Lead Concentrate: IMSBC Code Schedule

Lead concentrate is a dual-hazard solid bulk cargo under the IMSBC Code: Group A because the galena-rich fine material may liquefy above the Transportable Moisture Limit, and Group B (MHB TX, toxic) because lead dust presents a documented health hazard to crew from inhalation and skin contact. Its bulk density of 3.0 to 3.8 t/m³ makes it one of the densest cargoes carried in ordinary bulk carriers, generating extreme structural loads on the tanktop and an amplified heeling moment if any portion of the cargo liquefies. The combination of liquefaction risk, toxicity, and very high density makes lead concentrate one of the most technically demanding bulk cargoes to handle correctly.

The IMSBC Code, adopted under SOLAS Chapter VI by Resolution MSC.268(85) and first entering force on 1 January 2011, classifies solid bulk cargoes into three groups. Group A cargoes may liquefy at or above their Transportable Moisture Limit. Group B cargoes present a chemical hazard to the ship. Lead concentrate qualifies on both counts. The cargo’s individual schedule appears in IMSBC Code Appendix 1 under the Bulk Cargo Shipping Name LEAD CONCENTRATE, alongside dedicated entries for copper concentrate, zinc concentrate, iron ore concentrate, and other major concentrates. Smaller-volume lead-bearing products and polymetallic lead-zinc concentrates that do not match the LEAD CONCENTRATE entry fall under the MINERAL CONCENTRATES generic schedule.

Use the IMSBC bulk cargo finder at /calculators/imo-imsbc for the full schedule entry table. For TML moisture compliance, the IMSBC TML moisture check calculator supports the loading decision. For Group A/B/C classification screening, use the IMSBC group classification tool.

Schedule particulars

The IMSBC Code’s LEAD CONCENTRATE schedule records the following properties. The table below consolidates the key parameters; the shipper’s cargo declaration must state the actual measured values for each individual shipment, not the indicative ranges shown here.

The angle of repose entry is listed as “not applicable” for lead concentrate because the fine, cohesive nature of the cargo means it does not form a free-flowing cone. While dry, it holds a face angle; once the pore-water pressure exceeds the effective confining stress, it transitions rapidly from solid to fluid, which is exactly the liquefaction behaviour the Group A controls are designed to prevent.

The cargo: mineralogy, production, and trade

Mineralogy and composition

Lead concentrate is produced from lead-bearing ore, principally galena (PbS), the dominant lead mineral in economic deposits. Galena has a mineral specific gravity of 7.6, the highest of the common base-metal sulphides. This high specific gravity is what drives the cargo’s extraordinary bulk density: after flotation milling, filtering, and dewatering, a cargo that is 60 to 75% galena by mass will measure 3.0 to 3.8 t/m³ in the ship’s hold.

Galena rarely occurs in isolation. Commercial lead ore deposits typically contain sphalerite (ZnS, specific gravity 3.9 to 4.1), pyrite (FeS₂, specific gravity 5.0), and minor amounts of chalcopyrite (CuFeS₂) and argentite (Ag₂S). The silver content is often economically important: Peruvian and Australian lead concentrates can contain 400 to 1,200 grams of silver per tonne, which is recovered at the smelter as a byproduct. The zinc content is typically suppressed during flotation to produce a separate zinc concentrate stream, but residual sphalerite in the lead concentrate is common and affects the cargo declaration.

The resulting concentrate shipped to smelters has a lead content of roughly 60 to 75% Pb, together with 5 to 15% S (from sulphide minerals), and smaller percentages of zinc, iron, silica, and precious metals. Moisture at loading is typically 7 to 10%, the result of vacuum filtration to a point that reduces shipping weight while staying above the threshold at which lead dust becomes friable and airborne.

Processing: from ore to cargo

Open-pit and underground mining recovers the ore from the deposit. After crushing and grinding to liberation size, typically 50 to 150 micrometres for most lead deposits, froth flotation selectively concentrates the lead sulphide minerals. A depressant is added to suppress the zinc and iron sulphides during the lead flotation stage, producing a lead rougher concentrate that is cleaned through two to three further flotation stages. The cleaned concentrate is thickened in a settling tank, then filtered by vacuum belt filter or pressure filter to the target moisture. The filter cake is transported by conveyor to a storage shed or stockpile at the port, from which it is reclaimed and loaded.

