Gas vapor is not to be trifled with. The amateur linguist Benjamin Lee Whorf famously used this as an example of the principle later named the Sapir-Whorf hypothesis, ie., the idea that language itself shapes the way we perceive the world as opposed to just passively describing it. He noted that in his day job as a fire inspector, he observed that people were often careful around "full" gas barrels but fatally careless around "empties". He thought that this was because in English, "empty" often means entirely devoid of content, but can also mean, as here, merely empty of its usual contents. If it weren't for the customry "empty/full" metaphor, it would never occur to anyone to think of a gas barrel as ever being empty and thus safe to smoke around. No such contruction exists in Dineh Bizaad, for instance, You would say "the barrel containing air", or if you knew something about petroleum barrels, "the barrel containing vapor".
