question about shipping tanks

I don't work for any of the shipping companies including the USPS but I have shipped and received many scuba tank in the past through the most common shippers. Tanks are always shipped with the valves removed. When I inquired as to why, I was always told the same thing. It is against the law to send a pressurized DOT vessel via shipping companies. Makes sense that it would be but I have never looked up the law to verify. From a common sense point of view, why would you want to put yourself in jeopardy of being sued or imprisoned for damages should the tank be damaged in handling and cause an accident? I think I will keep removing the valves before I send a DOT thru the mail. Just my 2 cents.

On second thought I would think there would be some type of declaration and special shipping arrangements that could be made for high pressure vessels that are under pressure. I would think the shipper would have to pay a little extra for this sort of service.

https://www.law.cornell.edu/cfr/text/49/173.301

The link is to a Legal Information Institute 49 CFR 173.301 which is the general requirements for shipment of compressed gasses in cylinders (paraphrased for brevity)

I also found a link to a website that touches on how this shipper would possbily handle a declaration of shipment of pressurized gasses:
(basically requires special handling, some shipper require pressurized vessels be stored in explosion proof containers, etc.)
http://www.ercweb.com/resources/viewreg.aspx?id=8075
 
Thanks. I'm not to PCP yet, and have to travel an hr each way to get a tank filled. So when I get the tank we'll make a day of it, stopping my wife off to some craft stores, and to lunch. I'm certainly not versed in this at all and appreciate the info. I bought a used tank a couple days ago, and just thought if possible it would be nice to start off full. All this make sense to me. Thank you again. Brian Smith