Is it safe to open garage door, put windows down, then start engine?

In just a few minutes the accumulation of carbon dioxide from a running engine, even in a very large shop with the doors open is obvious even when it is a clean burning engine. Even a natural gas water heater’s carbon monoxide will quickly be noticed in a poorly ventilated area. It isn’t cyanide gas so it’s not as though you need to push the car out in the open to start it but it would be wise to open the garage door first and within a minute or so back out.

I suspect it had more to do with the battery technology at in the 30s&40s and anemic generators.

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