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The Deep Voice Gas – Sulfur Hexafluoride (SF6)

It was fun to see David Willey on The Tonight Show this evening doing some nice variations on the classic sulfur hexafluoride (SF6) demo. This is the inert gas that is six times heavier than the air we breath. If you breath in helium (six times lighter than the air we breath), the pitch of your voice goes up. However, if you breath sulfur hexafluoride (six time heavier than normal air), your voice sounds low. You’ll find a complete explanation of the sulfur hexafluoride demo or anti-helium experiment as some call it in my experiment library.


For the Tonight Show, David filled an open top plastic box with the gas and proceeded to float aluminum foil boats and bubbles on this very dense gas. These demos got a nice reaction from the audience. Instead of inhaling the SF6 gas from a balloon, David had Jay Leno dip his head down into the box and inhale some of the gas. As you might imagine, Jay had fun with his “Barry White” voice.

After showing the heavy gas demo on 9News last year, Scott Merrick from Snacks4thebrain visited our lab in Englewood, Colorado to tape this video of the sulfur hexafluoride experiment for YouTube.

29 replies
  1. kevin
    kevin says:


    per: http://en.wikipedia.org/wiki/Sulfur_hexafluoride

    A myth exists that SF6 is too heavy for the lungs to expel unassisted, and that after inhaling SF6, it is necessary to bend over completely at the waist to allow the excess gas to “spill” out of the body. In fact, the lungs mix gases very effectively and rapidly, such that SF6 would be purged from the lungs within a breath or two.

  2. Michaela
    Michaela says:

    Thank you for your caution about trying this. A mom was recently telling me about a party her daughter had attended where they were “huffing”. Her daughter confided details and one of them was that it made the huffers voice sound funny- really low- and the kids thought it was really funny. Hmmmm, I thought.
    Two nights ago, on Jay Leno, I saw an SF6 demo. “Harmless” “inert” “take a hit, Jay” were things that I heard…no more harmful than helium? My inquisitive science mind tells me that helium, lighter than air, is going to escape on it’s own… However, SF6 and various other inert heavy gases are going to stay put- like the invisible water in the aquarium on Leno -unless you forcibly expel them.
    As you said, do not try this- or anything like it with heavy gas- at home. What may seem like an innocent light-headed moment may truly be your body drowning. And should one pass-out in an upright position, it reasons that they can not help but “drown” as the heavy gas cannot pour out, and the body cannot push out. I enjoy science, Mr. Wizard was my hero, and magic- and I know not to mix elctricity and water…or play with heavy gases.
    I’ve enjoyed your many links- glad to have found you.

  3. Jeff Johnson
    Jeff Johnson says:

    The huffing that is going on at parties is freon, not sulfer hexaflouride. Kids steal it from AC units. Its heavier than air as well.

  4. Roger
    Roger says:

    If the party was at The Franklin Institute in Philadelphia, it may very well have been a demonstration of the density of gases and the effects on the vocal cords. The Franklin Institute does perform demonstrations with helium and sulfur hexafluoride; and it wouldn’t be uncommon for this demonstration to be performed at a birthday party. However, it should be noted that this is by no means “huffing” as the purpose of huffing is to obtain desired affects due to altered brain activity. Helium and sulfur hexafluoride do not alter brain function in any way shape of form, and the only possible damage that inhaling these gases can cause is aphxiation which would only occur if a participant brathed in only one of the previously mentioned gases continually to the point of denieing ones body and oxygen for a period longer than one can hold their own breath. This activity at The Franklin Institute is superfized by trained profesionals to prevent any such danger.

  5. Fred Bush
    Fred Bush says:

    Did you know that Sulfur Hexafluoride is the most potent greenhouse gas known, with a greenhouse footprint about 22000 times as potent as carbon dioxide?

    That means that a “vocal” experiment involving, say, a pound of SF6 releases as much greenhouse gas as running two typical passenger cars for a year. Given that, I think it’s irresponsible to market this particular experiment.



    • rj.alaskan
      rj.alaskan says:

      Guess what? my house contributes to CO2 in the atmosphere, You live your green life. I’ll live how I want to. Stop trying to force it on other people.

  6. Steve
    Steve says:

    Fred — Thanks for the follow-up information. I think it’s important to know all of the factors that contribute to global warming. Fortunately, we use very small amounts of the gas in each demonstration. A pound of the gas might last a teacher years and years worth of science demonstrations. Thanks for the information.

