J Burns wrote, on Wed, 10 Sep 2014 21:36:21 -0400:

Several states say they aren't legal for storing gas. I
wonder why not.

Probably because they're not airtight?

I've read the spec, but it has been a while since, so, what I
remember is that it can lose almost nothing (in ounces) after
so many days at such and such a temperature outside.