Maize: IMSBC Code and Grain Code Carriage

Maize (corn) is a Group C cargo under the IMSBC Code, carried under the generic GRAIN schedule, and is subject to the full stability and trimming regime of the International Grain Code. The dominant hazards are not chemical but physical and biological: grain shifting in improperly trimmed holds, self-heating and mould if loaded wet, oxygen depletion in enclosed spaces, phosphine exposure during fumigation, and grain dust explosion risk during loading operations. Global seaborne trade runs at approximately 180 to 200 million tonnes per year, making maize the second-largest grain cargo after wheat.

Maize is covered by the IMSBC Code under the broad GRAIN schedule in Appendix 1. The schedule classifies grain as Group C, meaning it does not liquefy and does not meet the criteria for a Material Hazardous only in Bulk (MHB) cargo. That Group C designation does not mean carriage is straightforward; it means the cargo’s hazards are managed through a separate, older regulatory instrument rather than through 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. Any 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 maize derive from the Grain Code and have not been substantively revised since the 1991 adoption.

The maize trade: volumes, grades, and routes

Global trade volumes and major exporters

Seaborne maize trade averaged approximately 185 million tonnes per year in the five marketing years 2018/19 to 2022/23, according to data published by the International Grains Council and the US Department of Agriculture. The United States, Brazil, and Argentina collectively account for approximately 70 to 75% of global maize export volume in most years, though the share of each exporter varies considerably with domestic production cycles, crop quality, and currency competitiveness.

The United States exports principally through Gulf ports (New Orleans, Houston, Corpus Christi) and Pacific Northwest ports (Portland, Longview). Gulf terminals load predominantly Panamax and Kamsarmax vessels (roughly 60,000 to 85,000 DWT) for long-haul routes to Asia and the Middle East; Pacific Northwest export goes primarily to Japan, South Korea, and Taiwan on Panamax vessels. Brazil exports through Paranaguá, Santos, and the rapidly expanding northern corridor ports of Itaqui (São Luís) and Barcarena, which provide shorter haul distances to Asian markets than Santos and have handled a growing share of total Brazilian grain export since 2015. Argentine export moves through Bahía Blanca and the Rosario-San Lorenzo complex on the Paraná River.

Ukraine was a major exporter averaging 30 to 35 million tonnes per year before February 2022, much of it to the EU, Egypt, China, and Iran via Black Sea ports. The disruption to Ukrainian export tightened global corn supply sharply in 2022/23, with partial recovery through the Black Sea Grain Initiative and subsequent arrangements. Romania, at the Danube-Black Sea confluence, emerged as a transshipment point for Ukrainian corn grain reaching global markets.

China shifted from near self-sufficiency in corn to a major importer during the 2020 to 2023 period, importing approximately 18 to 28 million tonnes annually, driven by domestic livestock industry expansion and the liquidation of strategic reserves that had kept prices artificially high. Mexico imports 15 to 18 million tonnes per year, almost entirely from the United States by virtue of geographic proximity and trade agreement terms. Japan, South Korea, Egypt, Iran, and Vietnam are consistent top-ten importers.

Commercial grades and their significance for carriage

Yellow dent corn (Zea mays indentata) is the dominant export form from the United States, Brazil, and Argentina. The indentation on the crown of the dried kernel is caused by differential drying of floury and horny endosperm. Yellow dent corn is the primary raw material for animal feed, wet milling for starch and sweeteners, and dry milling for ethanol. It is the form most bulk carriers carry.

White maize is produced in parts of Sub-Saharan Africa, Mexico, and South Africa primarily for human food consumption (as masa, ugali, and related products). It trades in smaller volumes, often on Handysize vessels to regional ports. The food-grade segregation requirement (no yellow contamination) makes hold preparation demands more strict than for feed-grade yellow corn, because even minor residues of yellow corn disqualify a parcel for food use at many destinations.

High-moisture corn (HMC) is harvested at 25% to 35% moisture and is normally ensiled on-farm rather than exported in bulk by sea. Bulk shipments of HMC are rare and would require special arrangements; the standard IMSBC GRAIN schedule applies to dry grain within normal moisture parameters.

