The optimal oxygen concentration for the body is between 19.5% and 23.5% oxygen.
About 20% of the atmosphere is made up of oxygen at sea level.
At sea level to about 300 metres, 100% of that is available.
If you are not acclimatised to working at altitude, you will generally pass out at 10%.
Altitude where 10% is? About 17100 metres.
Yet don’t be fooled.
The same effect as altitude reducing the available oxygen can be caused by chemicals or by swamping the body’s blood carrying red cells by carbon monoxide. See Post.
Yawning (and Oxygen).
You could be tired (or bored) but sometimes yawning is natures way of making you breath DEEPLY to increase your oxygen levels.
So, if you start yawning with a lit fire, lantern, or when cooking, just consider why.
You may be tired, bored, or simply starved of oxygen!
Oxygen levels of under 14 % will cause extreme exhaustion from physical activity.
Below 10 % you may become very nauseous or lose consciousness.
At 5% the body concentrates on keeping the brain going and eventually your other organs will fail as they are starved of oxygen.
Before that occurs, your heart would have failed as it is working flat-out to pump what oxygen is there to the brain.
In short you die of heart failure not shortage of oxygen.
So what simple visual clues will you have that your oxygen is getting low?
Most any common materials will burn at oxygen concentrations down to approximately 14% . That’s a camp fire glowing with flames.
Fuelled Flame is different though, and THAT needs a minimum of around 5%.
So when a candle stops burning, you’re in serious trouble.
Gas or fuelled Stoves.
Blue flame is good!
Red or yellow gas flames may be the sign of incomplete combustion, wasted gas and a serious safety hazard. With hydrocarbon flames, such as gas, the amount of oxygen supplied with the gas determines the rate of combustion, flame colour and temperature.
BAD PRODUCES CARBON MONOXIDE!