Diammonium Phosphate: IMSBC Schedule and Carriage

Diammonium phosphate (DAP) is a granular phosphate-nitrogen fertilizer and one of the most widely shipped solid bulk cargoes in the global dry-bulk trades. The IMSBC Code classifies it Group C: it doesn’t liquefy under normal voyage conditions and carries no IMDG chemical hazard designation. The key controls during carriage are preventing moisture ingress (which triggers caking and accelerates ammonia evolution), ensuring adequate hold ventilation, and applying enclosed-space entry precautions before any personnel enter cargo holds on a loaded DAP voyage.

Seaborne DAP trade runs at approximately 20 to 25 million tonnes per year, with major production concentrated in Morocco (OCP Group at Jorf Lasfar), Saudi Arabia (Ma’aden at Ras al-Khair), China, the United States, and Russia. India absorbs the largest single share of imports, driven by the kharif and rabi planting seasons that create sharp seasonal demand peaks between April and August. The IMSBC Code assigns DAP its own named individual schedule, which specifies the physical characteristics, hazards, and handling requirements that govern every bulk shipment.

What diammonium phosphate is

Diammonium phosphate has the chemical formula (NH4)2HPO4. It’s produced by reacting phosphoric acid with ammonia in a pipe reactor, then granulating the product to a uniform particle size. The 18-46-0 grade designation that appears on most commercial specifications means 18% total nitrogen and 46% phosphorus pentoxide (P2O5). This dual-nutrient profile is why DAP dominates the phosphate fertilizer trade: a farmer gets both nitrogen and phosphate in one product, at roughly the highest phosphorus analysis of any dry granular fertilizer.

The granulation process produces a hard, dense granule with a particle diameter of 2 to 4 mm and a bulk density of 0.9 to 1.0 tonne per cubic metre. The stowage factor falls in the range of 1.00 to 1.11 cubic metres per tonne depending on moisture content and granule size distribution. These are practical numbers for cargo planning: a Panamax bulk carrier loading 70,000 tonnes of DAP needs roughly 70,000 to 77,700 cubic metres of hold capacity, which is within the 90,000 to 95,000 cubic metre grain capacity of a typical Panamax.

DAP is chemically stable under normal temperature and pressure conditions. It doesn’t decompose spontaneously, doesn’t self-heat, and isn’t flammable. But it’s not chemically inert either: the ammonium salt chemistry means it slowly hydrolyzes and releases ammonia gas, particularly when conditions depart from the dry, moderate-temperature environment a well-sealed hold provides.

Monoammonium phosphate (MAP): the companion schedule

MAP (monoammonium phosphate, NH4H2PO4) appears in the IMSBC Code as a separate named schedule adjacent to DAP but with closely related properties. The commercial grade designation for MAP is typically 11-52-0 (11% N, 52% P2O5). MAP is slightly more acidic than DAP (its solution pH is around 4.5, vs approximately 8.0 for DAP), which affects its ammonia-evolution rate: DAP is more alkaline and evolves ammonia more readily, particularly at elevated temperatures or in contact with alkaline contaminants. Both are IMSBC Group C. Both are hygroscopic. Both require the same hold-preparation and ventilation regime.

Operationally, the main distinction between the two during a bulk voyage is that DAP’s higher ammonia-evolution potential makes enclosed-space precautions marginally more pressing during the first 24 to 48 hours after loading, when the freshly loaded mass has the most surface area exposed and gas generation is at its peak.

The IMSBC Code schedule for DAP

The IMSBC Code’s individual schedule for DIAMMONIUM PHOSPHATE (DAP) sets out the data that operators, masters, and terminals must use when planning and executing a bulk shipment. The key schedule parameters are summarized in the table below. Figures are drawn from the current IMSBC Code text as adopted at MSC 105.

The schedule explicitly identifies ammonia gas as a hazard that can accumulate in enclosed spaces. This is the single most operationally significant point in the schedule that differs from a fully inert Group C cargo such as limestone or pig iron.

The schedule also identifies corrosivity: DAP and MAP can corrode uncoated or damaged steel surfaces in the presence of moisture, and this is treated as a handling-level concern rather than a full chemical hazard designation. There’s no IMDG class 8 label applied to DAP, but the corrosive potential means hold coating integrity matters.

