Wheat: IMSBC Code and Grain Code Carriage

Wheat is the largest single commodity in global seaborne grain trade, carried as a Group C cargo under the IMSBC Code and subject to the full stability and trimming regime of the International Grain Code (IMO Resolution MSC.23(59)). The cargo’s hazards are not chemical but physical and biological: grain shifting in improperly trimmed holds, self-heating and mould growth when loaded wet, oxygen depletion and carbon dioxide accumulation in sealed spaces, phosphine exposure during fumigation, and grain dust explosion risk at loading terminals. Approximately 200 to 220 million tonnes move by sea each year, supplying food-import-dependent populations across the Middle East, North Africa, Sub-Saharan Africa, and Asia.

Wheat is covered by the IMSBC Code under the generic GRAIN schedule in Appendix 1. The schedule classifies grain as Group C, which means it does not liquefy and does not meet the criteria for a Material Hazardous only in Bulk (MHB) cargo. That classification does not mean carriage is straightforward. The Group C designation means wheat’s hazards are managed through a separate, technically demanding regulatory instrument rather than the Group A or B chemical-hazard controls. That instrument is the International Grain Code, adopted by IMO Resolution MSC.23(59) in 1991 and incorporated into SOLAS Chapter VI Part C. Every ship certified to carry grain must comply with both the IMSBC Code’s cargo declaration framework and the Grain Code’s stability, trimming, and grain-securing requirements.

The 2025 IMSBC Code edition, incorporating Amendment 07-23 adopted by Resolution MSC.539(107) on 8 June 2023 and mandatory from 1 January 2025, is the current operative text. The Amendment 07-23 changes to the GRAIN schedule are limited and procedural; the core hazard and carriage requirements for wheat derive from the Grain Code and have not been substantively revised since the 1991 adoption.

The wheat trade: volumes, exporters, and food-security context

Global volumes and major exporters

Seaborne wheat trade has run at approximately 200 to 220 million tonnes per year in recent marketing years, making wheat the highest-volume grain commodity moved by sea, ahead of maize (approximately 185 million tonnes) and soya beans (approximately 170 million tonnes) in most years. The major exporters and their approximate share of global seaborne supply vary considerably with annual crop outcomes, but the consistent top-tier suppliers are Russia, the United States, Canada, Australia, the European Union, Argentina, Ukraine, and Kazakhstan.

Russia became the world’s largest single wheat exporter by volume around 2017 and has maintained that position, typically shipping 35 to 45 million tonnes per year from Black Sea ports including Novorossiysk, Kavkaz, and Tuapse, and from Azov Sea ports. Russian wheat ships primarily to Egypt (the world’s largest single wheat importer), Türkiye, Nigeria, Sudan, Bangladesh, and Indonesia. The volumes on this single trade corridor, from Russian ports to North African and Middle Eastern receivers, represent the dominant physical flow in global wheat seaborne trade.

The United States exports 20 to 25 million tonnes per year in most years, shipped from Pacific Northwest ports (Portland, Longview) and Gulf ports (New Orleans, Galveston, Houston). US export grades include Hard Red Winter (the largest-volume class), Soft Red Winter, Hard Red Spring, Hard White, and Soft White. Pacific Northwest export goes primarily to the Philippines, Japan, South Korea, Taiwan, and China; Gulf export reaches Latin America, North Africa, and the Middle East.

Canada exports approximately 20 to 25 million tonnes per year, with the Canadian Prairies supplying both Pacific export through Vancouver and Prince Rupert (principally to Asian markets) and Atlantic and Great Lakes export (principally to Latin America and the EU). Canadian Western Red Spring (CWRS) is among the most consistently high-protein wheats on the market and commands a quality premium at many mills.

Australia exports approximately 20 to 25 million tonnes per year in good crop years, primarily from Kwinana (the largest grain export terminal in the Southern Hemisphere by throughput), Port Adelaide, Port Lincoln, Esperance, and Newcastle. Australian Standard White (ASW) and Australian Premium White (APW) are the standard commercial grades. Australian export goes primarily to Indonesia, the Philippines, Vietnam, China, Japan, and South Korea, making Australia the dominant supplier to Southeast Asian importers.

Argentina exports approximately 12 to 15 million tonnes per year, principally from Bahía Blanca and the Rosario-San Lorenzo complex on the Paraná River. Argentina’s wheat trade is complicated by periodic export restrictions imposed by domestic food policy, which can sharply curtail available supply in a given marketing year. Argentine wheat ships mainly to Brazil, Indonesia, and African markets.

Ukraine was a consistent 15 to 20 million tonne per year exporter before February 2022, with Black Sea port exports going to Egypt, Indonesia, Morocco, Tunisia, and other Mediterranean and Asian importers. The conflict-related disruption severely affected Ukrainian export in 2022, with partial restoration through the Black Sea Grain Initiative (operational July 2022 to July 2023) and subsequent arrangements. The disruption sharpened the food-security implications of wheat trade, because Ukrainian and Russian wheat together normally supply approximately 25% to 30% of global seaborne trade.

Wheat’s food-security centrality

Wheat is the primary caloric staple for approximately 35% of the world’s population, and for a larger fraction of the population in the Middle East, North Africa, and Central Asia. Egypt, the world’s largest single wheat importer, sources approximately 12 to 13 million tonnes per year, largely because domestic production of around 9 million tonnes covers only about 40% of national consumption. Egypt’s General Authority for Supply Commodities (GASC) is the largest single buyer of wheat in international markets and its procurement tenders are closely watched as a proxy for global price direction. Similar import dependencies characterize Algeria (approximately 8 to 9 million tonnes per year), Morocco (approximately 5 to 6 million tonnes), Nigeria (approximately 5 to 6 million tonnes), Indonesia (approximately 10 to 12 million tonnes), and Bangladesh (approximately 6 to 7 million tonnes).

