Class 1 (Explosives) & Class 2 (Gases) Classification

Class 1 (Explosives) & Class 2 (Gases) Classification

Under the IATA Dangerous Goods Regulations (DGR), dangerous goods are assigned to one of nine hazard classes based on their dominant physical and chemical properties. The first two classes—Class 1 (Explosives) and Class 2 (Gases)—present severe risk profiles during air transport due to the potential for rapid energy release, overpressurization, toxic atmosphere generation, and catastrophic structural damage to aircraft. Shippers and operators must possess an intricate understanding of the exact sub-divisions, compatibility codes, and transport restrictions governing these classes.

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Introduction to Hazard Class 1: Explosives

Class 1 encompasses any chemical substance, mixture, or article designed to function by explosion or pyrotechnic effect, or manufactured with a view to produce a practical, explosive, or pyrotechnic effect. Because aircraft in flight are uniquely vulnerable to sudden pressure waves, fire, and shrapnel, Class 1 is subject to the most stringent air transport prohibitions of all hazard classes.

Class 1 is divided into 6 divisions based on the nature of the explosive hazard:

• Division 1.1: Mass Explosion Hazard — Consists of substances and articles that have a mass explosion hazard (an explosion that affects almost the entire load instantaneously). Examples: TNT, dynamite, nitroglycerin. Forbidden on both passenger and cargo aircraft.
• Division 1.2: Projection Hazard — Consists of substances and articles that have a projection hazard but not a mass explosion hazard. Examples: Military rockets with inert warheads, explosive projectiles. Forbidden on both passenger and cargo aircraft.
• Division 1.3: Fire Hazard with Minor Blast/Projection Hazard — Consists of substances and articles that have a fire hazard and either a minor blast hazard or a minor projection hazard (or both), but not a mass explosion hazard. Examples: Sodium picramate, display fireworks, smokeless powder. Forbidden on both passenger and cargo aircraft.
• Division 1.4: Minor Explosion Hazard (any compatibility group other than S is forbidden on passenger aircraft) — Consists of substances and articles that present only a minor explosion hazard in the event of ignition or initiation during transport. The effects are largely confined to the package, and no projection of fragments of appreciable size or range is to be expected. Examples: Small arms ammunition, signal flares, consumer fireworks. Permitted on aircraft under strictly limited circumstances depending on Compatibility Group.
• Division 1.5: Very Insensitive Substances with a Mass Explosion Hazard — Consists of substances that have a mass explosion hazard but are so insensitive that there is very little probability of initiation or transition from burning to detonation under normal transport conditions. Examples: Blasting agents (ANFO). Forbidden on both passenger and cargo aircraft.
• Division 1.6: Extremely Insensitive Articles — Consists of articles that contain only extremely insensitive substances and demonstrate a negligible probability of accidental initiation or propagation. Forbidden on both passenger and cargo aircraft.

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Compatibility Groups for Explosives (Groups A through S)

To ensure safe stowage, handling, and segregation, every Class 1 explosive is assigned a Compatibility Group denoted by a letter. There are exactly 13 Compatibility Groups: A, B, C, D, E, F, G, H, J, K, L, N and S. The letters I, M, O, P, Q and R are not used (I and O are omitted to avoid confusion with the numerals 1 and 0).

The Operational Importance of Compatibility Group S

Among all compatibility groups, Group S holds critical significance in aviation. A substance or article assigned to Division 1.4, Compatibility Group S (1.4S) is engineered such that even if accidental initiation occurs inside a package during transport, all hazardous blast, thermal, and fragment effects remain contained entirely within the outer packaging. As a direct result, certain Division 1.4S items—such as UN 0012 (Cartridges for weapons, inert projectile) and UN 0454 (Igniters)—are permitted on both passenger and cargo aircraft, provided they satisfy packing instruction limitations and net quantity limits.

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Introduction to Hazard Class 2: Gases

Class 2 comprises pure gases, gas mixtures, articles containing gases, and aerosols. Under IATA DGR criteria, a substance is classified as a Class 2 Gas if it meets either of the following physical criteria:

1. Exhibits a vapor pressure exceeding 300 kPa (3.0 bar) at $50^\circ\text{C}$; or
2. Is completely gaseous at $20^\circ\text{C}$ at a standard atmospheric pressure of 101.3 kPa.

