# Are helium tanks heavier when full or empty? **URL:** \ **Category:** Factual Questions\ **Created:** [September 29, 2002, 11:26pm UTC](https://boards.straightdope.com/t/are-helium-tanks-heavier-when-full-or-empty/130161 "2002-09-29T23:26:42Z")\ **Posts on this page:** 17\ **Page:** 3
**Author:** ![Nametag](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nametag/32/406_2.png) [@Nametag](https://boards.straightdope.com/u/Nametag)\ **Post date:** [October 1, 2002, 7:03pm UTC](https://boards.straightdope.com/t/are-helium-tanks-heavier-when-full-or-empty/130161/41 "2002-10-01T19:03:11Z")
You’re mixing and matching, **Achernar**. There are two sites linked in Zut’s post, and the more technical one states: > [@](#): > > A 1-A cylinder of helium contains 8.3 m[sup]3[/sup] (293 ft[sup]3[/sup] ) of room-pressure gas that?s compressed into a space of less than 0.5 m[sup]3[/sup] (2.0 ft[sup]3[/sup]) at a pressure of 18.1 MPa (2640 psi). These cylinders weigh approximately 91 kg (200 lb) when empty, and the weight of the helium within a fully pressurized cylinder is approximately 1.4 kg (3 lb). I don’t see anything about “55 cubic feet”; as far as I can see, Zut’s guess is pretty close. Now, this is a standard gas cylinder, the size you see in laboratories and welding shops. The baby cylinders they sell at Party America are obviously much smaller, and less pressurized. ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [October 1, 2002, 7:04pm UTC](https://boards.straightdope.com/t/are-helium-tanks-heavier-when-full-or-empty/130161/42 "2002-10-01T19:04:54Z")
Hopefully, this link will put this one to rest. [http://www.tprhs.org/museum/helium.htm](http://www.tprhs.org/museum/helium.htm) ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [October 1, 2002, 7:12pm UTC](https://boards.straightdope.com/t/are-helium-tanks-heavier-when-full-or-empty/130161/43 "2002-10-01T19:12:09Z")
Hopefully, this link will put this one to rest. [http://www.tprhs.org/museum/helium.htm](http://www.tprhs.org/museum/helium.htm) ---
**Author:** ![zut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zut/32/2875_2.png) [@zut](https://boards.straightdope.com/u/zut)\ **Post date:** [October 1, 2002, 8:01pm UTC](https://boards.straightdope.com/t/are-helium-tanks-heavier-when-full-or-empty/130161/44 "2002-10-01T20:01:41Z")
> [@](#): > > \*Originally posted by Achernar \* > The page you quoted shows a “55 Cubic ft” Helium cylinder. I assume that means it holds 55 ft[sup]3[/sup] (= 1557 liter) of uncompressed Helium? That doesn’t quite work with the rest of your calculations. Yeah, I was mixin’ and matchin’ cites. I used the one you quoted because I wanted a cite for the pressure of helium bottles meant specifically for _balloon-filling_, and I used the other cite (with the larger size bottle) because he had done the calculations independantly. Gas cylinders (even for balloon fillers, evidently) come in different sizes. For instance, [these guys](http://www.bostonrentals.com/robinson-heliumtanks.htm) offer three sizes of tank for balloon-filling: 291 cu ft, 110 cu ft, and 30 cu ft, the first of which is apparently the same size as the one I was basing my calculations off. I suspect that the 291 cu ft size is the large, 4 ft tall type of gas cylinder, so 91 kg metal weight seems about right to me for that size. Also, to quote the relevant part of **scotth** ’s link: > [@](#): > > One of the most colorful myths about Helium tank [train] cars is that they’re lighter when they’re loaded than when they’re empty. That of course is untrue. They actually carry a load of 3000 lbs. of gas. As he says, that ought to put it to rest. ---
**Author:** ![Walloon](https://avatars.discourse-cdn.com/v4/letter/w/fbc32d/32.png) [@Walloon](https://boards.straightdope.com/u/Walloon)\ **Post date:** [October 2, 2002, 6:52am UTC](https://boards.straightdope.com/t/are-helium-tanks-heavier-when-full-or-empty/130161/45 "2002-10-02T06:52:13Z")
**Mass** is a constant; **weight** is not. Don’t confuse the two. A tank with helium in it is lighter than a tank that has air in it for the same reason that a balloon with helium in it is lighter than an empty balloon or a balloon with air in it. But don’t consider the case closed until you’ve actually lifted and/or weighed a full helium tank and an empty one. Empiricism trumps theory. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [October 2, 2002, 8:03am UTC](https://boards.straightdope.com/t/are-helium-tanks-heavier-when-full-or-empty/130161/46 "2002-10-02T08:03:11Z")
> [@](#): > > \*Originally posted by Walloon \* > \*\ ***Mass** is a constant; **weight** is not. Don’t confuse the two. A tank with helium in it is lighter than a tank that has air in it for the same reason that a balloon with helium in it is lighter than an empty balloon or a balloon with air in it. \*\* This is just wrong; the balloon is lighter than air because the volume of the helium is preserved and it is only slightly pressurised inside the baloon (in the case of nonelastic mylar balloons it need not be under pressure at all). In a tank, the helium is _ **compressed** _; when you add mass to a system without changing the volume, the weight will increase. (this is pretty much the definition of density). ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [October 2, 2002, 9:46am UTC](https://boards.straightdope.com/t/are-helium-tanks-heavier-when-full-or-empty/130161/47 "2002-10-02T09:46:06Z")
