Rice: IMSBC Code and Grain Code Carriage

Rice is classified as Group C under the IMSBC Code and carried under the generic GRAIN schedule, making the International Grain Code the governing technical instrument for stability and trimming. Unlike wheat and maize, a large share of world rice trade moves in bagged form; the portion that does ship in bulk brings the same physical and biological hazards: 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. India became the world’s largest rice exporter around 2012, and global seaborne rice trade runs at approximately 50 to 60 million tonnes per year.

Rice is one of the seven named grains in the IMSBC Code GRAIN schedule, which covers wheat, maize, oats, rye, barley, rice, pulses, and seeds under a single Bulk Cargo Shipping Name (BCSN). The classification is Group C: no liquefaction risk, no MHB chemical hazard. That designation says nothing about the difficulty of carriage; it means the hazard controls come through a parallel, older instrument rather than through the chemical-hazard framework of Groups A and B. That instrument is the International Grain Code, adopted by IMO Resolution MSC.23(59) in 1991 and given mandatory force by SOLAS Chapter VI Part C. Every ship loading bulk rice on an international voyage must comply with both the IMSBC Code’s cargo documentation requirements and the Grain Code’s stability, trimming, and securing provisions.

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

The rice trade: volumes, grades, and routes

Global seaborne trade volumes

Rice is the most-consumed staple cereal in Asia, but seaborne trade volumes are low relative to production because most rice-growing countries consume the bulk of their domestic crop. Global seaborne trade in rice ranges from 50 to 60 million tonnes per year, roughly one-quarter of the seaborne volume of wheat and one-third of maize, despite world rice production exceeding 500 million tonnes milled equivalent annually. The gap between production and trade reflects the combination of high domestic consumption, export-restricting policies (many Asian governments manage export volumes to protect domestic food security), and the predominance of subsistence and smallholder farming in major producing regions.

India has been the world’s largest rice exporter since roughly 2012, exporting 20 to 22 million tonnes per year in most recent marketing years. The principal loading ports are Kakinada and Vishakhapatnam (Andhra Pradesh) and Kandla (Gujarat) for non-basmati parboiled rice, and Mundra and Nhava Sheva for packaged and basmati grades. Thailand is the second or third largest exporter in most years (10 to 12 million tonnes), loading at Bangkok and Laem Chabang. Vietnam exports 7 to 8 million tonnes per year, primarily through Saigon (Ho Chi Minh City) and the Mekong Delta port of Can Tho. Pakistan exports 4 to 6 million tonnes annually from Karachi; Cambodia and Myanmar are smaller and growing sources for the Southeast Asian and African markets.

The United States exports approximately 2.5 to 3.5 million tonnes per year, mostly from Gulf ports (Houston, New Orleans, Lake Charles) and a smaller volume from Sacramento-area mills serving Asian customers with medium-grain California Calrose. US exports are almost entirely milled long-grain rice to the Caribbean, Latin America, and Northeast Africa.

Principal trade routes

The dominant flow in volume terms is Indian non-basmati parboiled rice to Sub-Saharan Africa. West African importers (Nigeria, Senegal, Ivory Coast, Benin, Guinea) collectively absorb 12 to 15 million tonnes per year; the majority travels on Handysize (25,000 to 35,000 DWT) and Supramax (50,000 to 60,000 DWT) bulk carriers or general cargo ships in bagged form. East African markets (Tanzania, Kenya, Mozambique) are supplied from Indian and Pakistani origins on similar vessel sizes. The India-West Africa voyage is approximately 18 to 22 days; the India-East Africa voyage around 7 to 12 days through the Indian Ocean.

The Philippines is consistently the single largest national importer, with the National Food Authority (NFA) and private importers together bringing in 3 to 4 million tonnes annually, primarily as milled white rice from Vietnam and Thailand but increasingly from India since 2023. Indonesia, Bangladesh, China (variable by year), Iran, Iraq, and Saudi Arabia are other major destinations. The Philippine government’s shift to open private-sector importation after the Rice Tariffication Law of 2019 substantially changed the trade’s commercial structure, moving from state-to-state contracts to private commercial tenders.

Commercial grades and their relevance for carriage

Paddy rice (rough rice) is the whole grain as harvested: kernel, bran layer, and husk intact. Seaborne paddy trade is limited; most paddy moves domestically from farm to mill. Paddy has a stowage factor of approximately 1.60 to 2.00 m3/t and bulk density of 0.50 to 0.62 t/m3, giving it a low grain-mass-to-space ratio that makes bulk shipment commercially inefficient except for specific contracts (seed rice exports, some South-South trade). Myanmar ships paddy to China by barge and coastal vessel on the Irrawaddy corridor; some Indian paddy moves to Bangladesh.

Brown rice is paddy with the husk removed but the bran layer (pericarp) intact. It is not a major seaborne bulk trade item; brown rice is milled to white at destination or at an intermediate processing hub. Stowage factor approximately 1.40 to 1.60 m3/t.

