The International Maritime Dangerous Goods (IMDG) Code is the IMO's mandatory standard for classifying, packing, marking, and stowing dangerous goods carried by sea. It assigns every hazardous substance a class, a UN number, and packing requirements that carriers and terminals must follow.
IMDG · Class 2
IMO Class 2 - Gases
Class 2 Gases
Subclass 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.
Subclass 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.
Subclass 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 of 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.
FAQ
Dangerous goods classification, explained
A substance is classed by its primary hazard, but many also carry a subsidiary risk — a toxic gas that's also flammable, for instance. The shipping documents and placarding reflect both, and segregation rules account for whichever hazard is more restrictive.
The UN number is assigned per substance (or group of similar substances) in the IMDG Code's Dangerous Goods List, not per class — two shipments in the same class can have different numbers, packing groups, and segregation requirements.
No — this is a plain-language reference for planning purposes only. Final classification, packing instructions, and stowage/segregation tables always come from the current edition of the IMDG Code and your carrier's dangerous goods desk.
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