IMDG Class 1 Explosives: Divisions, Groups, Stowage

Class 1 of the International Maritime Dangerous Goods Code is the most operationally constrained section of the entire dangerous goods regulatory system. A container of corrosive acid leaks and corrodes the deck; a container of Division 1.1 explosives catches fire and can destroy a ship and everything within several hundred metres in under a second. The mitigation regime reflects that difference at every level: construction, stowage position, quantity limits, segregation distances, documentation, pre-arrival notification, and the emergency response that tells the master to abandon rather than fight a developed magazine fire.

This article covers the Class 1 system as it stands under IMDG Amendment 42-24, which became mandatory on 1 January 2026, with notes on the changes from Amendment 41-22 (mandatory from 1 January 2024). The IMDG segregation calculator implements the full IMDG Chapter 7.2 segregation table for any pair of UN entries; the IMDG EmS lookup returns the F-x and S-y emergency schedules for any Class 1 UN number.

The regulatory basis

SOLAS Chapter VII and the IMDG Code

SOLAS Chapter VII (Carriage of Dangerous Goods) makes IMDG Code compliance mandatory for ships engaged on international voyages. Regulation VII/1 applies to packaged dangerous goods; Regulation VII/2 covers solid bulk cargoes in relation to the IMSBC Code. The IMDG Code itself is incorporated by reference as a mandatory instrument under SOLAS.

The current mandatory edition is IMDG Amendment 42-24, adopted by the Maritime Safety Committee at MSC 108 in May 2024 and in force from 1 January 2026. Voluntary application was permitted from 1 January 2025. The previous mandatory edition, Amendment 41-22, governed shipments from 1 January 2024 through 31 December 2025. Flag administrations issue implementing circulars; the US, for example, cross-references 49 CFR Parts 171-180 alongside the IMDG Code.

MARPOL Annex III (addressed in the MARPOL Annex III article) covers marine pollutants in packaged form; some Class 1 entries also carry a marine pollutant designation, which triggers additional marking and reporting requirements under MARPOL but doesn’t change the primary Class 1 stowage rules.

The UN Recommendations and the Orange Book

The IMDG Code Class 1 classification scheme mirrors the UN Recommendations on the Transport of Dangerous Goods (the Orange Book), currently in its 23rd revised edition (2023). The same six divisions and thirteen compatibility groups appear in ADR (European road), RID (European rail), ADN (European inland waterways), the ICAO Technical Instructions, and IATA DGR. A product classified 1.1D in one mode carries 1.1D in all modes.

Classification tests for new explosive substances are specified in Part I of the UN Manual of Tests and Criteria, 7th revised edition. The tests determine whether a substance belongs to Class 1 at all, which division applies, and whether it qualifies for a particular compatibility group. The competent authority of the producing country accepts or rejects the classification; the resulting UN number and proper shipping name then appear in the IMDG Code’s dangerous goods list.

The six hazard divisions

Class 1 is divided into six divisions based on the nature and scale of the hazard when the substance or article functions unintentionally. Understanding which division applies is the starting point for every subsequent decision about stowage, quantity limits, and emergency response.

Division 1.1: Mass explosion hazard

Division 1.1 covers substances and articles where the entire cargo load can be expected to detonate substantially instantaneously. Detonation propagates through the mass at speeds between 2,000 and 9,000 metres per second, depending on the explosive. The defining characteristic is that one package initiating can set off every adjacent package within milliseconds.

Typical entries include UN 0004 (ammonium picrate, dry or wetted with less than 10% water), UN 0027 (black powder), UN 0072 (RDX wetted with at least 15% water), UN 0081 (explosive, blasting, type A), UN 0082 (explosive, blasting, type B), UN 0143 (nitroglycerin desensitized with at least 40% water), and UN 0150 (PETN wetted with at least 25% water).

