Acceptable Limits for n-Hexane in Spacecraft Atmospheres.

The Spacecraft Maximum Allowable Concentrations (SMACs) for C2-C9 alkanes set by NASA in 2008 under the guidance and approval of the National Research Council specifically excluded SMACs for n-hexane. Unlike other C2-C9 alkanes, n-hexane can cause polyneuropathy after metabolism in humans or rodents and so requires more stringent SMACs than the other members of this group do. This document reviews the relevant published studies of n-hexane toxicity to develop exposure duration-specific SMACs for n-hexane of 200 ppm for 1 hour, 30 ppm for 24 hours, and 2.

Establishment of exposure guidelines for lead in spacecraft drinking water.

Background: Setting Spacecraft Water Exposure Guidelines (SWEGs) for lead (Pb) in spacecraft drinking water has special challenges related to estimating the increase in blood lead levels (PbB) due to the release of lead to systemic circulation via microgravity-induced bone loss.

Methods: The effects on the PbB of lead in drinking water (PbW) and lead released from bones, and changes in lead exposure before, during, and after spaceflight, were evaluated using a physiologically based pharmacokinetic model that incorporated environmental lead exposure on Earth and in flight and included temporarily increased rates of osteoporosis during spaceflight.

Results: The model predicts that in 2030 (the earliest potential launch date for a long-duration mission), the average American astronaut would have a PbB of 1.

Modeling of blood lead levels in astronauts exposed to lead from microgravity-accelerated bone loss.

Introduction: Most astronauts experiencing prolonged microgravity undergo accelerated bone loss at a whole-body rate of 0.5-1% per month, with some load-bearing bones losing mass at normalized rates up to about 2.6% per month.

Safe human exposure limits for airborne linear siloxanes during spaceflight.

Background: Low molecular weight siloxanes are used in industrial processes and consumer products, and their vapors have been detected in the atmospheres of the Space Shuttle and International Space Station. Therefore, the National Aeronautics and Space Administration (NASA) developed spacecraft maximum allowable concentrations (SMACs) for siloxane vapors to protect astronaut health. Since publication of these original SMACs, new studies and new risk assessment approaches have been published that warrant re-examination of the SMACs.

Ocular toxicity of authentic lunar dust.

Background: Dust exposure is a well-known occupational hazard for terrestrial workers and astronauts alike and will continue to be a concern as humankind pursues exploration and habitation of objects beyond Earth. Humankind's limited exploration experience with the Apollo Program indicates that exposure to dust will be unavoidable. Therefore, NASA must assess potential toxicity and recommend appropriate mitigation measures to ensure that explorers are adequately protected.