The food-security dimension of wheat seaborne trade has two practical implications for carriage. First, political pressure to discharge at the stated weight and quality is acute at destinations where wheat is a state-procured essential commodity; cargo weight shortages or quality failures at major government importers generate diplomatic-level disputes and legal claims with greater frequency than for industrial bulk commodities. Second, the regulatory and documentation environment at receiving ports is often rigorous, with government surveyors attending discharge and independent testing of moisture, protein, and impurity levels against the contract specifications.

Vessel types used on wheat routes

Wheat moves predominantly on Panamax (60,000 to 80,000 DWT), Kamsarmax (80,000 to 85,000 DWT), and Supramax (50,000 to 60,000 DWT) bulk carriers. The largest wheat-loading terminals can accept Capesize vessels (approximately 150,000 DWT), but the receiving infrastructure at many import ports, particularly in Africa and the Middle East, is limited to Panamax draft and beam, making that the practical upper limit for most routes. Handysize vessels (25,000 to 40,000 DWT) serve regional routes and smaller-draught ports, particularly in Sub-Saharan Africa and Southeast Asian archipelagic markets where berth depth or terminal capacity limits larger vessels.

IMSBC Code schedule for GRAIN: wheat particulars

Bulk Cargo Shipping Name and scope

The IMSBC Code Appendix 1 entry for GRAIN is the Bulk Cargo Shipping Name (BCSN) under which wheat is declared. The schedule uses the collective term “Grain” and lists wheat, maize (corn), oats, rye, barley, rice, pulses, seeds, and processed forms of these as falling within its scope. Wheat can be declared as “GRAIN (WHEAT)” on cargo documentation to identify the specific species, which is the preferred practice where receiving ports or national regulations require species-specific declarations.

The IMSBC Code does not publish a separate BCSN schedule for each grain species. The GRAIN schedule in Appendix 1 applies to all of them, and the species-specific properties (stowage factor, moisture limits, dust and fumigation characteristics) are understood within the broader GRAIN schedule framework. The Grain Code stability requirements apply identically to all grain species.

Schedule particulars

The bulk density and stowage factor values reflect hard wheat varieties at approximately 13% to 14% moisture. Hard red winter wheat at the US standard test weight of 60 lb/bu corresponds to a bulk density of approximately 0.77 t/m3 and a stowage factor of approximately 1.30 m3/t. Soft wheat varieties are lighter; soft red winter can have a stowage factor toward 1.35 m3/t. The 14% moisture ceiling is the IMSBC Code’s loading condition for the GRAIN schedule. Some receiving jurisdictions and charterparties impose tighter limits; EU milling standards typically specify 14.5% for storage but receivers frequently specify 14% or lower for long-voyage imports.

How the IMSBC Code and Grain Code interact

The IMSBC Code’s GRAIN schedule does not contain detailed stability or trimming requirements of its own. Instead, it cross-references the International Grain Code for all stability calculations, grain securing, and trimming provisions. The master’s obligation under the schedule is twofold: meet the IMSBC Code’s cargo declaration and documentation requirements (cargo declaration, moisture content certificate, cargo information form per IMSBC Code section 4), and meet the Grain Code’s stability and securing requirements before sailing.

This layered structure means the Grain Code is the operative technical instrument for the voyage, while the IMSBC Code provides the administrative and classification framework. A vessel that satisfies Grain Code stability requirements but fails to present proper cargo documentation under the IMSBC Code is in breach of both instruments. Port state control surveyors check for both the IMSBC cargo documentation and the Grain Code document on pre-departure inspections for grain voyages.

The International Grain Code: stability and trimming framework

History and mandatory status

The International Grain Code replaced predecessor IMO Grain Rules on 1 January 1994 for ships whose keels were laid on or after that date, and by 1 July 1995 for existing ships on international voyages. IMO Resolution MSC.23(59), adopted at the 59th session of the Maritime Safety Committee in 1991, is the adopting resolution. SOLAS Chapter VI Part C (Regulations 9 to 12) gives the Code mandatory force: a ship may not proceed to sea to load a bulk grain cargo unless it complies with the Code’s requirements, and a grain loading document must be on board before departure.

The Code applies to all ships carrying grain in bulk on international voyages. Ships of less than 500 GT loading grain for a domestic voyage under national regulations that the Administration accepts as equivalent may be exempted, but these are rare in practice. Every ship intending to carry grain on international voyages must have a Document of Authorization issued by the flag state administration or by a recognized organization acting on its behalf.

Multiple grain ship casualties in the twentieth century established the basis for this regime. Several vessels capsized after grain shifted in heavy weather, creating a rapid, large transverse heeling moment that the vessel’s residual stability could not resist. The Grain Code’s stability criteria and trimming requirements are calibrated to prevent this failure mode by ensuring that, even after a maximum credible grain shift, the vessel retains sufficient righting energy to survive.

The three grain stability criteria

The Grain Code establishes three minimum stability requirements that must be met simultaneously throughout the loaded condition:

The 12-degree heel limit. The vessel’s angle of static heel, calculated using the worst assumed grain heeling moment from the standard void tables in Appendix I of the Code, must not exceed 12 degrees. This limit applies after accounting for the free-surface effect of any slack tanks.

