Ammonium Nitrate Fertilizer: IMSBC Schedules

Ammonium nitrate based fertilizer (ANBF) is one of the most tightly regulated dry-bulk cargoes under the IMSBC Code. It ships as an oxidizer, a self-sustaining-decomposition hazard, or a Group C non-hazardous cargo depending on its exact composition, and Amendment 06-21 (MSC.500(105), mandatory from 1 December 2023) fundamentally restructured the schedule framework that had governed these shipments since the Code’s inception.

Seaborne trade in ammonium nitrate and AN-based fertilizers runs at approximately 7 to 8 million tonnes per year as of 2024, with Russia the single largest exporter at roughly 2.7 million tonnes annually, accounting for about 37% of global export volume. Brazil is the top destination for Russian AN; India and the United States are the next largest markets. The cargo is nitrogen-only or nitrogen-dominant: no phosphate or potash content, which distinguishes it from diammonium phosphate and urea, both of which are Group C. AN fertilizer’s hazard profile is categorically different from every other solid fertilizer in bulk trade, and the schedule structure under the IMSBC Code reflects that.

Chemistry and why it matters at sea

Ammonium nitrate (NH4NO3) is the ammonium salt of nitric acid. At ambient temperature it is a white crystalline or granular solid, water-soluble and hygroscopic. The marine hazard derives from three properties: it is a strong oxidizer, it can undergo self-sustaining thermal decomposition, and under specific conditions of confinement, contamination, and heat, it can detonate.

Oxidizer behavior

AN is an oxidizer because it contains nitrate (NO3-), an anion that releases oxygen when it decomposes. This oxygen release happens within the compound itself, without needing atmospheric oxygen. A fire in a hold containing AN fertilizer will not be suppressed by smothering: the cargo provides its own oxidant. Inert gas systems (CO2, N2) that are effective on hydrocarbon fires are largely useless against an AN fire because the oxidizer is chemically bound inside the cargo mass, not drawn from the surrounding atmosphere.

The IMDG Code classifies the high-concentration grades as Class 5.1 (oxidizing substances). The IMDG Class 5 article covers the broader oxidizer classification framework.

Decomposition: the staged hazard

AN decomposes in stages as temperature rises, each stage more dangerous than the last:

At 170 to 200 degrees Celsius, decomposition begins slowly, releasing nitrous oxide (N2O) and water vapor. This stage is still manageable.

Above 200 degrees Celsius, decomposition accelerates and the gas mix shifts toward nitrogen oxides (NOx), including toxic nitrogen dioxide (NO2). Cargo space atmosphere becomes immediately dangerous to enter without breathing apparatus.

Above approximately 230 to 250 degrees Celsius, the decomposition reaction can become self-sustaining: it continues propagating through the cargo mass after the external heat source is removed. This is the self-sustaining decomposition (SSD) threshold. SSD in bulk AN can raise cargo temperature hundreds of degrees further in minutes, generating large volumes of toxic gas and creating internal pressure that, under confinement, can transition to detonation.

The SSD phenomenon is composition-dependent. Higher ammonium nitrate concentrations and certain impurities (chlorides in particular) lower the threshold at which SSD initiates and increase the propagation rate through the cargo mass.

The detonation pathway

AN does not detonate spontaneously under normal handling. The detonation pathway requires a combination of: high ammonium nitrate concentration (above roughly 70% by mass in most formulations), contamination by a sensitizing agent (fuel oil, organic matter, sulphur, copper compounds, or chlorides), strong confinement (the cargo cannot vent rapidly), and sufficient initiating energy (a fire, explosion, or sustained heat source). Remove any one of these conditions and detonation risk drops sharply. The IMSBC schedule requirements for AN fertilizer target each condition individually.

The IMSBC schedule structure before Amendment 06-21

Before Amendment 06-21 became mandatory, the IMSBC Code contained three distinct schedules for AN-based fertilizers in bulk:

AMMONIUM NITRATE BASED FERTILIZER, UN 2067 (Group B, Class 5.1): High AN-content fertilizers, oxidizer-classified, requiring IMDG subsidiary risk handling. Composition limits: not less than 90% AN with not more than 0.2% total combustible organic material; or 70 to 90% AN with inorganic inerts and not more than 0.4% combustible material; or AN/ammonium sulphate mixtures above 45% AN and below 70% AN where the combined AN + ammonium sulphate content exceeds 70%. This was the workhorse schedule for straight ammonium nitrate fertilizer and for the blended grades that are predominantly AN.

AMMONIUM NITRATE BASED FERTILIZER, UN 2071 (Group B, Class 9): Lower AN-content compound fertilizers containing nitrogen, phosphate, or potash, with not more than 70% AN and not more than 0.4% combustible organic material, or not more than 45% AN with unrestricted combustible material. These were classified Class 9 for the SSD hazard rather than Class 5.1 for oxidizer risk. The IMSBC Code required a negative trough test result before bulk shipment: cargo for which the trough test showed self-sustaining decomposition propagating faster than 25 centimeters per hour could not be carried in bulk under this schedule.

AMMONIUM NITRATE BASED FERTILIZER (non-hazardous) (Group C): AN-based fertilizers that met specific low-risk composition criteria and did not exhibit SSD in the trough test. Carried as Group C with no IMDG class designation.

