Q: What is the average normal level of Carbon Mono-Oxide in near properly adjusted gas stoves in average USA household?

Answer: 5 to 15 ppm

0.1 ppm	Natural atmosphere level
0.5 to 5 ppm	Average level in homes
5 to 15 ppm	Near properly adjusted gas stoves in homes

Concentration	Symptoms
35 ppm	Headache and dizziness within six to eight hours of constant exposure
100 ppm	Slight headache in two to three hours
200 ppm	Slight headache within two to three hours; loss of judgment
400 ppm	Frontal headache within one to two hours
800 ppm	Dizziness, nausea, and convulsions within 45 min; insensible within 2 hours
1,600 ppm	Headache, tachycardia, dizziness, and nausea within 20 min; death in less than 2 hours
3,200 ppm	Headache, dizziness and nausea in five to ten minutes. Death within 30 minutes.
6,400 ppm	Headache and dizziness in one to two minutes. Convulsions, respiratory arrest, and death in less than 20 minutes.
12,800 ppm	Unconsciousness after 2–3 breaths. Death in less than three minutes.

References:

1. United States Environmental Protection Agency. Retrieved 2008-12-16.

2. Goldstein M (December 2008). "Carbon monoxide poisoning". Journal of Emergency Nursing: JEN: Official Publication of the Emergency Department Nurses Association 34 (6): 538–542.

3.Struttmann T, Scheerer A, Prince TS, Goldstein LA (Nov 1998). "Unintentional carbon monoxide poisoning from an unlikely source". The Journal of the American Board of Family Practice 11 (6): 481–484