The residual dynamic stability area. The area under the righting-moment (GZ) curve between the actual angle of heel and either 40 degrees or the angle of downflooding (whichever is less) must be at least 0.075 metre-radians. This represents the dynamic reserve of righting energy remaining after grain shift has already occurred.

The corrected GM. The initial metacentric height (GM) after correction for free surfaces in liquid tanks must be at least 0.30 metres at any point during the voyage.

A vessel that cannot meet all three requirements as loaded must either reduce the cargo weight, redistribute the cargo to improve the loading condition, or install grain-securing arrangements (shifting boards or feeders) that allow the applicable void volumes to be reduced to an approved level.

These three criteria are assessed against the loading condition using the assumed heeling moments from the Code’s Appendix I tables, not measured heeling moments. The tables give conservative heeling moment values computed from hold geometry and the presumed free-flowing behavior of grain under roll. The conservatism is intentional: the Code’s authors recognized that actual grain behavior under combined rolling and heaving in a seaway is not precisely predictable, and the tabulated values provide a safety margin over the median expected outcome.

The grain heeling moment calculation

The assumed grain heeling moment for a given hold is determined by the hold’s geometry, the load pattern (filled, partly filled, with or without securing arrangements), and the tabulated heeling moment factors in the Code’s Appendix I. The physical mechanism is as follows: when a ship rolls, grain at the top of the cargo mass can shift laterally into the void between the trimmed cargo surface and the hold boundary. This lateral shift moves the cargo’s center of mass away from the ship’s centerline, creating a transverse heeling moment.

The void volume over the trimmed surface in a large hold can be 2% to 5% of the loaded volume. For a fully laden Kamsarmax at 80,000 DWT with a wheat cargo, even a 2% surface void represents 1,600 tonnes of grain that could in principle shift laterally. The heeling moment produced by such a shift, depending on the hold beam, can readily exceed 1,000 tonne-metres per hold, enough to produce several degrees of static heel if the vessel’s GM is modest.

The Grain Code’s Appendix I provides tabulated heeling moment factors for the standard hold geometries: fully filled holds trimmed to the underdeck structure, partly filled holds with feeders, holds with shifting boards installed, and holds with alternative securing methods. A fully filled and trimmed hold has the lowest standard heeling moment factor. A partly filled hold without securing arrangements has the highest.

On a modern Kamsarmax or Panamax bulk carrier loaded with wheat, the grain heeling moment calculation is typically embedded in the vessel’s approved loading stability software, linked to the grain stability booklet. The master verifies before departure that the actual loading condition satisfies all three Grain Code criteria. The stability software assigns each hold’s heeling moment from the Appendix I table based on the hold type and loading pattern, then sums the contributions from all holds and computes the resulting static heel angle against the vessel’s GZ curve.

The grain heeling moment calculator on this site supports pre-voyage stability verification consistent with Grain Code methodology.

The Document of Authorization

A vessel must carry a current Document of Authorization (DOA) to load grain on an international voyage. SOLAS Chapter VI Regulation 9.1 states this requirement explicitly. The DOA is issued by the flag state or its delegated authority (typically a classification society acting as a recognized organization) and specifies the authorized loading conditions, the maximum allowable grain heeling moments by hold and pattern, and, where applicable, the approved grain-securing arrangements. The DOA is not a one-time certificate; it must reflect the vessel’s current approved grain stability booklet.

The grain stability booklet that accompanies the DOA contains: approved standard loading conditions (sample load cases demonstrating compliance with the three stability criteria); tables of maximum permissible heeling moments by hold and loading pattern; details of approved shifting boards or feeder arrangements if fitted; and form-pages for the master to record the actual load condition for each voyage. Before departure, the master completes the actual loading condition in the booklet and confirms compliance with all three stability criteria. Port state control surveyors examine this documentation as part of pre-departure inspections on grain voyages.

If the vessel has undergone structural changes, ballast tank modifications, or other alterations that affect its stability characteristics since the DOA was issued, the DOA may no longer be valid for the altered condition. Operators must ensure that the DOA and the grain stability booklet reflect the vessel’s current configuration. A vessel arriving at a loading port without a current DOA cannot load grain unless the Administration grants specific authorization in advance.

Trimming requirements

Trimming is the levelling and compaction of the grain surface within a hold to minimize the void volume available for grain to shift. The Grain Code distinguishes between “filled holds” and “partly filled holds,” and imposes different requirements for each.

Filled holds. A filled hold is one where grain has been loaded to the maximum practicable level, with the cargo surface as close to the underdeck framing as possible. The surface must be trimmed to fill all spaces under deck beams, under the hatch coaming structure, and in the wing spaces. On Panamax and Kamsarmax vessels with sloped topside tanks, trimming must ensure the upper wing spaces are packed with cargo or that shifting boards fill the gap. A correctly filled and trimmed hold qualifies for the lowest standard heeling moment factor in the Grain Code’s Appendix I tables.

Partly filled holds. A partly filled hold is one where the cargo does not reach the full hold capacity. Grain Code Regulation 9 requires either: (a) installation of securing arrangements (shifting boards running the full hold length, minimum 1.8 m deep, supported on the vessel’s underdeck framing) to convert the partly filled condition to an equivalent of a filled hold for heeling moment purposes; or (b) reliance on the tabulated values for the exact fill level, provided the stability criteria are still met. In practice, partly filled holds are uncommon on full wheat cargoes except at the fore and aft trimming holds.