The UN 2067 schedule covered the cargoes presenting the greatest hazard: high-AN-content fertilizers with real oxidizer and potential detonation risk. The UN 2071 schedule captured compound fertilizers where the AN content was lower and the primary concern was SSD rather than straight oxidizer activity. The non-hazardous schedule captured the lowest-risk blends.

Amendment 06-21: the restructured framework

IMO Resolution MSC.500(105), adopted at MSC 105 on 28 April 2022, overhauled the AN fertilizer schedule structure entirely. The amendment became available for voluntary implementation on 1 January 2023 and mandatory under SOLAS from 1 December 2023. This is the current applicable regime.

The amendment deleted three schedules: the pre-existing AMMONIUM NITRATE BASED FERTILIZER (non-hazardous) schedule, the UN 2067 schedule, and the UN 2071 schedule. In their place, it introduced two new schedules.

AMMONIUM NITRATE BASED FERTILIZER (Group C, new schedule)

This schedule covers AN-based fertilizers that meet specified composition limits and do not exhibit SSD. The Group C classification means the cargo is not liquefiable and carries no chemical hazard designation in the IMSBC sense. However, Group C does not mean the cargo is inert: it still contains ammonium nitrate and retains the associated oxidizer and decomposition chemistry. The carriage controls, while less onerous than Group B, still require hold cleanliness, segregation from incompatible cargoes, and cargo declaration.

The composition boundaries for Group C carriage are specified in the schedule. Straight nitrogen fertilizers with an AN content not exceeding 70% combined with inorganic inerts qualify, as do AN/carbonate mixtures up to 80% AN content, and AN/ammonium sulphate mixtures with AN content not exceeding 45%, provided the chloride content is below 2%. Compound NPK/NK/NP fertilizers with less than 20% AN content also qualify regardless of chloride, as do those with chloride below 2% regardless of AN content within the overall composition limits.

Critically: any cargo that is assigned Class 9 because the trough test confirms self-sustaining decomposition is excluded from this Group C schedule entirely. A positive SSD trough test result takes the cargo out of the IMSBC AN schedules and into the IMDG packaged-goods regime as a Class 9 dangerous good.

AMMONIUM NITRATE BASED FERTILIZER MHB (Group B, new schedule)

The MHB schedule captures AN-based fertilizers that are neither clearly low-risk enough for Group C nor classified as packaged dangerous goods under IMDG, but that present a thermal decomposition hazard (the MHB designation is OH, for “other hazards”). The characteristic that places a cargo in this schedule rather than the Group C one is elevated chloride content (2% or above) combined with meaningful AN content (20% or above), or the specific composition combination of not more than 70% AN with up to 0.4% combustible material, or not more than 45% AN with unrestricted combustible material and the elevated chloride threshold.

Chloride matters because chloride ions catalyze the thermal decomposition of ammonium nitrate, reducing both the initiation temperature for SSD and the energy needed to trigger it. A high-chloride AN fertilizer is more hazardous than a nominally identical low-chloride one, and the MHB schedule reflects this by imposing Group B controls: emergency schedule availability, enhanced crew awareness, and reporting requirements under SOLAS.

Like the Group C schedule, the MHB schedule also excludes materials assigned Class 9 for SSD based on the trough test. A cargo that fails the trough test has a hazard profile that exceeds what the MHB schedule is designed to accommodate.

Note that UN 2067 (Class 5.1, the high-AN oxidizer) and UN 2071 (Class 9, the SSD-classified compound fertilizer) remain valid UN numbers under the UN Recommendations on the Transport of Dangerous Goods and in the IMDG Code for packaged carriage. What Amendment 06-21 changed is specifically the IMSBC bulk-cargo schedule structure: the named individual IMSBC schedules bearing those UN numbers in their titles were deleted and the two new schedules above were substituted.

The trough test and self-sustaining decomposition classification

What the trough test is

The trough test is defined in the UN Manual of Tests and Criteria, Part III, Section 39. It is the standard method for determining whether a substance can undergo self-sustaining decomposition at a rate and temperature that poses a transport hazard. The test apparatus is a steel or aluminum trough, open along the top, with internal dimensions of 500 mm in length, 90 mm in width, and 90 mm in depth. The trough is filled with the test substance in its representative form (granule, prill, or crystal) to the full depth of 90 mm across the full 500 mm length.

An initiating heat source is applied at one end of the trough. The standard method uses a gas flame applied to the end face of the sample through a pilot flame or a tubular heater, typically reaching 500 to 600 degrees Celsius at the point of initiation. This initiates decomposition at the heated end of the sample. The heat source is then removed after a defined period, typically 10 minutes, enough to ensure the decomposition front has established itself.

What happens next is the pass/fail criterion. If decomposition propagates along the trough from the initiation end toward the unheated end, and if the propagation rate exceeds 25 millimeters per hour, the substance is considered to undergo self-sustaining decomposition under the conditions relevant to transport. The 25 mm/hour threshold translates to the decomposition front advancing at least 12.5 mm through a standard trough in the observation period after flame removal.

Temperature is measured by thermocouples embedded in the substance at defined positions along the trough length: typically at 50 mm, 200 mm, and 400 mm from the initiation end. The thermocouple readings confirm whether the decomposition front has reached each sensor position, and the time interval between sensors gives the propagation rate. Gas evolution, visible exothermic reaction, and surface melting or discoloration are secondary observations logged alongside the temperature data.

What a positive result means

A substance that passes the trough test at a propagation rate above 25 mm/hour is assigned to IMDG Class 9, Sub-type OH (other hazard: self-sustaining decomposition), regardless of its ammonium nitrate content. For AN-based fertilizers specifically, a positive trough test result has three direct regulatory consequences.