Milled white rice is the dominant seaborne trade form. The bran and germ are removed, leaving the starchy endosperm. Stowage factor approximately 1.20 to 1.35 m3/t; bulk density approximately 0.74 to 0.83 t/m3. Long-grain varieties (indica types, which dominate global trade) pack more densely than short-grain or medium-grain (japonica types). Parboiled rice, which has been steam-treated before milling, has a slightly denser and harder kernel than raw milled rice, with stowage factor in the lower end of that range.

Basmati rice is a long-grain aromatic variety from the Indo-Gangetic Plain (India and Pakistan). It has a stowage factor toward the upper end of the milled-rice range because of the length and slenderness of the kernel. Basmati is almost always shipped in bags (25 kg or 50 kg polypropylene woven sacks) rather than in bulk because of its premium quality and food-safety segregation requirements; a single contamination event in bulk stow would destroy the cargo value.

For carriage purposes, the grade distinction matters for the moisture threshold at loading, the stowage factor used in cargo calculations, and the required hold cleanliness standard (food-grade white rice imposes stricter requirements than parboiled feed-grade rice). The IMSBC Code group and the Grain Code requirements do not vary by rice grade.

IMSBC Code schedule for GRAIN: rice particulars

Schedule overview and Bulk Cargo Shipping Name

Rice is declared under the BCSN “GRAIN” in IMSBC Code Appendix 1. The schedule explicitly names rice as one of the grains within its scope. The shipper may specify the species on the cargo declaration as “GRAIN (RICE)” or, more specifically, “GRAIN (RICE, MILLED)” or “GRAIN (PADDY RICE)” to identify the grade and condition. This specificity is commercially standard and assists the receiving surveyor and port health authority in confirming the declared commodity matches the cargo on board.

Schedule particulars

The angle of repose for rice is generally similar to or slightly higher than maize. Paddy rice, with its irregular husk surface, develops a somewhat higher angle of repose than the smooth kernel of milled rice. This affects the assumed grain shift calculation and the applicable Grain Code heeling moment tables.

How the IMSBC Code and Grain Code interact for rice

Rice follows the same two-instrument framework as all bulk grains. The IMSBC Code provides the administrative backbone: cargo declaration, shipper documentation, and Group C classification. The International Grain Code provides the technical requirements: Document of Authorization (DOA), grain stability booklet, trimming procedure, and the three stability criteria. Neither instrument alone is sufficient; a ship that presents perfect IMSBC documentation but lacks a current DOA may not sail on a bulk rice voyage.

The interaction produces a documentation chain the master must assemble before departure: a completed cargo declaration naming the BCSN and cargo group; a moisture content certificate from a competent testing authority; a shipper’s cargo information form; and from the Grain Code, the completed grain loading condition sheet from the approved stability booklet. On voyages carrying fumigated rice, the fumigation certificate joins this chain.

International Grain Code stability regime for bulk rice

Mandatory status and ship eligibility

The International Grain Code became mandatory on 1 January 1994 for new ships and by 1 July 1995 for existing ships under SOLAS Chapter VI Part C. Ships of less than 500 GT on international voyages and ships on domestic voyages subject to equivalent national regulation are exempted. A ship wishing to carry bulk grain, including rice, must obtain a Document of Authorization from the flag state or a recognized organization delegated by the flag state. The DOA incorporates the approved grain stability booklet and defines the authorized loading conditions, maximum heeling moments, and, where fitted, the approved securing arrangements.

Without a current DOA, the ship cannot load bulk rice for an international voyage. This catches vessels that have not completed their annual or intermediate class survey, ships that have had underdeck modifications that altered the approved hold geometry, or vessels that simply never applied for grain certification because they primarily carry non-grain cargoes and the rice voyage is opportunistic.

The three stability criteria

The Grain Code establishes three criteria that must all be satisfied simultaneously in the fully loaded condition:

Criterion 1: Heel limit. The static angle of heel resulting from the worst assumed grain shift must not exceed 12 degrees. The assumed grain shift is calculated using the heeling moment tables in Grain Code Appendix I, applied to the actual loaded void volumes in each hold. A heel exceeding 12 degrees indicates the vessel’s righting arm at that angle is insufficient to guarantee recovery from the assumed grain shift.

Criterion 2: Residual dynamic stability. The area under the righting-moment (GZ) curve between the actual static angle of heel and 40 degrees (or the angle of downflooding, if less) must be at least 0.075 metre-radians. This residual area is the dynamic reserve: after the grain has already shifted and the vessel is heeled, there must still be sufficient dynamic righting capacity to prevent capsize from wave action.

Criterion 3: Corrected metacentric height. The initial metacentric height (GM) corrected for free surfaces in all liquid tanks must be at least 0.30 metres throughout the voyage, including at intermediate stages when ballast is being transferred.

A rice bulk carrier that cannot satisfy all three criteria as loaded has two options: change the loading plan to improve the GM (shift ballast, reduce cargo, or redistribute between holds), or install grain securing arrangements (shifting boards) in the deficient hold or holds to reduce the applicable heeling moment to a level that brings all three criteria into compliance.