On typical wheat voyages, the vessel is loaded full at all holds except the final trimming hold, which is loaded to exactly the weight needed to achieve the desired sailing draft. The trimming hold may have a modest surface void; the Grain Code’s tabulated value for that configuration is applied in the stability calculation for that specific hold, while the remaining full holds use the lower fully-filled heeling moment factor.

Telescoping conveyor spouts, spreading equipment, and mechanical trimmers are used at major export terminals to distribute wheat into the extremities of holds during loading. At terminals without spreading equipment, crew trimming or contracted terminal trimming gangs level the surface under the hatch opening and drive grain into the underdeck wing spaces using shovels or small front-end loaders lowered through the hatch.

Hazard 1: grain shifting

Bulk wheat has an angle of repose of approximately 20 to 25 degrees and flows freely under ship motion. Without proper trimming, wheat can shift in heavy weather and produce a large transverse heeling moment that may exceed the vessel’s righting capacity. The historical record of grain ship casualties, primarily from the 1950s to the 1980s, documents multiple losses directly attributable to grain shifting, and the Grain Code was developed specifically to prevent this failure mode.

Shifting boards are the principal physical securing measure for partly filled holds. A shifting board is a longitudinal partition, typically of timber or steel, positioned along the centerline or quarter-beam line of the hold, extending from the hatch coaming downward into the cargo mass, that divides the hold transversely and limits the width of the free-grain surface that can shift in one motion. The Grain Code specifies minimum board depth (1.8 m into the cargo), minimum board strength and support, and inspection requirements before departure.

Feeders are enclosed vertical shafts built into the hold structure that allow cargo from a full upper compartment to flow by gravity into a partly filled lower compartment as the lower cargo compacts and settles during the voyage. Where feeders are part of the approved design, the Grain Code credits the feeder volume in the heeling moment calculation.

Modern bulk carriers designed for the grain trade are typically built with the Grain Code requirements in mind. Holds have smooth surfaces to ease trimming, built-in feeder arrangements in some designs, and hatch coaming geometry that allows grain to be loaded close to the underdeck structure. On older or multipurpose vessels, achieving the grain-clean and properly trimmed condition can require more preparation and more complex securing arrangements.

Hazard 2: self-heating and mould growth

The moisture-temperature relationship in stored wheat

Wheat at or above 14% moisture supports microbial and fungal activity. The principal storage fungi are Aspergillus species (particularly A. glaucus group, A. candidus, and A. flavus) and Penicillium species. At moisture contents above approximately 13.5% and temperatures above 15°C, these fungi multiply rapidly, generating metabolic heat, carbon dioxide, and water vapor. The result is a self-reinforcing cycle: microbial heat raises the local temperature, which increases the metabolic rate, which generates more heat. In extreme cases, grain temperatures can rise above 60°C in a hot spot, causing irreversible protein damage, darkening, and a characteristic musty odor.

The mycotoxin concern in wheat is different from maize. The primary mycotoxin risk in wet or hot wheat is deoxynivalenol (DON, also called vomitoxin), produced by Fusarium graminearum and related species. DON contamination is detectable at the field stage but can increase during transit if the grain heats and mould populations expand. The EU maximum limit for DON in unprocessed wheat under Commission Regulation (EC) No 1881/2006 is 1,250 micrograms per kilogram; exceedance triggers rejection or denaturing. Zearalenone (produced by Fusarium species) and ochratoxin A (produced by Aspergillus ochraceus and Penicillium verrucosum) are secondary concerns.

Moisture limits in commercial practice

The IMSBC Code schedule states 14% as the maximum moisture content at loading. Commercial practice on wheat is often tighter. Australian wheat frequently exports at 12% to 13% moisture; Canadian CWRS is typically 13.5% or below; US Hard Red Winter may reach 13.5% to 14% at the Gulf export terminal, but Pacific Northwest loadings for the Asian market often specify 13.5% maximum. The charterparty moisture warranty determines the contractual maximum; the IMSBC schedule is the regulatory floor.

Moisture content is tested on a representative composite sample taken at the time of loading. The standard methods are AACC International Method 44-15A (air-oven method, the reference standard) and ISO 712 (the international reference for wheat moisture), though near-infrared (NIR) instruments are used for rapid at-terminal screening. NIR instruments require calibration against oven-reference samples; their readings are accepted commercially but the oven method governs disputes.

Moisture migration during the voyage

Bulk wheat loaded at uniform moisture will develop a moisture gradient during the voyage as the hold air temperature changes with geographic latitude and season. Cold external air or seawater lowers the temperature of the cargo near the hold sides and the hatch covers. Warm humid air rising from the main cargo body condenses on these cooler surfaces, producing drops that fall back into the surface grain layer. This “cargo sweat” raises the local moisture content of the surface grain and can initiate mould growth in a band just below the hatch coaming.

The risk is worst on northbound voyages from warm export regions to cold northern receivers in winter (such as the US Gulf or Argentina to Northern Europe, or Australia to Japan), and on voyages where the cargo was loaded in a hot, humid summer and discharged in cooler conditions. Ventilation strategy is the primary management tool; see the ventilation section below.

Commercial temperature monitoring

Cargo temperature during the voyage is monitored through temperature probes inserted through the hatch cover or through a permanent temperature-sensing port if fitted. Some charterers and receivers specify continuous monitoring with digital loggers on wheat voyages, particularly for high-value milling wheat where protein and baking quality must be preserved at discharge. Temperatures above 40°C require increased monitoring frequency. Cargo temperature above 55°C indicates active microbial heating; if temperature continues to rise after hatches are closed, emergency measures may be needed.

