- Brian Tyminski
As the cost of shipping hazardous materials becomes increasingly expensive, especially for compressed oxygen, we encourage customers to ship their oxygen bottles “empty” both to and from our facility. The cost savings can be substantial considering the cost of required containers (DOT31FP fire-rated boxes for shipments by air), compliance (DOT, IATA, ICAO training, etc.), and additional fees imposed by the carrier (who can blame them?).
The problem is that compressed gas cylinders, of any type, should never be truly empty. Ask your SCUBA-diving neighbor what he thinks about draining his tanks completely! Corrosion and contamination become an immediate issue anytime a cylinder is reduced to zero pressure.
So what’s the answer?
Leave 28 psi in the tank. That’s it!
I wish people just took my word for things, but the magic pressure to which the DOT subscribes comes to debate quite often, mostly from customers concerned of the legality of shipping a bottle with residual pressure.
So let me quote 49CFR Part 173.115 (Class 2, Divisions 2.1, 2.2, and 2.3 – Definitions):
(b) Division 2.2 (non-flammable, nonpoisonous compressed gas—including compressed gas, liquefied gas, pressurized cryogenic gas, compressed gas in solution, asphyxiant gas and oxidizing gas ). For the purpose of this subchapter, a non-flammable, nonpoisonous compressed gas (Division 2.2) means any material (or mixture) which—
(1) Exerts in the packaging a gauge pressure of 200 kPa (29.0 psig/43.8 psia) or greater at 20 °C (68 ° F), is a liquefied gas or is a cryogenic liquid, and
(2) Does not meet the definition of Division 2.1 or 2.3
Normally, a conversation after stating the above goes like this:
Woah, Brian, what’s the deal with psig vs. psia? In short, you can measure psig with a gauge, as it doesn’t include the atmospheric pressure which is included in psia. “PSI” as we know it is dumbed-down psig.
Ok fancy-pants, how do we know that the oxygen that we use on our airplane follows all of these other rules? According to the hazardous materials table in 49CFR 172.101 you are dealing with Oxygen, Compressed, UN 1072, class 2.2, sub-class 5.1. It is a non-flammable, oxidizing gas.
Well, I must have to put something on the box? Nope. With 28 PSI, the bottle doesn’t even meet the definition of a hazardous material! It is a good idea to put “empty cylinder,” or something to that effect on the outside of the box and on the cylinder itself in the case where the carrier decides to launch it off the door of a DC-10.
How do I know that there’s 28 PSI in the cylinder? 28 PSI can be stopped with your (clean) finger over the outlet. That’s probably a good place to start, but most gauges in the range you’re working with have the first little tick mark at 25 psi… perfect.
What about our fire bottles? We can’t help you on that one, as dumping Halon into the atmosphere is not only ridiculously illegal but quite expensive to replace. It’s ultimately cheaper to find someone who can ship haz-mat. Call us and we’ll get it worked out for you!
In short, the best way to save a boat-load of money on your oxygen bottles is to ship “empty” as defined by the DOT… that is, with 28 PSI left in the cylinder.