343 Flammable and Combustible Liquids
(Hazard Class 3)

343.1 Definition

The terms used in the standards that apply to Hazard Class 3 are defined as follows:

1. Flammable Liquid: A liquid that has a flashpoint of not more than 140° F (60° C), or any material in a liquid phase that has a flashpoint at or above 100° F (38° C).
2. Combustible Liquid: Any liquid that does not meet the definition of any other hazard class and has a flashpoint above 140° F (60° C) and below 200° F (93° C). A flammable liquid with a flashpoint at or above 100° F (38° C) that does not meet the definition of any other hazard class may be reclassified as a combustible liquid per 49 CFR § 173.120(b).

Note: A liquid with a flashpoint above 200° F (93° C) is not regulated as a hazardous material and may be mailed subject to the general packaging requirements in DMM 601, provided it possesses no characteristics of another hazard class.

343.2 Mailability and Packaging

343.21 Requirements for Flammable Liquids

The following conditions apply for mailing flammable liquids:

1. International Mail: Flammable liquids are prohibited.
2. Domestic Mail via Air Transportation: Flammable liquids are prohibited.
3. Domestic Mail via Surface Transportation: Flammable liquids with a flashpoint at or below 20° F (-7° C) are prohibited. Other flammable liquids may be mailed if they qualify as a Limited Quantity surface material and meet the criteria in Exhibit 343.21. Mailable flammable liquids must be prepared according to Packaging Instruction 3A in Appendix C.

 

Exhibit 343.21 

Flammable Liquids

Flashpoint	Mailability
20° F (–7° C) or below	Not acceptable for mailing.
Above 20° F (–7° C) but not more than 73° F (23° C)	Acceptable (with restrictions) for domestic mail via surface transportation only. Follow requirements for Packaging Instruction 3A in Appendix C, as applicable.
Above 73° F (23° C) but less than 100° F (38° C)	Acceptable (with restrictions) for domestic mail via surface transportation only. Follow requirements for Packaging Instruction 3A in Appendix C, as applicable.
100° F (38° C) and up to 140° F (60° C)	Acceptable (with restrictions) for domestic mail via surface transportation only. Follow requirements for Packaging Instruction 3A or 3B in Appendix C, as applicable. Note: If the flashpoint is between 100° F (38° C) and 140° F (60° C), the liquid may be eligible to be reclassed as a combustible liquid.
Over 140° F (60° C)	Refer to combustible liquids in 343.22. Follow requirements for Packaging Instruction 3B in Appendix C.

343.22 Requirements for Combustible Liquids

The following conditions apply for mailing combustible liquids:

1. International Mail: Combustible liquids are prohibited.
2. Domestic Mail via Air Transportation: Combustible liquids are mailable if they qualify as ID8000 materials (refer to 335) and meet the criteria in Exhibit 343.22. Packaging Instruction 3B in Appendix C must be followed.
3. Domestic Mail via Surface Transportation: Combustible liquids are mailable if they qualify as Limited Quantity and consumer commodity materials and meet the criteria in Exhibit 343.22. Packaging Instruction 3B in Appendix C must be followed.

 

Exhibit 343.22 

Combustible Liquids

Flashpoint	Mailability
Below 100° F (38° C)	Not a combustible liquid. Refer to flammable liquids in 343.21.
100° F (38° C) but not more than 140° F (60° C)	A flammable liquid that may be eligible to be reclassified as a combustible liquid under 49 CFR § 173.120(b). Refer to 343.1. Acceptable (with restrictions) in domestic mail via surface transportation only. Follow requirements for Packaging Instruction 3B in Appendix C as applicable.
Above 140° F (60° C) but not more than 200° F (93° C)	Acceptable (with restrictions) for domestic mail via air transportation or surface transportation. Follow requirements for Packaging Instruction 3B in Appendix C, as applicable.
Above 200° F (93° C)	The material is not regulated as a hazardous material. Such nonregulated materials must be properly and securely packaged to prevent leakage under the general packaging requirements in DMM 601.3.4.

343.23 Mailable Flammable and Combustible Liquids

The following flammable and combustible liquids are permitted for mailing under specified conditions:

1. Paint and Related Items (UN1263): A flammable or combustible liquid, which includes items such as lacquer, paint-thinning or paint-drying compounds, shellac, varnish, liquid aluminum, liquid bronze, liquid gold, liquid wood filler, and liquid lacquer base. They are mailable if they qualify as Limited Quantity surface material and meet the quantity limitations and packaging requirements stated in 343.21 or 343.22. Packaging Instruction 3A or 3B in Appendix C, as applicable, must be followed.

