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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

Hazardous gases, classified under Hazard Class 2, include flammable, nonflammable, and toxic gases. These materials are gases at standard temperature and pressure, and their classification depends on their flammability, toxicity, or ability to exert pressure. Specific regulations govern their mailability based on their division and mode of transportation.

342.11 Class 2 Divisions

Gases are categorized into three divisions:

  1. Division 2.1 - Flammable Gases
    1. A material that is a gas at 68° F (20° C) or less and 14.7 psi (101.3 kPa) of pressure.
    2. Includes materials with a boiling point of 68° F (20° C) or less at 14.7 psi (101.3 kPa) and either:
      1. Are ignitable at 14.7 psi (101.3 kPa) when in a mixture of 13 percent or less by volume with air; or
      2. Have a flammable range at 14.7 psi (101.3 kPa) with air of at least 12 percent regardless of the lower limit.

        3. Note: These conditions must be established in accordance with the American Society for Testing and Materials (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(a)(3)(v).

  2. Division 2.2 - Nonflammable, Nontoxic Gases
    1. Materials that do not meet the definitions for Division 2.1 or 2.3; and
    2. Exert 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
    1. 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
    2. 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 for mailing Hazard Class 2 items:

  1. International Mail: All gases are prohibited.
  2. Domestic Mail via Air Transportation:
    1. Division 2.1 (flammable gases) and Division 2.3 (toxic gases) are prohibited.
    2. Division 2.2 (nonflammable gases) are generally permitted if the material can qualify as an ID8000 material (refer to 335) and meet quantity limits and packaging requirements (refer to 342.3 and 342.4).
  3. Domestic Mail via Surface Transportation:
    1. Division 2.3 (toxic gases) are prohibited.
    2. Division 2.1 (flammable gases) and Division 2.2 (nonflammable gases) are generally permitted if the material can qualify as a Limited Quantity surface material and meet the quantity limits and packaging requirements (refer to 342.3 and 342.4).
342.22 Mailable Gases

Mailable gases may be sent via domestic mail under specific conditions, such as compliance with quantity limitations, packaging requirements, and applicable transportation methods (air or surface). Some examples of mailable gases include:

  1. Butane (UN1011): Division 2.1 flammable gases. Butane or butane mixtures are mailable via surface transportation as Limited Quantity materials, provided they comply with 342.3 and Packaging Instruction 2A in Appendix C.
  2. Oxygen, Compressed (UN1072): Division 2.2 nonflammable gas. Compressed oxygen is mailable if it qualifies as a Limited Quantity material, following 342.3 and Packaging Instruction 2B in Appendix C.
  3. Propane: Division 2.1 flammable gas. Propane is mailable via surface transportation as a Limited Quantity material only. Air transportation is prohibited. The requirements in 342.3 and Packaging Instruction 2A in Appendix C must be followed.
  4. Fire Extinguishers (UN1044): Division 2.2 nonflammable compressed gas. Fire extinguishers that contain nonflammable compressed gas are mailable if they do not contain methyl bromide gas mixtures, meet DOT container specifications, hold nonflammable, nonpoisonous, or noncorrosive gas, and comply with 49 CFR § 173.309(a) and the requirements in Packaging Instruction 2B in Appendix C. Only one extinguisher per mailpiece is permitted.

    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 are mailable under the same restrictions as when 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 with pressurized contents (except for any that may contain poisonous gases or others that may be specifically excluded by 49 CFR § 173.306) are mailable domestically as follows:
    1. Carbonated Beverages: These items are not regulated as hazardous materials and are mailable without restriction but must be properly packaged in accordance with DMM 601.
    2. Biological Products or Medical Preparations: Nonflammable solutions containing biological or medical products in nonrefillable metal containers preparation that heat could deteriorate may be accepted for domestic surface mail only, provided they comply with Packaging Instruction 2F in Appendix C.
    3. Foodstuffs and Soaps: These items are mailable if packaged in accordance with Packaging Instruction 2D in Appendix C.
    4. Electronic Tubes: These items are mailable without restriction if the volume does not exceed 30 cubic inches and the tube is charged with gas at 35 psig or less. Such tubes must be packed in strong outer containers and meet general packaging standards per DMM 601.
    5. Audible Fire Alarm Systems: These systems, if powered by compressed gas, are acceptable in domestic mail via surface transportation if they comply with conditions in Packaging Instruction 2E in Appendix C.

