Why don't we all die when we go to sleep in small bedrooms as we spew CO2 in the room? It's heavier than air, sure, but it eventually dissapates and works its way outside through infiltration. I bet most American garages have high enough infiltration that the cycling of the TCH ICE would spew less CO than that which could accumulate. Not that I'm gonna test my theory...but hey, it's just a thought.

 

CO is deadlier than CO2 (displaces oxgen in the body even if oxygen is present). But you are right, natural garage venting might reduce the amount of CO present even further if the engine is only on for short periods. In these parts, attached garages require vapor seals and automatic closing entry doors between house and garage too...

 

CO (carbon monoxide) is a poisonless gas. CO2 (carbon dioxide) is not poisonous. The only problem would be if you breathed straight CO2, not because it would kill you, but the lack of oxygen would.

 

Yes, it's true. I didn't mean for this to turn into a chemistry lesson, I was only trying to use it as an example...as bad as it may have been. For those that need a better, more direct comarison, I would argue that a gas fired stove (while spewing mostly water) does, in fact, spew a small amount of ick, including CO, into the kitchen. This doesn't alarm folks since its rate of accumulation is lower than the rate of infiltration.
I will now stick my head into the oven and test my theory

 

I hope it's an electric oven.

But you are right. Burning a gas oven and cooktop do the same. But it's a small enough quantity as to not be dangerous. I tend to think that natural gas must give off less as a byproduct, but that's just a guess.