I can't find the original article, but from Wikipedia(https://en.wikipedia.org/wiki/Deep_vein_thrombosis) [inflammation has been identified as playing a clear causal role] and studies(https://pubmed.ncbi.nlm.nih.gov/20387988/) ironically tobacco studies, of 5% CO2 show an inflammatory response. Another poster here cited 3% was be the safe limit, so its feasible that turning the system off to save money could put the CO2 over 5% quite quickly. Also the concentration of oxygen is listed on Wikipedia as a direct cause of DVT, which would obviously be affected.

Yeah, that one sounds weird on the face of it.

If anything would have an effect, I'd guess the relative absense of nicotine in people would be a big part.

Though I thought nicotine _causes_ blood clots, it's possible that that's a chronic effect and the acute effect would prevent them, I'm not sure.