Heeling moment tables and void volume

Rice presents a particular consideration in the heeling moment calculation: paddy rice, because of its higher stowage factor and lower bulk density, produces larger void volumes in a given hold than milled rice at the same deadweight. A hold loaded with 5,000 tonnes of paddy rice at 0.55 t/m3 occupies roughly 9,090 m3; the same mass of milled rice at 0.78 t/m3 occupies about 6,410 m3. The paddy stow leaves more void under the hatch coaming and in the upper wing spaces, producing a higher heeling moment for the same tonnage.

This means the grain stability booklet’s standard loading conditions, typically computed for one or two representative rice grades, may not directly apply to a paddy rice cargo if the ship is primarily certified for milled rice. Masters and operators need to verify that the approved loading conditions in the DOA and booklet cover the actual grade being loaded. A mismatch discovered at final departure check by port state control creates a commercial and legal problem that cannot be solved quickly at berth.

The Grain Code Appendix I heeling moment factors depend on hold geometry (beam, depth, hatch dimensions) and fill level. Modern bulk carrier stability software approved for grain carriage includes the Grain Code heeling moment calculation as a built-in module, linked to the vessel’s tankage and cargo data. The output is the three-criteria check for each load case entered by the chief officer or stability officer before departure.

Trimming requirements for rice

Trimming for rice follows the same Grain Code framework as other grains, with a practical difference for paddy rice: the husk creates a rougher particle surface that tends to pile at slightly steeper angles than polished milled kernels. The higher natural angle of repose means that hand-trimmed or mechanically trimmed paddy surfaces may hold slightly steeper profiles than milled rice, but the Grain Code requirement to fill all void spaces under deck beams and in the underdeck wings still applies regardless.

For a filled hold, the surface must be trimmed as close to the underdeck structure as practicable, filling the wing spaces and the spaces under the hatch coaming. A partly filled hold requires either installation of shifting boards (minimum 1.8 m deep, continuous for the full hold length) or acceptance of the higher heeling moment from the tabulated partly-filled condition, provided stability criteria are still met. In practice, partly filled holds are unusual on full bulk rice cargoes; the typical load plan fills all holds.

The grain heeling moment calculator and the bulk cargo displacement calculator support trip-planning and pre-departure Grain Code verification for rice voyages.

Bulk versus bagged rice: stowage and regulatory distinctions

Why so much rice moves in bags

The dominance of bagged rice in seaborne trade is a commercial, not a regulatory, choice. Bagged rice can be sold at retail or distributed through small traders without further processing or weighing infrastructure at the destination port. For many African and Asian importers, the bag is the point-of-sale unit: the 25 kg or 50 kg polypropylene woven sack that arrives on a truck from the port is the same sack that reaches the consumer market. Bulk discharging infrastructure (pneumatic grain suckers, conveyor discharge systems, grain silos for storage) is absent from many of the world’s smaller grain-importing ports, making bulk receipt impractical regardless of the freight-rate advantage of bulk carriage.

Bagged rice also protects quality more reliably on long voyages than bulk stow in holds with substandard ventilation or in ports where discharge takes many days. The bag provides a physical barrier against moisture ingress from hold condensation and from minor water ingress through weathered hatch seals, and it segregates the rice from hold wall contamination.

The freight cost advantage of bulk over bagged carriage is real: bulk rice on a Panamax bulk carrier typically freights at $10 to$25 per tonne below bagged rice on a general cargo vessel or container ship (depending on distance and market conditions), reflecting the more efficient hold utilization and faster port turnaround. State purchasing agencies (Philippines NFA, Indonesia’s Bulog, Iran’s GTC) that import millions of tonnes per year are the primary buyers of bulk rice, because the volume justifies the infrastructure for bulk discharge.

Regulatory framework for bagged rice

Bagged rice on a general cargo ship is not covered by the IMSBC Code. The IMSBC Code applies only to solid bulk cargoes, defined as homogeneous solid material loaded directly into the ship’s cargo spaces without any intermediate form of containment. Bagged rice is packed cargo; the regulatory framework for stowage, cargo securing, and documentation is the cargo securing manual (part of the vessel’s SOLAS compliance package) and any applicable national port regulations. When bagged rice is carried in shipping containers, the IMDG Code’s packed-goods framework and container stuffing procedures apply.

For a multi-purpose vessel or a bulk carrier carrying both bulk rice in some holds and bagged rice in other holds or on tweendeck, the bulk holds are subject to IMSBC Code and Grain Code requirements, while the bagged stow is subject to the general cargo standards for that vessel. Pre-departure stability and securing calculations must account for all cargo simultaneously.

Stowage of bagged rice

Bagged rice requires dunnage to protect bags from contact with the ship’s structural steel, to create air gaps for ventilation, and to prevent bags from absorbing moisture from bilge condensation. Standard practice for bagged rice in a general cargo hold is to lay two or three layers of dunnage board (typically 25 mm to 50 mm timber boards) on the tank-top, then build the bag stow in interlocked patterns to maximum height. In refrigerated or air-conditioned cargo spaces (occasionally used for premium basmati), the hold is cooled to 10°C to 15°C before loading.

Bags must be stowed clear of ship’s side frames where condensation runs down the hull plating in cold climates. A spacing of at least 300 mm from the ship’s side is conventional; wire mesh or battens (sparring) hold the stow away from the hull. In holds with high humidity risk, the top layer of bags is covered with kraft paper or plastic sheeting to deflect cargo sweat dripping from the hatch covers.

