USDOT HazMat Placards

Class 2 Compressed Gasses
49CFR 173.115


These page provide US DOT (U.S. Department of Transportation) definitions for class 2 compressed gasses. Title 49 of the United States Code of Federal Regulations (49CFR) also known as the Federal Motor Carriers Safty Regulations (FMCSR) requires the use hazardous materials placards when shipping hazardous materials cargo and dangerous goods in the United States. Canada, Mexico and many other countries have simular regulations that also require the use of these placards.

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Division 2.1 Flammable Gas

454 kg (1001 lbs) of any material which is a gas at 20°C (68°F) or less and 101.3 kPa (14.7 psi) of pressure (a material which has a boiling point of 20°C (68°F) or less at 101.3 kPa (14.7 psi)) which-

  1. Is ignitable at 101.3 kPa (14.7 psi) when in a mixture of 13 percent or less by volume with air; or
  2. Has a flammable range at 101.3 kPa (14.7 psi) with air of at least 12 percent regardless of the lower limit.

Except for aerosols, the limits specified in paragraphs (a)(1) and (a)(2) of this section shall be determined at 101.3 kPa (14.7 psi) of pressure and a temperature of 20°C (68°F) in accordance with ASTM E681-85, Standard Test Method for Concentration Limits of Flammability of Chemicals or other equivalent method approved by the Associate Administrator for Hazardous Materials Safety. The flammability of aerosols is determined by the tests specified in 49CFR 173.306(i).

Division 2.2 Non-flammable, Non-poisonus Gas

This division includes compressed gas, liquefied gas, pressurized cryogenic gas, compressed gas in solution, asphyxiant gas and oxidizing gas. A non-flammable, nonpoisonous compressed gas (Division 2.2) means any material (or mixture) which-

  1. Exerts in the packaging an absolute pressure of 280 kPa (40.6 psia) or greater at 20°C (68°F), and
  2. Does not meet the definition of Division 2.1 or 2.3.

Division 2.2 Oxygen

This is an optional placard to the 2.2 Non-flammable Gas placard for compressed Oxygen in either the gas or liquid state. Oxygen is considered a non-flammable because it in and of itself does not burn. It is, however, required for combustion to take place. High concentrations of oxygen greatly increases the rate and intensity of combustion.

2.3 Poison Gas

Gas poisonous by inhalation means a material which is a gas at 20°C or less and a pressure of 101.3 kPa (a material which has a boiling point of 20°C or less at 101.3kPa (14.7 psi)) and which:

  1. is known to be so toxic to humans as to pose a hazard to health during transportation, or
  2. in the absence f adequate data on human toxicity, is presumed to be toxic to humans because when tested on laboratory animals it has an LC50 value of not more than 5000 ml/m3. See 49CFR 173.116(a) for assignment of Hazard Zones A, B, C or D. LC50 values for values for mixtures may be determined using the formula in 49CFR 173.133(b)(1)(i)
Hazardous Materials Load & Segregation Chart
49CFR 177.848
 7  8 

49CFR 177.848(e)

'*' This indicates that segregation among different Class 1 materials is governed by the compatibility table in 49CFR 177.848(f)

'X' These materials may not be loaded, transported, or stored together in the same transport vehicle or storage facility during the course of transportation.

'O' Indicates that these materials may not be loaded, transported or stored together in the same transport vehicle or storage facility during the course of transportation, unless separated in a manner that, in the event of leakage from packages under conditions normally incident to transportation, commingling of hazardous materials would not occur.

'A' This note means that, notwithstanding the requirements of the letter 'X', ammonium nitrate fertilizer may be loaded or stored with Division 1.1 or Division 1.5 materials.

The absence of any hazard class or division or a blank space in the table indicates that no restrictions apply.

