conducted during the Apollo days. The lunar surface is blanketed with fine dust, much of it in the respirable size range (<10 micron). Eventually, there is likely to be a habitable base and rovers available to reach distant targets for sample acquisition. Despite designs that could minimize the entry of dust into habitats and rovers, it is reasonable to expect lunar dust to pollute both as operations progress. Apollo astronauts were exposed briefly to dust at nuisance levels, but stays of up to 6 months on the lunar surface are envisioned. Will repeated episodic exposures to lunar dust present a health hazard to those engaged in lunar exploration? Using rats exposed to lunar dust by nose-only inhalation, we set out to investigate that question.
This viewgraph presentation reviews the Lunar Airborne Dust Toxicity Assessment Group (LADTAG) plans and progress for 2010 and 2011. Provisional Permissible Exposure Limits (PPELs) from lavage fluid and blood data are also presented.
Before delineating specific ways that nanotechnology enterprises might contribute to better management of toxicological risks during spaceflight, I will show how ethical considerations and several theories of justice can be applied to nanotechnology strategic plans. The principles that guide an ethical technical enterprise include autonomy, beneficence, non-maleficence, veracity and justice. Veracity (truth) is the underpinning principle; however, beyond this, proponents of nanotechnology must think carefully about balancing conflicting principles. For example, autonomy must yield to beneficence when fearful individuals simply lack knowledge to appreciate nanotechnology's beneficial advances. Justice is a complex topic upon which I will place six models: utilitarian, distributive, free-exchange/choice, individual dignity (social participation), equity vs. greed, and liberation of the poor. After briefly summarizing each model, I will present what I call an iterative-hybrid model of justice to show specifically how our thinking can be applied to nanotechnology enterprises. Within that broad landscape, I will discuss a single feature: how our early effort to understand health risks of carbon nanotubes fits into the iterative model. Finally, I will suggest ways that nanotechnology might advance our management of toxicological risks during spaceflight, but always with an eye toward how such advances might result in a more just world.
Many lamps used in various spacecraft contain elemental mercury, which is efficiently absorbed through the lungs as a vapor. The liquid metal vaporizes slowly at room temperature, but may be completely vaporized when lamps are operating. Because current spacecraft environmental control systems are unable to remove mercury vapors, we considered short-term and long-term exposures. Using an existing study, we estimated mercury vapor releases from lamps that are not in operation during missions lasting less than or equal to 30 days; whereas we conservatively assumed complete vaporization from lamps that are operating or being used during missions lasing more than 30 days. Based on mercury toxicity, the Johnson Space Center's Toxicology Group recommends stringent safety controls and verifications for any hardware containing elemental mercury that could yield airborne mercury vapor concentrations greater than 0.1 mg/m3 in the total spacecraft atmosphere for exposures lasting less than or equal to 30 days, or concentrations greater than 0.01 mg/m3 for exposures lasting more than 30 days.