Enforcement of hazmat regulations when transporting cylinders

[TrimixToo]

Right, so the DOT rules are for transporting cylinders in commerce. In commerce is the key word and tricky phrase. 2Airishuman may carry 4500 lbs of cylinders in his van if they are for his and his friends use, but the minute he rents a cylinder out, or teaches a class with the cylinder, the case could be made that that cylinder is now in commerce, as someone is getting paid. The 1000# RQ is a placarding requirement, and doesn't apply if the tanks aren't transported in commerce. If you had to manifest and placard, the most likely hazard would be Compressed Gas, N.O.S. for any breathing gas.

That's what I'd always thought. But I'm not opposed to placarding if placarding will improve the safety of responders after an accident or in a fire.