I think people confuse OSHA regs with the DOT regs.
OHSA requires compressed gas cylinders to be transported, moved and stored vertically, but this applies only to construction sites:
29 CFR 1926.350(a)(9) Securing of Compressed Gas Cylinders
A. Purpose. This instruction emphasizes that the OSHA standard, 29 CFR 1926.350(a)(9), applies to transporting, moving and storing compressed gas cylinders at construction sites only.
The DOT regs apply only to interstate, intrastate and foreign commerce and the average diver going to and from home, dive shop and dive site is not engaged in commerce, as he/she is a customer transporting the gas for his/her own use, not for resale:
Sec. 171.1 Purpose and scope.
(a) This subchapter prescribes requirements of the Department of
Transportation governing--
(1) The offering of hazardous materials for transportation and
transportation of hazardous materials in interstate, intrastate, and
foreign commerce by rail car, aircraft, motor vehicle, and vessel
(except as delegated at Sec. 1.46(t) of this title), (except that until
October 1, 1998, this subchapter applies to intrastate carriers by motor
vehicle only in so far as this subchapter relates to hazardous waste,
hazardous substances, flammable cryogenic liquids in portable tanks and
cargo tanks, and marine pollutants).
Most importantly, the DOT regs do not prohibit the carriage of gas cylinders, other than DOT-4L liquid hydrogen cylinders, in a horizontal orientation as long as they are securly blocked and/or secured from moving:
Sec. 177.840 Class 2 (gases) materials.
(See also Sec. 177.834 (a) to (j).)
(a) Floors or platforms essentially flat. Cylinders containing Class
2 (gases) materials shall not be loaded onto any part of the floor or
platform of any motor vehicle which is not essentially flat; cylinders
containing Class 2 (gases) materials may be loaded onto any motor
vehicle not having a floor or platform only if such motor vehicle be
equipped with suitable racks having adequate means for securing such
cylinders in place therein. Nothing contained in this section shall be
so construed as to prohibit the loading of such cylinders on any motor
vehicle having a floor or platform and racks as hereinbefore described.
(1) Cylinders. To prevent their overturning, cylinders containing
Class 2 (gases) materials must be securely lashed in an upright position;
loaded into racks securely attached tothe motor vehicle; packed in boxes
or crates of such dimensions as to prevent their overturning; or loaded
in a horizontal position.
Specification DOT-4L cylinders must be loaded in an upright position and
securely braced.
(2) Cylinders for hydrogen, cryogenic liquid. A Specification DOT-4L
cylinder containing hydrogen, cryogenic liquid may only be transported
on a motor vehicle as follows:
(i) The vehicle must have an open body equipped with a suitable rack
or support having a means to hold the cylinder upright when subjected to
an acceleration of 2 ``g'' in any horizontal direction;
(ii) The combined total of the hydrogen venting rates, as marked, on
the cylinders transported on one motor vehicle may not exceed 60 SCF per
hour;
(iii) The vehicle may not enter a tunnel; and
(iv) Highway transportation is limited to private and contract
carriage and to direct movement from point of origin to destination.
(b) Portable tank containers containing Class 2 (gases) materials
shall be loaded on motor vehicles only as follows:
(1) Onto a flat floor or platform of a motor vehicle.
(2) Onto a suitable frame of a motor vehicle.
(3) In either such case, such containers shall be safely and
securely blocked or held down to prevent movement relative to each other
or to the supporting structure when in transit, particularly during
sudden starts and stops and changes of direction of the vehicle.
(4) Requirements of paragraphs (1) and (2) of this paragraph (b)
shall not be construed as prohibiting stacking of containers provided
the provisions of paragraph (3) of this paragraph (b) are fully complied
with.
States may have their own rules regarding transportation of gas cylinders but most regs I suspect mirror the federal regs to a great extent or defer to them completely. I'd alos bet that 90% of the time the average LEO has no clue what local ordinances may be regarding portable gas cylinders.