First, the cargo cannot be shipped in bulk under any current IMSBC AN fertilizer schedule, including both the Group C and the Group B MHB schedules introduced by Amendment 06-21. The individual schedules explicitly exclude substances assigned Class 9 for SSD.

Second, the cargo must travel in packaged form, fully subject to IMDG Code requirements for Class 9 dangerous goods. This means packaging, marking, labeling, placarding, stowage, and segregation per the IMDG Code individual schedule for the specific UN entry, not the relaxed bulk-cargo requirements of the IMSBC.

Third, the shipper must hold a current, valid trough test certificate from an accredited testing laboratory to demonstrate the negative result required by the schedule. Without that certificate, the cargo is presumed to have failed the trough test. Many port state control authorities in Europe and Asia will not permit loading to commence without sight of a valid certificate. Industry practice in major loading ports, including the Baltic ports that handle Russian AN exports, treats a certificate no older than three months as current. Some operators specify a 12-month validity period aligned with the production batch cycle, but the shorter period is the cautious standard.

Why composition controls the test result

The same AN-based fertilizer from the same plant does not always produce the same trough test result. Batch composition variation drives pass/fail outcomes. Key variables include the ammonium nitrate content itself, the chloride content (above approximately 1% chloride measurably reduces the SSD threshold), the presence of organic coatings used to reduce hygroscopicity (some coating agents are reducing agents that sensitize the AN mass), and the density and porosity of the granule or prill. A dense granule restricts gas permeability through the cargo mass, trapping decomposition gases and raising local pressure, which accelerates propagation.

Fertilizer producers shipping to regulated markets run trough tests on every production batch intended for bulk export. A single batch result showing propagation above 25 mm/hour cannot be blended away: the batch must be reprocessed, held, or diverted to packaged shipment.

Segregation and stowage requirements

The incompatibility list

AN fertilizer’s oxidizer chemistry, combined with its sensitivity to contamination and catalytic degradation, produces a long incompatibility list. The IMSBC Code individual schedules specify the applicable IMDG segregation table entries, which in turn reference the full segregation framework of IMDG Code Part 7. For bulk AN carriage, the practical requirements are:

Fuel oil and petroleum products. AN must be stowed clear of any fuel oil bunker tank, fuel service tank, or fuel settling tank unless separated by a cofferdam or a void space. The minimum separation in most flag-state interpretations is one structurally integral, dry, empty compartment between the AN hold and any adjacent fuel space. A tank top bulkhead is not sufficient. Fuel oil piping that passes through or along an AN hold boundary must be confirmed watertight before loading. The bunkering prohibition during the voyage extends to any bunkering activity where fuel delivery hoses pass within reach of open hatches.

Combustible materials. Coal, sulphur, grain, fishmeal, woodchip, and any organic cargo must not share an adjacent hold with AN fertilizer. The contact risk is not only via structural failure: coal dust or organic dust circulating in the hold ventilation system can deposit on AN cargo surfaces. The adjacent-hold rule, not just the same-hold rule, applies. For vessels with a two-hold separation standard applied at the shipper’s request, this means holds 1, 3, and 5 of a five-hold vessel should not all carry AN if holds 2 and 4 carry coal.

Chlorates and perchlorates. These are oxidizers that react with AN under heating, generating a combined oxidizer mass with lower decomposition threshold than AN alone. Chlorates are explicitly listed as incompatible in the IMDG segregation tables and must be stowed “away from” AN under the IMDG Code requirements.

Acids. Mineral acids, including sulfuric acid, hydrochloric acid, and nitric acid, react exothermically with AN and can initiate decomposition at concentrations and temperatures well below the AN self-ignition point. AN cargo must be segregated from acids consistent with the IMDG “separated from” requirement where packaged acids are co-loaded.

Metal powders and reactive metals. Copper powder, aluminum powder, and other reactive metal powders can sensitize AN to detonation. Ammonium nitrate in the presence of finely divided metals forms shock-sensitive compositions at lower concentrations than in the pure form.

Hypochlorites and halogenated oxidizers. Pool chemicals and bleaching agents containing hypochlorite or calcium hypochlorite are incompatible. The reaction of AN with hypochlorite in the presence of moisture generates chlorine gas and increases local decomposition risk.

No-hot-work regime

The no-hot-work requirement for AN cargo holds is absolute and extends beyond the immediate cargo boundary. Welding, cutting, grinding, flame-heating, and any other activity producing sparks or sustained open flame are prohibited in:

• The cargo hold itself
• The deck directly above the hold, including deck fittings, manholes, and hatch coamings
• Any machinery space or pump room sharing a bulkhead with the cargo hold
• Any void space or cofferdam adjacent to the hold

The prohibition runs from the commencement of cargo operations at the loading port through to the completion of discharge and hold cleaning at the discharge port. It is not suspended during port stays, at anchor, or during cargo operations. It must be captured in the vessel’s permit-to-work system as an active standing prohibition for each day of the AN voyage.

In practice, crews on AN voyages apply hot-work permits with a cargo-adjacent exception that requires the chief officer or master to personally authorize any exception in writing, with documentation of hold atmosphere checks (particularly NO2 monitoring) immediately before, during, and after any permitted work.