Division 1.1 is the most tightly controlled. Most flag states set a maximum net explosive quantity (NEQ) for Division 1.1 cargo on general cargo vessels, often 50 tonnes. Dedicated explosives carriers operating under special arrangements can carry more. Many commercial ports refuse Division 1.1 cargo at berth and require the vessel to anchor at a designated explosives anchorage.

Division 1.2: Projection hazard

Division 1.2 covers substances and articles with a projection hazard but not a mass explosion hazard. The detonation or deflagration is limited to one package or sub-stack rather than propagating instantaneously through the entire load. The dominant hazard is fragments projected at high velocity: artillery casings, bomb bodies, mortar tubes.

Typical entries include UN 0006 (cartridges for weapons with bursting charge), UN 0009 (ammunition, incendiary), UN 0073 (detonators for ammunition), and UN 0181 (rockets with bursting charge). Division 1.2 appears almost exclusively in military and government shipments, typically carried on dedicated explosives carriers or military vessels.

Division 1.3: Fire hazard

Division 1.3 covers substances and articles with a fire hazard and either a minor blast or minor projection hazard, but no mass explosion hazard. The cargo burns vigorously, possibly producing localised pressure waves, but does not detonate in the Division 1.1 sense.

Many fireworks fall in Division 1.3. UN 0335 (fireworks, Division 1.3) is one of the highest-volume Class 1 entries in commercial trade, moved in containers from manufacturing countries to consumer markets before each major holiday season. Smokeless powder and propellant charges are also common 1.3 entries.

Division 1.4: No significant hazard

Division 1.4 covers substances and articles presenting no significant hazard: any explosive effect is confined to the package itself, with no projection of fragments of appreciable size and no near-instantaneous explosion of the whole package contents if the package is involved in a fire.

Division 1.4 is subdivided at the compatibility-group level. 1.4S (compatibility group S) is the most permissive sub-category, reserved for substances so packaged that even accidental functioning is confined to the package. Division 1.4S is the only Class 1 category that may be carried in mixed stowage on conventional general cargo vessels and on passenger ships in limited quantities.

UN 0012 (cartridges for weapons, inert projectile), UN 0014 (cartridges for weapons, blank), and UN 0337 (fireworks, Division 1.4S) are frequent commercial entries. Small-arms cartridges are the dominant 1.4S volume globally: the global civilian small-arms trade moves hundreds of millions of rounds per year, mostly classified 1.4S.

Division 1.5: Very insensitive substances

Division 1.5 covers substances with a mass explosion hazard that are so insensitive under normal transport conditions that initiation or transition from burning to detonation has very low probability. The category exists primarily for blasting agents: ammonium-nitrate-fuel-oil (ANFO) compounds and similar products used in mining and quarrying.

UN 0331 (explosive, blasting, type B, agent blasting) and UN 0332 (explosive, blasting, type E) are the principal commercial entries. The insensitivity rating allows somewhat higher per-ship quantity limits than Division 1.1, but the mass explosion potential means the classification system still treats the cargo as Class 1 for stowage, documentation, and port notification purposes.

Division 1.6: Extremely insensitive articles

Division 1.6 covers articles containing only extremely insensitive detonating substances with a negligible probability of accidental initiation or propagation. The category was introduced in the 1990s to accommodate modern insensitive munitions designed to survive handling accidents and fires without functioning. Commercial entries are rare; the division is almost entirely military.

Summary comparison

The thirteen compatibility groups

Why compatibility exists as a concept

Within a single division, different explosive substances and articles can be chemically or functionally incompatible. A detonator (Group B) accidentally initiated in proximity to a bulk secondary explosive (Group D) could set off the secondary when the secondary would not have initiated on its own. Conversely, a pyrotechnic substance (Group G) burning in a fire produces intense flash that can initiate primary explosives (Group A) that no ordinary fire would reach.

The 13 compatibility groups, designated by the letters A, B, C, D, E, F, G, H, J, K, L, N, S (the letters I, M, O, P, Q, and R are not used), were developed by the UN working group on explosives over several revision cycles of the Model Regulations. Each letter encodes what the substance or article is, what makes it dangerous, and therefore what it can safely share space with.

