Breathing Easy on the Space Station

NASA The oxygen that humans and animals breathe on Earth is produced by plants and other photosynthetic organisms such as algae.

The removed CO₂ will be vented to space. Engineers are also thinking of ways to recycle the gas.

In addition to exhaled CO₂, people also emit small amounts of 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 -- which are by-products of metabolism -- in their urine and their breath.

Activated charcoal filters are the primary method for removing these chemicals from the air.

Maintaining a healthy atmosphere is made even more complex by the dozens of chemicals that will be used in the science experiments on board the ISS.

"In a 30 year period, there could be any number of different types of experimental facilities on board that could have any number of chemical reagents," Perry said.

Some of these chemicals are likely to be hazardous, particularly if they're allowed to combine in unforeseen ways, Perry said. Keeping these chemicals out of the air will be vital for the crew's health.

When the Space Station was first being designed, NASA engineers envisioned a centralised chemical-handling system that would manage and contain all the chemicals used for experiments. But such a system proved to be too complex.

"The ability for the Station to provide generic monitoring capability to try to cover the broad spectrum of chemicals that 15 plus years of basic research will require -- obviously that's not something that the Station itself can provide," Perry said.

NASA An illustration showing the location of Node 3, where the ECLSS life support equipment will be housed. Note that the Station components in the line of sight to Node 3 are transparent in this image.

A safety review for each proposed experiment will determine the level of containment that the rack-mounted experiment facilities must provide. In the event of a release, the crew will seal off the contaminated module and then follow procedures for cleanup, if possible.

But careful planning and well-designed hardware should minimise the risk of this scenario, enabling the crew of the Space Station to breathe easy.