Bull****. Sorry, I try not to use crudities, but bull****. This has been debunked so many times. You can call the DOT, or go to the DOT hazmat website where they post letters of interpretation, and it will say over and over again that this is not so. The DOT is a conglomeration of many branches of the gov, and has many areas of jurisdiction, however their authority in many of these areas is quite limited. The DOT's authority over scuba tanks and other HP cylinders arises from their use as commercial packagings for Hazmat, not from the DOT's purview over road safety, and is handled by the PHMSA (Pipeline and Hazardous Material Safety Administration). And as far as the PHMSA is concerned, private transportation of HP cylinders is just none of their business. There's even a DOT document concerning the use of HP cylinders as fuel tanks in alternate fuel vehicles, that says that they do not have to be hydrotested as long as the fuel in them isn't being resold! Some other department of the DOT, like the Highway Safety folks could decide to ban or regulate private transport if they saw the need, but that would not be on the PHMSA's authority, because the PHMSA just doesn't have any.
Oh, and Pesky, the distinction between "intra" and "inter" state tranport was eliminated in 1997:
"49 CFR Parts 171 and 173
SUMMARY: On January 8, 1997, RSPA published a final rule which amended the Hazardous Materials Regulations (HMR) to expand the scope of the regulations to intrastate transportation of hazardous materials. The intended effect of the January 8, 1997 rule is to raise the level of
safety in the transportation of hazardous materials by applying a uniform system of safety regulations to all hazardous materials transported in commerce throughout the United States."
The change is also reflected in many recent letters of interpretation, etc, as in :
"As specified in § 171.1, the HMR govern the transportation of hazardous materials in intrastate, interstate and foreign commerce."
You can move the tanks anywhere in your back yard, but LEGALLY (LITERALLY) can't hit a public road. The same logic applies to your car. You can drive your car in your back yard without a registration, but NOT on the public road. That is, the federal doesn't care if you are exploded with the tank in your back yard or not, just NOT in the public property.