No-smoking and ignition-source discipline

The no-smoking requirement applies throughout the cargo hold, its adjacent spaces, and the weather deck above the hold. Lighters, matches, portable electrical equipment not rated for use in explosive atmospheres, and non-intrinsically-safe communication equipment must be kept out of these zones. The cargo spaces of an AN-laden vessel are not classified as ATEX/IECEx explosive atmospheres in the same sense as a tanker’s pump room, but the ignition-source discipline is the same in practical terms: any spark or flame in contact with a decomposing AN mass at elevated temperature can initiate or accelerate the decomposition process.

Emergency response and firefighting

The water requirement

A fire in or adjacent to an AN cargo hold requires water, and a lot of it. The IMSBC Code emergency response guidance, aligned with IMO MSC circular guidance and International Fertilizer Association firefighting recommendations, specifies water as the agent of choice. The reasoning is direct: water absorbs heat, reduces cargo temperature toward and below the decomposition threshold, and dilutes the AN mass, reducing local AN concentration. A sustained flood-level application, not a surface spray, is required.

The IFA guidance (International Fertilizer Association) calls for water flows sufficient to achieve genuine bulk cooling, not surface cooling. Estimates for large bulk cargo holds suggest flow rates of 100 to 200 tonnes per hour may be required to penetrate an actively decomposing mass and arrest temperature rise. A ship’s fixed fire-suppression system delivers water at pressure, but the total volume available from deck monitors and fire mains on a typical bulk carrier may be 40 to 80 tonnes per hour. Full port fire brigade assistance, if available at anchor or alongside, changes the arithmetic.

Do NOT use steam, CO2, or dry chemical

Steam injection is actively contraindicated for AN fires. Steam can actually accelerate AN decomposition by driving the endothermic dehydration reactions in AN’s lower-temperature decomposition pathway, pushing the cargo mass faster through the stages toward SSD. CO2 and nitrogen inert gas are ineffective because the oxidant is inside the AN itself, not in the hold atmosphere. Smothering the hold, whether by closing hatches or injecting inert gas, removes the atmospheric oxygen contribution but leaves the chemically bound nitrate oxygen fully available for decomposition.

Dry chemical agents do not cool the cargo mass. They can knock down a surface flame but they cannot arrest decomposition propagating through a bulk AN mass. Their use is not incorrect as a supplementary surface measure, but it cannot be the primary response.

Do NOT confine the cargo

The confinement condition, cargo that cannot vent its decomposition gases, is one of the four preconditions for detonation. Closing hatches on an AN fire provides exactly this condition. The IMSBC emergency guidance is specific: open hatches, open ventilation, do not seal the hold. Counterintuitive as this runs against standard cargo-fire smothering practice, it is correct for AN. The toxic NOx gases released need to vent, and the internal pressure that drives the transition from SSD to detonation needs a pathway to dissipate.

Atmosphere monitoring during the response

Before any crew member enters or approaches the cargo hold for firefighting, the hold atmosphere must be tested for NO2. Nitrogen dioxide at 20 parts per million is the IDLH (immediately dangerous to life and health) level. A hold in which AN decomposition is active may have NO2 concentrations 10 to 100 times this level. Self-contained breathing apparatus (SCBA) is mandatory for any entry, even above-deck approach to an open hatch in an active decomposition event.

Fixed atmospheric monitoring systems on newer vessels can relay NO2 readings to the bridge without requiring manual hold entry. Portable multi-gas meters carried by the emergency team must include a calibrated NO2 sensor.

Evacuation and abandonment threshold

The master and chief officer must establish a temperature trigger at the start of every AN voyage: a cargo temperature or rate-of-rise threshold at which the emergency plan transitions from active firefighting to evacuation preparation. This threshold is not defined in universal regulation, because it depends on the cargo grade, the hold geometry, and the available firefighting resources.

The operational reality from documented AN fire incidents is that once cargo temperature in a bulk AN hold exceeds approximately 200 degrees Celsius at any sensor and continues to rise despite active water application, the window for effective intervention is closing rapidly. At that temperature, decomposition is producing NOx at rates that will overcome ventilation, and the cargo mass is approaching the SSD initiation zone.

The IMSBC Code emergency schedule for Group B cargoes, and the broader SOLAS Chapter II-2 fire safety requirements, require the master to have a clear written decision tree in the ship’s fire control plan. For AN specifically, industry practice (consistent with UK MCA guidance and class society recommendations) is that if water application at full available flow rate is not reducing measured cargo temperature after 30 to 60 minutes of firefighting, the vessel should be moved to open water if possible, all non-essential crew should be mustered at lifeboat stations, and the master should be prepared to authorize abandonment if temperature continues to rise.

Loading, monitoring, and documentation requirements

Pre-loading cargo inspection

The loading process for ANBF starts before the first tonne is weighed. The cargo superintendent or a qualified independent surveyor must confirm the cargo grade, the batch composition analysis, and the trough test certificate before loading commences. For AN cargoes that fall under the Group B MHB schedule, this inspection is a SOLAS requirement, not just a commercial prudence measure.

Cargo sampling at the warehouse or loading terminal, independent of the shipper’s own analysis, is standard practice for high-AN-content cargoes. The sample is tested for AN content, total combustible organic material, chloride content, and moisture. Results that deviate by more than 2% variance on AN content or more than 0.1% variance on combustible material from the declared values should trigger re-declaration and potential rejection of the batch.

The loading conveyor and chutes must be free of any hydrocarbon residue. If belt conveyors previously handled coal or other reactive cargo, the belt surface must be cleaned before AN loading begins. A visual inspection of the conveyor system by the cargo superintendent before loading starts is part of the pre-loading checklist.

