The DOT has very long arms and many sub-divisions. It wouldn't surprise me if they had their hands in the scuba industry.
However by DOT definitions, commerce applies to transit in vehicles. So, if you put a compressed air bottle in a vehicle, and drive it around it is involved in commerce. Quote
Definition= Commerce is a division of trade or production which deals with the exchange of goods and services from producer to final consumer. It comprises the trading of something of economic value such as goods, services, information or money between two or more entities.
So driving a tank around in my car does not meet the definition of commerce.