Google OBIGGS (On Board Inert Gas Generation Systems):
Honeywell's version:
On-Board Inert Gas Generation System (OBIGGS) - Honeywell Aerospace Engineering
Parker's version:
http://www.parker.com/literature/Air...k.inerting.pdf
NASA OBIGGS Test:
http://www.fire.tc.faa.gov/pdf/04-41.pdf
In short, they work a bit like your cars catalytic converter.