DAP vs MAP vs ammonium nitrate: the critical distinction

The single most important safety distinction in the fertilizer bulk trades is between ammonium phosphate fertilizers (DAP, MAP) and ammonium nitrate fertilizers. These are completely different hazard classes, and the consequences of treating them interchangeably during planning or hold assignment are serious.

Ammonium nitrate fertilizer is carried under one of several sub-entries in the IMSBC Code depending on nitrogen content and the presence of additives. High-purity ammonium nitrate (above about 80% AN by mass) is Class 1 if it meets detonation sensitivity thresholds. Agricultural grade ammonium nitrate fertilizer (ANSOL, calcium ammonium nitrate / CAN, and blends with inerts) falls into the MHB category as an oxidizer. The hazard profile is categorically different from DAP.

The practical risk of confusion arises at berth when a vessel is loading a mixed fertilizer cargo, or when hold allocation decisions are made by chartering staff unfamiliar with the individual schedules. DAP and ammonium nitrate must not share the same hold or be stowed adjacent without appropriate segregation. DAP and potash (potash: IMSBC Code schedule and carriage) are both Group C and physically compatible: dedicated fertilizer carriers routinely load them in adjacent holds.

For a fuller treatment of the ammonium nitrate carriage regime, see the ammonium nitrate fertilizer IMSBC schedule article.

Ammonia evolution: the primary hazard

DAP releases ammonia gas as a decomposition product. In a sealed or poorly ventilated hold, ammonia concentrations can reach levels that are harmful to respiratory health within hours. The short-term exposure limit (STEL) for ammonia in occupational settings is 25 ppm over 15 minutes (OSHA standard), and the IDLH (immediately dangerous to life or health) is 300 ppm. A hold loaded with warm, moist DAP can generate ammonia at concentrations well above these thresholds.

The chemistry is straightforward. DAP is the diammonium salt of phosphoric acid. In the presence of moisture or heat, the equilibrium shifts toward partial decomposition:

(NH4)2HPO4 → NH4H2PO4 + NH3 (gas)

This is a gradual, reversible process under normal conditions. It accelerates with temperature (the reaction rate roughly doubles for every 10-degree Celsius rise), with moisture (wet cargo surfaces react faster), and with alkalinity (an alkaline hold surface or contamination with lime/cement residues drives the equilibrium toward more ammonia release).

The practical consequence for ship operations is that a sealed hold on a loaded DAP voyage can accumulate ammonia concentrations above the STEL within 12 to 24 hours of loading, particularly if the cargo was loaded warm from a conveyor that had been running in direct sunlight. This is why the IMSBC Code schedule specifies ventilation requirements and why enclosed-space entry precautions are not optional for this cargo.

Conditions that increase ammonia evolution

Three conditions push ammonia release upward in a meaningful way, and all three are controllable:

Elevated temperature. Cargo loaded from a sun-heated conveyor system, or a vessel trading in tropical waters, can present cargo surface temperatures of 35 to 45 degrees Celsius in the upper layers of the hold. Each 10-degree rise roughly doubles the evolution rate. Hold monitoring is warranted during the first 48 hours of voyage.

Moisture ingress. Wet DAP releases ammonia faster than dry DAP. A hold with a seeping hatch coaming seal, a leaking bilge well cover, or condensation dripping from a cold steel hatch cover onto warm cargo creates a localized wet zone where ammonia generation is elevated. This is also where caking starts.

Alkaline contamination. DAP solution has a pH of approximately 8.0. If hold surfaces retain lime wash, cement dust, or concrete sealant from a previous preparation treatment, the alkalinity reacts with DAP moisture to accelerate decomposition. Holds that received a lime wash as a cleaning treatment for a previous cargo must be thoroughly neutralized and rinsed before DAP loading.

Ammonia monitoring and enclosed-space precautions

The IMSBC Code’s requirements for enclosed-space entry precautions apply to DAP. Before any crew member or shore worker enters a cargo hold on a loaded DAP voyage, the atmosphere must be tested and found safe. The relevant thresholds for ammonia are:

• Oxygen content: at least 20.9% by volume
• Ammonia: below 25 ppm (STEL)
• Other toxic gases: as appropriate

Testing equipment must be calibrated and approved. The test must be done at multiple levels in the hold, since ammonia is lighter than air (molecular weight 17.03, vs approximately 29 for air) and tends to accumulate at the top of the hold rather than at the bottom. This is different from cargoes that evolve heavier-than-air gases (CO2, H2S), which pool at the bilge.