Hold inspection and certification

The hold inspection for an ANBF cargo combines a structural check with a contamination check and a hardware audit.

Structural: hatch covers operate correctly, the hatch seals are intact, bilge covers are fitted with filter material to prevent cargo ingress, and the hold ventilation covers function. The bilge suctions must be tested before loading to confirm the bilge system works.

Contamination: the hold must be visually clean under inspection lighting. Swab testing for fuel oil residues, chloride, and sulphur is standard practice in ports serving high-value AN trades. A chloride swab positive above 5 milligrams per square meter on a hold surface is grounds for additional washing before acceptance.

Hardware audit: every copper or copper-alloy fitting inside the hold must be logged. Copper bronze valves on bilge suctions, copper fire-suppression sprinkler heads, and any copper piping within the hold boundary are the typical items. Fittings that cannot be removed must be coated or protected with non-reactive materials. The inspection log forms part of the cargo declaration package.

Temperature sensor placement during loading

Temperature probes or data loggers placed in the cargo mass during loading give the most reliable indication of cargo condition throughout the voyage. The standard practice is to place calibrated sensors at three depths in each hold: shallow (300 to 400 mm below the cargo surface), mid-depth (approximately 50% of cargo depth), and near the hold bottom. Sensors are embedded in the cargo as loading proceeds in layers, with the cable or telemetry line run to a deck connector that links to the bridge monitoring system.

The placement depth matters because decomposition, if it initiates, typically begins at a point of contamination or temperature concentration, which is rarely the cargo surface. A surface probe will not detect a deep-seated hot spot until it has propagated substantially toward the surface.

Monitoring during the voyage

Temperature readings from the embedded sensors must be logged at regular intervals throughout the voyage, with the interval specified in the individual schedule or the ship’s cargo plan. For Group B MHB cargoes, a 4-hour logging interval is typical; high-AN Group C cargoes with elevated ambient temperatures warrant the same. The log must record both absolute temperature and the rate of change per hour.

A temperature reading that exceeds ambient plus 10 degrees Celsius at any sensor position should be noted and monitored more closely. A rate of rise above 1 degree Celsius per hour that persists across two consecutive readings, particularly if the ambient temperature is not rising, is a warning sign requiring active investigation.

Hold atmosphere checks, including visual inspection of hatch seals and bilge systems, should be conducted at the same intervals as temperature monitoring. Any seepage of nitrous or acrid odor from a hold vent or hatch seal joint requires immediate hold atmosphere testing with a calibrated NO2 detector.

Cargo declaration: the full document set

The shipper’s cargo declaration for ANBF must be complete and correct before the vessel sails. Under SOLAS Regulation VI/2 and the IMSBC Code Section 4, the master is entitled to refuse to load if the cargo declaration is incomplete or inconsistent with the cargo actually presented. The declaration must include:

The IMSBC schedule name and the applicable Group (C or B MHB under the current post-06-21 framework), stated explicitly. A declaration that says only “ammonium nitrate fertilizer” without identifying the schedule is insufficient.

The ammonium nitrate content by percentage mass, as determined by batch analysis. The combustible organic material content by percentage mass. The chloride content by percentage mass. The moisture content at the time of loading. These four composition parameters are the data that determines which schedule applies; an error in any of them can place a Group B cargo under a Group C declaration or vice versa.

The trough test result: negative, confirmed by certificate reference (issuing laboratory, date of test, batch identifier). If the schedule being claimed requires a negative trough test, the certificate must be attached or referenced.

For multi-origin cargoes where cargo from more than one production batch is blended, the declaration must cover each batch component, and the trough test must cover the blended composition, not only individual batch components.

Port state control surveyors and flag-state inspectors have detained vessels for incomplete ANBF cargo declarations. A declaration that understates chloride content to avoid Group B classification is treated as document falsification, not as a paperwork error. Several European and Australian port state authorities have adopted a policy of independent batch sampling at loading to verify AN and chloride content where there is a prior history of mis-declaration by a shipper or loading terminal.

Cargo trimming and compaction limits

AN fertilizer prills and granules are free-flowing under normal conditions but can compact and cake under the weight of a full hold load. Compaction increases the density of the cargo mass, reduces gas permeability, and can trap decomposition gases if SSD initiates, creating localized pressure buildup. The IMSBC schedule guidance indicates the cargo should be trimmed level or slightly heaped, not deliberately compacted or vibration-settled beyond what occurs during loading.

Loading rates should not be so high that cargo is dropped from significant height into the hold, which can both compact the surface and generate AN dust. AN dust in the atmosphere above the cargo is, at minimum, a respiratory hazard and, at elevated temperatures, a potential ignition-source risk.

Historical incidents: what the regulations are responding to

The ammonium nitrate carriage regime is built on documented catastrophes. Three incidents frame the regulatory development, each distinct in character.

Oppau, Germany, 1921

On 21 September 1921, workers at BASF’s Oppau plant used explosive charges to break up hardened cakes of ammonium sulphate-nitrate fertilizer stored in a silo. The mixture, modified by a new spray-drying process earlier that year, had acquired properties that the existing handling procedure hadn’t anticipated. The stored mass detonated. More than 500 people died and approximately 1,000 were injured. Around 1,036 buildings were destroyed. The Oppau disaster established that AN-based mixtures with specific physical characteristics could detonate under industrial blasting intended only for mechanical loosening.