  7. Doug
    Doug says:

    Dear Fred,

    Let’s keep everything in perspective. We’re talking about a small balloon filled with sulfur hexafluoride. Read your reference and they’re talking about the gas being used in industry – not a teacher using the smallest amount in an effort to get kids turned onto science. Coming from the perspective of a veteran chemistry teacher, be careful about your use of the term “irresponsible.” America is pumping out a generation of people who are scientifically illiterate. Anything, absolutely anything, a teacher can do to get students excited about learning is a benefit. If you want to poison pen someone, aim your sights at industry and leave well meaning teachers alone.

    Doug Lefton

  8. Andrea L.
    Andrea L. says:

    Why isn’t anyone talking about how much SF6 is being released by industry instead of trying to nail a teacher for doing something good? Interesting stats from Eric, but why is he targeting a science demo?

  9. Eric
    Eric says:

    I’m not targeting anyone. I’m just stating the facts. Just because the military releases over 200,000 lbs of SF6 per year with their 38 AWACS aircraft (Tinker AFB), or Con Edison in NY releases nearly 40% of the 160,000 lbs. of gas they purchase every year doesn’t mean the smaller intentional releases should be overlooked or ignored.

    I’m not a tree-hugging environmentalist by any stretch, but I work for a company that works exclusively with SF6 – in virtually all industrial, medical, utility, and educational applications.

    Yale, for example, has 30,000 lbs. of SF6 in their linear accelerator. Intel, AMD, Samsung, and other semi-conductor manufacturers use this gas in power supplies on their Varian Ion-implantation fab tools.

    The difference with almost every one of these other applications is that the gas releases are not intentional. Yes, there are leaks, and in some cases, venting of gas is an unavoidable process in the application. But even in those cases, now that the full environmental impact of SF6 is understood, end users and manufactures of gas insulated equipment are doing everything possible to improve new designs and even retro-fit existing applications to minimize or eliminate all emissions.

    That’s why, when I hear that people are intentionally venting gas – for whatever noble or altruistic reason – I think it’s important that they understand not only the impact but also the science and facts behind it.

    Companies that work with SF6 spend tens, if not hundreds of thousands of dollars to recover/reclaim even the smallest amounts of gas in order avoid all emissions. Here’s a quick example: Most applications involving SF6 cause the gas to break down or become wet over time. Users must periodically test the gas for moisture and for decomposition – and take corrective action if either value exceeds equipment manufacture limits. The testing of gas involves releasing less than 0.5 oz (less than half of one lung full) of SF6. Yet, the industry is now requiring even that amount to be recovered. This means in addition to the cost of the test equipment, users are shelling out an additional $12,000 for a small recovery system that recaptures this 0.5oz of gas.

    How do you think they’d feel, knowing that they spend this kind of money and effort to recover the ‘trivial’ amount of gas – when someone else is running around venting several times more gas (intentionally) in the name of promoting science? Keep in mind that many European countries (among them Switzerland) have made it illegal to intentionally vent ANY gas.

    Look, I’m all in favor of encouraging interest in Science. And I do believe the good that comes from these types of demonstrations probably outweighs the ‘drop in the ocean’ amount of gas being vented. But at the same time, I think anyone involved should know exactly what they’re doing. For example, the claim from Doug that one pound might last several years, is only true if the demonstration is performed with only one single inhalation, and then no more than 3x per year.

    Finally – one last issue on safety. Pure, clean SF6 is safe to inhale. Once it’s been heated (faulted) it can produce by products that can be lethal (S2F10, among others). Utility users that work with SF6 take extreme caution not to expose themselves to ANY gas since they do not know the quality. Even though a bottle may be new, and even have a seal on it from Praxair, AirGas, Honeywell, or other suppliers, it may still be contaminated. Here’s why: When users in the field recover faulted/heated gas, they usually pump it into cylinders – cylinders that belong to the gas vendor. They do not tell the vendor, and while they remove MOST of the gas from the bottle before they return the cylinder to the supplier, the decomposed by products are still present. When the supplier gets the cylinder back, they simply add more gas and put it back out on the market. They receive too many cylinders in their rotation to test each one of them. Consequently, we have many seen many cases where users receive brand new cylinders with faulted gas. Inhaling faulted gas can make you very, very sick (think cancer, permanent lung damage, etc) – if not kill you. Unless the cylinder has been lab certified (independently from the vendor) to ensure medical grade quality, it is a risk not worth taking, no matter how ‘cool’ you may sound.

    Sorry for the long post, but I think this info needs to be distributed anytime someone encourages the release of any SF6 – regardless of quantity.