Hazard 3: oxygen depletion and carbon dioxide accumulation

The enclosed-space hazard in wheat holds

Wheat kernels respire continuously, consuming oxygen and releasing carbon dioxide. A living wheat kernel at 12% moisture and 25°C consumes approximately 0.05 mL of oxygen per hour per gram of dry matter; this rate roughly doubles for every 10°C increase in temperature and increases sharply with moisture content above 14%. In a sealed Panamax hold of approximately 15,000 m3 loaded with approximately 12,000 tonnes of wheat, the initial oxygen content of 21% can fall below the 19.5% safe-entry threshold within 2 to 4 days if the hold is sealed, depending on cargo temperature and moisture.

Carbon dioxide, which is denser than air (density 1.96 kg/m3 at standard conditions versus 1.29 kg/m3 for air), accumulates in the bilge area. At concentrations above 3%, carbon dioxide causes breathing difficulty and impairs cognitive function. At 7% to 10%, it is rapidly fatal. A surveyor entering a sealed wheat hold without atmospheric testing can lose consciousness within seconds of inhaling an oxygen-deficient, CO2-elevated atmosphere, with no warning odor or sensory signal. This pattern has killed seafarers on bulk grain carriers repeatedly.

The hazard is compounded where phosphine fumigation has taken place. Phosphine is generated from aluminum phosphide tablets placed in the hold; the gas accumulates as the tablets react, reaching concentrations of thousands of ppm in an active treatment. The decomposition reaction also produces carbon dioxide as a co-product, independently compounding the oxygen depletion. Bilge spaces beneath the cargo retain both gases at the highest concentrations.

Regulatory framework for enclosed-space entry

The SOLAS Chapter VI Regulation 3 and the IMSBC Code section 3.2 require atmospheric testing before any entry into a cargo hold. SOLAS Regulation XI-1/7.3 (effective 1 January 2015) requires bulk carriers to conduct enclosed-space entry drills at least once every two months. The STCW Basic Safety Training includes enclosed-space entry awareness as a mandatory module. The ISM Code requires a documented enclosed-space entry procedure in the ship’s Safety Management System.

Before any person enters a grain hold during or after a voyage, the atmosphere must be tested for:

• Oxygen content: must be above 19.5%
• Carbon dioxide: must be below 0.5% (5,000 ppm)
• Fumigant residue (phosphine or other): must be below the relevant occupational exposure limit; for phosphine, below 0.1 ppm for routine entry

Testing must be carried out at the hatch rim, at mid-hold level, and at the lowest accessible level (bilge). The tests must use calibrated instruments operated by a person competent in their use. A signed entry permit issued by the master or designated responsible officer must be in place before entry proceeds.

Despite this regulatory framework, maritime incident reports document one to three enclosed-space fatalities per year in the bulk grain carrier sector. The common pattern is entry by a crew member to check cargo condition or retrieve fallen equipment, in the belief that enough time has passed since hatch closure or fumigation to render the atmosphere safe. That belief is often wrong.

Hazard 4: fumigation with phosphine

Why wheat is fumigated

Insect infestation of bulk wheat is the primary reason fumigation is applied. Common stored-grain pests include the grain weevil (Sitophilus granarius), the rice weevil (S. oryzae), the lesser grain borer (Rhyzopertha dominica), and the flat grain beetle (Cryptolestes pusillus). At sea temperatures above 15°C during a 20 to 40 day voyage, a moderate initial infestation can multiply to a population that causes measurable weight loss and quality degradation at discharge. Many importing countries, including Japan, South Korea, Australia, and the EU member states, impose strict phytosanitary standards that require evidence of pest-free status at discharge; infestation found at discharge triggers quarantine procedures and cargo rejection or treatment.

Phosphine (PH3), generated from aluminum phosphide (AlP) tablets or magnesium phosphide (Mg3P2) tablets, is the dominant in-transit fumigant for bulk wheat. The reaction with ambient moisture proceeds as:

AlP + 3H2O → Al(OH)3 + PH3

Magnesium phosphide reacts faster than aluminum phosphide and is sometimes preferred for shorter-voyage treatments or in cooler weather. Tablets are placed in the hold before or shortly after hatch closure and generate gas over 24 to 72 hours, penetrating the bulk cargo mass. Minimum effective concentrations depend on temperature and pest species; commercial treatments typically target 2,000 to 3,000 ppm cumulative concentration-time (CT) product over 3 to 7 days at temperatures above 15°C.

Regulatory framework for fumigation

The operative international standard is IMO MSC.1/Circ.1358/Rev.2, the Revised Recommendations on the Safe Use of Pesticides in Ships Applicable to the Fumigation of Cargo Holds. These recommendations are not mandatory convention text, but flag states, port states, and P&I clubs widely adopt them as the operating standard. The Circular requires fumigation to be carried out by trained personnel, gas-tight hatch sealing to be verified before treatment, adjacent holds not under treatment to be monitored for phosphine migration, and all crew to be warned before treatment begins.

National regulations add requirements at each end of the voyage. Australia requires fumigations in Australian waters to use operators accredited under the Australian Fumigation Accreditation Scheme (AFAS). The United States requires compliance with EPA regulations under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) for any in-transit fumigation. Japan requires advance notification to the Ministry of Agriculture, Forestry & Fisheries for fumigated grain imports. Phytosanitary certificate requirements from importing countries often mandate pre-shipment fumigation before export is permitted.