Ventilation before entry: the hold must be mechanically ventilated until ammonia readings fall below 25 ppm at all tested elevations. Gravity-only natural ventilation is insufficient in a sealed hold that has been building up ammonia over several days. A portable fan unit directed into the lower hold, drawing ammonia-laden air out through a separate opening, is the practical solution.

Continuous monitoring is required during any hold entry while cargo is present or residues remain. A standalone ammonia detector or an approved multi-gas monitor with an ammonia sensor must accompany the entry team.

For broader context on enclosed-space hazards aboard bulk carriers, the marine cargo hold ventilation article covers the general regime across cargo types.

Hygroscopic caking: the discharge-complication hazard

Caking is the second major handling hazard of DAP. When DAP absorbs moisture during transit, individual granules dissolve slightly at the surface and then recrystallize as the moisture redistributes, binding granules together into hard masses. In severe cases, the entire upper layer of a hold becomes a solid crust that cannot be discharged by grab crane without mechanical breaking. Preventing moisture ingress during loading and voyage is far cheaper than breaking a caked cargo at the discharge port.

DAP’s equilibrium relative humidity (ERH) is approximately 73 to 76% at 20 degrees Celsius. This means that if ambient relative humidity in the hold exceeds about 75%, DAP will absorb moisture from the air and begin to cake. In practice, holds loaded at a humid port, or voyages through tropical waters where condensation forms on cooled steel surfaces and drips onto the cargo, present exactly this condition.

The caking mechanism is cumulative. The first few days of a voyage through humid air may create only a thin surface crust. A 30-day voyage through the South Atlantic in austral summer, with daily temperature cycling between 28 and 36 degrees Celsius and humid port stays at both ends, can produce a caked layer 200 to 400 mm deep in the top section of the hold. That’s enough to block grab operation and require manual breaking with pneumatic picks, extending discharge time by 12 to 24 hours per hold.

Voyage planning to minimize caking

The captain and first mate should consider voyage routing and timing in relation to seasonal weather in the loading and discharge regions when planning a DAP voyage. Specific mitigations:

Hatch cover condition. Every hatch cover must be pressure-tested (hose test or ultrasonic test) before loading. A cover that passed the hose test 18 months ago may have developed compression seal wear since. The standard is IMO MSC/Circ.1071, which sets out the procedure for hose testing of hatch covers.

Bilge well covers. The perforated bilge well covers in each hold must be in place and watertight relative to the cargo space. DAP granules are approximately 2 to 4 mm diameter: they can enter bilge wells through standard 2 mm perforations and block bilge pumps. Cover the bilge wells with burlap or filter fabric before loading and seal the edges.

Ventilation management during voyage. Once loaded, the holds should remain closed unless ammonia monitoring and atmospheric testing confirm it is safe to ventilate. Inadvertent ventilation of holds during humid port stays or tropical squalls draws moist air across the cargo surface. The general rule for hygroscopic cargoes is to ventilate only when the dewpoint of outside air is below the dewpoint of hold air. This requires a dewpoint meter, not just a thermometer.

Corrosivity to steel

DAP in the presence of moisture is mildly corrosive to uncoated steel. The mechanism is electrochemical: DAP solution (pH about 8.0) is mildly alkaline, and ammonium ion (NH4+) can participate in metal oxidation reactions. The practical concern isn’t sudden perforation but accelerated rusting of exposed steel at hold floors, frames, and weld seams where paint coating has been abraded or chipped.

Vessels carrying DAP regularly should keep hold paint coatings in good condition and should wash holds promptly after discharge. A prolonged residue of wet DAP left in a hold after discharge is more corrosive than the bulk cargo during transit, because the concentrated surface moisture and ammonia in the residue creates a more aggressive microenvironment than the bulk mass.

The IMSBC Code schedule records this characteristic under “Corrosion / Reaction with water.” It’s not an IMDG Class 8 designation, and no corrosive label is applied to the cargo. But charter parties for DAP cargoes routinely require hold inspection reports, coating survey at loading, and post-discharge wash certificates for exactly this reason.