Group-by-group definitions

Group A covers primary explosive substances: highly sensitive initiating compounds such as lead azide, mercury fulminate, and silver azide. Group A substances initiate at very low energy inputs (mechanical shock, static electricity, friction, heat). They are not normally carried in commercial sea trade; they appear in laboratory and government consignments.

Group B covers articles containing a primary explosive substance without two or more effective protective features separating the initiating compound from an external stimulus. Detonators, blasting caps, and electric detonators fall here. The absence of protective features means the item can be initiated without a deliberate trigger impulse.

Group C covers propellant explosive substances and other deflagrating explosives, or articles containing them. Smokeless powder (single-base, double-base, triple-base), solid rocket propellant, and propelling charges for guns are Group C entries. The hazard is rapid burning rather than detonation.

Group D covers secondary detonating explosive substances, black powder, and articles containing a secondary detonating explosive without their own means of initiation, combined where necessary with a propelling charge. TNT, RDX, HMX, PETN in bulk form, dynamite, and pentolite are Group D. These substances require a strong initiating impulse (the output of a Group B detonator) to detonate; they don’t go off from a spark.

Group E covers articles containing a secondary detonating explosive substance without a means of initiation but with a propelling charge. Tank gun ammunition without primer or fuse is the principal example. The article has propellant and a main filling of secondary explosive, but no initiator; a detonator must be separately fitted before the article can function.

Group F covers articles containing a secondary detonating explosive with their own means of initiation, with or without a propelling charge. Complete artillery rounds with a fuse, bomb assemblies ready for arming, and mines with their fuzes fitted are Group F. The integrated initiator makes these articles much more sensitive to handling than Group E, so they must be kept away from heat sources and other initiating stimuli.

Group G covers pyrotechnic substances and articles containing pyrotechnic substances, or articles containing both an explosive substance and an illuminating, incendiary, tear-producing, or smoke-producing substance. Signal flares, illumination cartridges, colored smoke signals, and white-star parachute illuminants are Group G. The pyrotechnic reaction produces intense heat and light that can initiate adjacent primary explosives, hence the separation requirement.

Group H covers articles containing both an explosive substance and white phosphorus. White phosphorus ignites spontaneously in air above about 34°C and burns intensely; its combination with an explosive substance creates a dual initiation hazard.

Group J covers articles containing both an explosive substance and a flammable liquid or gel. Thermite and incendiary bombs with an explosive burster and a flammable fill are Group J entries.

Group K covers articles containing both an explosive substance and a toxic chemical agent. Chemical munitions are the primary example. Group K is tightly controlled under OPCW/CWC obligations and almost never appears in commercial shipping.

Group L covers explosive substances or articles presenting a special risk due to factors not captured by other groups: water-activated devices, hypergolic propellants, and other entries where the hazard mechanism requires isolation from all other Group L entries as well as all other Class 1 groups. Each Group L item gets its own magazine.

Group N covers articles containing only extremely insensitive detonating substances: the Division 1.6 category. The articles demonstrate negligible probability of accidental initiation; they can be stowed together but must be separated from all other compatibility groups.

Group S covers substances or articles so packaged or designed that any hazardous effects arising from accidental functioning are confined within the package, unless the package is degraded by fire. This is the 1.4S category. Group S has the most relaxed handling rules in Class 1 and can be co-stowed with most other Class 1 groups under certain conditions.

The IMDG compatibility table

IMDG Code Table 7.2.6.3.1 specifies which groups may be stowed in the same compartment. The governing principles are:

• Groups involving primary explosives (A, B) must be kept away from everything except each other, and Group A may only be stowed with Group A.
• Groups with integrated initiators (B, F) must be separated from secondary explosives (D, E) to prevent inadvertent initiation.
• Pyrotechnics (G) produce flash hazards that can initiate primaries; Group G is separated from Groups A and B, and from Groups H, J, K.
• Group L is incompatible with all other groups and must have its own dedicated magazine.
• Group N (Division 1.6) may only be stowed with itself.
• Group S is the most permissive and can be stowed with most other groups.

