Sulfur hexafluoride (SF6) is a colorless, odorless, inorganic, non-flammable gas. SF6 is also an excellent electrical insulator. Sulfur hexafluoride is about six times heavier than the air we breathe.
The density of sulfur hexafluoride affects the resonance frequencies of the vocal tract, thus changing the vocal sound qualities of those who inhale it.
When sulfur hexafluorid (SF6) is inhaled, the pitch of a human's voice decreases dramatically because the speed of sound in sulfur hexafluorid is considerably less than it is in air. Sound travels through air at about 340 m/s , through helium at about 900 m/s and through sulfur hexafluorid at only about 120 m/s.
Sulfur Hexafluoride - Deep Voice Gas
Credits: SpanglerScienceTV
Sulfur hexafluoride (SF6) is used to provide a retinal tamponade in vitrectomy procedures.
Vitrectomy using Sulfur Hexafluoride
Credits: Steven Cohen