MAP is slightly less corrosive than DAP because its solution is more acidic (pH approximately 4.5), which suppresses the ammonia-driven corrosion mechanism. But the acidity of MAP creates its own mild steel-attack pathway through hydrogen ion activity, so the hold-coating requirement applies equally.

The global DAP trade: cargo flows and vessel types

Global DAP production is heavily concentrated. Morocco’s OCP Group is the world’s largest phosphate rock miner and controls a large share of global DAP/MAP production from its complex at Jorf Lasfar near El Jadida on the Atlantic coast. Saudi Arabia’s Ma’aden Wa’ad Al Shamal complex at Ras al-Khair on the Persian Gulf is the second-largest dedicated DAP export facility globally, with a rated capacity of 3 million tonnes per year. The United States (Mosaic Company, from its Florida and Louisiana operations) and Russia (PhosAgro from Cherepovets, and EuroChem) are additional major producers.

The principal import destinations are:

India. India imports 8 to 10 million tonnes of DAP per year, making it by far the largest single buyer. Imports are heavily seasonal, concentrated in the period before the kharif planting season (June to September) and again before rabi (October to December). Port Kandla (now Deendayal Port) in Gujarat and Paradip in Odisha are the primary DAP import terminals. India’s government subsidizes DAP purchases for farmers, which means import decisions are partly policy-driven rather than purely market-driven: sudden policy changes can cause sharp swings in shipment volume.

Brazil. Brazil’s agricultural export machine consumes approximately 6 to 7 million tonnes of phosphate fertilizer per year (in P2O5 terms), with DAP and MAP making up a large portion. The main import ports are Santos, Paranagua, and the new Ponta da Madeira region. Brazil imports from Morocco, the Middle East, and the United States depending on freight economics.

Other Asia. Pakistan, Bangladesh, Vietnam, and Thailand import DAP for domestic food production. Combined imports from these four countries run to approximately 2 to 3 million tonnes per year. Indian subcontinent and Southeast Asian imports are often sourced from the Persian Gulf on shorter voyage legs.

Vessel sizes. DAP moves on a wide range of dry-bulk vessel sizes. Handysize (25,000 to 40,000 DWT) vessels serve smaller ports without the draft clearance or berth length for larger ships. Supramax (50,000 to 60,000 DWT) and Panamax (65,000 to 80,000 DWT) are the workhorse vessel types on the main trade lanes from Morocco and Saudi Arabia to India and Brazil. Capesize vessels (above 100,000 DWT) are used at major export terminals with deep-water berths: Ma’aden at Ras al-Khair can load Capesize vessels.

Dedicated fertilizer carriers are clean bulk carriers with coated holds, covered bilge wells, and closed conveyor systems that minimize moisture and contamination during loading. Most DAP shipments move on conventional bulk carriers with appropriate hold preparation rather than dedicated units.

Hold preparation for DAP loading

Hold preparation for a DAP cargo starts with the previous cargo. The sequence below reflects the requirements of the IMSBC Code schedule and general industry practice for cargo hold preparation standards.

Step 1: Remove all previous cargo residues. Sweeping and washing must leave the hold clean to a standard where no residue of the previous cargo is visible. Residues of fertilizer (any grade), grain, coal, or mineral ore must be completely removed. Any previous cargo that was an oxidizer (ammonium nitrate, calcium nitrate, potassium nitrate) requires particularly thorough cleaning, followed by a witness inspection before loading DAP.

Step 2: Check and clean bilge wells. Bilge wells must be dry and clear of cargo residue from previous voyages. Where a previous cargo left fine particles in the bilge sump, the sump must be pumped out and inspected. Bilge pipes must be clear. Test bilge pumps before loading DAP: if a pump fails during the voyage with water accumulating in the bilge under a DAP cargo, the resulting wet DAP accelerates caking in the bilge zone and may damage the pump mechanism if sucked in.

Step 3: Inspect and repair hold paint coatings. Touch up any areas of bare steel. Spot-blast and apply two coats of approved hold paint to any areas showing active corrosion or delamination. Allow the paint to cure fully (typically 24 hours at ambient temperature) before loading. New paint that isn’t fully cured can release volatile organic compounds that contaminate the cargo and may produce a hold atmosphere hazard.