The IMDG segregation calculator implements the full matrix for any pair of UN entries, returning a stowage decision that accounts for both the inter-class and intra-class compatibility rules.

UN classification codes in practice

The complete classification code for a Class 1 substance appears as division + compatibility group: 1.1D for a Division 1.1 secondary explosive (bulk TNT, for example), 1.3C for a Division 1.3 propellant (smokeless powder), 1.4S for fireworks (UN 0337), 1.5D for a blasting agent (UN 0331). This code appears on the package label, the placard, the MDGF, and the stowage plan. A placard reading “1.4S” authorizes stowage under the 1.4S rules; a placard reading only “1.4” (without S) triggers the more restrictive 1.4 non-S treatment.

Stowage rules and magazine construction

Magazine types defined in IMDG Chapter 7.1

Class 1 cargo is stowed in a magazine, a defined cargo space constructed to specific standards. IMDG Code Chapter 7.1 defines four types:

Magazine Type A: a closed cargo space surrounded by steel plating, with openings only for secured access doors with inward-opening hinges. No through-openings for ventilation. Required for most Division 1.1 and 1.2 cargoes. The construction spec includes minimum plate thickness, resistance to projection hazard, and non-sparking internal surfaces.

Magazine Type B: a closed steel-plated cargo space with the possibility of limited ventilation openings to the deck. Suitable for Division 1.2 and most Division 1.3 cargoes. The ventilation is needed for some propellant-heavy cargoes that off-gas under heat.

Magazine Type C: a closed cargo space not meeting the full structural standard of Types A or B. Used for some Division 1.4 cargoes where the confined-to-package hazard profile permits reduced structural protection.

Magazine Type D: a portable magazine, typically a freight container or vehicle constructed to magazine standards and treated as a temporary magazine for the voyage. Suitable for Division 1.4S and limited Division 1.4 quantities. The portability allows ships without permanent magazine spaces to carry low-hazard Class 1 cargo.

The required magazine type for a given UN entry is specified in the IMDG dangerous goods list for that entry. A vessel that doesn’t have the required magazine type must decline the cargo; there’s no workaround for missing magazine construction.

On-deck versus under-deck stowage

The IMDG dangerous goods list entry for each UN number specifies stowage category, controlling whether the cargo goes on deck or under deck:

On deck only: many Division 1.4 and 1.5 cargoes in containers. On-deck stowage allows the master to jettison the container in an emergency without requiring entry to the cargo hold. The trade-off is exposure to weather, impact from cargo gear, and greater fire risk from hot work or mooring lines.

On deck or under deck: most Division 1.1, 1.2, and 1.3 cargoes when in an approved magazine. Under-deck placement provides structural protection and separation from the weather, but makes jettison impossible once the vessel is underway.

Under deck only: a minority of entries where fume or gas evolution must be contained; venting to atmosphere is not permitted.

For on-deck containers carrying Class 1, the IMDG Code specifies minimum separation distances from heat sources, from accommodation, and from the ship’s side, expressed in metres. These are separate from and in addition to the class segregation requirements.

Segregation from other dangerous goods classes

IMDG Code Chapter 7.2 defines four separation grades, applied between Class 1 and the other eight principal dangerous goods classes. The four grades, from least to most restrictive, are:

1. Away from: different rows in the same compartment, or separated by an intervening tier.
2. Separated from: different cargo holds, or different compartments above deck separated by a complete deck.
3. Separated by a complete compartment or hold from: the two cargoes must be in holds or compartments with no structural element shared.
4. Separated longitudinally by an intervening complete compartment or hold from: the most restrictive; the two cargoes must be separated fore-and-aft by a full empty hold or compartment.

Class 1 cargoes face the most restrictive separation grades from Class 5.1 (oxidizing substances). Division 1.1 with ammonium nitrate (a Class 5.1 entry) is prohibited in certain configurations without specific flag-state authority. The Texas City disaster (see below) illustrated precisely this hazard: ammonium nitrate fertiliser in a fire became a Division 1.5-class event.