I’ve just fired off an email to the UK contact of [http://www.boc.com](http://www.boc.com) : > [@](#): > > Dear [contact name] > > I am writing to you as a member of a popular internet message board ( [http://boards.straightdope.com](http://boards.straightdope.com) - run by the Chicago Reader newspaper). > > The prevailing ethic of the board is to uncover hard facts (this is in fact the meaning of the term ‘the straight dope’) on any given subject and this is where a representative of your company may be able to assist. > > A question has arisen regarding the weight of full containers of compressed helium vs the weight of the same containers in their unpressurised ‘empty’ state; (for reference)the question and subsequent discussion may be found here: [http://boards.straightdope.com/sdmb/showthread.php?&threadid=137298](http://boards.straightdope.com/sdmb/showthread.php?&threadid=137298) > > The discussion appears to have polarised into two camps: > -Those who are arguing from a theoretical viewpoint and are stating that pushing extra mass into a fixed volume can only result in an increase in weight. > -Those with first-hand experience of handling the containers who claim that the ‘empty’ state feels heavier than the charged state. > > By now, I suppose it’s obvious what I’m asking; I wonder if a qualified representative of your company would be kind enough to definitively settle this debate by citing the actual weights of charged and empty containers of helium. The motto of this message board is “fighting ignorance since 1973” - I would be most grateful indeed if you would see fit to contribute to the endeavour. > > Many thanks. > > [My IRL name] I have attempted to frame the question in as neutral a fashion possible, although my email address is similar to my username here. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [October 2, 2002, 9:52am UTC](https://boards.straightdope.com/t/are-helium-tanks-heavier-when-full-or-empty/130161/48 "2002-10-02T09:52:46Z")
Here’s one theory on why a full tank might seem lighter. When pressure is increased, the air speed inside the tank will also increase. I believe this causes the tank to ring at a higher pitch when struck. We tend to associate high pitch sounds with lighter things, so one might get the impression that a full tank is lighter. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [October 2, 2002, 9:55am UTC](https://boards.straightdope.com/t/are-helium-tanks-heavier-when-full-or-empty/130161/49 "2002-10-02T09:55:39Z")
Um, I meant the _sound speed_ inside the tank will increase. By the way, does nobody have a can of balloon gas around? They are often sold in small cans that look like spray cans. It’d be trivial to weigh one, empty it and weigh it again. I’ll check a couple of stores on the way home tonight if I have time. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [October 2, 2002, 9:59am UTC](https://boards.straightdope.com/t/are-helium-tanks-heavier-when-full-or-empty/130161/50 "2002-10-02T09:59:48Z")
I was wondering about that myself, **scr4** ; it may indeed be that full containers _sound_ emptier that empty ones. ---
**Author:** ![Walloon](https://avatars.discourse-cdn.com/v4/letter/w/fbc32d/32.png) [@Walloon](https://boards.straightdope.com/u/Walloon)\ **Post date:** [October 2, 2002, 10:13am UTC](https://boards.straightdope.com/t/are-helium-tanks-heavier-when-full-or-empty/130161/51 "2002-10-02T10:13:12Z")
> [@](#): > > \*Originally posted by Mangetout \* > **In a tank, the helium is _compressed_** So is the helium in a rubber balloon. That’s why it explodes if pricked. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [October 2, 2002, 10:19am UTC](https://boards.straightdope.com/t/are-helium-tanks-heavier-when-full-or-empty/130161/52 "2002-10-02T10:19:03Z")
Hardly the same degree of compression as when it’s in the tank. If you made a balloon that allowed you to compress helium to a greater density(total density including the substance of the balloon) that was greater than that of air, it would not float. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [October 2, 2002, 10:24am UTC](https://boards.straightdope.com/t/are-helium-tanks-heavier-when-full-or-empty/130161/53 "2002-10-02T10:24:55Z")
Or to put it another way; if you made a balloon that weighed (when empty) the same as an ordinary one, but was of a tougher material that required exactly twice the amount of helium to inflate it to the same size, do you think it would be lighter or heavier? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [October 2, 2002, 10:46am UTC](https://boards.straightdope.com/t/are-helium-tanks-heavier-when-full-or-empty/130161/54 "2002-10-02T10:46:29Z")
