No, due to ventilation. Even an indoor fireplace for example is -always- vented, so the gasses can escape via the chimney. If you close the damper with a fire blazing, you'll not have a good time.

Outdoor fires well, are outdoors, so there's plenty of oxygen.

People die nearly every year in the brutal cold from getting desperate and bringing grills and such indoors to light, which is a big no no.

Not all indoor fireplaces are ventilated in the US, actually. (Source: have one unventilated fireplace that is probably mostly for aesthetics and not to be used for extended perios of time)

Downvoting because this isn't the case in the US at least. It's still legal to install internally vented gas burning fireplaces.

AFAIK it's not illegal to run your grill indoors, either. Being legal isn't the same as being a good idea. Ventless fireplaces are also not legal in a lot of places in the US, for good reason.

Legality is a signal for safety for most people. The natural gas industry, and the manufacturers of indoor gas ovens, stoves, fireplaces, etc all claim that what they sell is safe for indoor use. People have an expectation that the federal government will regulate things which are bad for us. In my opinion, they're failing miserably in this particular area.

Nitpick: CO.

Otherwise - no, if there is enough oxygen coming in. When fireplace is done properly it is not a problem.

Technically, I believe the problem is the CO concentration and exposure time, not displacement of oxygen. CO binds to hemoglobin more effectively than oxygen, preventing enough oxygen from getting to the body's tissues. CO poisoning is common: 20,000 hospital visits per year in the United States, and in many countries is the most common form of poisoning. [1]

[1] https://en.wikipedia.org/wiki/Carbon_monoxide_poisoning

carbon monoxide is CO, not CO2.