Specialty corns including high-oil corn, high-amylose corn, and waxy corn move in small dedicated lots. Their physical properties do not differ materially from yellow dent for carriage purposes.

For bulk carriage purposes the grade distinction matters principally for hold cleanliness requirements and for the acceptable moisture range at loading rather than for any difference in cargo group or hazard classification.

IMSBC Code schedule for GRAIN: maize particulars

Schedule overview and Bulk Cargo Shipping Name

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

Schedule particulars table

The bulk density and stowage factor values reflect yellow dent corn at approximately 14% moisture at the standard US test weight of 56 lb/bu. Drier corn (below 12%) or denser flat-dent varieties may have slightly higher bulk density. The 14% moisture ceiling is the IMSBC Code’s stated loading condition for the GRAIN schedule; cargoes above this threshold require special approval or shipper certification in many jurisdictions.

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.

The International Grain Code: stability and trimming framework

History and mandatory status

The International Grain Code replaced the predecessor IMO Grain Rules on 1 January 1994 for ships whose keels were laid after that date, and by 1 July 1995 for existing ships on international voyages. It was adopted by IMO Resolution MSC.23(59) at the 59th session of the Maritime Safety Committee in 1991. SOLAS Chapter VI Part C (Regulations 9 to 12) gives it 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 Grain Code applies to all ships carrying grain in bulk on international voyages, with limited exemptions for ships of less than 500 GT and for ships carrying grain on domestic voyages under equivalent national regulations. A ship wishing to carry grain must have a Document of Authorization for the carriage of grain issued either by the flag state administration or by a recognized organization acting on its behalf. This document identifies approved loading conditions, the grain stability booklet, and the vessel’s eligibility to carry grain under the Code’s requirements.

The grain stability standard

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 residual area represents the dynamic reserve of stability 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. The Grain Code’s Appendix I tables give the standard volumetric heeling moments for different hold geometries and loading configurations; for each combination of hold type, cargo depth, and hatch arrangement, a tabulated heeling moment value is applied in the stability calculation.

Grain heeling moment calculation

The assumed grain heeling moment for a given hold is the product of the void volume within the hold (expressed in cubic metres) and a heeling moment coefficient. The void volume is the space between the trimmed cargo surface and the hold boundary; grain does not fill the upper corners of a hold, and the void over a trimmed surface in a large hold can be 2% to 5% of the loaded volume. When the ship rolls, this void allows the grain surface to shift to one side, effectively moving cargo mass away from the centreline. The heeling moment is the resultant lateral shift in the cargo’s centre of gravity multiplied by the cargo mass.

The Grain Code’s Appendix I provides tabulated heeling moment factors for the standard hold geometries (filled holds, partly filled holds with feeders, holds with shifting boards installed). For a fully filled hold trimmed to the underdeck structure, the tabulated factor is lower than for a partly filled hold because there is less free volume for grain to shift into. For a partly filled hold without any securing arrangement, the tabulated factor is the highest and corresponds to a large potential grain shift.

On a modern Kamsarmax or Capesize bulk carrier loaded with corn, the grain heeling moment calculation is typically part of the vessel’s approved loading stability software, tied to the grain stability booklet. The master is required to verify before departure that the actual loading condition satisfies all three Grain Code criteria.

The Document of Authorization

A vessel must carry a current Document of Authorization (DOA) to load grain on an international voyage. The DOA is issued by the flag state or its delegated authority (typically a classification society) and specifies the authorized loading conditions, the maximum allowable grain heeling moments, and, where applicable, the approved securing arrangements. The DOA incorporates the approved grain stability booklet for the vessel.

The grain stability booklet contains approved loading conditions (standard 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 fill in the actual load condition for each voyage. Before departure, the master completes the loading condition in the booklet and confirms compliance. Port state control surveyors verify this document as part of pre-departure inspection on grain voyages.

