Aside from risk of fire (which for this question we will assume has been fully mitigated) what is the real risk of suffocation if one were to use a stove, lantern, or candle lantern in a tent?
There have been some reports of death from this (whether it be from CO2 or CO), but others have used such products in their tents without issue.
I'll answer a question in the comments:
I will be curious to know what is the average amount of Co2 produced by a stove vs the average amount of co2 generated by human breathing. My guess would be that stove will win but I heard of people suffocate in closed cars while sleeping
To make things simple, lets assume assume your body burns 2,600 calories (~11 MJ) per day, and burns purely glucose.
At 3.75 calories (9.83 kJ) per gram, you'll be burning around 690 grams of glucose per day, or a little under 24 oz (710 mL) per day.
40% of that glucose is carbon, so the 9.60 oz (280 mL) per day of carbon in glucose yields about 35 oz (1 L) of CO2 per day, a little over 2 pounds (0.9 kg). About 1.5 oz (44 mL) of CO2 per hour.
This value is close enough to what wikipedia has, so we can assume 1.5 oz (44 mL) of CO2 per hour to be correct.
A typical canister stove has an 80/20 mix of isobutane and propane. If we look at the 8.3 oz (250 mL) MSR ISOPRO canister with a superfly stove, that will give us a burn time of about 60 minutes.
That 8.3 oz (250 mL) MSR stove is mostly carbon by mass, with 6.8 oz (200 mL) of carbon, which when burned will produce about 25 oz (740 mL) of CO2.
So, sitting in your tent, you'll be producing 1.5 oz (44 mL) of CO2 per hr, while your stove will be pumping out 25 oz (740 mL) per hr, 16 times as much.
In the course of an hour, that CO2 would occupy about a half cubic meter, which in a tent can easily raise the CO2 concentration well above toxic levels.
CO and CO2 dangers are real, and most tents aren't ventillated well enough without outside wind to make it safe.
CO2 dissolves well in water, especially cold water, and your body has mechanisms to deal with it. Somewhat surprisingly, what causes you to breathe harder is not lower oxygen concentrations in the blood, but higher CO2. It's just one of those quirks left over from the long, convoluted history of mechanisms that seemed to work found by accident and refined by selection that we call "evolution".
CO is the more serious danger because your body doesn't sense it and it silently displaces oxygen in the blood, eventually starving the brain of real oxygen so that you get light headed, make stupid choices, and eventually pass out.
Ideal combustion of hydrocarbons produces only CO2 and water, but no such combustion is ideal, especially in something like a camp stove that was optimized for other qualities like small size and light weight.
How much is too much? I don't know, but I'm not going to run a stove in a tent or a fuel-based lantern. Fortunately, there are now much better ways to make light than to burn fuel. I don't think a single candle is much of a issue in a normal size tent that has ventillation holes open. The amount of CO that a candle can produce is limited by the C in the tiny amount of wax it uses. Some fraction of that wax is H, not C, and most of the C will be burned to CO2, not CO. The resulting amount of CO from a single candle is therefore small, but I wouldn't ever burn more than that in a tent. Actually I wouldn't burn a candle either, since again, there are now far better ways to make light, not to mention the inherent danger of the open flame. I don't bring candles with me in the first place.
In addition to Olin Lathrop's great answer.
CO output depends on specific conditions:
Definitely, CO output may be too high inside a tent and there is no stove which is CO-free.
To answer this question one could analyse the death/poisoning reports to determine, how much ventilation is NOT enough.
Speaking theoretically, high CO concentration (>0.5%) is dangerous if you breathe it a couple of minutes, so if your ventilation is good enough to substitute all the air in the tent with a fresh one each 5 minutes, maybe you are ok. But please don't count on this rough estimations.
Accodring to the reports, people often don't realize thay are getting poisoned, so don't be overconfident. Probably, the best way aside from not cooking inside the tent (well, sometimes CO risk is less than the risk to get frozen) is to have someone else in another non-cooking tent, who will check you every now and again.
As for practice, we strictly avoid cooking inside a closed inner tent of a two-layer tent and try to keep an outer tent as open as possible.
Please note, that CO poisoning is not the only poisoning risk of cooking inside: there is also a risk of breathing propane/butane escaped from a loose stove-to-canister joint or even faulty canister in your backpack. So never store fuel inside a (inner) tent.