Class 1 vs Class 3 (flammable liquids) and Class 4 (flammable solids, described in the IMDG Class 4 article) require “separated longitudinally by an intervening complete compartment or hold” for the higher divisions, because flammable liquid or solid fires can produce the heat flux needed to initiate Class 1 detonation.

Class 1 vs Class 2 gases require at minimum “separated from” because compressed gases under fire conditions can fail explosively, adding a fragmentation hazard that can initiate nearby Class 1 packages.

Net explosive quantity limits and quantity management

Net explosive quantity (NEQ) is the mass of explosive substance itself in a consignment, excluding packaging material, inert fill, metal casings, and propellant that is not itself the main explosive filling. For a box of detonators, the NEQ is the mass of the primary explosive in each detonator times the number of detonators; the brass shell, cardboard packaging, and other components don’t count.

NEQ matters because the energy release in a mass detonation event scales roughly with the explosive mass. Flag states set per-ship NEQ limits that reflect both the vessel type and the division. Typical published limits for general cargo vessels under several flag state circulars are:

• Division 1.1: 50 tonnes NEQ maximum per vessel; some flags set lower limits or prohibit Division 1.1 altogether on general cargo tonnage.
• Division 1.2: limits vary between 100 and 500 tonnes depending on flag, vessel type, and magazine capacity.
• Division 1.3: limits set by magazine capacity.
• Division 1.4 and 1.4S: typically quantity limited only by available stowage.
• Division 1.5: blasting agents, often 200-500 tonnes per ship on general cargo vessels with appropriate magazines.

Port states overlay their own per-berth and per-anchorage limits. The shipowner and charterer must verify that both the flag and port limits are satisfied before fixing a voyage involving Class 1 cargo.

Documentation requirements

The Multimodal Dangerous Goods Form

The shipper of any Class 1 consignment must supply the carrier with a Multimodal Dangerous Goods Form (MDGF) before the cargo is accepted. IMDG Code Section 5.4.1 sets out the mandatory fields:

• UN number and proper shipping name (from the IMDG dangerous goods list).
• Class (1) and division (e.g., 1.1).
• Compatibility group (e.g., D).
• Subsidiary hazards where applicable (e.g., Class 6.1 toxic for Group K entries).
• Number and type of packages.
• Net explosive quantity in kilograms.
• Marine pollutant indicator if the substance appears in MARPOL Annex III.
• EmS codes (e.g., F-B, S-A).
• 24-hour emergency contact number capable of providing technical assistance.

Class 1 has no packing group (I, II, or III) in the IMDG system; the packing group field on the MDGF is left blank for Class 1. This differs from Classes 3, 4, 5.1, 6.1, and 8, which use the packing group to grade the hazard severity for packaging selection purposes. For Class 1, the division and compatibility group serve the equivalent function.

Container packing certificate

For Class 1 cargo packed in a freight container, road vehicle, or rail wagon, IMDG Code Section 5.4.2 requires a Container/Vehicle Packing Certificate signed by the packer. The certificate confirms:

• The container was clean, dry, and apparently fit at the time of loading.
• Packages were securely loaded, braced, and blocked to prevent movement.
• Compatibility groups within the container are mutually compatible per the IMDG table.
• All packages are correctly marked and labeled; the container carries the correct Class 1 placard on all four sides and on the roof.
• The MDGF accompanies the certificate.

Without a valid Container Packing Certificate, the carrier should decline to load the unit. An unsigned or incorrect certificate shifts liability to the carrier if the cargo causes an incident.

Marking and placarding requirements

Each Class 1 package carries the diamond-shaped Class 1 hazard label: orange background, black explosion symbol, division number in the lower area, and “EXPLOSIVES” in the lower band. For Group S (1.4S) and for other 1.4 entries, the label shows the specific division-group code.

