I have had some conversation with DOT and they just will not give a clear answer.
They say a privately owned, filled and transported tank does not fall under DOT regulation in one breath and in the next breath say that a DOT spec cylinder that is not in hydro can not be filled or transported. So which is it, it appears they are hedging their bets.
It is typical government speak and is an artifact of previous administrations and a resulting conflict between the "hands off" don't tell states or other entities what to do" approach demanded by those administrations and existing regulations that were intended to tell states and agencies exactly what to do.
This is not strictly a DOT issues but appleis to several govenrment agencies. The result is a middle of the road fence sitting type of behavior where most guidance given is informal and done only in response to a direct written request or in the course of making a formal compliance finding. And in those cases, any letters of response or compliance findings that are drafted are written so as to narrowly apply to the precise situation so that they cannot be generalized to other similar situations and consequently be construed as formal guidance telling anyone what to do.
This gets real interesting when someone in the field cites someone for violating a regulation for which the guidance is unclear. Fair or not, in most cases the violation will still be viewed as the defendant's fault and at a minimum they are going to have to spend money lawyering up to defend themselves. To make it worse, enforcement tends to wax and wane with changes in administration or agency officials who ask for more or less based on politics or personal beliefs.
Sometimes it is simply something petty like a field inspector trying to make a name for himself (ie. Airshow pilot Bob Hoover losing his medical certificate and his livelihood and taking years to get it back because the FAA inspector who started it just wanted a high profile case to get recognized.)
In terms of the DOT, an individual inspector, regional office or the agency itself at one point in time or another, may take the approach that the hydro requirement applies to any tank that could
potentially be used in interstate commerce, since even the current owner/user/fill station has no way of knowing if the tank may be used in interstate commerce in the future.
Consequently, in the extreme if a shop fills a tank that is out of hydro an inspector could decide it is a violation as the tank is
capable of being used in interstate commerce and/or that the shop has no real way of knowing that the owner/user will not in fact use it in interstate commerce.
