According to The Other Wiki:
On earth, CO2 is 0.039% of the atmosphere.
1% (10,000 ppm) will make some people feel drowsy.
Concentrations of 7% to 10% cause dizziness, headache, visual and hearing dysfunction, and unconsciousness within a few minutes to an hour.
I could not find a percentage listed on the Shara system wiki section Gartaga.
As far as the Eucharis goes, there's an air-containment forcefield available for the main ramp that could be used to keep the local air out.