Step 4: No lime wash. DAP loading holds must NOT be lime-washed. Lime is strongly alkaline (calcium hydroxide solution, pH above 12) and reacts with DAP to accelerate ammonia evolution. This is the opposite of the hold preparation required for cargoes where lime wash is a standard cleaning technique (such as sugar). Document the hold preparation survey and verify the pH of any hold surface residue before loading DAP.

Step 5: Hatch cover inspection. Confirm hatch covers seal properly. Replace or repair compressed rubber seals showing cracking, gaps, or compression set. Hose test all covers and document the result. The first officer’s hold inspection report for DAP loading should confirm the hatch cover test result explicitly.

Step 6: Pre-loading atmosphere check. Before the first tonne of DAP enters the hold, conduct an enclosed-space atmosphere test at both the top and bottom of the hold. This establishes a baseline and also detects any residual gas from a previous cargo (hydrogen sulfide from some mineral concentrates, for example) before the hold is occupied.

Loading operations

DAP loads via shore conveyor systems and shiploaders at major export terminals. Terminal loading rates at facilities like Jorf Lasfar and Ras al-Khair typically run between 1,500 and 5,000 tonnes per hour per loader. At 4,000 tonnes per hour, a Panamax loading 70,000 tonnes completes in approximately 17 to 18 hours of effective loading time, often spread across one to two calendar days including weather delays, draft surveys, and trim corrections.

Dust. Modern export terminals apply dust suppression by spraying a fine water mist ahead of the falling cargo stream. This controls airborne dust at the terminal boundary. On older conveyor systems, dust generation can be higher, creating a layer of fine DAP dust on deck and hatches. This dust is hygroscopic: if left in place during rain, it can wash into hatch cover drainage channels and create acidic residue that accelerates corrosion. A basic deck wash after loading and before closing covers removes the dust and protects the deck.

Trimming. The IMSBC Code schedule specifies DAP must be trimmed. Untrimmed cargo with a peaked load profile concentrated under the hatch opening creates an uneven weight distribution that can impose excessive local stress on the tank-top structure. Trimming distributes the cargo to a level, or specified profile, within the hold. At most modern terminals, trimming is done by the shiploader’s retractable tripper conveyor, which extends forward and aft from the hatch opening to spread cargo across the hold length. Where this isn’t available, a bulldozer lowered into the hold is used, which requires enclosed-space entry procedures before and during the operation.

Cargo temperature monitoring. The first officer should record cargo temperature at the hold surface at the beginning of the voyage and at 24-hour intervals for the first 48 to 72 hours. Significant temperature rise (more than 5 degrees Celsius above ambient) in the cargo mass would be unusual for DAP and, if observed, warrants investigation into whether the cargo has been contaminated. DAP doesn’t self-heat, so temperature rise in excess of ambient warming is a diagnostic signal, not a normal characteristic.

Draft survey. The ship’s cargo officer and the terminal’s independent surveyor conduct a draft survey to determine the loaded quantity. The survey establishes displacement by measuring drafts at six points (fore and aft on each side, and amidships), correcting for trim and density, and comparing to the vessel’s deadweight scale. For a 70,000-tonne Panamax cargo at $450 per tonne, a 0.5$157,500. Draft surveys for DAP cargoes typically achieve accuracy within 0.2 to 0.3%.

Voyage monitoring

The loaded voyage for DAP requires attention to three monitoring tasks: atmosphere checking before any hold access, hatch cover condition, and bilge monitoring.

Atmosphere checking. Any hold access during the voyage (for hold inspection, to check for hatch cover leaks, or to investigate an unusual odor) must be preceded by an atmosphere test. Ammonia readings should be below 25 ppm before entry. The test equipment must be calibrated. If readings exceed 25 ppm, the hold must be ventilated and retested before entry. The ventilation procedure: open two hatches (one for intake, one for exhaust), run a fan for at least 30 minutes, then retest. In tropical conditions with a freshly loaded warm cargo, the first test may read 50 to 150 ppm of ammonia, requiring repeated ventilation-and-retest cycles before the hold is safe to enter.

Hatch cover condition. After every significant rainfall or head sea that sends water over the deck, the first mate should visually inspect the hatch cover seals for leakage. Wet cargo inside a hold normally appears first as discolored or darker-toned cargo near the hatch coaming periphery. If wetted cargo is found during a hold inspection (after proper atmosphere clearance), the cause must be identified and stopped, and the affected zone should be documented for a moisture damage report at discharge.