If a vessel does not have a current DOA, it cannot sail with a bulk grain cargo unless specific alternative arrangements are agreed with the Administration in advance. This requirement catches vessels that may not have a current classification survey or where the approved loading conditions were computed under an older vessel condition (after a hold modification, ballast tank conversion, or deadweight increase).

Trimming requirements

Trimming is the levelling 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 the requirements differ:

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 that loaders might otherwise miss. On large Panamax or 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 has the lowest standard heeling moment factor under the Grain Code’s 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 the equivalent of a filled hold for heeling moment purposes; or (b) carrying a reduced grain heeling moment by using the tabulated values for the exact fill level, provided the stability criteria are still met. In practice, partly filled holds are uncommon on full grain cargoes except at the fore and aft holds. Many operators prefer to fill all holds to capacity and top off the remaining tonnage in one or two holds trimmed to exact draft, avoiding the complexity of securing arrangements.

On typical corn voyages from US Gulf or Brazilian ports, the vessel is loaded full at all holds. Trimming of the final trimming hold (often hold 1 or hold 7) is done with care to approach but not exceed the intake for the desired draft. Telescoping spouts or spreader conveyors are used to pack grain into the extremities of holds during loading; after the main flow stops, hand trimming or mechanical trimming equipment is used to level the surface under the hatch opening and in the underdeck spaces.

Hazard 1: Self-heating and mould growth

The moisture-temperature relationship in stored corn

Corn at or above 14% moisture supports microbial activity. Fungi such as Aspergillus species colonize grain at moisture contents above approximately 13.5% at 25°C; their activity generates heat, carbon dioxide, and water vapor, creating a self-reinforcing cycle of temperature and humidity increase that can lead to substantial grain heating and mycotoxin contamination. The principal mycotoxin concern in corn is aflatoxin B1 (produced by Aspergillus flavus and A. parasiticus) and fumonisin B1/B2 (produced by Fusarium verticillioides and related species). Both are regulated in the EU under Commission Regulation (EC) No 1881/2006 and successor instruments, and breaches result in cargo rejection.

The International Grain Trade Rules and the IMSBC Code schedule both require that moisture content be below 14% at loading. If the moisture content is above 14%, many charterparties permit the master to refuse loading without penalty; some charterparties impose a maximum of 13.5% for the EU trade. Commercial practice is to test moisture content at the loading terminal, at intermediate sampling during loading, and again at discharge. Surveyors representing receivers frequently attend loading to take samples at regular tonnage intervals, particularly on long voyages where moisture migration is a concern.

Moisture migration and condensation

Bulk corn loaded at uniform temperature will develop moisture gradients during the voyage as the hold air temperature changes with latitude and season. Cold external temperatures lower the temperature of the cargo near the hold sides and the hatch covers; the cooler surfaces condense moisture from the warm air over the main cargo body. The condensate drips back into the surface grain, raising the local moisture content and creating a wetter band below the hatch and at the cargo perimeter. This “cargo sweat” is distinct from “ship sweat” (condensation on the hold steel) but both are managed partly by ventilation and partly by ensuring the cargo is loaded dry.

US export standards for corn specify maximum 14% moisture, minimum 54 lb/bu (approximately 0.72 t/m3) test weight, and maximum 3% damaged kernels for No. 2 Yellow Corn (the primary export grade). Brazilian corn tends to export at moisture near 13%, partly because of tropical shipping conditions and partly because drier corn commands a quality premium at Asian receivers. Argentine corn exports at 13% to 14% moisture.

Mould and mycotoxin risk in transit

If hot spots develop, mycotoxin contamination can advance far during a long voyage, particularly in the warmer months. The US Gulf to East Asia haul is approximately 25 to 30 days for Kamsarmax vessels; the Brazil to China route via the Cape of Good Hope is 35 to 45 days. These transit times are long enough for mould populations to multiply through multiple generations in warm, moist hot spots if the grain was loaded at borderline moisture. Cargo insurance claims for mycotoxin contamination occur on a regular basis in the grain trade; P&I clubs have issued guidance on temperature monitoring and ventilation to reduce the frequency.