Phosphine concentration and occupational exposure

The occupational exposure limits for phosphine are:

• OSHA permissible exposure limit (PEL): 0.3 ppm as an 8-hour time-weighted average
• OSHA short-term ceiling (15-minute): 1 ppm
• NIOSH IDLH (immediately dangerous to life or health): 50 ppm

During active treatment, hold concentrations routinely reach 10,000 to 30,000 ppm. No entry is possible or permissible during treatment without self-contained breathing apparatus rated specifically for phosphine service. After treatment, ventilation requires opening hatches and running mechanical ventilation for 24 to 48 hours in a large Panamax hold to bring phosphine levels reliably below 0.1 ppm at all depths.

Fumigation certificates, including the treatment date, fumigant used, quantity applied, application method, and name of the accredited fumigator, are required cargo documents under MSC.1/Circ.1358/Rev.2. Port state control examines these documents at the discharge port. P&I clubs also require copies, because fumigation-related personal injury claims are a material source of P&I liability in the grain bulk carrier sector.

Fumigation warning notices must be posted at all hold entrance points during and after treatment, listing the fumigant used, date of application, date the hold was re-opened for ventilation, and the name of the responsible fumigator. These notices are mandatory whether the fumigation was done by shore personnel before departure or by a licensed fumigator in transit.

Hazard 5: grain dust explosion and health

Dust characteristics of wheat

Wheat grain generates dust primarily during loading, when kernels break at conveyor transfer points, pass through shiploader chutes, and fall into the hold. The combustible fraction consists of fine particles below 75 micrometres: bran fragments, starch granules, and dried gluten particles. Wheat flour and fine bran dust has a minimum explosible concentration (MEC) of approximately 50 to 100 g/m3 in air, a minimum ignition energy of approximately 20 to 50 mJ, and a Kst value of 100 to 200 bar.m/s, placing it in Explosion Class St 1 (moderate hazard).

The practical implication is that concentrations above the MEC occur transiently at the fall zone below the loading spout and in the lower section of the hold immediately above the cargo surface during loading. Any ignition source at the fall zone, including sparks from metal-on-metal contact, static discharge, or electrical faults in conveyor equipment, can initiate an explosion. Shore grain elevator explosions, historically involving wheat dust, have caused fatalities and structural destruction at major export facilities. On ships, the risk is concentrated at the loading terminal during the period when the conveyor is running and the hold below is partly filled.

Several incidents in grain ship holds during loading have involved flash fires or minor explosions attributed to grain dust ignition. The IMSBC Code Appendix 6 (guidance on dust explosions in cargo holds) and national regulations such as OSHA 29 CFR 1910.272 (for grain facilities in the United States) require dust suppression by water spray at the fall zone, control of all ignition sources during loading, and post-loading hold ventilation to bring residual dust concentrations below the MEC before any hot work is attempted.

Occupational health from dust inhalation

Respirable wheat dust contains bran particles, flour particles, storage mite feces, fungal spores, and endotoxins from gram-negative bacteria. Occupational exposure at high intensities (as at land-based grain elevator workers) is associated with occupational asthma, organic dust toxic syndrome (ODTS), baker’s asthma (from wheat flour allergens), and chronic bronchitis. On bulk carriers, crew exposure is primarily during loading and discharge in port, where the exposure period is brief compared with land-based grain handlers. Personal protective equipment rated at FFP2/N95 or higher is appropriate during loading operations, particularly in holds that are partly filled and where the fall zone below the loading spout concentrates dust. Crew members working in the vicinity of the hatch during loading and any trimming operations inside the hold must wear appropriate respiratory protection.

Hold preparation and grain-clean standards

What grain-clean means in practice

A grain-clean hold is not a single parameter but a composite condition requiring: absence of all residue from the previous cargo; absence of odors that could taint the wheat (particularly petroleum hydrocarbons, fertilizer residues, and chemical cargo residues); absence of moisture standing in bilges or on structural surfaces; absence of insect or rodent evidence; and absence of visible mold or degraded grain from previous cargoes. Structural surfaces including frames, longitudinals, bilge limbers, and tank top must be visually clean.

The difficulty of achieving grain-clean condition depends on the previous cargo. Holds previously carrying:

• Coal: require complete residue removal (brooms, pressure washers), drying, and frequently two rounds of washing plus drying. Coal dust stains are cosmetic only, but any coal residue in wheat is a commercial contamination issue and triggers cargo rejection at food-grade discharge ports.
• Mineral fertilizers (urea, ammonium nitrate, potassium chloride): require intensive washing with fresh water to remove hygroscopic and corrosive residues, plus thorough drying. Urea residues are particularly persistent in bilge frames and limber holes.
• Clinker or cement: leaves an alkaline residue. Multiple washing cycles are required; some surveyors require liming and re-washing to confirm the residue is fully removed.
• Petroleum products or chemicals: require specialized cleaning, ventilation to remove solvent odors, and in some cases gas-free certification before grain loading is permitted.
• Previous grain: requires sweeping, washing, drying, and inspection, but is generally achievable at lower cost than an industrial cargo transition.

Commercial practice is to have a professional hold-cleaning company (rather than vessel crew) perform hold cleaning at major export ports. Independent surveyors representing the charterer, shipper, or receiver inspect holds before loading and issue a grain-clean certificate or a list of deficiencies requiring further work. Failure to obtain a grain-clean certificate before loading exposes the vessel owner to cargo quality claims at discharge.