Texas City, Texas, 1947

On 16 April 1947, the French freighter SS Grandcamp was loaded with 2,300 tonnes of ammonium nitrate fertilizer (bagged) in the hold when a fire started, origin unconfirmed. The hatches were closed to smother the fire, creating the confinement condition. At 09:12 local time, the hold detonated. The blast killed 581 people, injured approximately 3,500, destroyed the ship, and set fire to a second AN-laden vessel, the SS High Flyer, which detonated sixteen hours later. Texas City remains the deadliest industrial accident in United States history. The cargo was bagged rather than bulk, but the mechanism, sealed hold plus oxidizer plus heat plus contamination, is directly analogous to the risks in bulk AN carriage.

Beirut Port, Lebanon, 2020

On 4 August 2020, approximately 2,750 tonnes of ammonium nitrate detonated at Beirut Port, killing 218 people and injuring around 7,000. The Beirut material is not directly analogous to a compliant IMSBC bulk shipment. The ammonium nitrate was technical-grade, not a fertilizer formulation; it had been confiscated from the abandoned cargo vessel MV Rhosus in 2014 and stored without proper controls in a port warehouse for six years; it was not subject to temperature monitoring, segregation from ignition sources, or cargo declaration. The proximate cause was a fire in an adjacent warehouse storeroom that communicated heat to the confined AN mass. The fact that this is not a maritime-carriage incident does not reduce its relevance to the regulatory framework: it confirms what the IMSBC controls are preventing when they work correctly, and Lebanese port authorities had received multiple written warnings from customs officials that the stored AN presented a detonation risk.

The IMSBC Code carriage regime eliminates the conditions that led to Beirut: compliant holds are cleaned of contaminating residues before loading, cargo is declared by composition, temperature is monitored throughout the voyage, and the cargo is never confined with fire-starting materials. The Beirut disaster tightened regulatory attention to port storage practices and AN traceability globally, but it is a port storage failure, not a ship carriage failure.

Contamination: the principal detonation pathway at sea

The single most documented pathway to catastrophic AN behavior aboard ship is contamination, not temperature alone. AN is chemically reactive toward several common shipboard and cargo-related substances:

Fuel oil and hydrocarbon liquids. AN mixed with hydrocarbon creates a mixture with dramatically reduced detonation threshold. This is the basis of ANFO (ammonium nitrate/fuel oil), a commercial mining explosive, which uses approximately 94% AN and 6% fuel oil as a formulation optimized for blasting. Fuel oil contamination of an AN cargo hold, from a spill during bunkering, from a previous cargo, or from a failing bulkhead to an adjacent fuel tank, converts part of the AN cargo mass into a product with detonation sensitivity approaching a commercial explosive. The IMSBC Code requirement for no bunkering adjacent to AN holds and the strict previous-cargo sweep are both responses to this.

Copper and copper alloys. Copper reacts with AN to form copper ammonium nitrate complexes. These complexes are shock-sensitive, meaning they can be initiated by mechanical impact rather than requiring the temperature and confinement conditions needed for pure AN detonation. Any copper piping, copper-bearing fire-suppression nozzles, copper fittings in bilge systems, or bronze valves that contact the cargo or the cargo atmosphere are a concern. Pre-loading inspection must identify and isolate all copper-bearing hardware in the hold.

Chlorides. Chloride ions catalyze AN decomposition by reducing the initiation energy and lowering the SSD onset temperature. This is why the Amendment 06-21 framework uses chloride content as a classification criterion: fertilizers with 2% or more chloride go to the MHB Group B schedule, not the Group C one.

Sulphur and organic dust. Sulphur and organic materials (grain dust, coal dust, wood flour) are reducing agents that react exothermically with AN under heat. A hold that carried coal or grain and was not properly cleaned before AN loading provides exactly this initiating condition.

Acids. Acid contamination (from leaking battery acid, or from acidic cleaning residues) can initiate AN decomposition directly.

Hold preparation

The IMSBC schedule requirements for ANBF hold preparation are more demanding than those for most other bulk cargoes, for exactly the contamination reasons above.

Previous cargo sweep. The hold must be swept and washed of all residues. Previous cargoes that are incompatible: coal, sulphur, grain, any organic cargo, any oxidizing cargo (other AN grades, calcium nitrate), and any cargo containing chlorides. Each of these leaves a chemical residue that, in contact with AN, either increases decomposition risk or, in the fuel oil or copper cases, creates genuine detonation sensitization. The sweep must produce a clean, visually residue-free hold surface, confirmed by a qualified surveyor.

No lime wash. Lime (calcium hydroxide, pH above 12) accelerates AN decomposition. A lime-washed hold is not acceptable for AN loading. Holds that received lime wash treatment for a previous cargo must be stripped, washed, and pH-verified before AN loading begins.

Coating integrity. Bare steel should be coated to prevent direct contact with AN. Ammonium nitrate in the presence of moisture is mildly corrosive to steel. More importantly, bare steel surfaces can serve as sites for localized heating under decomposition conditions.

Copper isolation. All copper and copper alloy fittings that will contact the cargo or cargo atmosphere must be identified on the pre-loading inspection. The standard practice is to cover or remove accessible copper-bearing fittings and to document those that cannot be removed.

Bilge system. Bilge wells must be clean, dry, and free of any oily residue. Bilge water under an AN cargo would dissolve AN and carry it toward the bilge pumps. AN solution in the bilge, if it contacts oily residue, creates a localized contamination hazard. The bilge wells must be sealed with appropriate filter coverings.

