Can I Mail Backpacking Gas Canisters? YES! If ...

OK, first, I'm talking about domestic US Mail (USPS) in the contiguous 48 US states only.  This post does NOT apply to packages sent outside the United States.  This post does not apply to UPS, FedEx, or other private shippers.  I'm just talking about US Mail (USPS) within the contiguous 48 states – surface mail only.  No air mail.  No international mail.  No Alaska.  No Hawaii.  No overseas APO's or FPO's.

First, you generally can't send fuel in the US Mail, but there are exceptions.  The exceptions are for what is called "Otherwise Restricted Material – Domestic" (ORM-D), material in other words, that would otherwise be restricted but is NOT under certain conditions.  The conditions?  The conditions are laid out in USPS Publication 52.  See below for relevant sections.

NOTE:  If you refill your own canisters, check with the Postal Service before mailing.  I suspect that refilled canisters cannot be mailed.

Here's a summary:

• The canisters must contain butane mixes.  This is not a problem since that's what backpacking canisters contain.
• The volume of the canisters cannot be more than one liter (but multiple canisters may be included in one package).  This is not a problem because backpacking canisters are smaller than one liter in volume.  A 450 g canister is about 780 ml of fluid for example.
• Canisters have to be well packaged.  Use a good strong box and plenty of tape.
• You have to label the package "ORM-D, Consumer Commodity, Surface Only."
• Canisters have to be padded against shock.  In other words you can't just throw some canisters in a box and mail it.  You need to use bubble wrap, wadded up newspaper, artificial "peanuts", or other similar packing materials to absorb any shocks during shipping.

So, can you mail backpacking gas canisters? Yes – if you meet the conditions.

And of course, be up front with the USPS.  Tell them what you're doing, show them the relevant sections from Publication 52 (best printed from the USPS website, not my clips), and show them how you've labeled everything properly.  Some people have reported having problems with postal workers that simply won't believe that a flammable gas can be mailed – even after being shown the relevant portions of Publication 52. Your best bet then is to either ask to speak to a supervisor or to just take it to another post office.

HJ

From USPS Publication 52:

342.1 Definition

Hazard Class 2 consists of three divisions:

Division 2.1, Flammable Gases. A material that is a gas at 68° F (20° C) or less and 14.7 psi (101.3 kPa) of pressure. Flammable gases also include materials that have a boiling point of 68° F (20° C) or less at 14.7 psi (101.3 kPa) and that are ignitable at 14.7 psi (101.3 kPa) when in a mixture of 13 percent or less by volume with air or that have a flammable range at 14.7 psi (101.3 kPa) with air of at least 12 percent regardless of the lower limit. These conditions must be established in accordance with ASTM E681–85, Standard Test Method for Concentration Limits of Flammability of Chemicals, or other approved equivalent method. The flammability of aerosols must be determined using the tests specified in 49 CFR 173.306(i).

342.22 Mailable Gases

The following are examples of mailable gases: [emphasis added]

Butane. Butane (UN1011) and Receptacles, small (UN2037) with butane or butane mixtures are Division 2.1 flammable gases. Butane gases that can qualify as ORM–D materials are acceptable only in domestic mail via surface transportation when properly prepared under 342.3 and Packaging Instruction 2A in Appendix C.

342.3 Packaging

b. Metal Containers. Mailable nonflammable and flammable compressed gases are acceptable in metal primary receptacles that have a water capacity up to 33.8 fluid ounces (1 liter or 61.0 cubic inches). The liquid content of the material and the gas must not completely fill the primary receptacle at 130° F (55° C). Additionally, the following apply:

1. A DOT 2P container must be used if the internal pressure is from 140 psig to 160 psig at 130° F (55° C).
2. A DOT 2Q container must be used if the pressure is from 161 psig to 180 psig at 130° F (55° C).
3. A container with an internal pressure over 180 psig at 130° F (55° C) is prohibited from mailing.
4. Packaging Instruction 2A or 2B, as applicable, must be followed.

c. Flammable Gases. A mailable flammable compressed gas is restricted to 4 fluid ounces in a nonmetal primary receptacle or 33.8 fluid ounces (1 liter) in a metal primary receptacle per mailpiece Packaging Instruction 2A must be followed.

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Notice that in section 342.3 that b.1 and b.2 call for either a US Department of Transportation (DOT) 2P or 2Q container.  How do I know if I have a 2P or 2Q container?  Well, that is what backpacking canisters are, but you'll need to be able to show that to the Post Office.  Printed somewhere on the canister, you should see something like this:

On the canister, look for the DOT permit number, typically DOT-SP followed by some numbers.
This canister has DOT special permit 9758.

You can look these numbers up on the US Department of Transportation website on the PHMSA Special Permit List.   In the case of DOT SP 9758, we find the following:
"This special permit authorizes the transportation in commerce of a Division 2.1 material in a non-refillable, non-DOT specification inside container conforming to the DOT Specification 2P except ... "
Basically this special permit is an extension of DOT 2P and therefore meets the requirements for mailability.  You should be able to just show the DOT permit on your phone (if they even ask), but be prepared to give them a hard copy print out.