Freight containers and vehicles must be placarded on all four sides and the roof with the Class 1 placard. The placard shows the division number and compatibility group letter so that port-state control and stevedores can immediately identify what is inside the unit and apply the correct segregation rules without opening the container.

Pre-arrival notification

Most ports require notification of Class 1 cargo at least 24 to 72 hours before the vessel arrives. The notification typically includes the vessel name and IMO number, ETA, berth or anchorage requested, manifest of Class 1 entries with UN numbers and NEQ, stowage plan, and flag state’s loading authorization or permit reference.

Ports that designate an explosives anchorage will direct the vessel to anchor there rather than proceed directly to berth. Tugs or port fire-fighting craft may be stationed nearby. The port health and safety authority may board the vessel for a pre-cargo inspection before authorizing transfer to the berth.

Failure to notify is not merely a procedural oversight. Under most national port regulations, undeclared Class 1 cargo discovered during port-state control inspection triggers cargo removal at the owner’s expense, possible detention of the vessel, and prosecution of the master and the agent.

Emergency response: the EmS system

Structure of the EmS Guide

The Emergency Response Procedures for Ships Carrying Dangerous Goods (EmS Guide) assigns two schedule codes to every dangerous goods entry in the IMDG Code: a Fire schedule (F-xx) and a Spillage schedule (S-xx). The fire schedule governs how the crew responds to a fire involving or threatening the cargo; the spillage schedule governs the response to a spill or leak.

For Class 1, the fire schedules are the critical ones. The EmS Guide 2024 edition assigns:

F-A: applies to Division 1.4S entries and minor Class 1 entries where the hazard is confined to the package. The response is conventional fire-fighting with water; full boundary cooling; no prohibition on fighting the fire.

F-B: applies to most Division 1.1, 1.2, and 1.3 entries. This schedule tells the master that if fire reaches the magazine or the cargo itself: do not fight the fire from adjacent positions, apply water cooling to the magazine boundaries from a safe distance, and prepare to abandon ship. A developed fire in Division 1.1 cargo doesn’t give the master time to mount a suppression response.

F-C: for Division 1.4 entries stowed on deck only, where jettison is the primary emergency response. The master can jettison the unit overboard if the fire is detected early enough; once the fire reaches the explosives, jettison is no longer safe.

F-D: Class 1 entries with combustible packaging contributing a secondary fire risk. The packaging fire can be fought; the cargo itself must be kept cool.

F-E: Class 1 entries with toxic combustion products. The fire-fighting response follows F-B rules but adds full breathing-apparatus requirements for all crew in the vicinity.

The IMDG EmS lookup calculator returns the assigned F-xx and S-xx codes for any UN number and links to the full schedule text.

What F-B means operationally

The F-B instruction “abandon ship” when fire reaches a Division 1.1 magazine is not a default safety precaution; it is the operationally correct decision. The Halifax explosion of 1917 involved 2,653 tonnes of explosives and produced the largest man-made explosion before nuclear testing. The entire event, from first fire on the Mont-Blanc to complete detonation, took approximately 20 minutes. At Texas City in 1947, the ammonium nitrate in the SS Grandcamp detonated after approximately 90 minutes of fire, with no effective suppression attempted. Both events illustrate that once Class 1 cargo starts burning without suppression in the first minutes, there is no second chance.

The master’s duty is to protect the crew. Boundary cooling is still appropriate at distance, to slow heat transfer to adjacent magazines or cargo, and it requires crews well back from the affected area. Any crew closer than the safe distance specified in F-B is at higher risk from the explosion than from abandoning the response.

Notable casualties and lessons

Halifax, 1917

The Halifax Explosion of 6 December 1917 occurred when the French munitions ship SS Mont-Blanc, loaded with approximately 2,653 tonnes of explosives (TNT, picric acid, wet guncotton, benzol drums on deck), collided with the Norwegian vessel SS Imo in Halifax Harbour. A fire on the Mont-Blanc spread to the benzol drums and then to the cargo hold. The crew abandoned the burning ship. The burning ship drifted to Pier 6, where a crowd gathered to watch. At 09:04:35, the entire load detonated.

