 It is possible to safely <unk> dense gases such as xenon or sulfur hexafluoride when they are in a mixture of at least 20 % oxygen . Xenon at 80 % concentration along with 20 % oxygen rapidly produces the unconsciousness of general anesthesia ( and has been used for this , as discussed above ) . <unk> mixes gases of different densities very effectively and rapidly so that heavier gases are purged along with the oxygen , and do not accumulate at the bottom of the lungs . There is , however , a danger associated with any heavy gas in large quantities : it may sit <unk> in a container , and if a person enters a container filled with an <unk> , colorless gas , they may find themselves breathing it unknowingly . Xenon is rarely used in large enough quantities for this to be a concern , though the potential for danger exists any time a tank or container of xenon is kept in an <unk> space . 