Hazard 1: Moisture migration and self-heating

The moisture-temperature mechanism in rice

Rice grain, like all cereals, is hygroscopic: it absorbs or releases water vapor to equilibrium with the surrounding air. At moisture contents above 14% for milled rice (or 13.5% for paddy), microbial activity in the grain mass generates heat, carbon dioxide, and water vapor. The heat produced raises the local temperature, which increases the vapor pressure of water in the grain, which accelerates moisture release into the hold air, which condenses on cooler surfaces. The cycle is self-reinforcing: a grain mass that starts at borderline moisture can develop hot spots that climb through 30°C, 40°C, and into the 50°C to 60°C range within two to three weeks if unchecked.

The principal moulds in moist rice are field fungi (Fusarium species, which colonize during growing and harvest) and storage fungi (Aspergillus glaucus group, A. candidus, A. flavus, and Penicillium species, which colonize during storage and transit). Storage fungi are the primary transit concern; their growth rates are highest at 25°C to 35°C and above 70% relative humidity in the grain intergranular air. Aspergillus flavus produces aflatoxins, which are regulated in the EU, the US, Japan, and virtually every destination market. Fusarium species produce fumonisins and zearalenone. Both families of mycotoxins are heat-stable; cooking destroys the mould but not the toxin.

On a 25-day voyage from India to West Africa, a milled rice cargo loaded at 13.5% moisture but with pockets at 14.5% (a realistic variance from a poorly conditioned lot) can develop measurable aflatoxin contamination in those pockets. A 35-day voyage from Vietnam to the Middle East at borderline moisture is more risky still. P&I clubs track aflatoxin and total aflatoxin cargo rejections at destination as a recurrent loss type in the rice trade.

Paddy rice and uneven moisture distribution

Paddy rice’s husk makes moisture assessment by standard methods more complex. The husk absorbs water without necessarily transferring it to the grain kernel on short time scales, so a surface moisture reading from a near-infrared (NIR) instrument or a standard capacitance meter on a paddy sample may underestimate the internal kernel moisture. During a voyage in warm, humid conditions, the moisture stored in the husk migrates inward into the kernel and into the intergranular air of the bulk, elevating local humidity.

This husk-moisture migration effect means that paddy rice loaded at a measured moisture of 13% may develop effective grain moisture of 14% or above at the surface of the pile during a tropical voyage. The IMSBC Code’s conservative threshold of 13.5% for paddy, relative to 14% for milled rice, reflects this dynamic.

Cargo sweat and ship sweat

Moisture damage to rice cargo comes from two distinct condensation phenomena, and the practical response to each differs:

Ship sweat is condensation on the ship’s steel structure (hold sides, frames, tank top, hatch underside) when the steel temperature falls below the dew point of the hold air. This occurs when a vessel loads in a warm, humid port and then transits through cooler latitudes or seasons; the external cooling reduces the steel temperature faster than the large grain mass, and the exposed metal sweats. Water from ship sweat drips onto the cargo surface and potentially migrates through the top layer of bags or penetrates the bulk surface. The primary defense is ensuring the hold air’s dew point is below the steel temperature before and during the cold-climate transit, managed through ventilation policy.

Cargo sweat is condensation on the cargo surface itself when the cargo surface is colder than the incoming ventilation air’s dew point. This happens when warm, humid outside air is admitted into a hold where the cargo mass has been chilled by a cold-climate transit. The warm air cools upon contact with the grain and deposits moisture directly on the cargo. The defense is to stop ventilating when outside dew point exceeds hold dew point.

Both phenomena are addressed by the same decision rule: ventilate only when the outside dew point is below the hold air dew point (as measured by wet-and-dry-bulb readings at both locations). The marine cargo hold ventilation article covers this dew-point decision rule in full detail.

Hazard 2: Oxygen depletion and carbon dioxide accumulation

Grain respiration and atmospheric change in rice holds

Rice kernels, even after milling, are biologically active seeds. Respiration (the oxidative metabolism of starch to produce CO2 and water) continues at measurable rates at hold temperatures above approximately 10°C. At 25°C and 14% moisture, carbon dioxide production from a large grain mass is sufficient to raise hold CO2 concentrations from atmospheric (0.04%) to above 0.5% in a sealed or poorly ventilated hold within a few days. In sealed holds carrying warm, moist rice over 20 or more days, CO2 concentrations of 3% to 5% are not unusual where grain respiration is supplemented by microbial activity.

Carbon dioxide is 1.52 times denser than air and accumulates at the lowest accessible point of the hold: the bilge well and the area between the lower cargo surface and the tank top. An oxygen concentration below 19.5% and a CO2 concentration above 0.5% define the atmosphere in these areas as immediately dangerous to entry without self-contained breathing apparatus.

