Question came up;
Does the catalytic converter on a gasoline automobile remove carbon monoxide to where it may be safe/safer to be in a confined space (garage with door closed) with engine running???
Absolutely not!
Yes, it will be ‘safer’ but still not safe by any stretch of the imagination.
Please do not try this. It’s a good way to die.
Not safe, safer in some small degree. It’s really not safe but your exposure to CO would be far less than it was before the days of catalytic converters and other pollution control and efficiency improvements in car engines. There have been claims that people trying to commit suicide or accidentally staying in a garage with a car running have not been dying as rapidly, or as thoroughly as once before. The result is brain damage instead of death.
No. Modern Cars produce less CO than in the past, but not safe enough to run in a confined space.
Thanks all for the supportive replies.
This question came in when an emergency care worker overheard another telling a pt. that was found in a running car inside a building that a car with a catalytic converter will not produce enough Co to be lethal.
My thinking is a cold engine will produce much more Co than a hot engine running at hwy speeds, but that is just a WAG.
The person was removed from the exposure very early and a 72 hour hold was initiated by LEO.
A cold-start will indeed produce most of the emissions associated with a short trip, for a couple of reasons:
#1: cold-start enrichment. When the engine is cold, fuel doesn’t vaporize well, so the ECU injects extra fuel to ensure the formation of a combustible mixture. This means some unburned hydrocarbons and CO are carried out of the engine with the exhaust gas.
#2: cold cat. The catalytic converter doesn’t become active until it warms up, so the extra-dirty exhaust of a cold-start actually does make it all the way out to the environment.
Assuming:
-A warmed-up engine at idle
-with a properly functioning emissions control system
-in a late-model car
the exhaust will have very low CO concentration, on the order of a few hundred ppm. while this is usually not enough to kill a healthy adult, it can make you pretty damn sick. If any of the above assumptions are not true, then exhaust CO concentration is likely to be much higher.
IOW, no, it is generally regarded as not safe to run a car in an enclosed space.
Note also that portable generators don’t have the same emissions control systems that cars do, so they put out a LOT more CO/NOx/UHCs. Whenever there’s a prolonged power outage, you inevitably see a news report where someone fired up a generator in the garage or basement and killed their whole family with CO poisoning. 
Part of our house is over the garage. One time Mrs. FtG left the car running in the garage for a bit to go back and get something. Our CO alarm went from 0 to some low, single digit number. Not enough to set off the alarm, but alarming nonetheless. (This was with the her car’s garage door open!) We try to avoid that now.
What will happen is that O2 decreases in the air, the incorrect burning will occur, and the CO is produced.
Anyway the engine is turned to run when driving and at idle it may run very poorly and ungreen. especially its not keeping the Cat convertor hot enough to work ?
Pt=???
Part time?
Physical therapist?
Platinum.
patient
Sadly, no it isn’t. It used to be, but now it is just a good way to turn yourself into a brain-damaged babbling idiot. CO suicides in garages are now rarely successful, for this reason.
If I may … a garage full of CO[sub]2[/sub] is also very unhealthy …
Cue jokes about suicide in a garage with a Tesla…
Point
I’ve seen cases of elderly folks in little townhomes dying after forgetting to turn their car off and closing their one car garage door. They weren’t even in the garage, but there was enough CO in the house to cause problems.
So now I’m curious: What happens to the CO once it’s out in the air? It has to become something less toxic (CO2?) pretty quickly. If not anyone next to a busy road would die.
The difference is that a high concentration of CO2 produces very unpleasant sensations and compels you to seek fresh air; try holding your breath for a while and you’ll feel what I mean. This is why suicide-by-plastic-bag-over-head generally also requires a strong sedative i.e. to ensure that the victim does not try to remove the bag.
Low CO concentrations may give you a headache before they render you insensate, but they won’t cause the same panicky “gotta get fresh air” compulsion as CO2. A high concentration of CO will quickly render you unconscious, no time for a headache.
The good news: It takes an atom from 02 to form CO2. The bad news is the spare O joins with O2 to form O3: ozone. CO is a significant cause of ozone pollution in urban areas.
So what is the issue in a closed garage? The reaction is not quick enough allowing too much CO to build up? Or does the reaction require sunlight?