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Publication 52 - Hazardous, Restricted, and Perishable Mail > 3 Hazardous Materials > 34 Mailability by Hazard Class > 342 Gases (Hazard Class 2)

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342 Gases (Hazard Class 2)

342.1 Definition

Hazard Class 2 consists of three divisions:

  1. 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).
  2. Division 2.2, Nonflammable, Nontoxic Gases. A material that does not meet the definition of Division 2.1 or 2.3 and exerts in its packaging an absolute pressure of 40.6 psia (280 kPa) or greater at 68° F (20° C).
  3. Division 2.3, Toxic Gases. A material that is poisonous by inhalation and is a gas at 68° F (20° C) or less and a pressure of 14.7 psi (101.3 kPa), or a material that has a boiling point of 68° F (20° C) or less at 14.7 psi (101.3 kPa).

342.2 Mailability

342.21 General

The following conditions apply to the mailing of gases:

  1. International Mail. All gases are prohibited.
  2. Domestic Mail via Air Transportation. Flammable gases in Division 2.1 and toxic gases in Division 2.3 are prohibited. Nonflammable gases in Division 2.2 are generally permitted if the material can qualify as a ID8000 material (see 335) and meet the quantity limitations and packaging requirements in 342.3 and 342.4.
  3. Domestic Mail via Surface Transportation. Toxic gases in Division 2.3 are prohibited. Flammable gases in Division 2.1 and nonflammable gases in Division 2.2 are generally permitted if the material can qualify as a Limited Quantity surface material and meet the quantity limitations and packaging requirements in 342.3 and 342.4.
342.22 Nonmailable Gases

When any gas that is nonmailable is discovered in the mailstream, the procedures in POM 139.117 must be followed if the materials present an immediate threat to persons or property. The procedures in POM 139.118 are followed when there is no immediate threat to persons or property.

The following are some specific types of nonmailable gases:

  1. Cigarette Lighters (NA1057). Generally, lighters charged with fuel and having an ignition system or any similar heating, lighting, or ignition device are a Class 3 flammable liquid and are nonmailable. However, if an approval number is obtained from DOT, consideration for mailing may be requested from the director, PCSC, under the provisions in 343.25.
  2. Oxygen, Refrigerated Liquid. Liquid oxygen (UN1073) is prohibited from mailing under any circumstances.
  3. Fire Extinguishers. Fire extinguishers (UN0275, UN0276, UN0323, or UN0381) that contain propellant explosives are prohibited from mailing.

    4. Note: See 342.23 for mailable types of fire extinguishers.

  4. Toxic Gases. All Division 2.3 toxic gases are prohibited from mailing.
342.23 Mailable Gases

The following are examples of mailable gases:

  1. Butane. Butane (UN1011) and Receptacles, small (UN2037) with butane or butane mixtures are Division 2.1 flammable gases. Butane gases that qualify as a Limited Quantity surface material are acceptable only in domestic mail via surface transportation when properly prepared under 342.3 and Packaging Instruction 2A in Appendix C.
  2. Oxygen, Compressed. Oxygen (UN1072) is a Division 2.2 nonflammable gas and is acceptable in domestic mail only if it can qualify as a Limited Quantity material. The requirements in 342.3 and Packaging Instruction 2B in Appendix C must be followed.
  3. Propane. Propane is a Division 2.1 flammable gas and is acceptable in domestic mail via surface transportation only if it can qualify as a Limited Quantity ground material. The requirements in 342.3 and Packaging Instruction 2A in Appendix C must be followed. Propane is nonmailable in domestic mail via air transportation.
  4. Fire Extinguishers. Extinguishers that contain a Division 2.2 nonflammable compressed gas and are assigned UN1044 are mailable if they do not contain methyl bromide gas mixtures and the contents are held in DOT specification 2P or 2Q containers. Only one extinguisher per mailpiece is permitted, and the compressed gas contained within the fire extinguisher must be nonflammable, nonpoisonous, or noncorrosive as required under 49 CFR 173.309(a). The requirements in Packaging Instruction 2B in Appendix C must be followed.

    5. Note: Fire extinguishers assigned UN1774 are mailable as Class 8 corrosives subject to the limitations for corrosives in 348.

