The CO emissions for an old classic car could be as high as 4.5% (45,000 ppm). So once a tent has filled with exhaust fumes that's more than enough concentration to be lethal very quickly:
6,400 ppm (0.64%) Headache and dizziness in one to two minutes. Convulsions, respiratory arrest, and death in less than 20 minutes.
12,800 ppm (1.28%) Unconsciousness after 2–3 breaths. Death in less than three minutes.
6,400 ppm (0.64%) Headache and dizziness in one to two minutes. Convulsions, respiratory arrest, and death in less than 20 minutes.
12,800 ppm (1.28%) Unconsciousness after 2–3 breaths. Death in less than three minutes.