As a safety and hazardous materials consultant, trainer, and a scuba diver, I am amazed how many people transport scuba tanks in their cars, vans and trucks illegally.  Scuba tanks or as the US DOT (Department of Transportation) classifies them PRESSURE CYLINDERS are regulated by the DOTs Pipeline and Hazardous Materials Safety Administration.  In small quantities the tanks should be secured from moving and protected in case of an accident. Have you ever see a tank move after the value has been damaged?  3000psi can give the tank the force of a torpedo.

Be aware that in accordance with 49 CFR (Code of Federal Regulations), parts 100-185, ANYONE Loading, Unloading pressure cylinders MUST have hazmat training every 3 years, unless you are moving small quantities, such as 2 or 3 tanks?  If you transport filled cylinders there are certain federal regulations you must follow, and if the load weights over 1000 pounds (about 20 tanks) you MUST placard your vehicle and have a hazmat driving license.  Additionally, pressure tanks must be certified to pass DOT regulations for hydrostatic testing and visual inspection  (49CFR part 178.605).  The DOT can fine each violation up to $50,000.  Dive shop owners and instructors should be aware of these regulations and how it affects them.