Pre-loading certification. For UN 2067 cargoes and for the Group B MHB schedule under the post-06-21 regime, the cargo declaration and hold inspection report must be completed before the first tonne enters the hold.

Carriage controls during the voyage

Temperature monitoring

The IMSBC schedule for the oxidizer grades (previously UN 2067, now the comparable Group B or high-AN Group C cargoes) requires cargo temperature monitoring throughout the voyage. The monitoring interval and sensor placement are set out in the individual schedule. Cargo temperature above approximately 40 degrees Celsius above ambient, or any sustained rise that cannot be attributed to ambient warming, is a warning sign. The practical target is to detect any localized decomposition before it reaches the self-sustaining threshold.

Surface temperature measurement at hatch openings is the minimum; calibrated temperature sensors placed in the cargo mass before sealing the hold give a more reliable picture of internal conditions. Some operators use continuous logging systems with bridge alarm outputs on AN voyages.

Atmosphere monitoring

Nitrogen dioxide (NO2, a component of the NOx generated by AN decomposition) is toxic above 3 ppm (OSHA 8-hour TWA) and immediately dangerous above 20 ppm. If cargo temperature is rising or if the crew detects a sharp, acrid odor from a hold, the hold atmosphere must be tested before any entry. Enclosed-space entry precautions apply to all ANBF-loaded holds throughout the voyage.

CO2 monitors are less useful for early detection than NO2 detectors for AN cargoes. Standard enclosed-space atmosphere testing for oxygen content and combustible gases should be supplemented with specific NOx detection for AN holds.

No hot work

Welding, cutting, grinding, and all other hot work are prohibited in or adjacent to AN cargo holds during loading, the entire voyage, and discharge. This prohibition extends to the deck above the holds and to spaces sharing a boundary with the cargo hold. The no-hot-work requirement must be entered in the ship’s permit-to-work system for every day of the AN voyage, not just flagged at departure.

No adjacent bunkering

Bunkering with fuel oil must not take place when fuel delivery involves hoses passing over or adjacent to open AN hatches, or when there is any risk of fuel oil reaching the cargo. The contamination threshold for fuel oil in AN is extremely low: even a small fuel spill into an AN hold creates locally sensitized material.

Segregation from incompatible cargoes

The IMSBC Code and the IMDG Code both specify segregation requirements for AN cargoes. Under the IMSBC Code Group B cargo framework, AN must be segregated from acids, oils, organic materials, and certain other hazardous substances. In practice, this means:

• No adjacent hold carrying coal, sulphur, or grain residues
• No adjacent fuel tank without a confirmed-watertight bulkhead
• No comingled loading with mixed fertilizer types that include incompatible additives

For vessels carrying multiple fertilizer types in different holds, the pre-loading planning must confirm compatibility of all adjacent holds. AN in one hold and a chloride-rich fertilizer in an adjacent hold is not a significant risk if segregation is maintained, but the holds must not be mixed.

Fire response

A fire in or adjacent to an AN cargo hold is one of the most operationally complex emergencies a ship’s crew can face. The standard IMSBC guidance, consistent with industry firefighting doctrine, is:

Water, not inert gas. Large quantities of water are the recommended firefighting agent. The goal is to cool the cargo mass and prevent the temperature from reaching the decomposition and SSD thresholds. Water must be applied in sufficient volume to absorb the heat being generated: a surface douse will not penetrate to a deep-seated fire. CO2 and nitrogen inert gas systems will not suppress an AN fire because the cargo supplies its own oxidant.

Ventilate. Open hatches and ventilate holds to reduce the concentration of toxic NOx gases and to prevent the pressure buildup that contributes to the confinement condition for detonation. Counterintuitive as it may seem after cargo management has involved keeping hatches sealed, ventilation during a fire reduces one of the key detonation-enabling conditions.

Evacuate non-essential personnel. All personnel not involved in fire control should move to the muster station and prepare for abandonment.

Recognise the limits of control. If cooling with water is not reducing cargo temperature, or if temperature continues to rise despite firefighting efforts, the transition to SSD and potentially to detonation may be imminent. IMSBC and industry guidance is explicit: when thermal runaway cannot be controlled, the vessel should be abandoned and the crew allowed to reach a safe distance. A detonating ship cannot be saved by remaining aboard it.

The decision to abandon is among the hardest a master will make. The fact that the Texas City SS Grandcamp crew attempted to fight the fire in a closed hold, and that the hatches were sealed to smother it, contributed directly to the detonation. Modern IMSBC guidance reflects that lesson.

Cargo declaration requirements

The shipper’s cargo declaration for any ANBF shipment must specify:

• The applicable IMSBC schedule (Group C or Group B MHB under Amendment 06-21 rules, or the applicable IMDG entry for packaged goods)
• The ammonium nitrate content by percentage mass
• The total combustible organic material content
• The chloride content
• The trough test result (negative), with certificate reference, for cargoes where the trough test applies
• Any other specified composition data required by the individual schedule

A declaration that understates the AN content, misreports the chloride level, or fails to disclose a positive trough test is a document falsification with direct safety consequences. Port state control authorities in many jurisdictions now sample-test ANBF shipments at loading to verify declaration accuracy, partly in response to cases where shippers underreported AN content to avoid the more demanding Group B handling requirements.