342.3 Packaging

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

The following conditions apply:

  1. Nonmetal Containers: Mailable gases in nonmetal primary receptacles are acceptable if the water capacity does not exceed 4 fluid ounces (7.22 cubic inches). 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 with a water capacity up to 33.8 fluid ounces (1 liter or 61.0 cubic inches). The contents must not completely fill the receptacle at 130° F (55° C). Additional requirements include:
    1. A DOT 2P container must be used for internal pressures between 140 psig and 160 psig at 130° F (55° C).
    2. A DOT 2Q container must be used for pressures between 161 psig and 180 psig at 130° F (55° C).
    3. Packaging Instruction 2A or 2B, as applicable, must be followed.
  3. Flammable Gases: Mailable flammable compressed gases are limited 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.
  4. Nonflammable Gases: Mailable nonflammable gases are permitted in individual nonmetal primary receptacles of 4 fluid ounces or metal primary receptacles of 33.8 fluid ounces (1 liter). Multiple primary receptacles are permitted as long as they are securely packed within a strong outer packaging, that does not exceed a total weight of 25 pounds. Packaging Instruction 2B must be followed.
  5. Prohibited Containers: Containers with internal pressures exceeding 180 psig at 130° F (55° C) are prohibited from mailing.

342.4 Marking and Documentation

Labels and text markings must appear on the address side of the mailpiece unless otherwise specified in 221.1 and 325.1. Packages containing mailable gases must be marked as follows:

  1. Air Transportation: Packages containing Class 2 materials must display the DOT diamond-shape marking, with a black top and bottom, a black border, and a white or contrasting background. A black symbol "Y" must be clearly visible at the center of the diamond-shape. Each mailpiece must also be marked with the proper shipping name ("Consumer Commodity") and identification number ("ID8000"), with an approved DOT Class 9 hazardous material warning label (refer to Exhibit 325.4(b)). A completed Shipper‘s Declaration for Dangerous Goods, prepared in triplicate, must be affixed to the outside of the mailpiece.
  2. Surface Transportation: Packages containing Class 2 materials must be plainly and durably marked on the address side with an approved DOT Limited Quantity surface marking (refer to 325.5). The Limited Quantity surface marking is sufficient for surface shipments; neither the proper shipping name nor the identification number is required. A shipping paper is also not required for surface shipments of mailable Class 2 materials.
  3. Marking Specifications: The diamond-shaped border must be at least 2 mm in width, with a minimum side dimension of 100 mm, unless the package size necessitates a reduced 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 must include the following information:

  1. Documentation indicating whether 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 verifying whether 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 per mailpiece.
  6. The design methods intended to prevent accidental discharge of the contents.
342.51 Nonmailable Gases

If a nonmailable gas is found in the mailstream, appropriate procedures must be followed based on the nature of the threat posed (refer to POM 139.117 or 139.118).

The following are examples of nonmailable gases:

  1. Cigarette Lighters (NA1057): Generally classified as Class 3 flammable liquid, lighters charged with fuel and having an ignition system (or similar heating, lighting, or ignition device) 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 (UN1073): (Also known as liquid oxygen) is prohibited from mailing under any circumstances.
  3. Fire Extinguishers (UN0275, UN0276, UN0323, or UN0381): Fire extinguishers that contain propellant explosives are prohibited from mailing. Refer to 342.22 for mailable types of fire extinguishers.
  4. Toxic Gases: All Division 2.3 toxic gases are prohibited from mailing.



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