Propellant Off-Gassing and Implications for Triage and Rescue.

INTRODUCTION: Hypergolic propellants can be released in large amounts during space launch contingencies. Whether propellant-contaminated suit fabric poses a significant risk to rescue crews, due to off-gassing, has not been explored in detail. In this study, we addressed this issue experimentally, exposing space suit fabric to propellants (dinitrogen tetroxide [N2O4] and monomethyl hydrazine [MMH]).METHODS: The NASA Space Shuttle Program Advanced Crew Escape System II (ACES II) is similar to the NASA Orion Crew Survival System (OCSS) and was utilized here. Suit fabric was placed and sealed into permeation cells. Fabric exterior surface was exposed to constant concentrated hypergolics, simulating permeation and leakage. Fabric was rinsed, and permeation and off-gassing kinetics were measured. Experimental parameters were selected, simulating suited flight crewmembers during an evacuation transport without cabin air flow.RESULTS: The fabric allows for immediate permeation of liquid or vaporized MMH and N2O4. NO2 off-gassing never exceeded the AEGL-1 8-h level (acute exposure guideline level). In contrast, MMH off-gassing levels culminated in peak levels, approaching AEGL-2 10-min levels, paralleling the drying process of the fabric layers. DISCUSSION: Our findings demonstrate that MMH off-gassing is promoted by the drying of suit material in a delayed fashion, resulting in MMH concentrations having the potential for adverse health effects for flight and rescue crews. This indicates that shorter decontamination times could be implemented, provided that suit material is either kept moist to prevent off-gassing or removed prior to medical evacuation. Additional studies using OCSS or commercial crew suits might be needed in the future.Schwertz H, Roth LA, Woodard D. Propellant off-gassing and implications for triage and rescue. Aerosp Med Hum Perform. 2020; 91(12):956961.

Gel formation in protein amyloid aggregation: a physical mechanism for cytotoxicity.

Amyloid fibers are associated with disease but have little chemical reactivity. We investigated the formation and structure of amyloids to identify potential mechanisms for their pathogenic effects. We incubated lysozyme 20 mg/ml at 55C and pH 2.5 in a glycine-HCl buffer and prepared slides on mica substrates for examination by atomic force microscopy. Structures observed early in the aggregation process included monomers, small colloidal aggregates, and amyloid fibers. Amyloid fibers were observed to further self-assemble by two mechanisms. Two or more fibers may merge together laterally to form a single fiber bundle, usually in the form of a helix. Alternatively, fibers may become bound at points where they cross, ultimately forming an apparently irreversible macromolecular network. As the fibers assemble into a continuous network, the colloidal suspension undergoes a transition from a Newtonian fluid into a viscoelastic gel. Addition of salt did not affect fiber formation but inhibits transition of fibers from linear to helical conformation, and accelerates gel formation. Based on our observations, we considered the effects of gel formation on biological transport. Analysis of network geometry indicates that amyloid gels will have negligible effects on diffusion of small molecules, but they prevent movement of colloidal-sized structures. Consequently gel formation within neurons could completely block movement of transport vesicles in neuronal processes. Forced convection of extracellular fluid is essential for the transport of nutrients and metabolic wastes in the brain. Amyloid gel in the extracellular space can essentially halt this convection because of its low permeability. These effects may provide a physical mechanism for the cytotoxicity of chemically inactive amyloid fibers in neurodegenerative disease.