The global ammonium nitrate fertilizer trade

Russia produces approximately 12 million tonnes of ammonium nitrate per year, roughly 47% of global output, and exported about 2.7 million tonnes in 2024. Brazil is the largest single destination for Russian AN exports; India and the United States follow. Egypt (through Helwan and El Nasr fertilizer plants), Trinidad and Tobago (YARA Trinidad), and Ukraine (when production has continued) are other significant exporters.

The trade is sensitive to sanctions and export restrictions. Russia periodically imposes AN export quotas for domestic supply security reasons: a quota of 2.6 million tonnes was in place for December 2025 to May 2026. Quota announcements create short-term freight volatility on AN-heavy routes.

Major import terminals for bulk AN fertilizer include Paranagua and Santos (Brazil), Kandla and Paradip (India), and East Coast US ports. The cargo typically moves on Handysize and Supramax bulk carriers (25,000 to 60,000 DWT): the chemical hazard requirements, strict hold preparation, and the need for inspection and certification at both ends make the very large Capesize vessels less common on AN trades, even where terminal capacity would permit them.

Physical properties of AN fertilizer vary by product type and production method. Straight ammonium nitrate (prill or granule) typically has a bulk density of 0.80 to 0.88 tonnes per cubic metre and a stowage factor of around 1.14 to 1.25 cubic metres per tonne. The prilled forms are generally more permeable and run cooler than dense granule. Calcium ammonium nitrate (CAN), the 27% nitrogen blended grade containing calcium carbonate, has a bulk density of approximately 0.95 to 1.05 tonnes per cubic metre.

Comparison with related fertilizer cargoes

The contrast between AN fertilizer and the phosphate and urea fertilizers (urea IMSBC schedule, DAP) is large. DAP and urea are both Group C, both non-oxidizers, and neither has a plausible detonation pathway. Their handling hazards, ammonia evolution and hygroscopic caking, are real but do not involve the risk of catastrophic energy release.

Regulatory framework

The IMSBC Code is mandatory under SOLAS Chapter VI, Regulation 1-1, for all vessels carrying solid bulk cargoes on international voyages from 1 January 2011. The current edition incorporating Amendment 06-21 is the governing instrument for all ANBF bulk shipments from 1 December 2023.

The IMSBC Code is a living instrument: amendments follow the standard IMO two-year cycle through the Sub-Committee on Carriage of Cargoes and Containers (CCC). For AN specifically, additional guidance has been issued through IMO circular CCC.1/Circ.4, which addresses self-sustaining decomposition, and through SOLAS Chapter II-2 on fire protection requirements applicable to dangerous-cargo carriers.

The Code sits within a wider regulatory stack. SOLAS Chapter VII governs the carriage of dangerous goods in ships. The IMDG Code, mandatory under SOLAS VII, applies when AN is carried in packaged form rather than in bulk. The Classification Society rules, particularly for structural matters like hold coatings and bilge systems, interact with the cargo requirements. Port state control inspections under the Paris MOU and Tokyo MOU verify compliance with the cargo declaration requirements, hold preparation, temperature monitoring, and segregation controls: a vessel with improper hold preparation documentation for an AN cargo can be detained.

The IMSBC Code overview article, the Group B cargoes article, and the Group C cargoes article give broader context on the regulatory structure within which the AN schedules sit.

Related calculators

• IMSBC Ammonia Nitrate UN1942
• IMSBC Ammonia Nitrate Based Fertilisers UN2067
• IMSBC Urea Ammonium Nitrate
• IMSBC Calcium Nitrate
• IMSBC Ammonium Sulphate
• IMDG EmS Emergency Schedule

Limitations

This article summarizes the IMSBC Code schedule framework for ammonium nitrate based fertilizers as restructured by Amendment 06-21 (MSC.500(105), mandatory from 1 December 2023) and reflects the Code’s individual schedule requirements as documented through publicly available primary IMO sources. It is not a substitute for the full IMSBC Code text, which masters, operators, and cargo superintendents must consult directly.

Schedule boundaries, composition limits, and trough test requirements are reproduced here to the precision available in publicly accessible documents. The definitive text is the 2022 IMSBC Code edition incorporating Amendment 06-21, as published by the IMO. Any conflict between this article and the official IMSBC Code text must be resolved in favor of the Code.

The fire response guidance summarized here reflects the IMSBC Code’s own emergency procedures and general maritime firefighting doctrine for AN cargoes. It is not vessel-specific and cannot substitute for the Emergency Response Procedures required to be maintained aboard every vessel carrying Group B cargoes. Masters must follow the vessel’s own approved emergency plan and the specific schedule requirements for the cargo grade actually aboard.

Cargo properties, trade flows, and specific composition limits vary by production batch, commercial grade, and shipper. The production and trade figures in this article are sourced from industry data as of 2024 and may not reflect current conditions, particularly given the volatility in Russian AN export policy.

See also

• IMSBC Code
• IMSBC Group B Cargoes
• IMSBC Group C Cargoes
• IMDG Class 5: Oxidisers and Organic Peroxides
• Diammonium Phosphate: IMSBC Schedule and Carriage
• Urea: IMSBC Schedule and Carriage
• Potash: IMSBC Schedule and Carriage
• Sulphur: IMSBC Schedule and Carriage
• Coal: IMSBC Schedule and Carriage
• Phosphate Rock: IMSBC Schedule and Carriage
• Cargo Hold Preparation Standards
• Marine Cargo Hold Ventilation