Whenever something burns there is a risk for CO (Carbon Monoxide) gas to form. Out of all the gasses that you are likely to encounter in your daily life, it is definitely one of the most dangerous ones, especially since it can be formed so easily. In fact, you don’t need to be exposed for more than a short while before you start having serious side-effects, such as dizziness and nausea, so you can imaging how difficult it will be to get yourself to safety.
There is a danger in homes that are underpressured in connection with CO gas. Usually, the smoke from anything that burns is funneled out the chimney in your home, but if the pressure is lower inside your home than outside, it could actually such the fumes back in, causing you to be exposed to CO gas.
Often you will notice soot around the area where the gas gets sucked in, and that will let you know there is a problem. You can also use a smoke pencil to see where the airflow in your home takes the smoke.