On corn cargoes where the shipper’s quality is uncertain, receivers or their surveyors increasingly specify continuous temperature monitoring through penetrometer temperature probes installed at multiple depths (surface, mid-depth, and bottom) in representative holds. This is not a Grain Code or IMSBC Code requirement but a commercial quality protection measure.

Hazard 2: Oxygen depletion and carbon dioxide accumulation

The enclosed-space hazard in grain holds

Respiration by the grain kernel and by any microorganisms present consumes oxygen and releases carbon dioxide. In a sealed or poorly ventilated hold, oxygen levels can fall below the 19.5% safe entry threshold (the OSHA standard, adopted as the IMO reference level for enclosed-space entry) within days of hatch closure. Carbon dioxide levels can rise above 0.5% (5,000 ppm), which at concentrations of 3% to 5% causes incapacitation and at 7% to 10% is rapidly fatal. Carbon dioxide is denser than air and accumulates at the lowest point of the hold bilge area.

The hazard is compounded where fumigation has taken place. Phosphine (PH3) from aluminum phosphide or magnesium phosphide fumigant tablets begins to generate gas within minutes of tablet placement; the generated gas mixes with air in the sealed hold throughout the treatment period. Even after the treatment period and initial ventilation, residual phosphine can persist in the lower bilge areas. Carbon dioxide is a co-generated product of the tablet decomposition reaction, independently compounding the oxygen-depletion risk.

Hold entry during or after fumigation requires atmospheric testing for phosphine (below 0.1 ppm for routine entry), oxygen (above 19.5%), and carbon dioxide (below 0.5%) before any person enters. This three-parameter check is required by the IMO Revised Recommendations on the Safe Use of Pesticides in Ships (MSC.1/Circ.1358/Rev.2). Testing is done at the hatch opening level, at the midpoint of the hold, and at bilge level; the lower levels are the most critical because both carbon dioxide and phosphine are denser than air at typical hold temperatures.

Practical management of enclosed-space risk

Ships carrying fumigated grain are required to post warning notices at the hold entrances listing the fumigant used, the date of application, the date the hold was re-opened, and the name of the responsible fumigator. These notices are required whether the fumigation was done by shore personnel before departure or by a licensed fumigator in transit. Crew members must not enter holds bearing these notices without atmospheric testing and the explicit authorization of the master.

A common incident pattern in grain casualty reports is entry to retrieve fallen equipment or to inspect cargo condition without testing, on the assumption that adequate time has passed. Carbon dioxide has no odor; a seafarer who enters a hold with elevated CO2 loses consciousness within seconds of inhaling the oxygen-deficient atmosphere and cannot self-rescue. This type of accident kills one to three seafarers per year in the bulk carrier sector globally according to IMO data on enclosed-space fatalities.

The IMSBC Code section 3.2 and the associated SOLAS Regulation VI/3-1 require ships to have an enclosed-space entry procedure (part of the ship’s Safety Management System under the ISM Code) and to use it. The GRAIN schedule’s special requirements section notes the oxygen depletion hazard and the fumigation precautions. These requirements don’t stand independently from the broader enclosed-space entry framework; they reinforce it.

Hazard 3: Fumigation with phosphine

Why bulk grain is fumigated

Insect infestation of bulk corn is the principal reason fumigation is applied. Stored grain pests including grain weevils (Sitophilus granarius and S. oryzae), grain borers (Prostephanus truncatus and Rhyzopertha dominica), and saw-toothed grain beetles (Oryzaephilus surinamensis) can establish populations within a bulk corn cargo rapidly if viable adults or eggs are present at loading. At tropical sea temperatures during a 30- to 40-day voyage, a moderate initial infestation can grow to a population that causes measurable weight loss, heat generation, and quality degradation.

Phosphine is the dominant fumigant for in-transit grain fumigation internationally. It is generated from aluminum phosphide (AlP) tablets or pellets, with water vapor in the hold air initiating the reaction:

AlP + 3H2O → Al(OH)3 + PH3

Magnesium phosphide (Mg3P2) is also used; it reacts faster and is sometimes preferred for shorter-voyage treatments. Both generate phosphine gas that penetrates the bulk cargo mass, reaching insects at all levels within the hold.

