There have been a couple of reports of extremely high carbon dioxide in homes. Here's one:
https://www.cdc.gov/mmwr/preview/mmwrhtml/mm5350a5.htm

There was another incident in 2007 of high carbon dioxide levels (>6000 ppm or 0.6%) in northern
Illinois homes that were hit with heavy rains. The source of the
carbon dioxide appeared to be limestone present in the soil that was lifted
up by rainwater. Carbon dioxide gas seems have entered three homes
through the sump hole. Homeowners were unable to light their pilot because
oxygen was displaced by the carbon dioxide, and they called the fire
department. Their carbon dioxide measurement devices could only read up to
6000 ppm, so levels were at least 6000 and could be considerably higher.

There was an incident in Kansas as well. Unfortunately, the news stories of the IL and KS incidents are no longer available online, but I'd kept some notes with the weblinks. You could contact the newspapers to get more info:

https://www.beloitdailynews.com/articles/2007/08/23/news/news02.txt
http://www.rrstar.com/homepage/x1359806021
http://www.kansas.com/188/story/529039.html