Why is compressed air flammable?

I have a can of compressed air. The type you use to clean the insides of computer. It's "100% ozone friendly" and "pure compressed gas". So I assume its everyday regular breathable air. I used it to try blow out a candle. It had precisely the opposite effect.


Why?




Assuming the contents are what is written on the outside, *compressed air* is a mixture of about $78~\%$ nitrogen, $21~\%$ oxygen, $1~\%$ argon and about $0.04~\%$ carbon dioxide. None of these compounds are flammable. Oxygen, however, is able to support combustion. So increasing the amount of oxygen a flame gets will increase combustion.


The principle difference between blowing canned compressed air onto a candle flame and simply blowing into said candle flame is the focus of the air flow. These cans are designed to blow air in a rather defined way to a defined target so you can assume the air flow to be very focused. Blowing using your mouth would create a very unfocused air flow because there is only one constraint (your lips) and air can pass through at a variety of angles.


When reaching the candle flame, the focused air flow causes the mixing of gaseous wax (required for combustion) and oxygen from the air (both the canned and the uncanned) to improve, hence increasing the rate and heat of combustion. The small focused flow will create small whirls that help mixing. The mouth-blown air, however, will come as a strong wave, practically pushing the entire candle flame away. Therefore, the flame will go out. (That and only that is the mechanism of blowing out candles: blowing the flame away.)


 3

Most probably some hydrocarbon like butane = big flame. A quick way to check is if the can makes a sound when you shake it. If it does then it's most likely hydrocarbon. It would have been less confusing if it said "compressed gas".


 3

In former centuries the word "air" was used to descrive gases generally, not what chemists call "air" today. Hydrogen used to be "fire air". Sometimes this usage still creeps in, I've heard people use "air knives" for devices that wipe excess coating off a hot dip galvanized strip with *nitrogen* gas.


Don't rely on just the product name used to sell the product. Check *all* the labelling. If there is something (in)flammable, the manufacturer is required to report that information.


 3

I would guess that because in the process of compressing air, we use oil to remove heat and lubricate the rotors in the air compressor. There is a separator in the tank that removes the oil from the air however they have been known to leave traces of oil in the compressed air and if there is excess oil in the reservoir then that's also going into the compressed air. They probably put flammable as a warning just in case a faulty separator is the cause of a can or two of having a percentage of oil in it.


This could be totally wrong tho, lmk


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