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 are widely adopted by flag states, port states, and P&I clubs as the operating standard. The Circular requires that fumigation only be carried out by trained personnel, that gas-tight hatch sealing be verified, that neighboring holds not under treatment be monitored for phosphine migration, and that all crew be warned before treatment begins.

National regulations add specific requirements. The Australian Fumigation Accreditation Scheme (AFAS) requires that phosphine treatments in Australian waters or on vessels loading in Australia use AFAS-accredited fumigators. The United States requires that in-transit fumigation comply with EPA regulations under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and that the fumigant products used be EPA-registered for maritime in-hold use. Many export loading countries (including the US, Brazil, and Argentina) require phytosanitary certificates that may mandate pre-shipment fumigation before export is permitted, particularly for deliveries to countries with strict biosecurity requirements (Australia, Japan, South Korea, China).

Phosphine concentration and exposure limits

The minimum effective phosphine concentration for insect control depends on the pest species, the temperature, and the exposure duration. For most stored-product pests, the Grain Code of Practice (FAO/WHO, Codex Alimentarius CAC/RCP 21-1979) specifies minimum concentrations and minimum exposure times; typical commercial treatments target 2,000 to 3,000 ppm cumulative concentration-time (CT) exposure, achieved over 3 to 7 days at sea temperatures above 15°C. At lower temperatures, the required CT product and the required treatment duration increase.

The occupational exposure limits for phosphine are:

• OSHA permissible exposure limit (PEL): 0.3 ppm as an 8-hour time-weighted average
• OSHA ceiling (not to be exceeded at any time): 1 ppm
• IDLH (immediately dangerous to life or health): 50 ppm

Phosphine at 1,000 ppm is fatal within a few minutes. The hold atmosphere during active treatment routinely reaches 10,000 to 30,000 ppm; no entry is possible or permissible during treatment without self-contained breathing apparatus designed specifically for phosphine service.

Post-fumigation ventilation and clearance

Ventilation after fumigation requires opening hatches and running mechanical ventilation for a period sufficient to bring phosphine levels below the entry threshold. In practice, 24 to 48 hours of forced ventilation is required on a large Panamax hold before levels reliably fall below 0.1 ppm at all depths. Many fumigators use continuous gas monitoring via sampling tubes inserted through sealed hatch covers during the treatment period to track the concentration curve and determine when ventilation can begin.

Fumigation certificates, including the treatment date, fumigant used, quantity, application method, and the name of the accredited fumigator, are required cargo documents under MSC.1/Circ.1358/Rev.2 and are examined by port state control at the discharge port. Many bulk carrier P&I clubs require copies to be sent to them as well, because fumigation-related incidents are a material source of personal injury claims.

Hazard 4: Grain dust explosion and health

Dust characteristics of corn

Corn grain generates dust primarily during loading, when kernels break during conveyor transfer, pass through shiploader chutes, and fall into the hold. The fine fraction below 75 micrometres, composed primarily of pericarp fragments, starch particles, and dried silk residues, is the combustible component. Corn dust has a minimum explosible concentration (MEC) of approximately 55 to 80 g/m3 in air, a minimum ignition energy of approximately 30 to 40 mJ, and a Kst value (normalized rate of pressure rise) of 100 to 200 bar.m/s, placing it in Explosion Class St 1 (moderate hazard) under European classification.

The practical implication during loading is that concentrations above the MEC can occur transiently at the fall zone below the loading spout and in the lower section of the hold immediately above the cargo surface. The combination of the dust cloud at the fall zone with any ignition source (sparks from metal-on-metal contact, static discharge, electrical faults in conveyor equipment) creates explosion risk.

