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A habitable atmosphere is a fundamental requirement for human spaceflight. To meet this requirement, the cabin atmosphere must be constantly scrubbed to maintain human life and system functionality. The primary system for atmospheric scrubbing of the US on-orbit segment (USOS) of the International Space Station (ISS) is the Trace Contaminant Control System (TCCS). As part of the Environmental Control and Life Support Systems' (ECLSS) atmosphere revitalization rack in the US Lab, the TCCS operates continuously, scrubbing trace contaminants generated primarily by two sources: the metabolic off-gassing of crew members and the off-gassing of equipment in the ISS. It has been online for approximately 95% of the time since activated in February 2001. The TCCS is comprised of a charcoal bed, a catalytic oxidizer, and a lithium hydroxide post-sorbent bed, all of which are designed to be replaced on-orbit when necessary.

The management of off-nominal situations on-board the International Space Station (ISS) is crucial to its continuous operation. Off-nominal situations can arise from virtually any aspect of ISS operations. One situation of particular concern is the inadvertent release of a chemical into the ISS atmosphere. In sufficient quantities, a chemical release can render the ISS uninhabitable regardless of the chemical's toxicity as a result of its effect on the hardware used to maintain the environment. This is certainly true with system chemicals which are integral components to the function and purpose of the system. Safeguards, such as design for minimum risk, multiple containment, hazard assessments, rigorous safety reviews, and others, are in place to minimize the probability of a chemical release to the ISS environment thereby allowing the benefits of system chemicals to outweigh the risks associated with them. The thermal control system is an example of such a system.