The explosion killed approximately 2,000 people, injured 9,000, and destroyed the north end of Halifax. It was the largest man-made explosion before the Trinity nuclear test of July 1945. Its immediate regulatory consequence was the introduction of explosives officer training requirements and the standardization of explosives stowage rules in the pre-IMDG era regulations.

Texas City, 1947

The Texas City Disaster of 16 April 1947 began when the French Liberty ship SS Grandcamp, carrying approximately 2,300 tonnes of ammonium nitrate fertiliser, caught fire at the dock. The ammonium nitrate was not classified as a Class 1 explosive; it was an agricultural fertiliser carried under Class 5.1 oxidizer rules. At approximately 09:12, after roughly 90 minutes of fire and failed suppression, the cargo detonated.

The explosion killed approximately 580 people, triggered a secondary explosion aboard the SS High Flyer (also loaded with ammonium nitrate) 16 hours later, and destroyed the Texas City industrial waterfront. The disaster drove the reclassification of ammonium nitrate: ANFO and ammonium-nitrate-based blasting agents are now classified as Division 1.5D; fertilizer-grade ammonium nitrate above certain contamination or oil-content thresholds also gets Class 1 treatment in the IMDG Code’s dangerous goods list. The lesson about co-storage of Class 5.1 oxidizers with organic combustibles echoes in every version of IMDG Chapter 7.2 since.

Tianjin, 2015

The Tianjin port explosion of 12 August 2015 occurred at the Ruihai International Logistics hazardous goods storage facility in Tianjin, China. Stored materials included approximately 800 tonnes of ammonium nitrate, 500 tonnes of potassium nitrate, 700 tonnes of sodium cyanide, and quantities of Class 1 fireworks. Two sequential explosions occurred, with seismic-station yields estimated at 3 tonnes and 22 tonnes of TNT equivalent, respectively; the total fireball was estimated at 21 and 240 tonnes TNT equivalent by separate analyses. 173 people died, including 99 firefighters who did not know the nature of the cargo they were attacking.

Tianjin’s core failure was co-storage of incompatible classes in a facility where actual inventory didn’t match the declared inventory, and where first responders had no access to accurate materials information. The IMDG Class 5 article covers the ammonium nitrate oxidiser classification that sits at the center of both Tianjin and Texas City.

Beirut, 2020

The Beirut port explosion of 4 August 2020 occurred when approximately 2,750 tonnes of ammonium nitrate stored in Hangar 12 of the Port of Beirut detonated. The ammonium nitrate had been confiscated from the MV Rhosus in 2014 after the vessel called at Beirut in financial difficulty. Rather than disposing of the cargo or shipping it on, port and customs authorities stored it in Hangar 12 for six years, without adequate segregation, without adequate fire prevention, and without a functioning fire suppression system.

A fire of undetermined origin, possibly involving fireworks stored in the same hangar, ignited the ammonium nitrate. The resulting explosion had a yield estimated at 0.5 to 1.1 kilotonnes of TNT equivalent by various analyses; it killed approximately 218 people, injured over 7,000, and rendered approximately 300,000 homeless. Structural damage was recorded 10 km from the port. Beirut reinforced the case that long-term storage of Class 1 or Class 5.1 oxidizer materials without active management of separation and fire-prevention controls is not a regulatory grey area; it is an accident waiting for a trigger.

The IMDG Code limited quantities provision

Division 1.4S substances and articles may in some cases qualify for transport in limited quantities, under IMDG Code Chapter 3.4. Limited quantity packing exempts the consignment from some labeling, marking, and placarding requirements if each inner package contains no more than the per-substance limited quantity (LQ) value published in the dangerous goods list, and the total gross mass per outer package does not exceed 30 kg.

Not all 1.4S entries have a limited quantity value; the dangerous goods list entry must specify “LQ” and a value for the exemption to apply. The IMDG limited quantity calculator implements the LQ check for any UN entry. Class 1 limited quantities are more restricted than most other classes; Divisions 1.1 through 1.3 have no limited quantity provision at all.