Bilge monitoring. Check bilge wells at least daily. DAP granules have a density greater than water (bulk density approximately 0.95 to 1.0 tonne per cubic metre): any granules that entered the bilge well through the filter covering will sink rather than float. Bilge water appearing in a DAP cargo hold is a serious indicator: it means either that hull plating is leaking, or that condensation drainage is bypassing the filter cover. Bilge water with dissolved DAP is mildly corrosive and will attack uncoated bilge components if left.

Discharge operations

Discharge of DAP at the receiving terminal uses grab cranes in most ports. Pneumatic discharge systems (vacuum trucks) are used at some specialized facilities but are less common for DAP because of the volume of material and the granule’s tendency to bridge under negative pressure.

Grab operation. Standard discharge grabs for bulk fertilizers have capacities of 12 to 25 tonnes per grab cycle. At 8 cycles per hour for a 20-tonne grab, a single crane discharges approximately 960 tonnes per hour. A Panamax cargo of 70,000 tonnes discharges in approximately 72 to 80 hours of effective crane operation with two cranes, or 36 to 40 hours with four.

Caked cargo. Where caking has occurred, the grab may not penetrate the crust. The sequence is: a bulldozer or Bobcat equipped with a hydraulic breaker enters the hold to break the crust (after atmosphere clearance); the broken fragments are then discharged by grab. For a crust covering the full top 300 mm of a hold with 10,000 tonnes of cargo, the breaking operation takes 4 to 6 hours per hold. Charter parties for DAP cargoes frequently specify the ship’s responsibility (or otherwise) for caked cargo that develops during the voyage.

Hold cleaning after discharge. After discharge, residues of DAP remain in the bilge wells, in structural crevices at frames and brackets, and as fines on the hold floor. These must be washed out promptly. DAP residues left for more than 48 hours in a warm humid hold start to generate ammonia gas concentrations that make re-entry difficult without full atmosphere clearance. The wash water from DAP cleaning is high in phosphate and ammoniacal nitrogen: most ports require this wash water to be disposed of ashore rather than pumped overboard.

For bulk carrier operators carrying DAP regularly, keeping an ammonia detector calibrated and aboard is a basic housekeeping measure, not an extraordinary precaution.

DAP versus urea: a practical comparison

Both DAP and urea are Group C fertilizers with similar handling precautions: hygroscopic, caking-prone, mildly corrosive to steel, and evolving gas that requires enclosed-space precautions. The differences matter for cargo planning:

Urea’s bulk density is lower (approximately 0.70 to 0.78 tonne per cubic metre, vs 0.90 to 1.00 for DAP), so a given hold volume holds less urea by mass. A Panamax loading maximum grain capacity (say 95,000 m3) achieves approximately 66,500 to 74,100 tonnes of urea but approximately 85,500 to 95,000 tonnes of DAP. Voyage economics differ accordingly.

Urea evolves ammonia more slowly than DAP under identical conditions, because urea’s decomposition chemistry (CO(NH2)2 → CO2 + 2NH3) requires higher temperature activation. In practice, the enclosed-space precautions are the same for both: measure before entering.

Urea is also more hygroscopic than DAP at lower relative humidities. Urea starts absorbing moisture above about 72% relative humidity at 25 degrees Celsius; DAP’s ERH is closer to 74 to 76%. The practical handling standard is the same: both cargoes require weathertight holds and humidity-conscious voyage ventilation management.

Charter party considerations

A standard IMSBC voyage charter for DAP will address several cargo-specific points that are not covered by the Code’s minimum requirements:

Hold preparation warranty. The shipper typically warrants that the cargo is fit for shipment and the charterer typically warrants that the holds are suitable. The hold preparation survey by an approved supercargo or SGS/Bureau Veritas inspector provides the evidence of suitability.

Caking liability. Charter parties commonly specify whether caking is a shipper’s risk (the cargo was loaded with excess moisture), a vessel’s risk (hatch covers leaked), or shared. When a cargo damage claim for caking arises, the surveyors examine the cargo moisture content at loading (from samples taken during the survey), the voyage weather logs, and the hatch cover condition reports. The evidence trail must be complete.

