Mythbuster Adam Savage having fun with Gas!
Physiological effects and precautions
Another effect is the gas's ability to alter vocal sound waves. The gas can be inhaled in a small, safe amount and cause the breather's voice to sound very deep. This, too, is due to the gas density. Unlike helium, which is much less dense than air, SF6 is approximately 5 times more dense than air, and the velocity of sound through the gas is 0.44 times the speed of sound in air. Unlike a gas such as helium, the speed of sound in which is greater than the speed of sound in air, the result of inhaling SF6 is the opposite of inhaling helium, a lowering of the frequency of the formants of the vocal tract.
This was demonstrated (Sept. 3, 2008) on the Mythbusters television program (along with an inhalation of helium, to show higher pitched sound).
Although inhaling SF6 can be a novel amusement, the practice can be dangerous because, like other inert gases, it displaces not only the oxygen needed for life, but also the CO2 that is the primary trigger of the breathing reflex. In general, dense, odourless gases in confined areas present the hazard of suffocation. 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.