View source for HAZMAT Class 2 Gases

The '''HAZMAT Class 2''' in [[United States]] law includes all gases which are compressed and stored for transportation.  Class 2 has three divisions: [[Flammable]] (also called ''combustible''), Non-Flammable/Non-Poisonous, and Poisonous. This classification is based on the United Nations' Recommendations on the Transport of Dangerous Goods - Model Regulations. In Canada, the ''Transportation of Dangerous Goods Regulations'', or TDGR, are also based on the UN Model Regulations and contain the same three divisions.

==Divisions==
[[File:Propane Rail Tanker - post-fire.jpg|thumbnail|right|A [[propane]] tank car after a fire, the HAZMAT 1075 symbol can be seen in red as a warning of the danger posed by the gas.]]

A [[gas]] is a substance which
#(a) at 50&nbsp;°C (122&nbsp;°F) has a [[Vapour pressure|vapor pressure]] greater than 300 kPa (43.51 PSI) or
#(b) is completely gaseous at 20&nbsp;°C (68&nbsp;°F) at a standard pressure of 101.3 kPa (14.69 PSI).

Gases are assigned to one of three divisions

#division 2.1 Flammable gas
#division 2.2 Non flammable, Non-toxic gas
#division 2.3 Toxic gas

[[Aerosol]]s also fall into Class 2 divisions where an aerosol is defined as an article consisting of any non-refillable receptacle containing a gas compressed, liquefied or dissolved under pressure, the sole purpose of which is to expel a nonpoisonous (other than a Division 6.1 Packing Group III material) liquid, paste, or powder and fitted with a self-closing release device allowing the contents to be ejected by the gas.

[[File:US Army container loading.jpg|thumbnail|right|Loading a container (with the hazmat Class 2 symbol on the rear doors) aboard a ship.]]
'''Division 2.1''': Flammable, Non-Toxic Gas

Flammable gas means any material that:
#Is ignitable at 101.3 kPa (14.7 psia) when in a mixture of 13% or less by volume with air; or
#Has a flammable range at 101.3 kPa with air of at least 12% regardless of the lower limit.
#Is determined to be flammable in accordance with ASTM E681-85, Standard Test Method for Concentration Limits of Flammability of Chemicals

The following applies to aerosols:
#An aerosol must be assigned to Division 2.1 if the contents include 85% by mass or more flammable components and the chemical [[heat of combustion]] is 30 kJ/g or more; 
#An aerosol must be assigned to Division 2.1 if it is deemed flammable in accordance with the appropriate tests of the UN Manual of Tests and Criteria for flammability.

'''Division 2.2''': Non-Flammable, Non-Toxic 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:

A non-flammable gas means any material that:
#Exerts in the packaging an absolute pressure of 280 kPa (40.6 psia) or greater at 20&nbsp;°C (68&nbsp;°F), and
#Does not meet the definition of Division 2.1 or 2.3.

The following applies to aerosols:
#An aerosol must be assigned to Division 2.2 if the contents contain 1% by mass or less flammable components and the heat of combustion is less than 20 kJ/g.

'''Division 2.3''': Toxic Gas

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

#Is known to be so toxic to humans as to pose a hazard to health during transportation, or
#In the absence of adequate data on human toxicity, is presumed to be toxic to humans because when tested on laboratory animals it has an LC<sub>50</sub> value of not more than 5000 ml/m<sup>3</sup>. See 49CFR 173.116(a) for assignment of Hazard Zones A, B, C or D. LC<sub>50</sub> values for mixtures may be determined using the formula in 49 CFR 173.133(b)(1)(i)

==Placards==

{| class=wikitable width=99% align=center
|-
| valign=top align=center width=33% | {{HAZMAT Cat 2-1}}
| valign=top align=center width=33% | {{HAZMAT Cat 2-2}}
|<!-- Deleted image removed:  [[File:2.3 toxic gas placard.png|120px|thumb|2.3 placard]] -->
|-
| valign=top align=center | {{HAZMAT Cat 2-2 Alternate}}
| valign=top align=center | {{HAZMAT Cat 2-3 Alternate}}
|-
|}