The fumigation amplifier

Phosphine fumigation in sealed holds compounds the oxygen-depletion hazard in two ways. First, the aluminum phosphide decomposition reaction consumes oxygen and generates CO2 as a side product, independently reducing O2 and raising CO2 irrespective of grain respiration. Second, the phosphine gas itself, at the in-hold concentrations of 2,000 to 30,000 ppm used during treatment, is acutely toxic; it acts as an asphyxiant and a systemic cellular toxin simultaneously, so the hazard is not merely the oxygen deficit but the additive effect of CO2 and PH3 in the same atmosphere.

The standard three-parameter atmospheric test required by MSC.1/Circ.1358/Rev.2 before hold entry (O2 above 19.5%, CO2 below 0.5%, PH3 below 0.1 ppm) must be performed at three levels: hatch-opening level, mid-hold level, and bilge level. Many seafarers mistakenly test only at the hatch rim, where natural convection delivers the freshest air. The hold bilge can be acutely toxic even when the hatch rim reads acceptable oxygen and CO2; the denser gases settle.

Enclosed-space entry procedure requirements

The SOLAS framework requires enclosed-space entry procedures in the ship’s Safety Management System under ISM Code Chapter 7. SOLAS Regulation XI-1/7 (effective 1 January 2015) requires enclosed-space entry drills on tankers and bulk carriers at least every two months. STCW Basic Safety Training includes enclosed-space entry awareness and rescue for all seafarers.

Despite these requirements, the IMO’s casualty statistics show repeated enclosed-space fatalities on bulk grain carriers each year. The typical incident pattern: a seafarer enters a hold after fumigation to inspect cargo condition or retrieve fallen equipment, having been told by a colleague (incorrectly) that “enough time has passed.” Carbon dioxide has no odor and no immediately noticeable physiological effect at 3% to 5% concentration until the victim is already losing consciousness. Self-rescue is impossible in an oxygen-deficient atmosphere once collapse occurs; the rescuers who enter without equipment often die alongside the first victim.

The IMSBC Code section 3.2 and the GRAIN schedule’s special requirements section both reference the enclosed-space entry hazard and fumigation precautions. These requirements reinforce the broader ISM and SOLAS enclosed-space entry framework rather than standing alone from it.

Hazard 3: Infestation and phosphine fumigation

Stored-product pest biology in rice

Rice is among the most susceptible of all grain cargoes to insect infestation. The principal pests are the rice weevil (Sitophilus oryzae) and the lesser grain borer (Rhyzopertha dominica), both of which develop entirely within or on individual kernels and are impossible to eradicate by cooling alone. Adults of S. oryzae can survive at temperatures between 15°C and 40°C; egg-to-adult development takes approximately 30 days at 30°C, meaning a moderate initial infestation can go through one full generation during a long tropical voyage.

Grain borers (Prostephanus truncatus) and saw-toothed grain beetles (Oryzaephilus surinamensis) are surface feeders that also infest milled rice in transit. Saw-toothed beetles in particular are frequently found in the crevices of bags and in broken grain at the bag-seam areas of bagged cargoes; they can penetrate the woven polypropylene bags through small defects or punctures.

The combination of long voyages, tropical temperatures, and existing on-farm infestation at loading origin (particularly from smaller Asian mills with inadequate silo aeration) means fumigation before loading, in transit, or both is standard commercial practice on rice shipments to markets with strict phytosanitary requirements.

Phytosanitary certificate requirements

Nearly every major rice-importing country requires a phytosanitary certificate issued by the exporting country’s plant health authority (NPPO: National Plant Protection Organization). The certificate declares that the consignment has been inspected, found free from specified pests and diseases, and (where required) treated with an approved pesticide. Australia and New Zealand require phytosanitary certification for all rice imports as a biosecurity measure; the US requires phytosanitary certificates for all imported grain under USDA-APHIS regulations.

In practice, the phytosanitary certificate for rice often specifies the fumigation treatment applied before loading: the fumigant, the concentration achieved, the exposure duration, and the name of the accredited fumigator. Many large importers (Philippines NFA, Bangladesh government procurement) also require an independent pest-inspection certificate from a named international surveying company (SGS, Bureau Veritas, Intertek) as part of the Letter of Credit conditions.

Phosphine application and regulatory framework

The operative international standard for in-transit fumigation is IMO MSC.1/Circ.1358/Rev.2, the Revised Recommendations on the Safe Use of Pesticides in Ships. These recommendations are not mandatory convention text but are incorporated by reference into many flag state and port state regulations and are treated as the operating standard by P&I clubs.

The Circular requires that fumigation be carried out only by trained and certified personnel, that hatches and hold penetrations (ventilator caps, bilge suction openings, pipe tunnel accesses) be gas-tight before treatment begins, that neighboring holds not under treatment be monitored for phosphine migration through inter-hold voids, and that all crew receive written notification of the treatment before it begins.

Effective phosphine concentration for insect control depends on temperature and exposure time. The general industry target for tropical-temperature treatment (above 20°C) is a minimum CT product of 300 to 450 ppm-hours for susceptible pest stages, with many national protocols requiring higher CT values to cover resistant strains. At 25°C, this typically means maintaining 200 to 300 ppm for 3 days, or 100 to 150 ppm for 5 to 7 days. Below 15°C, phosphine liberation from aluminum phosphide tablets slows significantly, treatment efficacy falls, and treatment duration must be extended or the alternative fumigant magnesium phosphide (which reacts faster) may be substituted.

