# Helium - how much?



## spiwak2005 (Jan 7, 2010)

I have a rider from a German touring group that wants helium for their 2 meter long zeppelin. They asked for a 5 liter bottle of helium...and our local company sells it in bottles of 230 cubic feet for $90. What's the conversion here (looks to me like over 6000 liters)? Is that way too much for something this size?


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## epimetheus (Jan 7, 2010)

I'm not sure how much help I can be, but I'd guess 5 liter refers to the bottom size the group typically gets, and 230 cubic feet refers to how much gas your local company actually puts in the bottle. In other words, one of your numbers seems to be the volume of the bottle, and the other the volume of gas. Since gas is compressible, you can put a large volume of gas into a bottle with a small volume.

It's hard to compare unlike quantities.


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## ajb (Jan 7, 2010)

To expand on epimetheus's comment, the 230cf your supplier quoted is actually standard cubic feet, which refers to a quantity of substance rather than volume, and as such is convertible to moles of helium. You can't convert it to unqualified liters because volume of a gas is dependent on temperature and pressure according to the combined gas law. You can, however, convert SCF to standard cubic meters because, like SCF, an SCM is defined as a unit of volume at a standardized temperature and pressure.

But all that isn't really necessary to answer your question, because unless you're buying cryogenic gas (which you aren't), the temperature inside the gas bottle is the same as outside, which means that you only need to know the ratio of bottle pressure to atmospheric pressure in order to determine how many SCF of helium are in that 5L bottle. And fortunately, there is a unit of pressure called the Atmosphere that is roughly equivalent to atmospheric pressure on Earth at sea level. So if you identify the pressure of their usual 5L helium bottle in atm (or bar, the units are nearly equivalent), you can use that directly as the ratio of expansion when you crack open the bottle and all that He rushes out into the air--well, assuming your atmospheric conditions inside your venue are reasonably close to STP, which they probably are if you're not at a very high elevation. You can also adjust the ratio based on another target pressure--say you want to fill a football to 5psig (~19.7psia), you can use this pressure to determine the quantity of helium in scf or scm that will be required.

Nerdiness aside, here's the bottom line:

here's an example: if the 5L bottle of Helium has an internal pressure of 250atm, then it contains 5L * 250 = 1250L @STP = 1.25 SCM = 43 SCF. According to wikipedia, standard pressure for bottled gases is 200-400 atm, so based on that range they're requesting a quantity of somewhere between 34.3 and 68.8 SCF.


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## jwl868 (Jan 7, 2010)

Ask your gas supplier about the size of the cylinder. There are a limited number of standard sizes, and he should be able to look that up. Verify the pressure of the helium in the tank, and then ask the client if that will suit their needs. I suspect that all helium gas tanks are provided at the same pressure regardless of the supplier, but check anyway. (There may be multiple pressures available, and US suppliers may use a different "standardized" cylinder pressure than in Europe.) 

Joe


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## spiwak2005 (Jan 7, 2010)

Thanks so much! This all makes much more sense now.


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## Kelite (Jan 7, 2010)

So would it take two or perhaps three tanks to properly satisfy party-goers at a mid-sized birthday party? (Assuming of course there will be no balloons to fill, just funny voices to make...  )


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## DuckJordan (Jan 7, 2010)

Kelite said:


> So would it take two or perhaps three tanks to properly satisfy party-goers at a mid-sized birthday party? (Assuming of course there will be no balloons to fill, just funny voices to make...  )



as fun as that would be i only think one would do too many people i have seen have passed out as a result of stupidity lol, i have as a mater of fact done just that, lol.

the voices are fun though


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## jwl868 (Jan 7, 2010)

A couple other things to consider:

- Does the client need a regulator and/or other fittings? Are you supposed to povide them?

- Do you have a proper place to store the cylinder? A compressed gas cylinder needs to be secured so it doesn't fall and become a torpedo. 

- Get some cylinder handling information. The gas vendor may be able to provide some. Or check OSHA or one of the major compressed gas providers. (An Air Products example link is below.)

http://www.airproducts.com/nr/rdonlyres/e3529882-8771-4c5b-b9a1-88db0b69192b/0/safetygram05.pdf

Joe


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## Van (Jan 7, 2010)

A quick check reveals you'll need approx. 96 - 126 cu. ft. of He to fill this ballon.


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