  10. Steve
    Steve says:

    Let me jump back into the conversation. I really appreciate the incredible depth of information that Eric shares on this topic. He has given all of us who perform the demo some fantastic information to share with our students, especially when it comes to the corrective action taken by people in industry who are using SF6 to recapture just a small amount of the gas. Speaking to the safety issue, I can tell you that we’ve gone to incredible expense and care to ensure the medical grade quality of the gas used. What is of concern to me is that none of Eric’s information appeared in any of the research we did before I started doing the demo. It’s time to dig a little deeper.

  11. Eric
    Eric says:

    Thanks for the acknowledgment Steve. The information regarding the global warming potential (GWP) of SF6 can be found on the EPA website (someone gave the link earlier). It’s 23,900 x more than CO2. It’s so damaging that even the current Bush administration, who up until recently vehemently denied global warming even existed, initiated a voluntary Memorandum of Understanding (MOU) partnership between US electric utilities and the EPA (http://www.epa.gov/electricpower-sf6/pdf/finalmou.pdf). I personally work with the current program manager (and worked with her previous three predecessors).

    Of 3,500 electric utilities that were solicited by the EPA, only about 1500 had enough SF6 in their systems to qualify to register. Of those, only about 85 signed up. However, those 85 represent about 60% of the total electric utility SF6 use. So, the program has been relatively successful. Electric parters who join must submit annual SF6 emission reports, and provide a written policy that they will implement to reduce their current rates.

    The idea is that utilities policing themselves – and to a certain extent, that has been working well. Unlike years past, it is very rare for me to meet with substation crew where anyone even hints at intentionally letting gas go.

    We have been receiving calls from government contract research firms asking very specific questions relating to emissions trading credit. This means the government is showing interest in beginning mandatory regulations on SF6 use. Given the global outcry against the gas, this administration has had little choice but to accept the science. I wish I could reveal a bit more about how our military is using the gas… However, I can tell you that in the nearly two decades I’ve worked with SF6, the Department of Defense has only cared about SF6 availability. There was NO consideration given to the environmental impact. Just this year (this week, actually) they initiated a $1.5M project to reduce emissions on their AWACs aircraft. I can assure you, this would not have happened if the pressure weren’t real.

    Again, I commend you and your enthusiasm for brining science to life for so many young minds. It is really encouraging. I just wanted to shed some light on the darker side of the gas. It is the single most potent greenhouse gas known to man.

  12. Joe
    Joe says:

    Steve and/or any others willing to help me,
    i have to do a chemistry project for my advanced chemistry class, and i am looking at using sulfur hexafluoride. but the problem is that this project is a semester long project, do you have any ideas on a type of experiment my partner and i could do?


  13. Steve Spangler
    Steve Spangler says:

    It’s important to breath fresh air (big, deep breaths) after doing the demo to get oxygen back into your lungs. Again, only someone who is properly trained should be doing this demo.

  14. Marcus
    Marcus says:

    Ever since I saw the clip from 9News, I’ve been wanted to get some SF6 for my classroom, and have been looking around regarding pricing, etc. Now that I’ve read more about the EPA regulations and the environmental dangers of SF6, I’ve finally decided that I’m much better off showing the clip to my students, rather than paying the monetary and environmental cost to demonstrate it in person. Besides, the 9News clip demonstrates both He and SF6, and uses male and female voices for comparison — it’s an ideal, detriment-free demonstration. Thanks, Steve!

  15. jason
    jason says:

    Is there any way to get the same desired effect, but less of it? I’m interested in applications for slightly raising the pitch of my voice, but not as drastically as with pure helium.

  16. Hunter
    Hunter says:

    I am considering doing a project like this for my school’s science fair. After showing my science teacher this video, along with the MSDS, I was given the OK to proceed. I would like to know how I would go about acquiring this gas in a small quantity.

    • Susan Wells
      Susan Wells says:

      This gas is not widely available for purchase. I suggest checking with your chemistry teacher on how to acquire it and make sure you have the proper adult supervision. The gas is not something to treat with extreme caution and should be left for the pros.

  17. Mitchell Dullnig
    Mitchell Dullnig says:

    Could someone please tell me if it is possible to contain SF6
    gas in a clear or visible location like aquarium etc for a long period of time in order to have a
    fairly permanent display of it floating something . I have put it
    in an aquarium with lid and silicone seal etc. but within a few
    hours it tends to escape. I have even tried mason jars with lids
    etc. Even tried an underwater seal- nothing seems to work more
    than a few hours. Thanks!! Max

  18. Greg V
    Greg V says:

    I wanted to re-create the “floating boat” experiment for a kid’s summer camp. Where do you purchase the Sulfur Hexaflouride and is it expensive? Love your stuff. Thanks


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