For bagged rice, fumigation gas distribution through the stow is more difficult than for bulk rice. The bags, particularly tightly packed polypropylene sacks, impede gas diffusion. Fumigators serving bagged rice voyages typically use probes to inject phosphine at multiple levels within the stow rather than relying solely on surface tablet placement. Treatment periods for bagged stows are correspondingly longer than for equivalent-volume bulk stows.

Post-fumigation ventilation and documentation

Ventilation after phosphine treatment requires 24 to 48 hours of mechanical ventilation through open hatches to reduce phosphine concentrations to below 0.1 ppm at bilge level before hold entry is permitted. Continuous gas monitoring through sampling lines during ventilation is recommended by MSC.1/Circ.1358/Rev.2. The monitoring record, showing the phosphine concentration curve from treatment through clearance, is a required annex to the fumigation certificate.

Fumigation certificates must travel with the cargo documents and must be presented to port state control authorities at the discharge port. Port state control officers on rice voyages from India, Vietnam, and Thailand routinely request and inspect fumigation documentation; deficient or missing certificates result in hold detention and, in some jurisdictions, mandatory re-treatment under port supervision.

Phosphine occupational exposure limits

The occupational exposure thresholds for phosphine are:

• OSHA permissible exposure limit (PEL): 0.3 ppm as an 8-hour TWA
• OSHA ceiling limit (never to be exceeded): 1 ppm
• IDLH (immediately dangerous to life or health): 50 ppm

In-hold phosphine during active treatment routinely reaches 10,000 to 30,000 ppm. Entry without full self-contained breathing apparatus (SCBA) designed for phosphine service is acutely lethal. Airline respirators and filter-type respirators do not provide protection against phosphine; only pressure-demand SCBA or supplied-air respirators with escape bottle are suitable for entry into an atmosphere that may contain phosphine above the IDLH value.

Hazard 4: Grain dust from rice

Dust characteristics

Rice grain generates dust primarily during loading operations: when kernels fracture on conveyor belts, fall from loading spouts into the hold, and impact the growing cargo surface. Milled rice dust is composed of starch fragments, bran particles (pericarp), and dried endosperm. Paddy rice dust includes the additional component of husk fragments, which are lignocellulosic and highly flammable. Rice husk dust has a minimum explosible concentration (MEC) of approximately 40 to 60 g/m3 and a minimum ignition energy of 10 to 30 mJ, making it a more sensitive dust than milled rice. Rice husk dust has an explosion class St 1 (some testing places it at the boundary of St 2), with a Kst value typically in the range 100 to 180 bar.m/s.

During loading of milled rice, the dust hazard is generally lower than for paddy, but the finer fraction from broken kernels still creates transient combustible-dust clouds at the fall zone. Any ignition source in or near the hold during loading (cutting equipment, electrical faults in shore conveyor systems, static discharge from non-conductive conveyor belts) represents a real, if low-probability, explosion hazard.

Dust control measures

The IMSBC Code’s Appendix 6 guidance on dust explosions in cargo holds applies to rice. The measures required are: no hot work within the hold or on deck immediately above the hold during loading; dust suppression by water spray at the shiploader head or spout; electrical bonding of the loading equipment to the vessel to equalize static potential; and post-loading hold ventilation to bring residual airborne dust concentrations below the MEC before sealing hatches.

Most major grain loading terminals in India, Thailand, and Vietnam operate under national port health and safety regulations that specify dust suppression, enclosed-space monitoring, and hot-work prohibition during grain loading. Terminal employees and ships’ officers both carry responsibility for maintaining these controls.

Health effects from rice dust

Rice dust contains endotoxins from gram-negative bacteria resident on the grain surface, fungal spores, and in the case of parboiled rice, trace amounts of process chemicals from the parboiling operation. Occupational exposure to rice dust at land facilities is associated with occupational asthma and organic dust toxic syndrome (ODTS). On bulk carriers, crew exposure is limited to the loading and discharge periods in port; the total exposure hours per voyage are far below the levels associated with chronic disease in land-based grain workers. Dust masks rated FFP2/N95 or higher are appropriate for crew on deck during rice loading.

Hold preparation and grain-clean standards for rice

Grain-clean condition: what it requires

A grain-clean hold for rice means: all residues of the previous cargo are removed from the tank top, frames, underdeck structure, and bilge wells; no odors from the previous cargo are detectable (particularly critical for rice, which absorbs petroleum, fertilizer, and chemical odors readily); no standing moisture or condensation on any structural surface; no insects or rodent evidence; and no mold or degraded grain from any previous cargo.

The practical difficulty of reaching grain-clean condition for rice depends on the previous cargo more than on any property of rice itself. Holds that previously carried:

Coal require complete residue removal by dry brushing and pressure washing, then drying. Coal dust penetrates seams between structural members and can be redistributed by condensation water during a subsequent voyage. Black staining from coal dust on structural surfaces is cosmetic for feed-grade cargoes but unacceptable to receivers of food-grade white rice.

