Many gases are produced on the Station by its crew members, by science experiments and by mechanical systems. The people especially act like living chemical factories. Carbon dioxide exhaled out by Station crew members is removed from the air by a machine that acts like a molecular screen. In addition to the carbon dioxide, people also emit small amounts of several other gases. Methane and carbon dioxide are produced in the intestines, and ammonia is created by the breakdown of urea in sweat.
People also emit acetone, methyl alcohol and carbon monoxide as byproducts of metabolism.
Filters made of activated charcoal are the primary method to remove these other chemicals from the air. Maintaining a healthy atmosphere is made more complicated by dozens of chemicals that will be used in the science experiments on board the Station. Keeping such chemicals out of the air is vital for the crew's health. A safety review for all proposed experiments will determine how much containment each rack-mounted facility must provide. If a chemical release occurs, the crew will seal off the contaminated module and then follow the correct procedures to clean it up.