Here’s another [snippet](http://outreach.web.cern.ch/outreach/public/nl/physics_fair/Exp13.html), the important parts being: > [@](#): > > The volume of the balloon decreases by the low temperature, because the gas inside is cooled down. At room-temperature the helium balloon is lighter than air with the same volume of the air, which makes it go up. At low temperatures its volume is too small, so it is heavier than the same volume of air. > … > The helium-filled balloon flies up in the air, because the average density of the balloon and helium together is lower than the density of air. Just like a piece of wood, held under water, tends to rise to the surface of the water. When the balloon is cooled, the volume of the balloon is greater, resulting in a greater average density of the balloon and helium. This makes the balloon come down That the helium was rendered smaller in volume by cooling rather than compression is irrelevant; when you compress a substance, the density increases. A given volume (the tank) of a more dense substance (compressed helium) is heavier than the same volume of a less dense substance (residual helium at 1atm pressure). ---
**Author:** ![zut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zut/32/2875_2.png) [@zut](https://boards.straightdope.com/u/zut)\ **Post date:** [October 2, 2002, 11:58am UTC](https://boards.straightdope.com/t/are-helium-tanks-heavier-when-full-or-empty/130161/55 "2002-10-02T11:58:02Z")
> [@](#): > > \*Originally posted by Walloon \* > **Mass** is a constant; **weight** is not. Don’t confuse the two. A tank with helium in it is lighter than a tank that has air in it for the same reason that a balloon with helium in it is lighter than an empty balloon or a balloon with air in it. No one is confusing the two. And we’re talking about a _full_ tank of helium, which is compressed to a pressure about 140 times that of normal atmospheric pressure with miniscule volume change. A balloon is pressurized at far less than one atmospheric pressure (gauge pressure), but has substantial volume change. > [@](#): > > But don’t consider the case closed until you’ve actually lifted and/or weighed a full helium tank and an empty one. Empiricism trumps theory. You’re not offering empirical evidence; you’re offering subjective anecdotes. How much heavier is an empty tank than a full one? What did you use to weigh it? What was the accuracy of the measurement device? What was the pressure in the tank? What was the construction of the tank? Additionally, why would your observation trump that from the cite **scotth** found, which _directly contradicts_ what you say? ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [October 2, 2002, 1:14pm UTC](https://boards.straightdope.com/t/are-helium-tanks-heavier-when-full-or-empty/130161/56 "2002-10-02T13:14:52Z")
> [@](#): > > \*Originally posted by Walloon \* > \*\ ***Mass** is a constant; **weight** is not. Don’t confuse the two. A tank with helium in it is lighter than a tank that has air in it for the same reason that a balloon with helium in it is lighter than an empty balloon or a balloon with air in it. > > But don’t consider the case closed until you’ve actually lifted and/or weighed a full helium tank and an empty one. Empiricism trumps theory. \*\* This case is closed. This experiment has been. The physical laws of bouyancy were determined doing experiments just like this. I would without hestitation put my life at stake (I am not kidding or exagerating, I really would would not hesitate to do this) on the results of this experiment. Any arguing to the contrary just indicates that you don’t understand the principals involved here. Perceived weight on the surface of this planet is determined by two variables, the mass of the object and its displacement. With a balloon (which gets larger in displacement when filled) the displace increase faster than it mass when filled with helium, therefore its weight decreases as it is filled. The helium tank is a rigid structure and does not change displacement as it is filled. The only thing that happens as you fill it with helium is that its mass increases. If you wish to understand this, study how a boat floats. The pricipals are exactly the same, but may be easier to grasp for the first time in that context. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [October 2, 2002, 1:26pm UTC](https://boards.straightdope.com/t/are-helium-tanks-heavier-when-full-or-empty/130161/57 "2002-10-02T13:26:08Z")
The same principles govern why ice floats (water and ice are the same substance, but ice has greater volume/displacement for the same mass) and why hot air ballons rise (hot air occupies more volume for the same mass) and why an ordinary rock sinks in the ocean (greater mass than the same volume of water). [Previous page](https://boards.straightdope.com/t/are-helium-tanks-heavier-when-full-or-empty/130161.md?page=2)