  5. Empty Compressed Gas Containers. Empty used containers of compressed gas are mailable subject to the same restrictions that applied when the container was filled (because residual amounts of the hazardous material might remain present). Empty, unused (i.e., new) containers are mailable without restriction.
  6. Aerosol Paint Products. Aerosol paint products that are defined as flammable compressed gases are acceptable in the domestic mail via surface transportation only if they can qualify as a Limited Quantity ground material and meet the quantity limitations and applicable packaging requirements in 342.3 and 342.4.
  7. Other Mailable Gases. Materials whose contents are under pressure, such as carbonated beverages, biological/medical products, cosmetics, foodstuffs and soaps, electronic tubes, and audible fire alarm systems (except for any that may contain poisonous gases or others that may be specifically excluded by 49 CFR 173.306), are acceptable in the domestic mail as follows:
    1. Carbonated Beverages. These items are not regulated as hazardous materials and are acceptable without restriction. Carbonated beverages must be properly packaged under DMM 601.1-7.
    2. Biological Products or Medical Preparations. A product or preparation in a nonrefillable metal primary receptacle charged with a nonflammable solution (containing a biological product or a medical preparation that heat could deteriorate) may be accepted for domestic surface mail only, provided the conditions in Packaging Instruction 2F in Appendix C are followed.
    3. Foodstuffs and Soaps. These materials are mailable provided the conditions in Packaging Instruction 2D in Appendix C are met.
    4. Electronic Tubes. These materials are mailable without restriction if the volume is 30 cubic inches or less and the tube is charged with gas to a pressure of 35 psig or less. Such tubes must be packed in a strong outer container and meet the general packaging requirements in DMM 601.1-7.
    5. Audible Fire Alarm Systems. An audible fire alarm system powered by a compressed gas is acceptable in the domestic mail via surface transportation provided the conditions in Packaging Instruction 2E in Appendix C are followed.

342.3 Packaging

Mailable compressed gases must be packaged to protect valves and fittings and to ensure integrity of the primary receptacle during transport. Containers must use recessed valves, screw thread caps, tap closures, or other means to prevent accidental discharge.

The following conditions apply:

  1. Nonmetal Containers. A mailable gas is acceptable in an other–than–metal primary receptacle if the water capacity is 4 fluid ounces (7.22 cubic inches) or less. Packaging Instruction 2A or 2B, as applicable, must be followed.
  2. 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. Packaging Instruction 2A or 2B, as applicable, must be followed.
  3. A container with an internal pressure over 180 psig at 130° F (55° C) is prohibited from mailing.
  4. 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.
  5. Nonflammable Gases. A mailable nonflammable gas is permitted in individual 4 fluid ounce nonmetal primary receptacles or 33.8 fluid ounce (1 liter) metal primary receptacles. Multiple primary receptacles may be securely packed within a single, strong outer packaging. Each mailpiece must not exceed a total weight of 25 pounds. Packaging Instruction 2B must be followed.

342.4 Marking and Documentation

All labels and text markings must be placed on the address side of the mailpiece unless specified in 221.1 and 325.1. Parcels containing mailable gases must be marked as follows:

  1. For air transportation, parcels must bear the DOT square-on-point marking. The top and bottom portions of the square-on-point and the border forming the square-on-point must be black, and the center must be white or of a suitable contrasting background. The symbol “Y” must be black, located in the center of the square-on-point, and clearly visible. Mailpieces must also be marked with the proper shipping name “Consumer Commodity” and identification number “ID8000.” Each mailpiece must also bear an approved DOT Class 9 hazardous material warning label (see Exhibit 325.3b). A properly completed shipper’s declaration for dangerous goods prepared in triplicate must be affixed to the outside of the mailpiece.
  2. For surface transportation, parcels must be plainly and durably marked on the address side with an approved DOT Limited Quantity marking (see 325.4). Surface shipments bearing the Limited Quantity ground marking are not required to include the proper shipping name and identification number. A shipper’s declaration for dangerous goods is not required for mailable gases sent via surface transportation.
  3. Markings must be durable, legible, and readily visible, and must be applied on at least one side or one end of the outer packaging. The border forming the square-on-point must be at least 2 mm in width, and the minimum dimension of each side must be 100 mm, unless the package size requires a reduced size marking of no less than 50 mm on each side.

342.5 Mailability Rulings

In addition to the information required in 215.2 and 324, requests for mailability rulings on gases and products containing compressed gases need to include the following information:

  1. Documentation indicating whether or not the contents are a flammable mixture when dispersed.
  2. The internal pressure within the primary receptacle at 70° F (21° C) and 130° F (55° C).
  3. Documentation as to whether or not the liquid contents completely fill the container at 70° F (21° C) and 130° F (55° C).
  4. The bursting strength of the primary receptacle.
  5. The capacity of the primary receptacle and the number of primary receptacles proposed to be packed within a single mailpiece.
  6. The design methods intended to prevent accidental discharge of the contents.



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