Here is the full list of all 7 Low Oxygen achievements.
Find the black key near the rocket.
Find the white key near a lot of ladders.
Enter the lush caverns of the facility.
Find the blue key up high outside the facility.
01101000 01100101 01100101 01101100 01101111
Find the red key somewhere under a ceiling lamp.
Find the yellow key near the crashsite.