Several grain elevator explosions at shore facilities have involved corn dust. On ships, dust explosion risk is highest during loading at terminals with pneumatic or high-speed conveyor systems. The IMO’s Dust explosions in cargo holds section of the IMSBC Code guidance (Appendix 6) and relevant national regulations (including OSHA 29 CFR 1910.272 in the United States for grain facilities) require dust suppression by water spray, control of ignition sources, and post-loading hold ventilation to bring residual dust concentrations below the MEC before any hot work is permitted.

Occupational health from dust inhalation

Respirable corn dust contains endotoxins from gram-negative bacteria, fungal spores, storage mite feces, and pericarp fragments. Occupational exposure in grain handlers at land facilities is associated with organic dust toxic syndrome (ODTS), occupational asthma, and chronic bronchitis. On bulk carriers, crew exposure is primarily during loading and discharge in port. The exposure period is brief compared with land-based grain handlers, but on vessels handling multiple cargoes over a season, cumulative exposure is a legitimate concern. Personal protective equipment (dust masks rated FFP2/N95 or higher) is appropriate during loading operations.

Hold preparation and grain-clean standards

What grain-clean means in practice

A grain-clean hold is not a single-parameter standard; it is a composite condition requiring: absence of all residue from the previous cargo; absence of odors that could taint the grain (particularly petroleum hydrocarbons, fertilizer residues, and chemical cargo residues); absence of any moisture standing in bilges or on structural surfaces; absence of insects and rodent evidence; and absence of visible mold or degraded grain from previous cargoes.

The difficulty of achieving grain-clean condition depends heavily 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 coal residue in grain is a commercial contamination issue.
• Mineral fertilizers (urea, ammonium nitrate, potassium chloride): require intensive washing with fresh water to remove the hygroscopic and corrosive residues, plus drying. The residual salts from urea are particularly difficult to remove from bilge frames.
• Clinker or cement: leaves an alkaline residue that affects grain quality. Multiple washing cycles are required; in some cases holds are limed and re-washed.
• Timber: generally leaves the hold in better condition for grain, but residues of bark, preservative treatments, or dunnage must be removed.
• Previous grain: requires sweeping, washing, drying, and inspection but is generally achievable at lower cost than an industrial cargo.

Commercial practice is to have a professional hold-cleaning company, rather than vessel crew, perform hold cleaning at terminals in major export ports (Houston, Santos, Paranaguá, Odesa). Independent surveyors representing the charterer, shipper, or receiver inspect the holds before loading, issue a grain-clean certificate or note deficiencies requiring further work. Failure to obtain a grain-clean certificate before loading puts the vessel owner at risk for cargo quality claims.

Ventilation at loading terminals

Many loading terminals require holds to be inspected and certified grain-clean before any corn is moved to the silo loading system. The sequence at a typical US Gulf terminal is: vessel arrival and berth assignment; hold inspection by terminal supervisor and independent surveyor; grain-clean certificate issue or deficiency list; remediation if required; then commencement of loading. The terminal’s environmental permits may require dust suppression water spray on the cargo fall zone from the moment loading begins.

Loading, trimming, and stowage

Loading rates and equipment

Major US Gulf grain terminals load at rates of 3,000 to 6,000 tonnes per hour per berth. Brazilian terminals at Paranaguá load at 2,000 to 4,000 t/h; the northern ports (Itaqui, Barcarena) are newer and some berths reach 4,000 t/h. Loading a 75,000 DWT Kamsarmax vessel at 4,000 t/h therefore requires roughly 18 to 19 hours of continuous loading, assuming holds are filled sequentially.

Trimming is a separate operation from loading. On modern loading terminals with trimming spreader machines, the loading spout itself distributes grain to the hold extremities. On terminals without spreading equipment, the vessel’s crew must perform trimming using trim buckets or trimming boards passed through the hatch, or by using the vessel’s own trimming gear where fitted. The Grain Code requirement to fill all void spaces under deck beams requires positive effort; corn does not flow freely around the hatch coaming structure or into deep under-deck pockets without mechanical assistance.