Note: Latex paint and water-based paint that are non-flammable and non-combustible are unrestricted and not regulated as a hazardous material. Package these mailpieces in accordance with DMM 601.

2. Canned Heat (Sterno): Considered a flammable liquid and typically has a flashpoint between 40° F (4° C) and 80° F (27° C). It is mailable if it qualifies as a Limited Quantity surface material and meets quantity limitations and packaging requirements stated in 343.21. Packaging Instruction 3A in Appendix C must be followed.
3. Lighter Fluid: Considered a flammable liquid and typically has a flashpoint between 20° F (-7° C) and 55° F (13° C). It is permitted only in domestic mail via surface transportation provided the fluid can qualify as a Limited Quantity surface material and is sent within the quantity limitations and packaging requirements stated in 343.21. Packaging Instruction 3A in Appendix C must be followed.
4. Diesel Fuel (NA1993): A combustible liquid with a typical flashpoint between 110° F (43° C) and 190° F (88° C) and is mailable if it qualifies as a Limited Quantity surface material and meets the conditions stated in 343.22. Packaging Instruction 3B in Appendix C must be followed.
5. Fuel Oil (NA1993): A flammable liquid with a typical flashpoint below 100° F (38° C) is mailable if it qualifies as a Limited Quantity surface material and meets the quantity limitations and packaging requirements stated in 343.21 “or” 343.22, as applicable. Packaging Instruction 3A or 3B in Appendix C must be followed.
6. Adhesives and Cements (UN1133): A flammable liquid with an approximate flashpoint of 73° F (23° C) is mailable only if it qualifies as a Limited Quantity surface material and meets the conditions in 343.21 or 343.22 as applicable. Packaging Instruction 3A or 3B in Appendix C, as applicable, must be followed.

Note: Adhesives and cements may be extremely toxic (Division 6.1). Division 6.1 materials are mailable only as permitted in 346.21.

7. Cleaning Agents and Solvents: A flammable liquid. It is mailable if it qualifies as Limited Quantity surface materials and meet the conditions in 343.21 as applicable. Packaging Instruction 3A in Appendix C must be followed.

Note: Certain cleaning agents and solvents may be extremely toxic (Division 6.1) or corrosive (Class 8). Division 6.1 toxic materials and Class 8 corrosives are mailable only within the conditions of 343.21 and 348.2, respectively.

8. Model Fuel (for Glow-Plug Engines): A flammable liquid with a flashpoint ranging from 65° F to 75° F. It is mailable only if it qualifies as a Limited Quantity surface material and meets the quantity limitations and packaging requirements stated in 343.21. Packaging Instruction 3A in Appendix C must be followed.
9. Waxes and Polishes: Considered flammable or combustible liquids with varying flashpoints. It is mailable if they qualify as Limited Quantity surface materials and meet the conditions stated in 343.21 and 343.22, as applicable. Packaging Instruction 3A or 3B in Appendix C, as applicable, must be followed.
10. Inks: Classified as flammable or combustible liquids. Defined as colored liquids used for writing, drawing, and printing, and often composed of pigments such as carbon black suspended in a drying oil. They are mailable if they qualify as Limited Quantity surface material and meet requirements stated in 343.21 or 343.22, as applicable. Follow Packaging Instruction 3A or 3B in Appendix C, as applicable. Additional conditions include:
1. Primary receptacles containing inks must be cushioned with absorbent material sufficient to contain any leakage.
2. The primary receptacle(s) and the absorbent cushioning must be enclosed in a sealed, leakproof outer packaging.
3. Flammable or combustible inks must adhere to the quantity restrictions, packaging requirements, and transport conditions outlined in 343.2.

Note: Inks with no hazardous characteristics are not regulated as hazardous materials and are mailable if packaged in accordance with the standards in 451.3 and DMM 601.3.4.

343.24 Lighters

Lighters with ignition elements and containing liquid fuel are classified as a Class 3 flammable liquid; those containing flammable gas are Division 2.1. Mailing is permitted only for domestic surface transportation only under the following conditions:

1. Certification: Lighter design must be certified by a DOT-approved lighter testing agency per 49 CFR § 173.21(i) and 173.308, with an issued Approval Number (LAA****).
2. Authorization: Mailers must submit a written request to mail lighters, to the PCSC director, accompanied by a legible copy of the official DOT approval notice described in 343.24a, along with a sample lighter within the proposed packaging. The request must also include the quantity of lighters being mailed and the post office location where the mailings will be entered. An approval letter must be obtained from the PCSC director prior to mailing.
3. Packaging: Packaging must secure the lighter‘s sparking mechanism against accidental ignition, and all preparation and packaging requirements in the PCSC director‘s approval letter must be met. Packaging Instruction 3C in Appendix C must be followed.
4. Labeling: The address side of the mailpiece must display the following:
1. Proper Shipping Name (Lighter(s) or Lighter Refill(s))
2. Approval Number (LAA*****)
3. Surface Only or Surface Mail Only
5. Documentation: A legible copy of the PCSC director‘s approval letter must be presented at the time of the first mailing at each Postal Service facility. A shipping paper is not required.

