Sulfur Hexafluoride: The Gas That Lowers Your Voice

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Plus, how gases affect your voice & how to enjoy them safely
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You’ve probably inhaled a birthday balloon full of helium before and giggled at how squeaky and high-pitched your voice gets (we’ve all done it!). But, did you know there’s another gas that can lower your voice? Introducing sulfur hexafluoride (SF6)! (It may not roll off the tongue as easily as helium, but it’s definitely just as entertaining.) Read on to learn more about this heavy gas that makes you sound like a supervillain, including the science of how it deepens your voice and just how safe it is to use.

Lowering Your Voice with Gas

Inhale a deep breath of sulfur hexafluoride (SF6) to lower your voice. SF6 is non-toxic and 5 times heavier than air. Since it’s heavier, sound waves from your voice travel more slowly through it, making your voice sound deeper. It’s the opposite effect from helium, which is lighter than air and raises your voice.

Section 1 of 5:

Is there a gas that makes your voice deeper?

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  1. Sulfur hexafluoride is a gas that’s about 5 times heavier than air, which means sound waves travel more slowly through it than they would through normal air. When you inhale it, your voice has to travel through this heavy gas, making it sound much deeper than normal (kind of like you’re talking in slow motion, except at a normal pace). [1]
    • The voice-changing effect of SF6 is not permanent and your voice will return to normal after a few minutes (or sooner if you exhale it all intentionally).
    • Don’t believe us? Watch this video demonstration of SF6 from MythBusters —it really works!
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Section 2 of 5:

How Gases Change Your Voice

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  1. To make vocal sounds, air travels from your lungs, up your throat, through your mouth, and then out into the room. The moving air makes your vocal cords vibrate, creating sound waves that radiate through your whole airway and mouth to produce the sound of your voice. When a new gas is introduced to your lungs, the density of the air changes and affects how quickly these sound waves move: [2]
    • Since SF6 is heavier than air, sound waves move more slowly through it. As the waves slow down and get stretched longer, listeners hear a deeper pitch than your normal voice (even though you’re producing sound within the same fixed pitch range you always do).
    • The opposite is true for helium . Because it’s about 7 times lighter than air, sound waves travel through it much more quickly when you inhale it , resulting in a higher perceived pitch.
    • The other factors that affect the pitch and sound of your voice (like the length and thickness of your vocal cords or the shape of your mouth cavity, etc.) are not affected by gases.
    • Fun fact: Nearly all of the pitches produced by the human voice fall between 200 and 8,000 Hz (meaning the sound waves vibrate 200 to 8,000 times per second).
Section 3 of 5:

Is sulfur hexafluoride safe to inhale?

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  1. Sulfur hexafluoride has few potential side effects in gas form, assuming you’re only inhaling it every once in a while for a demonstration or party trick. [3] This isn’t totally risk-free, though; since SF6 is a heavy gas, it can sit in your lungs and reduce how much air and oxygen you’re able to breathe in. If you inhale a very large amount of it without exhaling or talking it out, it may lead to asphyxiation. [4]
    • To avoid asphyxia and lightheadedness: Take several deep breaths and exhale fully after each one. This will move the SF6 out of your lungs, making room for normal air. It will also bring your voice back to normal more quickly than letting the SF6 filter out on its own.
    • While SF6 is harmless in small doses, a highly concentrated dose or frequent repeated exposure can have negative side effects including: [5]
      • Nose and throat irritation
      • Lung irritation, coughing, or shortness of breath
      • Headaches, confusion, dizziness, or fainting
    • The risk of accidental exposure to SF6 is incredibly low for the general public. The EPA hasn’t assigned the gas any health risk values, but does acknowledge its danger as a heavy greenhouse gas. [6]
  2. Since it's non-toxic, SF6 won't damage your lungs or airway, and as long as you're just taking one inhale of it, the chances of negative side effects or asphyxiation are very low (just make sure to exhale the gas after a few sentences to clear your lungs). [7] Often, SF6 is demonstrated by scientists or science communicators as a fun way to learn about sound waves, gas density, and other physics and chemistry concepts. If you have the chance to try inhaling it in a supervised scenario like this, go for it!
    • A professional SF6 demo will have pure and non-toxic SF6 to use, guidance on how much to inhale, and access to medical help in case of an emergency.
    • The main safety issue with SF6 is inhaling too much of the gas in a short period. A guided demo will ensure you inhale an appropriate dose.
    • We don’t recommend trying this yourself at home. The fun of changing your voice could lead to over-inhalation, and while the chances are low that you’ll injure yourself, it’s best not to risk it.
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Section 4 of 5:

Where can you get sulfur hexafluoride?