Stowage factor and cargo calculations

The stowage factor for maize at approximately 1.35 m3/t means that a 75,000 DWT Kamsarmax with total hold volume of approximately 95,000 m3 will carry approximately 70,000 to 75,000 tonnes of corn grain at typical loadings. The exact cargo quantity depends on the actual stowage factor for the specific shipment, which varies with moisture content, variety, and test weight, and on the vessel’s actual deadweight and freshwater allowance.

Cargo calculators for bulk grain, including the grain heeling moment calculator and the bulk cargo displacement calculator, are useful for trip-planning and stability verification, particularly when planning mixed-hold loading conditions. The IMSBC Group A/B/C classification calculator confirms the cargo group for declaration purposes.

Interaction between loading sequence and stability

On a multi-hold vessel, the order in which holds are loaded affects the vessel’s intact stability and the immersion of the load line marks at each stage of loading. Stability during loading must be monitored continuously; the loading computer is updated with each tank-sounding and hold tonnage. 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 loading can have worse stability than the full-load condition (particularly during the double-bottom ballast exchange sequence, where ballast tanks are discharged as cargo is loaded). The vessel’s grain stability booklet typically specifies the sequence of hold loading and ballast discharge that maintains acceptable stability throughout.

Ventilation during the voyage

Surface versus through-hold ventilation

The IMSBC Code GRAIN schedule specifies that holds carrying dry grain may be ventilated. Ventilation serves two purposes: dissipation of heat generated by grain respiration and the removal of carbon dioxide and moisture vapor. For dry grain (below 14% moisture), both surface ventilation (opening ventilators to let air circulate over the cargo surface without drawing air through the bulk) and through-hold ventilation (using mechanical ventilation to draw air down through the cargo from the ventilator inlets to the bilge vents) are generally acceptable.

Ventilation with cold, moist air that is colder than the cargo surface can cause condensation on the cargo. This is “cargo sweat” and is the primary risk with excessive ventilation in cold weather. The standard guidance from the Grain Code and from cargo underwriters is to ventilate only when the dew point of the outside air is below the dew point of the hold air, determined by simultaneous temperature and humidity measurements at both the outside atmosphere and the hold air. When ventilation would cause condensation, holds should remain closed.

Through-hold ventilation is not generally recommended for cargo that is above 14% moisture, because circulating air through a warm, moist grain body accelerates evaporation from the outer layers, which then condenses in the cooler upper section of the cargo. For dry corn at 12% to 13.5% moisture, through-hold ventilation with dry, warm air can help dissipate any minor heat build-up and reduce carbon dioxide levels.

Ventilation records

Ship’s logs should record hold temperature measurements (taken through a thermometer tube inserted through the hatch or through a temperature-sensing port if fitted) at regular intervals, typically once per day or more frequently if temperatures are rising. Cargo temperature above 40°C requires increased monitoring frequency. Temperatures above 55°C in grain cargo indicate active microbial heating; if temperature continues to rise after ventilators are closed, emergency measures including sealed hold and CO2 flooding may be required.

These records matter commercially because cargo temperature histories are used by P&I clubs and cargo insurers to assess whether the master exercised proper care of the cargo, particularly when a mycotoxin contamination or overheating claim is made at discharge. Many charterparties specifically require the master to maintain and present a voyage temperature log.

Enclosed-space entry procedures

The three-parameter check

Before any person enters a grain hold during or after a voyage (for inspection, fumigation supervision, or any other purpose), the atmosphere must be tested for:

• Oxygen content: must be above 19.5% (OSHA standard; IMO reference for enclosed-space entry is also 19.5%)
• Carbon dioxide: must be below 0.5% (5,000 ppm)
• Fumigant residue (phosphine or other): must be below the occupational exposure limit relevant to the fumigant used; for phosphine, below 0.1 ppm for routine entry

Testing must be carried out at the hatch rim, at mid-hold level (lowering a probe through the hatch), and at the lowest accessible level. The tests must be carried out by a person competent in the use of the detection equipment, using calibrated instruments. A signed entry permit, issued by the master or designated responsible officer, must be in place before entry.

