I realize there are a few carbon monoxide topics here already, but after reading about it a bit I'm really worried about my family's situation, and the posted topics don't fully answer my questions.

We moved to our current townhouse about a month ago, and the backdoor opens to a large parking lot shared with all the other residents. Recently we've been hearing a strange beeping noise coming from the backdoor, and when my mom went to check it out she found a carbon monoxide detection alarm, and the alarm reads 97ppm. I decided to do some research on it and found that "OSHA limits long-term workplace exposure levels to 50 ppm", which concerns me since our alarm detects a much higher amount of CO in our home, and my mom and I are home almost all the time, on the first floor too. Also, the back only opens to the parking lot, there are only windows in the front and there's no other way to circulate the air. It's been beeping for days now, and I read that when you hear it beep you should immediately leave the house and get help.

I'd really like to know about how much exposure to CO and how long it would be before it becomes lethal. My mom and I have been experiencing headaches recently and I know this is a symptom of CO poisoning, I wonder if the poison works that fast or it's just my imagination. We're moving as soon as possible, whether they were aware of the dangers of CO poisoning or not, it was still poorly designed since the whole first floor only has two windows in the front of the house. I hope I was clear enough about the situation and I hope to find an answer soon, thanks in advance.

Edit: I also wanted to add that since moving here my mom had a retina desconnection, though the retina specialist did say this is usually because of aging, I also found eyesight worsening a sympton of CO poisoning as well, just wondering if it's related.