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  1. SF6 isn’t as easy or cheap to find as a helium balloon. It’s an industrial gas, so you’ll have to order it directly from a medical, welding, or industrial gas supplier like Norco or Airgas USA . You may also be able to call a local gas provider and see if they can order SF6 for you. [8]
    • Unfortunately, SF6 is expensive once you can find some. It’s not as common as other industrial gases, and prices can fluctuate between locations and times of year. A 40-pound (18 kg) cylinder may cost around $550 USD.
    • Unlike helium, SF6 is not naturally occurring and must be synthetically produced.
    • Warning: To ensure you’re getting pure SF6, only order from reputable gas suppliers. A cheaper dose from a less regulated supplier could contain trace amounts of other gases or substances and be potentially dangerous.
Section 5 of 5:

More About Sulfur Hexafluoride

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  1. The sulfur atom sits at the center of the molecule, surrounded by fluorine. The Greek prefix hexa- means 6 and is where the name “sulfur hexafluoride” comes from. [9]
    • There are several types of sulfur-fluorine compounds, all with different numbers of fluorine atoms. For example, sulfur tetrafluoride (SF4) only has 4 fluorine atoms (and is considerably more lethal than SF6!).
  2. In science talk, inert means that the gas doesn’t chemically react with other substances in normal conditions (AKA, you don’t have to worry about it dangerously reacting with something nearby on accident). [10] It’s also colorless and odorless, so it appears very much like normal air (minus the fact that it’s about 5 times heavier than air).
    • SF6 is not the only heavy, inert gas that could change your voice, but it is the safest and most practical. For example, Xenon (one of the noble gases) is non-toxic, heavy, and inert, but is incredibly rare and expensive. Nitrous oxide (laughing gas) could also work, but you may be distracted by its loopy side effects (it’s also not totally inert and can become reactive at high temperatures). [11]
  3. Because SF6 is so stable and unreactive, it can accumulate and stay in the atmosphere for hundreds or even thousands of years, trapping Earth’s heat and contributing to global warming. It’s even worse than the most common culprit, carbon dioxide (CO2). Over a 100-year span, SF6 is 23,500 times more effective at trapping heat compared to an equivalent amount of CO2. [12]
    • Thankfully, SF6 is not produced in very high quantities. However, because of its potency, even a small release into the atmosphere can have long-reaching effects.
  4. SF6 has strong dielectric properties, meaning it can transmit electrical force without actually conducting electricity. Since the 50s, the electric power industry has used it to insulate circuit breakers, gas-insulated substations, and other switchgear used in transmission systems to safely manage very high voltages. Basically, it keep electric current from “arcing” or traveling between 2 charged points via the air. [13]
    • You can see a demonstration of this property in this video . When a taser is lowered into a tank of SF6 gas, the electric connection between the 2 prongs is extinguished.
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      Warnings

      • Do not take more than 1 breath of sulfur hexafluoride or helium to avoid asphyxiation risks. Stop immediately if you feel lightheaded or dizzy. Helium will float out of your lungs eventually because it’s lighter than air, but heavy SF6 may stay in your lungs and cause complications. [14]
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      References

      1. ↑ https://www.bealsscience.com/post/2017/10/27/sulfur-hexafluoride-gas-makes-you-sound-like-darth-vader
      2. ↑ https://www.scienceabc.com/eyeopeners/helium-makes-voice-squeaky-can-something-make-low-deep-sulphur-sulfur-hexafluoride.html
      3. ↑ https://www.denix.osd.mil/cmrmp/ecmr/sf6/thebasics/
      4. ↑ https://www.bealsscience.com/post/2017/10/27/sulfur-hexafluoride-gas-makes-you-sound-like-darth-vader
      5. ↑ https://www.nj.gov/health/eoh/rtkweb/documents/fs/1760.pdf
      6. ↑ https://www.denix.osd.mil/cmrmp/ecmr/sf6/thebasics/
      7. ↑ https://www.bealsscience.com/post/2017/10/27/sulfur-hexafluoride-gas-makes-you-sound-like-darth-vader
      8. ↑ https://www.bealsscience.com/post/2017/10/27/sulfur-hexafluoride-gas-makes-you-sound-like-darth-vader
      9. ↑ https://www.bealsscience.com/post/2017/10/27/sulfur-hexafluoride-gas-makes-you-sound-like-darth-vader
      1. ↑ https://www.epa.gov/system/files/documents/2022-05/sf6_byproducts.pdf
      2. ↑ https://www.scienceabc.com/eyeopeners/helium-makes-voice-squeaky-can-something-make-low-deep-sulphur-sulfur-hexafluoride.html
      3. ↑ https://www.epa.gov/eps-partnership/sulfur-hexafluoride-sf6-basics
      4. ↑ https://www.epa.gov/eps-partnership/sulfur-hexafluoride-sf6-basics
      5. ↑ https://www.scienceabc.com/eyeopeners/helium-makes-voice-squeaky-can-something-make-low-deep-sulphur-sulfur-hexafluoride.html

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