==Compatibility table==
{| width=99% align=center class=wikitable
|-
! colspan=23 | Load and Segregation Chart
|-
! rowspan=2 width=4% | &nbsp;
! colspan=2 rowspan=2 | Mass
| rowspan=2 style="text-align:center;background-color:orange;" width=4% | '''1.1'''
| rowspan=2 style="text-align:center;background-color:orange;" width=4% | '''1.2'''
| rowspan=2 style="text-align:center;background-color:orange;" width=4% | '''1.3'''
| rowspan=2 style="text-align:center;background-color:orange;" width=4% | '''1.4'''
| rowspan=2 style="text-align:center;background-color:orange;" width=4% | '''1.5'''
| rowspan=2 style="text-align:center;background-color:orange;" width=4% | '''1.6'''
| rowspan=2 style="text-align:center;background-color:red;color:white;" width=4% | '''2.1'''
| rowspan=2 style="text-align:center;background-color:green;color:white;" width=4% | '''2.2'''
| rowspan=2 style="text-align:center;background-color:yellow;" width=4% | '''2.2'''
| colspan=2 style="text-align:center;background-color:white;" width=8% | '''2.3'''
| rowspan=2 style="text-align:center;background-color:red;color:white;" width=4% | '''3'''
| rowspan=2 style="text-align:center;background-color:red;color:white;" width=4% | '''4.1'''
| rowspan=2 style="text-align:center;background-color:red;color:white;" width=4% | '''4.2'''
| rowspan=2 style="text-align:center;background-color:blue;color:white;" width=4% | '''4.3'''
| rowspan=2 style="text-align:center;background-color:yellow;" width=4% | '''5.1'''
| rowspan=2 style="text-align:center;background-color:yellow;" width=4% | '''5.2'''
| style="text-align:center;background-color:white;" width=4% | '''6.1'''
| rowspan=2 style="text-align:center;background-color:yellow;" width=4% | '''7'''
| rowspan=2 style="text-align:center;background-color:white;" width=4% | '''8'''
|-
| style="text-align:center;background-color:white;" width=4% | '''A'''
| style="text-align:center;background-color:white;" width=4% | '''B'''
| style="text-align:center;background-color:white;" | '''A'''
|-
| style="text-align:center;background-color:red;color:white;" | '''2.1'''
| colspan=2 style="text-align:center;background-color:red;color:white;" | '''{{convert|1001|lb|kg|abbr=on}}''' || {{na}} || {{na}} || {{na}} || style="text-align:center;" | '''O''' || {{na}} || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || {{na}} || style="text-align:center;" | '''O''' || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | '''O''' || style="text-align:center;" | '''O''' || style="text-align:center;" |  &nbsp;
|-
| style="text-align:center;background-color:green;color:white;" | '''2.2'''
| style="text-align:center;background-color:green;color:white;" | '''{{convert|1001|lb|kg|abbr=on}}''' || style="text-align:center;" width=4% | '''B''' || {{na}} || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || {{na}} || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || {{na}} || style="text-align:center;" | '''O''' || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" |  &nbsp;
|-
| style="text-align:center;background-color:yellow;" | '''2.2'''
| style="text-align:center;background-color:yellow;" | '''{{convert|1001|lb|kg|abbr=on}}''' || style="text-align:center;" width=4% | '''B''' || {{na}} || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || {{na}} || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || {{na}} || style="text-align:center;" | '''O''' || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" |  &nbsp;
|-
| style="text-align:center;background-color:white;" | '''2.3A'''
| colspan=2 style="text-align:center;background-color:white;" | '''Any quantity''' || {{na}} || {{na}} || {{na}} || style="text-align:center;" | '''O''' || {{na}} || style="text-align:center;" | &nbsp; || {{na}} || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || {{na}} || {{na}} || {{na}} || style="text-{{na}} || {{na}} || {{na}} || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || {{na}}
|-
| style="text-align:center;background-color:white;" | '''2.3B'''
| colspan=2 style="text-align:center;background-color:white;" | '''Any quantity''' || {{na}} || {{na}} || {{na}} || style="text-align:center;" | '''O''' || {{na}} || style="text-align:center;" | &nbsp; || style="text-align:center;" | '''O''' || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | '''O''' || style="text-align:center;" | '''O''' || style="text-align:center;" | '''O''' || style="text-align:center;" | '''O''' || style="text-align:center;" | '''O''' || style="text-align:center;" | '''O''' || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp; || style="text-align:center;" | &nbsp;
|-
! colspan=23 | Key
|-
| colspan=23 | The absence of any hazard class or division or a blank space in the table indicates that no restrictions apply.

*'''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.
*'''B''': For domestic shipments of compressed [[oxygen]], or [[Liquid oxygen|refrigerated liquid oxygen]] the "[[:File:DOT hazmat class 2.2 (alt).svg|Oxygen]]" placard may be used instead of a "[[:File:DOT hazmat class 2.2.svg|Non-flammable Gas]]" placard. See §172.504(f)(7).

<br><small>'''Source:''' United States Code of Federal Regulations, Title 49 CFR §177.848 - Segregation of hazardous materials.<ref>{{cite web |last1=Pipeline and Hazardous Materials Safety Administration (PHMSA) |author-link1=Pipeline and Hazardous Materials Safety Administration |title=49 CFR 177.848 - Segregation of hazardous materials |url=https://www.govinfo.gov/content/pkg/CFR-2011-title49-vol2/pdf/CFR-2011-title49-vol2-sec177-848.pdf |publisher=Government Publishing Office |page=853 |access-date=16 July 2019 |archive-url=https://web.archive.org/web/20190716093805/https://www.govinfo.gov/content/pkg/CFR-2011-title49-vol2/pdf/CFR-2011-title49-vol2-sec177-848.pdf |archive-date=16 July 2019 |format=PDF |date=October 1, 2011}}</ref> </small>
|}

== References ==
<references />
*{{USGovernment|url=https://www.govinfo.gov/content/pkg/CFR-2009-title49-vol2/pdf/CFR-2009-title49-vol2-subtitleB.pdf|title=Subtitle B—Other Regulations Relating to Transportation|agency=US Government Printing Office}}
*United Nations, Recommendations on the Transport of Dangerous Goods - Model Regulations 
*49 CFR 173.115 (a) (U.S. Code)
*49 CFR 173.115 (b) (U.S. Code)
*49 CFR 177.848 (U.S. Code)

{{Hazardous materials}}

[[Category:Hazardous materials]]