The SOLAS Regulation XI-1/7 (Measures to prevent accidents with lifeboats) and Regulation III/19 (Emergency training and drills) include enclosed-space entry training as a mandatory drill item. The ISM Code requires a documented enclosed-space entry procedure in the ship’s Safety Management System, and STCW Basic Safety Training (BST) for all seafarers now includes enclosed-space entry awareness. SOLAS Regulation XI-1/7.3 (effective from 1 January 2015) requires enclosed-space drills on tankers and bulk carriers at least once every two months.

Despite these requirements, the maritime industry records several enclosed-space fatalities every year, a substantial fraction of which involve grain and organic bulk cargo holds. The combination of self-sealing holds (hatches that form a tight seal after loading) and the time-lag between entry and onset of symptoms in oxygen-deficient atmospheres explains the repeated pattern.

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 maize, the required documents are:

• Cargo declaration stating the BCSN (GRAIN or GRAIN (MAIZE)), 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 of the cargo and the date and method of testing. The Grain Code requires this for all grain shipments.
• Phytosanitary certificate issued by the exporting country’s plant health authority, required by virtually all importing countries for grain shipments and by most charterparties.
• Certificate of origin, required for customs purposes at destination.
• Fumigation certificate if the cargo has been or will be fumigated, as required by MSC.1/Circ.1358/Rev.2.

Where a quality analysis is required by the receiver or the charterparty (USDA grade certificate, ISO 6540 moisture test certificate, mycotoxin analysis certificate), these are commercial rather than IMSBC Code documents, but they travel with the Bills of Lading and are presented at discharge.

The shipper’s responsibilities under the IMSBC Code

Section 4.2.2 of the IMSBC Code requires the shipper to provide a cargo information form specifying the physical and chemical properties of the cargo relevant to safe carriage. For Group C grain, the key data items are moisture content, bulk density, stowage factor, and information on any fumigation treatment. The shipper’s declaration that the 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 some 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. A single-loading sample check is often supplemented by a surveyor’s pre-loading inspection, particularly on first-time voyages from a new loading terminal or shipper.

Related cargoes and IMSBC schedules

Maize is one of several bulk grain cargoes regulated under the generic GRAIN BCSN. The carriage framework is identical in structure for all of them:

Wheat IMSBC Schedule covers the largest single grain trade and shares the Grain Code stability and trimming requirements. Wheat’s stowage factor (approximately 1.25 to 1.30 m3/t) is lower than maize, meaning a given hold volume holds more wheat than corn by mass. Hold preparation requirements and fumigation practices are essentially the same.

Soya beans IMSBC Schedule differs from maize in one material respect: soya beans have a higher oil content (approximately 18% to 20% by dry weight) and present a greater self-heating risk at elevated moisture than corn. The Grain Code applies to soya beans as to all grain. Soya beans are declared as SOYA BEANS under the IMSBC Code’s Appendix 1 rather than under the generic GRAIN entry.

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 for paddy) than milled rice (approximately 1.5 to 1.7 m3/t) and both are lower-density cargoes than yellow corn. The Grain Code applies; paddy rice presents a particular moisture sensitivity because the husk’s absorbency creates uneven moisture distribution.

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 full technical and commercial requirements for achieving grain-clean condition and other hold preparation standards, with cross-cargo comparisons.

Marine cargo hold ventilation covers the theoretical and practical aspects of ventilation strategy for bulk cargoes including grain, with the dew-point decision rule explained in detail.

Limitations

The IMSBC Code schedules, the International Grain Code, and the supporting IMO circulars on fumigation are the authoritative sources for maize 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 yellow dent corn. Actual values for any specific cargo must be obtained from certified pre-shipment tests and declared on the cargo documentation. Specialty grades (white corn, high-amylose, waxy) 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 worked parameters in this article are illustrative of the Code’s methodology; they do not constitute a certified stability assessment for any vessel or voyage. Masters and operators must apply the Code to their specific vessel’s approved loading conditions.

Fumigation regulations vary by flag state, port state, and receiving country. The 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) impose additional requirements. The accredited fumigator contracted for each voyage is responsible for compliance with applicable national regulations at the loading port.

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