Ammonia odor at discharge. Ammonia odor on the quayside during DAP discharge is not, in itself, a sign of cargo damage. It is normal off-gassing from granules exposed to air at the grab discharge point. Terminal workers should be informed in advance; some require respiratory protection for personnel near the discharge stream.

Fumigation restrictions. DAP must not be fumigated with phosphine (methyl bromide alternatives) without specific technical review. Phosphine reacts with moisture to generate phosphine gas, and the presence of ammonia in a DAP hold creates a complex mixed-gas atmosphere that standard fumigation protocols aren’t designed for. Fumigation of DAP cargoes for phytosanitary purposes at grain-importing countries (some Southeast Asian markets require fumigation of imported fertilizers) requires port-state approval and a specific risk assessment.

Regulatory framework

The IMSBC Code is the primary regulatory instrument. It was made mandatory under SOLAS Chapter VI Regulation 1-1 by amendments that entered force 1 January 2011. The Code is currently in its 2023 edition, incorporating amendments adopted at MSC 105 (MSC.500(105)). The individual DAP schedule is reproduced in Section 3 of the Code as a named entry.

IMSBC Group C cargoes as a class are defined in the Code as solid bulk cargoes that are neither liable to liquefy (Group A property) nor possess chemical hazards (Group B property) when carried in bulk. DAP meets both conditions: it doesn’t liquefy under normal voyage conditions, and it doesn’t carry an IMDG class designation. The ammonia-evolution characteristic is treated within the Code as a cargo-specific special requirement rather than a Group B chemical hazard designation.

SOLAS Chapter XII applies to bulk carriers constructed on or after 1 July 1998 and governs structural requirements for bulk carriers, including requirements for double-bottom spaces and hatch cover integrity. The enhanced hold inspection and hatch cover requirements under SOLAS XII are directly relevant to DAP carriage: a hatch cover that passes SOLAS XII requirements is by definition suitable for DAP from a water-tightness standpoint.

The Paris MOU (for European-flag and European-port states) and the Tokyo MOU (for Asia-Pacific) conduct Port State Control inspections that include verification of compliance with IMSBC Code carriage requirements. Inspectors have authority to detain a vessel if the IMSBC schedule requirements are not being met: inadequate hold preparation documentation, absence of enclosed-space entry precautions, or missing atmosphere testing equipment can all result in a detention.

Related calculators

The IMSBC Code schedule for DAP links to several cargo and voyage calculators on this site:

• IMSBC DAP (Diammonium Phosphate): the named schedule reference calculator
• IMSBC MAP (Monoammonium Phosphate): companion calculator for the MAP schedule
• IMSBC Group A/B/C Classification: Group classification reference

Limitations

This article summarizes the IMSBC Code Group C schedule for diammonium phosphate as published in the 2023 edition of the Code and general industry practice as of 2026. It is not a substitute for the full IMSBC Code text, which mariners and cargo operators must consult directly. The Code is subject to amendment between editions through MSC circulars; always verify the current amendment state of any individual schedule against the IMO’s official publications.

Specific cargo properties (bulk density, moisture content, angle of repose, caking tendency) vary between shipments depending on production batch, storage conditions, and loading port humidity. Any individual shipment should be assessed against the shipper’s declaration and the cargo samples drawn at loading, not against the nominal schedule values in this article.

The ammonia-evolution rates and enclosed-space hazard timelines described here are based on documented industry experience and the IMSBC Code’s own text. Actual evolution rates depend on cargo temperature, moisture content, and hold atmosphere conditions that vary by voyage. Atmosphere testing before every hold entry remains mandatory regardless of elapsed voyage time since loading.

Charter party terms for DAP cargoes are highly variable: the allocations of liability for caking, ammonia damage, and hold cleaning described here reflect common market practice but are not universal. Legal review of the specific charter party terms is required for any dispute resolution.

See also

• IMSBC Code
• IMSBC Group C Cargoes
• Urea: IMSBC Code Schedule and Carriage
• Ammonium Nitrate Fertilizer: IMSBC Code Schedule and Carriage
• Potash: IMSBC Code Schedule and Carriage
• Phosphate Rock: IMSBC Code Schedule and Carriage
• Cargo Hold Preparation Standards
• Marine Cargo Hold Ventilation
• Bulk Carrier