It is possible to safely breathe 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 produce the unconsciousness of general anesthesia ( and have been used for this , as discussed above ) . Breathing mix 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 invisibly in a container , and if a person enter a container filled with an odorless , 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 exist any time a tank or container of xenon is kept in an unventilated space .