Physical States of Class 2 Gases

Gases are transported in one of five primary physical states:

• Compressed Gas: A gas (other than in solution) which when packaged under pressure for transport is entirely gaseous at $-50^\circ\text{C}$.
• Liquefied Gas: A gas which when packaged under pressure is partially liquid at temperatures above $-50^\circ\text{C}$.
• Refrigerated Liquefied Gas (Cryogenic Liquid): A gas which when packaged is made partially liquid because of its low temperature.
• Dissolved Gas: A gas which when packaged under pressure is dissolved in a liquid phase solvent (e.g., Acetylene dissolved in acetone).
• Adsorbed Gas: A gas which when packaged is adsorbed onto a solid porous material.

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Class 2 Sub-Divisions

Class 2 is divided into three sub-divisions based on the primary chemical hazard:

                    ┌─────────────────────────────────────────┐
                    │          CLASS 2: GASES                │
                    └────────────────────┬────────────────────┘
                                         │
         ┌───────────────────────────────┼───────────────────────────────┐
         ▼                               ▼                               ▼
┌─────────────────┐             ┌─────────────────┐             ┌─────────────────┐
│  Division 2.1   │             │  Division 2.2   │             │  Division 2.3   │
│  Flammable Gas  │             │ Non-Flammable,  │             │    Toxic Gas    │
│ (e.g., Propane) │             │ Non-Toxic Gas   │             │(e.g., Chlorine) │
└─────────────────┘             │ (e.g., Nitrogen)│             └─────────────────┘
                                └─────────────────┘

Division 2.1: Flammable Gases

Gases which at $20^\circ\text{C}$ and standard pressure of 101.3 kPa:

• Are ignitable when in a mixture of 13% or less by volume with air; or
• Have a flammable range with air of at least 12 percentage points regardless of the lower flammable limit.

Common Examples: UN 1978 (Propane), UN 1001 (Acetylene, dissolved), UN 1033 (Dimethyl ether), UN 1969 (Isobutane).

Division 2.2: Non-Flammable, Non-Toxic Gases

Gases which are transported at a gauge pressure of not less than 200 kPa at $20^\circ\text{C}$, or as refrigerated liquids, and which:

• Are asphyxiants (dilute or replace ambient oxygen); or
• Are oxidizing (may cause or contribute to the combustion of other material more than air does); or
• Do not meet the criteria of Division 2.1 or Division 2.3.

Common Examples: UN 1066 (Nitrogen, compressed), UN 1013 (Carbon dioxide), UN 1002 (Air, compressed), UN 1977 (Nitrogen, refrigerated liquid).

Division 2.3: Toxic Gases

Gases which:

• Are known to be so toxic or corrosive to humans as to pose a hazard to health; or
• Are presumed to be toxic or corrosive to humans because they have an acute inhalation toxicity ($LC_{50}$) value less than or equal to 5,000 mL/m³ (ppm) when tested on laboratory animals.

Common Examples: UN 1017 (Chlorine), UN 1050 (Hydrogen chloride, anhydrous), UN 1076 (Phosgene).

CRITICAL AIR TRANSPORT RULE: All gases assigned to Division 2.3 (Toxic Gases) — and gases carrying a subsidiary 2.3 risk — are forbidden on passenger aircraft. Most Division 2.3 entries also show "Forbidden" in the cargo aircraft columns of Section 4.2. Where such an entry carries Special Provision A2 in Column M, it may be moved on a cargo aircraft only with the prior approval of the State of Origin and the State of the Operator. Never assume from the division alone — read Columns I through M of the Section 4.2 entry.

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Aerosol Classification Criteria (UN 1950)

Aerosols (Aerosol dispensers, UN 1950) are non-refillable receptacles made of metal, glass, or synthetic material containing a gas compressed, liquefied, or dissolved under pressure, fitted with a release device allowing contents to be ejected as solid/liquid particles in suspension in a gas, or as a foam, paste, or liquid.

Aerosols are assigned to Division 2.1 or Division 2.2 based on their flammable components percentage by mass and heat of combustion:

1. Division 2.1 (Flammable Aerosol): Assigned if the contents contain more than 85% flammable components by mass and the chemical heat of combustion is $\ge 30\text{ kJ/g}$, or if they pass standardized ignition distance and enclosed space test protocols.
2. Division 2.2 (Non-Flammable Aerosol): Assigned if the contents contain 1% or less flammable components by mass and the heat of combustion is $< 20\text{ kJ/g}$.
3. Intermediate Range (1% to 85%): Must undergo official flammability testing (Ignition Distance Test, Enclosed Space Ignition Test, and Foam Test) to determine whether Division 2.1 or 2.2 applies.
4. Subsidiary Risks: If aerosol contents possess toxic (Division 6.1) or corrosive (Class 8) characteristics, subsidiary risk labels are mandatory. Aerosols with Division 2.3 toxic gas constituents are strictly forbidden.