Urea or ammonium nitrate fertilizer require intensive fresh-water washing to remove hygroscopic and corrosive residues from all surfaces, including bilge wells and frame webs. Fertilizer residues on the grain surface or in the bilge drainage create a contamination risk for food-grade rice. Several cargo quality claims involving fertilizer-tainted rice have resulted in total cargo loss claims.

Fish meal or fishmeal residues are perhaps the most difficult previous cargo for rice: the persistent strong odor from fishmeal penetrates hold coatings and can be detectable in a rice cargo even after multiple washing cycles. Charterparties for food-grade rice often prohibit recent carriage of fishmeal.

Petcoke or petroleum products deposit oily residues on structural surfaces that are extremely difficult to remove completely and that migrate into overlying grain. Grain-clean certification after petcoke may require lime-washing or chemical treatment followed by re-washing.

Independent surveyor inspection

Commercial practice on rice voyages is to have independent surveyors representing the shipper, charterer, or receiver inspect and certify holds as grain-clean before loading begins. Major surveying companies in Asian grain ports (SGS, Bureau Veritas, Cotecna, Intertek, CCIC) offer hold inspection services at all the major loading ports. The grain-clean certificate they issue (or a noted deficiency report requiring further cleaning) is a commercially significant document: if the carrier loads without a grain-clean certificate and quality problems emerge at discharge, the absence of that certificate substantially weakens the carrier’s defense.

Port health authorities at some receiving ports also inspect holds. The Philippine Bureau of Plant Industry (BPI) and Indonesia’s BKSDA (quarantine authority) inspect rice cargoes and holds on arrival; holds not meeting sanitary standards are subject to mandatory treatment.

The cargo hold preparation standards article covers the full technical and commercial framework for achieving grain-clean and other hold cleanliness standards.

Ventilation strategy during a rice voyage

The dew-point decision rule

Ventilation of bulk rice holds during a voyage follows the same dew-point decision rule as all bulk grain: ventilate when the outside dew point is below the hold dew point; keep hatches closed when the outside dew point exceeds the hold dew point. This rule prevents both cargo sweat (outside warm moist air cooling on the grain surface and condensing) and ship sweat (outside air raising the hold humidity above the condensation temperature of the ship’s steel) when applied correctly.

The dew point of the outside air and the dew point of the hold air are both measured by wet-and-dry-bulb psychrometry or by electronic humidity instruments at the same time. On modern vessels with automated hold atmosphere monitoring, the decision is made by software from continuous sensor inputs; on older vessels, the chief officer or the duty officer takes manual readings twice daily and records the decision in the cargo log.

Surface versus through-hold ventilation for rice

Surface ventilation (admitting external air to circulate over the cargo surface) is the standard approach for dry milled rice in good condition. It dissipates heat generated by rice respiration, removes CO2, and prevents moisture saturation in the intergranular air near the surface. Through-hold ventilation, drawing air down through the bulk and out via bilge ventilators, can be applied to dry rice as well and is more effective at dissipating heat from deeper within the cargo. Both methods are appropriate for rice below 14% moisture.

For paddy rice or for rice at borderline moisture (13.5% to 14%), through-hold ventilation carries a slightly higher risk of redistributing moisture within the cargo as humid air passes through the warmer grain layers. Surface ventilation is the more conservative choice in these conditions.

Ventilation during rain or in fog is inappropriate regardless of dew-point comparison, because rain or condensing fog on the hatch coaming and ventilator inlets can introduce free water into the hold.

Temperature monitoring and records

Hold temperature should be measured daily, using thermometer tubes inserted through the hatch covers or through dedicated temperature ports if fitted. On rice voyages where the cargo is at borderline moisture or where the previous cargo history suggests possible cross-contamination risk, monitoring every 12 hours is prudent. Any steady upward trend in cargo temperature above the ambient hold-air temperature is an indicator of microbial activity in the grain.

Temperature above 40°C requires increased monitoring frequency and consideration of closing ventilators to deny oxygen to the active microbial population. Temperature above 55°C in the grain mass indicates advanced microbial heating; at this stage, options are limited but may include sealed-hold isolation (to starve the aerobic organisms of oxygen) or, in extreme cases, early discharge at an intermediate port to prevent total cargo loss.

The temperature record forms part of the P&I club and cargo insurer’s assessment of whether the carrier exercised proper care of the cargo. A carrier that can demonstrate regular measurements, decision-consistent ventilation records, and escalating responses to rising temperatures is in a substantially better position than one with blank log books.

Cargo declaration and pre-shipment documentation

Mandatory IMSBC Code documents

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

Cargo declaration: names the BCSN (GRAIN or GRAIN (RICE)), states the cargo group (C), gives the estimated quantity, and declares whether the cargo has been or will be fumigated.

Moisture content certificate: issued by a competent testing authority using an approved method. The certificate must state the moisture content and the testing date. For rice, particularly paddy rice, the test method matters: NIR (near-infrared) instruments and grain moisture meters calibrated for rice differ from those calibrated for wheat; an incorrect calibration produces a systematically wrong moisture reading. The competent testing authority’s certificate should specify the method used.

Phytosanitary certificate: issued by the national plant protection organization of the exporting country. Required by IMSBC Code section 4 for grain cargoes and by the importing country’s biosecurity regulations. The certificate must cover the specific consignment and lot number.