343.25 Authorization to Mail Ethanol-Based Flammable Liquids or Solids

Flammable liquids or solids containing ethanol (ethyl alcohol) are mailable by domestic air only with prior written authorization.

Mailers must submit a request to the director, Product Classification (refer to 214 for contact information). The request must include product specifics (e.g., brand, container size and type), an SDS for each product, the post office of mailing, and expected frequency and quantity of mailings (e.g., four 6-ounce bottles per package). Initial approval is for 1 year, extendable (in 1- to 3-year increments) based on performance.

Conditions for approved mailings include:

1. Authorization: A copy of the authorization letter from the director, Product Classification, is required. Mailings not supported by an authorization letter will be refused.
2. Package Limits:
1. Packages containing ethanol-based products with no more than 70% ethanol by volume must not exceed 25 pounds. Primary receptacles must not exceed the following:
1. Non-glass: 16 ounces (liquid) or 1 pound (solid).
2. Glass: 8 ounces (liquid) or 1/2 pound (solid).

Note: Total volume per mailpiece must not exceed 96 ounces (liquid) or 16 pounds (solid).

2. For packages containing ethanol-based products exceeding 70% ethanol by volume must not exceed 16 pounds. Primary receptacles must not exceed the following 8 ounces (liquid) or ½ pound (solid).

Note: Total volume per mailpiece must not exceed 48 ounces (liquid) or 8 pounds (solid).

3. Entry and Labeling: Packages must be entered using either Priority Mail Express or Priority Mail and include the following information:
1. Sender name and return address.
2. "Contains Air-Eligible Ethyl Alcohol - Authorization Number XXXXX (number issued by the Postal Service at time of approval)" text in at least 14-point type.
4. Notice to Addressee: A written notice to the addressee must be included, advising against re-mailing the contents by air. The notice must be as follows:

"Flammable liquids or solids contained in these packages may be mailed only by consumers (the addressee) via surface transportation in accordance with Publication 52, 343. Full responsibility rests with the mailer to comply with all Postal Service and other statutes and regulations regarding mail. Information regarding postal statutes, regulations, and mailing requirements is available from your local postmaster or district manager, Business Mail Entry, and at the Postal Service‘s mailing standards website, Postal Explorer, at pe.usps.com."

5. Compliance: Warning and labeling requirements set forth in 21 CFR § 700, 701.3, and 740.1 must be met and quantity, packaging, and marking requirements in Packaging Instruction 3D in Appendix C must be followed.

343.3 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 flammable or combustible liquids must be marked as follows:

1. Air Transportation: Packages containing mailable Class 3 materials must display the DOT diamond-shaped 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 325.4b). 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 mailable Class 3 materials must be plainly and durably marked on the address side with an approved DOT Limited Quantity surface marking (refer to Exhibit 325.5). The Limited Quantity ground 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 3 materials.
3. Marking Specifications: Markings must be durable, legible, and readily visible, applied to at least one side or end of the outer packaging. 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.
4. Lighters: Lighters containing flammable liquids or gases must be marked as specified in 343.24.
5. Ethanol-based Flammables: Ethanol-based flammable liquids or solids must be marked as specified in 343.25 and, Packing Instruction 3D in Appendix C.

343.31 Nonmailable Flammable and Combustible Liquids

When flammable liquids and combustible liquids that are nonmailable under 343.21 or 343.22 are found in the mailstream, the procedures in POM 139.117 must be followed if the materials present an immediate threat to persons or property.

The following materials are nonmailable:

1. All flammable liquids having a flashpoint of 20° F (-7° C) or below are prohibited from mailing.
2. Gasoline (UN1203) is a flammable liquid that normally has a flashpoint of -50° F. Gasoline is nonmailable under any circumstances.
3. Acetone (UN1090) normally has a flashpoint of 0° F, Benzene (UN1114) normally has a flashpoint of 12° F, and Hexane(s) (UN1208) normally have flashpoints in the vicinity of -15° F. All are nonmailable unless diluted with less flammable or nonflammable materials sufficient to raise the flashpoint to 20° F or higher.