2.11001 lb XXXOX    XO      OO 
2.21001 lbBX   X    XO         
2.21001 lbBX   X    XO         
2.3Aany qty XXXOX X    XXXXXX  X
2.3Bany qty XXXOX O    OOOOOO  O

49CFR 173.115

  1. Non-liquefied compressed gas. A non-liquefied compressed gas means a gas, other than in solution, which in a packaging under the charged pressure is entirely gaseous at a temperature of 20°C (68°F).
  2. Liquefied compressed gas. A liquefied compressed gas means a gas which in a packaging under the charged pressure, is partially liquid at a temperature of 20°C (68°F).
  3. Compressed gas in solution. A compressed gas in solution is a non-liquefied compressed gas which is dissolved in a solvent.
  4. Cryogenic liquid. A cryogenic liquid means a refrigerated liquefied gas having a boiling point colder than -90°C (-130°F) at 101.3 kPa (14.7 psi) absolute. A material meeting this definition is subject to requirements of this subchapter without regard to whether it meets the definition of a non-flammable, non-poisonous compressed gas in paragraph (b) of this section.
  5. Flammable range. The term flammable range means the difference between the minimum and maximum volume percentages of the material in air that forms a flammable mixture.
  6. Service pressure. The term service pressure means the authorized pressure marking on the packaging. For example, for a cylinder marked "DOT 3A1800", the service pressure is 12410 kPa (1800 psi).
  7. Refrigerant gas or Dispersant gas. The terms Refrigerant gas or Dispersant gas apply to all non-poisonous refrigerant gases, dispersant gases (fluorocarbons) listed in 49CFR 172.101, 173.304(a)(2), 173.314(c), 173.315(a)(1) and 173.315(h), and mixtures thereof, or any other compressed gas having a vapor pressure not exceeding 1792 kPa (260 psi) at 54°C (130°F), and restricted for use as a refrigerant, dispersant or blowing agent.

Assignment of hazard zones
49CFR 173.116

  1. The hazard zone of a Class 2, Division 2.3 material is assigned in Column 7 of the 49CFR 172.101 Table. There are no hazard zones for Divisions 2.1 and 2.2. When the §172.101 Table provides more than one hazard zone for a Division 2.3 material, or indicates that the hazard zone be determined on the basis of the grouping criteria for Division 2.3, the hazard zone shall be determined by applying the following criteria:
    Inhalation toxicity
    ALC50 less than or equal to 200ppm.
    BLC50 greater than 200 ppm and less than or equal to 1000 ppm
    CLC50 greater than 1000 ppm and less than or equal to 3000 ppm
    DLC50 greater than 3000 ppm and less than or equal to 5000 ppm
  2. The criteria specified in paragraph (a) of this section are represented graphically in 49CFR 173.133, Figure 1 (below).


Last updated: Feb 2007

Related Resources

  • Guide for Handling Household Chemicals
    Things you can do to make your home safer.
  • USDOT Hazardous Materials Table 49 CFR 172.101
    An online version of the USDOT hazardous materials table from 49CFR 172.101. This table can be sorted by proper shipping name, UN/NA ID and/or by primary hazard class/division.
  • ERG (Emergency Response Guidebook)
    Have you ever wondered what those four digit numbers on the placards on the side of trucks and rail cars mean? Our online 2004ERG will give you your answer. This is an online version of the guidebook produced by the USDOT for first responders during the initial phase of a Dangerous goods/HazMat incident.
  • Chemical Database
    This database focuses on the most common chemical compounds used in the home and industry.

Copyright Notice

While excerpts from the Code of Federal Regulations Title 49 (49CFR) and the "Emergency Response Guidebook" are in the public domain, the image files on these pages, the design of these pages as well as all other materials on this site and graphics files are copyrighted by J.K. Barbalace, inc. Copyrighted material on this site, including graphics files, MAY NOT BE REPRODUCED in any form without the express permission.


WARNING: These pages are for general reference and educational purposes only and MUST NOT be relied upon as a sole source to determine regulatory compliance or where matters of life and health are concerned. This site and the author do not warrant or guarantee the accuracy or the sufficiency of the information provided and do not assume any responsibility for its use.

To ensure regulatory compliance when transporting hazardous materials or dangerous goods, one must receive proper training and certification from a qualified instructor and refer to the current year's Code of Federal Regulations Title 49 (49CFR) or your country's shipping regulations. In matters regarding workplace safety, refer to current OSHA regulations (29CFR) and NIOSH guidelines or your own country's health and safety regulations. No one should ever enter into a hazardous environment without proper training from qualified instructors.

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