Fumigation certificate: required if the cargo has been or will be fumigated in transit, as specified by MSC.1/Circ.1358/Rev.2. Must identify the fumigant, quantity, application method, treatment date, and the accredited fumigator.

Commercial quality certificates

Receivers of rice frequently require additional quality documentation not mandated by the IMSBC Code but routinely included in Letter of Credit terms: a quantity and quality certificate from a named international surveyor covering physical analysis (moisture, whiteness for milled rice, percentage of broken kernels, percentage of foreign matter), a mycotoxin analysis certificate (aflatoxins, fumonisins) from an accredited laboratory, and, for parboiled rice, a gelatinization test result. These documents travel with the bills of lading and are presented at discharge port alongside the mandatory regulatory certificates.

Shipper’s responsibility and master’s right to refuse

The shipper’s declaration of moisture content is a representation that the cargo is suitable for loading under the IMSBC Code GRAIN schedule. A false declaration (knowingly overstating dryness) exposing the ship to avoidable cargo damage creates liability for the shipper in both contract and tort. The master has the right under SOLAS and the IMSBC Code to refuse loading if the stated moisture content appears inconsistent with the cargo’s observed condition, if the cargo shows signs of heating or infestation before loading begins, or if the documentation is incomplete or unsigned.

At major Indian loading ports (Kakinada, Kandla, Vishakhapatnam), the volumes and pressures of state-procurement loading programs make it commercially awkward for a master to reject a consignment without a clear factual basis. Having an independent pre-loading surveyor’s report in hand, and raising concerns with that surveyor and with the charterer’s agent in writing before loading commences, is the proper procedural protection for the master.

Related cargoes and IMSBC schedules

The Grain Code and IMSBC GRAIN schedule provide identical regulatory frameworks for all bulk grains. The practical differences between cargoes come from physical properties (stowage factor, moisture threshold, dust characteristics) rather than from different regulatory instruments.

Wheat IMSBC Schedule covers the largest seaborne grain cargo at roughly 200 million tonnes per year. Wheat’s stowage factor (approximately 1.25 to 1.30 m3/t) is broadly similar to milled rice; its moisture ceiling is 14%; fumigation and Grain Code requirements are identical to rice. Major loadings on Panamax and Kamsarmax vessels from Black Sea, Australian, and North American ports.

Maize IMSBC Schedule covers the second-largest seaborne grain trade at roughly 185 million tonnes per year. Maize has a higher stowage factor (approximately 1.30 to 1.45 m3/t) than milled rice, a 14% moisture ceiling, and identical Grain Code and fumigation requirements. Yellow corn’s angle of repose (20 to 25 degrees) and grain-shifting hazard are essentially the same as for milled rice.

Soya Beans IMSBC Schedule has a distinct BCSN (SOYA BEANS rather than GRAIN) in IMSBC Appendix 1, reflecting the higher oil content (approximately 18% to 20% by dry weight) and greater self-heating tendency of soya beans versus rice. The Grain Code applies to soya beans as to all grain. Stowage factor approximately 1.38 to 1.43 m3/t.

IMSBC Code provides the full regulatory context for all bulk cargo group classifications, Appendix 1 structure, and documentation requirements.

IMSBC Group C cargoes explains the Group C classification framework and lists the range of cargoes within it.

Cargo hold preparation standards covers the technical and commercial requirements for grain-clean condition and other hold preparation standards.

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

Related IMSBC calculators for rice sub-products:

• IMSBC Rice in Bulk
• IMSBC Grain: Rice Bran
• IMSBC Rice Husks
• IMSBC Rice Bran (B)
• Grain Heeling: Volumetric Heeling Moment
• Bulk Cargo Displacement: Grain
• IMSBC Group A/B/C Classification

Limitations

The IMSBC Code schedules, the International Grain Code, and the supporting IMO circular MSC.1/Circ.1358/Rev.2 on fumigation are the authoritative sources for rice bulk 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; Amendment 08-25 was under preparation at the time of writing.

Stowage factors, bulk densities, and moisture thresholds cited are typical commercial values for the grades described. Actual values for any specific cargo must come from certified pre-shipment tests and must be declared on the cargo documentation. Rice varieties outside the main trade types (fragrant jasmine, specialty short-grain japonica, black and red pigmented rices) may have physical properties outside the ranges stated.

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 illustrate the Code’s methodology; they are not a certified stability assessment for any vessel or voyage.

Fumigation regulations differ by flag state, port state, and receiving country. MSC.1/Circ.1358/Rev.2 is the international baseline, but national regulations (EPA FIFRA in the US, the Australian Fumigation Accreditation Scheme, EU Regulation 528/2012 for biocidal products) impose additional requirements. The accredited fumigator contracted for each voyage is responsible for compliance with the applicable national regulations at the loading port.

Mycotoxin regulatory limits, rice grade standards, rice tariff and import quota regimes, and the commercial terms of rice charterparties are within national food-safety law, commodity market rules, and private contract rather than within the IMSBC Code or Grain Code framework. This article does not cover those subjects.