The cargo hold preparation standards article covers the full technical and commercial requirements for achieving grain-clean condition across cargo transitions.

Terminal inspection sequence

At major wheat export terminals, the sequence before loading begins is: vessel arrival and berth assignment; hold inspection by the terminal supervisor and the independent surveyor; grain-clean certificate issue or deficiency list issued; remediation if required; and then commencement of loading. The terminal’s operating permit may require dust suppression water spray on the cargo fall zone from the start of loading. Some terminals with aggressive dust control programs require the hold to be wet-fogged before loading begins.

Loading, trimming, and stowage

Loading rates

Major Australian wheat terminals at Kwinana load at rates of 2,500 to 4,000 tonnes per hour per berth. US Pacific Northwest terminals at Portland and Longview load at 3,000 to 5,000 t/h. US Gulf terminals at New Orleans, Houston, and Galveston load at 2,000 to 4,500 t/h. Russian Black Sea terminals load at 2,000 to 5,000 t/h depending on the terminal. Argentine terminals at Bahía Blanca reach 3,000 to 5,000 t/h at the largest berths.

Loading a 75,000 DWT Kamsarmax vessel at an average loading rate of 4,000 t/h requires roughly 18 to 19 hours of continuous loading, assuming sequential hold filling. Trimming adds several hours depending on the terminal’s equipment and the number of holds requiring active trimming under deck beams.

Stowage factor and cargo calculations

Wheat’s stowage factor of approximately 1.28 m3/t means that a Kamsarmax with total hold volume of approximately 90,000 m3 will carry approximately 70,000 tonnes of wheat at standard loading. The precise cargo quantity depends on the actual stowage factor for the specific shipment, which varies with variety, moisture content, and test weight. Hard wheats with test weights of 60 lb/bu or above pack more tightly than soft wheats, giving a lower stowage factor and a higher cargo intake for a given hold volume.

The wheat cargo calculator and the bulk cargo displacement calculator support cargo planning and stowage calculations for bulk wheat shipments. The IMSBC Group A/B/C classification calculator confirms the cargo group for declaration purposes.

Loading sequence and intermediate stability

On a multi-hold vessel, the order in which holds are loaded affects intact stability at each intermediate stage. Stability during loading must be monitored continuously using the loading computer. The stability at full load, as confirmed against the Grain Code’s three criteria, must be achieved for the final sea condition. But intermediate stages during the double-bottom ballast exchange sequence (where ballast tanks are discharged as cargo is loaded) can be the worst condition for stability, not the full-load condition.

The vessel’s grain stability booklet typically specifies the sequence of hold loading and ballast discharge that maintains acceptable stability throughout the loading operation, not only at completion. Port state control surveyors examining the vessel before departure will ask the master to demonstrate the stability calculations for the actual loading sequence, not just the final loaded condition.

Ventilation during the voyage

The dew-point decision rule

The IMSBC Code GRAIN schedule specifies that holds carrying dry grain may be ventilated. Ventilation serves to dissipate metabolic heat from grain respiration and to remove carbon dioxide and moisture vapor. For dry wheat (below 14% moisture), both surface ventilation (opening ventilators to circulate air over the cargo surface) and through-hold ventilation (mechanical ventilation drawing air through the bulk from inlets to bilge vents) are generally acceptable.

The standard guidance, followed by cargo underwriters and P&I clubs, is the dew-point decision rule: ventilate only when the dew point of the outside air is lower than the dew point of the hold air. When outside air is cooler and drier than the hold air, ventilation removes moisture from the hold. When outside air has a higher dew point than the hold air, ventilating draws moist air into the hold where it condenses on the cooler cargo surface, causing cargo sweat.

This rule requires measuring both the outside air temperature and relative humidity and the hold air temperature and relative humidity, then computing the respective dew points. Portable psychrometers or digital hygrometers are used. Ventilation records, including the outside temperature, humidity, and the decision made, should be logged daily. These records are used by P&I clubs and cargo insurers to assess whether the master exercised proper care in managing the cargo, particularly when overheating or moisture damage claims arise at discharge.

The marine cargo hold ventilation article covers the dew-point calculation method and the practical ventilation decision framework in detail.

Through-hold ventilation for wheat

Through-hold ventilation (circulating air through the cargo mass using mechanical blowers) is generally used only when the cargo is dry and warm, and the outside air is cooler and drier. For wheat at 12% to 13.5% moisture, through-hold ventilation with appropriate outside air can dissipate minor heat build-up and reduce carbon dioxide to safe levels. Through-hold ventilation is not recommended for cargo above 14% moisture, because drawing air through a warm, moist grain body accelerates surface evaporation that then condenses in the cooler upper section.

On voyages from Southern Hemisphere origins (Australia, Argentina) to Northern Hemisphere receivers in winter, the outside air becomes progressively cooler and drier as the vessel moves into higher latitudes. These conditions favor surface ventilation to prevent ship sweat (condensation on the hold structure) rather than cargo sweat. Hold temperatures should be monitored at least once daily; cargo temperature above 40°C requires increased monitoring frequency.

Cargo declaration and pre-shipment documentation

Mandatory documents

The IMSBC Code section 4 requires the shipper to provide specific cargo information before loading. For bulk wheat, the required documents are:

• Cargo declaration stating the BCSN (GRAIN or GRAIN (WHEAT)), the cargo group (C), the estimated quantity, and whether the cargo is or has been subject to fumigation.
• Moisture content certificate issued by a recognized competent body, stating the moisture content and the date and method of testing.
• Cargo information form per IMSBC Code section 4.2.2, specifying the physical properties relevant to safe carriage: moisture content, bulk density, stowage factor, and fumigation information.
• Phytosanitary certificate from the exporting country’s plant health authority, required by virtually all importing countries.
• Fumigation certificate if the cargo has been or will be fumigated, as required by MSC.1/Circ.1358/Rev.2.
• Grain loading document (the completed voyage condition in the grain stability booklet), required before departure under SOLAS Chapter VI.

