Compressed Air Can Mystery: What's Going On?

[Pengwuino]

I was wondering something. I have this can of compressed air and when its upright and used, it fires out a bunch of air. If i turn it onto its side where the nozzle points up however, half the time the air is actually visible! (or too cold?). What is causing this? It also does it when you turn the bottle upside down but still point the nozzle in the normal horizontal direction. Finally, if you have the can upside down and baaaarely pull the trigger, little specks of liquid (kind of like when you accidently spit through your teeth) fly out and large drops of liquid fall down and quickly evaporates. What is going on here in each of those cases :)

 

[Azimuth]

sounds to me like you are talking about a compressed air duster for electronic devices and such, if so it should have on of these two labels...

1,1,1,2-tetrafluoroethane or difluoroethane. These are two common "compressed air" products. They are simple asphyxiants (since they displace the oxygen you should be breathing, in a closed space you could become oxygen-deprived). Both solvents are considered "ozone-friendly," that is they do not deplete ozone like the older chlorofluorocarbons.

The reason for the 'liquid' is because straight compressed air products would have their own set of problems. An aerosol dispenser of compressed air would probably be at a much higher internal pressure in order to contain a reasonable amount of "product." The two fluoroethanes mentioned above are liquid under relatively modest pressure, and only become gaseous as you depress the spray tip and allow product to escape. You can even get some of the liquid solvent to spray out if you invert the can and press the spray tip (as you mentioned).

Another issue with straight compressed air is it would tend to be a bit corrosive unless all the moisture were removed when the aerosol can got filled. Compressed air usually gets a bit of oil contamination (picked up from compressor components) and would need to be carefully filtered, or it would just grease up whatever you tried to dust off.

This is probably WAYYY more than you cared to know about "compressed air cans" but I went on a roll...

 

[Pengwuino]

Its 1,1,1,2-tetrafluoroethane. Cool to know all that. What i really want to know is how the liquid continued to be a liquid when i placed it upside down and lightly pulled the trigger. It fell down through hte air as a liquid adn i wondered why it didnt instantly vaporize.

Also, i was ID'ed when i purchased one. What is with that? The woman at office depot said they recently started ID'ing people for compressed air and that you had to be 18 to get it...

 

[Azimuth]

yes you do have to be 18 purchase it, tetrafluoroethane is neither toxic nor flamable, but I would assume that since the reaction (instant freezing and evaporating) is, i believe, a milder form of liquid nitrogen reactions you would want to restrict sales to adults only. I think there is some kind of warning on the bottle about burnings or skin damage from contact but I've never had a problem with it.

i really don't know for sure why it remains liquid at that point except that maybe since you are releasing a minimal amount of compressed air and the liquid is right by the nozzle that it would "leak" out and still remain in its original state. From that point i would assume its something to the effect of freezing rain, you'll notice how the 'tube' on the nozzle will crystalize and freeze? the falling tetrafluoroethane is well below freezing point, but will remain a liquid until contact with a solid is formed, then it reacts as normal... hope that answers your question

that last paragraph is all speculation so i wouldn't take it at face value if i were you...

 

[Pengwuino]

The thing is, I've purchased it before and was under 18... maybe they were using a different chemical... but the can before also had the skin-burn warnings... i think ill go take a look online about it :D

 

[Azimuth]

good idea...post what you find out...

 

[Pengwuino]

Cant seem to find anything! Maybe the woman was lieing to me... bah... she shall suffer!

 

[pete worthington]

The propellant used in these "dustoff" cans are typically heavy gases (R2 etc...). A recent craze called "dusting" has one inhaling the spray and settling the heavy gases in ones lungs, starving oxygen and bringing a 10 minute light-headed buzz. There was a 15 year old male who recently died from this, his parents found him in his bed with the nozzle still stuck in his nose. I am a high school science teacher and this story has made it's way through most school districts. Un-real eh ?

 

[Pengwuino]

lol i wish i were surprised...

 

[Rogue Physicist]

Actually, even if it isn't illegal for minors to purchase a specific product, obviously if the clerk thought you might harm yourself, she would have insisted on I.D. as a reasonable precaution. In fact, even without specific laws, both a retailer and employees serving the public can probably be sued for criminal negligence or carelessness causing grevious bodily harm if they don't pay attention to dangers to minors with any product.

Probably a good thing that she carded you.

 

[chroot]

The substance exists in two phases inside the can: liquid at the bottom, gas above it. When you hold the can upright, the gas escapes from the nozzle. (Liquid inside the can quickly evaporates and replaces it.) When you turn the can upside down, the liquid itself comes out of the nozzle.

- Warren

 

[Danger]

A recent craze called "dusting" has one inhaling the spray and settling the heavy gases in ones lungs, starving oxygen and bringing a 10 minute light-headed buzz. There was a 15 year old male who recently died from this

According to a CBC news feature last week, there is a movement afoot in Canada to ban the stuff because there have been at least 3 or 4 deaths from it up here. I think that only one of them was 'accidental' in that the victim was using the product for its intended purpose, but in an enclosed space. The rest were deliberate attempts to get high, and are categorized the same as a heroin overdose.

 

[Pengwuino]

Too much chlorine in the gene pool i think.