Hazard Class 2 — Gases
Compressed, liquefied and dissolved gases — oxygen cylinders, aerosols, fire extinguishers and more.
Overview
Class 2 covers gases that are compressed, liquefied, dissolved under pressure or refrigerated. The class is split into three divisions: 2.1 flammable, 2.2 non-flammable / non-toxic, and 2.3 toxic. A subsidiary risk (e.g. 5.1 oxidiser for oxygen) is often added.
Acceptance rules vary widely with the division. Flammable gases (2.1) are forbidden on passenger aircraft except under narrow exceptions; non-flammable gases (2.2) are broadly accepted under their dedicated packing instructions; toxic gases (2.3) are heavily restricted or forbidden on aircraft.
Divisions within Class 2
| Division | Description |
|---|---|
| 2.1 | Flammable gas |
| 2.2 | Non-flammable, non-toxic gas |
| 2.3 | Toxic gas |
Aviation context
Aviation MRO deals frequently with Class 2 articles: portable and installed oxygen cylinders, nitrogen for tyre and accumulator servicing, CO2 fire extinguishers, halon bottles, and a long list of aerosol products (cleaners, lubricants, paint primers).
Cylinder testing dates, valve protection and overpack handling are common acceptance issues at airline cargo facilities — a cylinder past its hydrostatic test date will be refused even if the SDS is perfect.
Typical UN numbers in aviation MRO
| UN Number | Proper Shipping Name | Notes |
|---|---|---|
| UN1002 | Air, compressed (2.2) | Used in calibration kits and tyre servicing |
| UN1066 | Nitrogen, compressed (2.2) | MRO accumulator servicing |
| UN1072 | Oxygen, compressed (2.2, subsidiary 5.1) | Crew and passenger oxygen cylinders |
| UN1950 | Aerosols (2.1 or 2.2 depending on contents) | Cleaners, lubricants, dry-film coatings |
| UN1044 | Fire extinguishers (2.2) | Cabin and engine fire-suppression bottles |
Packaging and marking essentials
- Cylinders must be within their periodic inspection / test date, properly capped or valve-protected, and packaged in a way that prevents accidental discharge.
- Aerosols are typically packed under PI203 / PI Y203 with strict net-quantity-per-package limits — exceeding the limit pushes the shipment into Section I with much more restrictive rules.
- Subsidiary risk labels (e.g. 5.1 oxidiser on oxygen cylinders) must be applied in addition to the primary Class 2 label.
Frequently Asked Questions
Can I ship an aircraft oxygen cylinder by air?
Yes — UN1072 oxygen compressed is permitted under specific packing instructions on both passenger and cargo aircraft, provided the cylinder is within test date, properly valve-protected and labelled with both the 2.2 and 5.1 hazard labels.
Are all aerosols dangerous goods?
Aerosols (UN1950) are regulated when they contain a propellant or substance that meets a hazard class threshold. A water-based aerosol with no flammable propellant and no toxic content may fall outside the DG scope, but always verify against Section 14 of the current SDS.
What about empty cylinders?
Cylinders that have been depressurised and cleaned to remove residual hazard may be shipped as non-DG under specific conditions. Cylinders that retain residual pressure remain fully regulated as Class 2 and must be declared accordingly.
Need to classify a specific part?
DG Copilot identifies the UN number, hazard class and air transport status from a part number — in seconds.
Other hazard classes
This information is provided for guidance only. Always verify against the current IATA DGR edition. Final classification and DGD must be validated by a certified DG specialist.