Commercial documents that travel with the cargo but are not IMSBC Code requirements include: USDA Federal Grain Inspection Service (FGIS) grade certificate (for US export), ISO 712 moisture test certificate (the international reference method), mycotoxin analysis certificate where required by the receiver, and certificate of origin for customs.

The shipper’s declaration and the master’s right to refuse

Section 4.2.2 of the IMSBC Code places the responsibility for the accuracy of the cargo information on the shipper. The shipper’s declaration that moisture content is below 14% is a representation on which the master’s acceptance of the cargo depends. A false declaration by the shipper leading to cargo damage or vessel harm exposes the shipper to liability under the contract of carriage and, in several jurisdictions, to criminal sanction.

The master has the right and the duty to refuse loading if the moisture content stated by the shipper appears inconsistent with the cargo’s condition, if the cargo shows signs of heating or infestation before loading, or if the documentation is incomplete. Many charterparties reinforce this right with a warranty of moisture content and a provision entitling the master to test and reject cargo above the warranted level. The cost of independent testing is typically allocated to the party whose declaration proves incorrect.

Related cargoes and IMSBC schedules

The carriage framework for wheat applies identically in structure to all bulk grains under the generic GRAIN BCSN:

The maize IMSBC schedule covers the second-largest grain trade. Maize’s stowage factor (approximately 1.30 to 1.45 m3/t) is somewhat higher than wheat’s, meaning a given hold volume holds less maize than wheat by mass. The Grain Code stability and trimming requirements, the fumigation practices, and the hold preparation standards are essentially the same.

The soya beans IMSBC schedule applies to soya beans, which differ from wheat in their higher oil content (approximately 18% to 20% by dry weight), creating a greater self-heating risk at elevated moisture. Soya beans are declared under the separate SOYA BEANS BCSN in IMSBC Appendix 1, not under the generic GRAIN entry.

The rice IMSBC schedule covers milled and paddy rice. Paddy rice in the husk has a higher stowage factor (approximately 1.7 to 2.0 m3/t) than milled rice (approximately 1.5 to 1.7 m3/t) and both are lighter than wheat. The Grain Code applies to all rice in bulk.

IMSBC Code provides the full regulatory context for all bulk cargo group classifications, Appendix 1 schedule structure, and documentation requirements. IMSBC Group C cargoes explains the Group C classification framework and the range of cargoes that fall within it.

Cargo hold preparation standards covers the technical and commercial requirements for achieving grain-clean condition across cargo transitions.

Marine cargo hold ventilation covers the dew-point calculation and the practical ventilation decision framework for bulk grain cargoes.

Limitations

The IMSBC Code schedules, the International Grain Code, and the supporting IMO circulars on fumigation are the authoritative sources for wheat carriage requirements. This article describes those requirements as of the 2025 IMSBC Code edition (Amendment 07-23, mandatory from 1 January 2025). Future IMSBC amendments may revise the GRAIN schedule; the current amendment cycle is Amendment 08-25, which was under preparation at the time of writing.

Stowage factors, bulk densities, and moisture thresholds cited in this article are typical commercial values for wheat varieties commonly traded internationally. Actual values for any specific cargo must be obtained from certified pre-shipment tests and declared on the cargo documentation. Specialist wheats (durum, club, hard white, soft white) may have physical properties outside the ranges stated here.

Stability calculations under the International Grain Code must be performed using the vessel’s approved grain stability booklet and Document of Authorization. The parameters in this article illustrate the Code’s methodology; they are not a certified stability assessment for any vessel or voyage. Masters and operators must apply the Code to their specific vessel’s approved loading conditions, using the stability software linked to the vessel’s grain stability booklet.

Fumigation regulations vary by flag state, port state, and receiving country. IMO circular MSC.1/Circ.1358/Rev.2 provides the international baseline, but national regulations (EPA FIFRA in the United States, AFAS in Australia, EU Regulation 528/2012 for biocidal products, Japanese MAFF requirements) impose additional requirements. The accredited fumigator contracted for each voyage is responsible for compliance with applicable national regulations at both the loading and discharge ports.

Trade volume figures cited in this article are drawn from publicly available data published by the International Grains Council, the US Department of Agriculture, and national agricultural ministries. Annual figures vary substantially with crop outcomes; the figures cited represent approximate recent averages and are not fixed forecasts.

This article does not cover mycotoxin regulatory limits, wheat grade standards, the commercial terms of grain charterparties, or flour milling quality specifications, which are subjects within national food-safety law, commodity exchange rules, and private contract rather than within the IMSBC Code or Grain Code framework.

See also

• Maize: IMSBC Code and Grain Code Carriage
• Rice: IMSBC Code and Grain Code Carriage
• Soya Beans: IMSBC Code Carriage
• IMSBC Code
• IMSBC Group C Cargoes
• Cargo Hold Preparation Standards
• Marine Cargo Hold Ventilation
• Wheat Cargo Calculator
• Grain Heeling Moment Calculator
• Bulk Cargo Displacement Calculator
• IMSBC Group A/B/C Classification