Competent authority role in classification

For substances and articles not already listed in the IMDG Code’s dangerous goods list, the manufacturer or importer must apply to the competent authority of the country of origin for a classification approval. The competent authority reviews the test data submitted under the UN Manual of Tests and Criteria Part I series, assigns the division and compatibility group, and issues a classification authority.

For novel military explosives or classified formulations, the competent authority may issue a classification under a code name or reference number without revealing the exact chemical composition. The shipping description on the MDGF then reads something like “Explosive, blasting, type F, n.o.s., 1.1F, UN 0083” using the IMDG Code’s generic not-otherwise-specified (n.o.s.) entries.

The flag state’s competent authority may also issue a special arrangement (SA) under SOLAS Regulation VII/12 and IMDG Code 1.5 for shipments that cannot meet a specific IMDG requirement, provided the overall safety level is demonstrated to be at least equivalent. SAs are used for prototype munitions, classified government cargoes, and one-off transport tasks that fall outside the standard classification framework.

Interaction with the CTU Code

The IMO/ILO/UNECE Code of Practice for Packing of Cargo Transport Units (CTU Code) governs how Class 1 cargo is packed into containers and road/rail vehicles before being presented to the carrier. The CTU Code requirements for dangerous goods packing include:

• Pre-packing inspection of the unit for cleanliness, structural integrity, and absence of residues incompatible with the new cargo.
• Blocking and bracing of packages to prevent any movement during the voyage (IMDG Code loads routinely experience 3G longitudinal and 2G transverse forces in heavy weather).
• Verification of compatibility between all Class 1 items in the unit before sealing.
• Correct application of marks, labels, and placards to the unit.
• Preparation and retention of the Container Packing Certificate.

For magazines Type D (portable containers), the CTU Code requirements are supplemented by the IMDG Code’s additional structural requirements for magazine construction. A standard ISO freight container doesn’t qualify as a Type D magazine without modification; the modification typically involves lining, securing of access doors, and earthing arrangements to prevent static discharge.

Limitations

This article describes the Class 1 system as specified in IMDG Amendment 42-24. National implementing legislation varies; the US 49 CFR regime, the EU RID/ADR cross-application rules, and specific flag-state circulars add layers that the IMDG Code itself doesn’t contain. Verification against the current edition of the Code and against flag-state and port-state requirements is mandatory before accepting any Class 1 cargo.

NEQ limits cited here for general cargo vessels are representative of several flag-state circulars but are not universal; exact limits must be confirmed with the flag administration for each vessel and voyage. Port-state NEQ limits change independently of flag-state limits and must be confirmed with the port agent for each port call.

The compatibility table in IMDG Section 7.2.6.3.1 is the authoritative source for inter-group stowage decisions. The summary descriptions in this article are explanatory; the full table governs. The IMDG segregation calculator implements the full table and should be used for any operational stowage decision.

This article does not cover bulk Class 1 transport under IMSBC Code solid bulk provisions (a separate regulatory path for ammonium nitrate in bulk solid form), nor the ICAO/IATA regime for air transport of Class 1 (much more restrictive than IMDG, with many Division 1.1 and 1.2 entries prohibited on all aircraft).

See also

• SOLAS Chapter VII: Carriage of Dangerous Goods
• MARPOL Annex III: Harmful Substances in Packaged Form
• IMDG Class 2: Gases
• IMDG Class 3: Flammable Liquids
• IMDG Class 4: Flammable Solids, Self-Reactive Substances
• IMDG Class 5: Oxidisers and Organic Peroxides
• IMSBC Code: Solid Bulk Cargoes
• IMDG Segregation Calculator
• IMDG EmS Lookup
• IMDG Limited Quantity Calculator
• IMDG Packing Group Calculator
• Container IMDG Class Lookup
• IMDG Tank Container Calculator
• IMDG Class 7 Radioactive