The Broken Hill-type and Irish-type stratiform deposits that supply much of global lead production, including Cannington (Australia), McArthur River (Australia), and Tara (Ireland), are polymetallic. Their concentrates reflect the shared mineralogy: lead concentrate from these operations always contains measurable zinc and silver, and the bulk density and TML both reflect the specific mineralogy of that batch.

Global seaborne trade

Global lead concentrate seaborne trade is approximately 4 to 6 million dry metric tonnes per year. This is substantially smaller than copper concentrate trade (roughly 25 to 30 Mt/year) or iron ore concentrate trade, reflecting both the smaller size of the global lead market and the higher metal content per tonne of concentrate shipped.

The principal supply regions are Australia (McArthur River, Cannington, Mount Isa, and other Queensland operations), Peru (Cerro de Pasco, Antamina, and Milpo operations through Callao), Mexico (Peñoles and Grupo Mexico operations through Pacific Coast ports), and Kazakhstan. Receiving smelters are concentrated in China (which accounts for over 50% of global refined lead production), South Korea, India, Japan, and Europe (Germany, Bulgaria, and Spain have major lead smelters). Russian lead concentrate exports were disrupted after 2022 due to sanctions, reducing Far Eastern supply flows. Port facilities at the loading end include Port of Townsville (Australia) and Port of Callao (Peru), which have dedicated concentrate handling equipment.

The Group A liquefaction hazard

Why lead concentrate is Group A

Lead concentrate qualifies as Group A under the IMSBC Code definition because the cargo may liquefy when its moisture content reaches or exceeds the TML. The physical mechanism is the same as for zinc concentrate, copper concentrate, and the other base-metal sulphide concentrates described in the MINERAL CONCENTRATES schedule. The fine particle size produced by flotation milling creates a dense packing of small grains with correspondingly small inter-particle pores. Under the cyclic motion of the vessel at sea, load pulses transmit through the cargo as pore-water pressure. The low permeability of the fine matrix means the water cannot drain fast enough to dissipate these pressure cycles, and pore pressure accumulates until the effective stress between grains approaches zero and the cargo transitions from solid to fluid. The full mechanism is described in the companion article on cargo liquefaction.

Lead concentrate has one additional physical feature that makes the consequences of liquefaction worse than for most other Group A cargoes: the very high bulk density. At 3.0 to 3.8 t/m³, the cargo is approximately twice as dense as iron ore fines (1.9 to 2.2 t/m³) and noticeably denser than zinc concentrate (2.4 to 2.8 t/m³). A small volumetric shift of liquefied cargo generates a much larger heeling moment than the same volumetric shift of a lighter cargo. The relationship is direct: a 1 m³ shift of lead concentrate at 3.5 t/m³ produces a heeling moment 3.5 tonnes higher than a 1 m³ shift of fresh water. On a loaded Handysize bulk carrier, a shift of even 10 to 20 m³ of high-density liquefied cargo is enough to produce a list that exceeds the vessel’s righting capability.

Pore-pressure accumulation under ship motion

The liquefaction sequence in a lead concentrate hold is not immediate. At moisture contents well below the TML, the cargo acts as a stiff solid. As moisture approaches the TML, pore pressure rises more rapidly under each roll cycle. At moisture equal to the TML, defined as the 90% safety margin on the Flow Moisture Point, the rate of pore-pressure generation under representative sea conditions is at the practical threshold: the cargo has not yet liquefied, but the safety factor against liquefaction is exhausted. Any further moisture input, from rainfall infiltration through a hatch seal, from condensation cycling, or from the inherent measurement uncertainty in the shipper’s moisture certificate, can push the effective pore pressure past the threshold within hours at sea.

The visible signs of incipient liquefaction are subtle and often misread. The cargo surface above a liquefying lower layer looks dry and normal. Bilge well levels may rise slowly rather than suddenly; the rise is attributable to moisture migrating from the cargo but the volume may not seem alarming until the list is already developing. The roll period of the vessel may lengthen, which is a measurable sign of reduced metacentric height, but in moderate seas this change is not dramatic enough to alarm an officer who does not know what to look for. By the time a visible list develops and corrective ballasting is attempted, large-scale cargo shift may already be irreversible.

The TML and the formula

The TML is the single regulatory threshold that separates permissible loading from prohibited loading. For the flow table test and the penetration test, the relationship between TML and Flow Moisture Point (FMP) is:

The FMP is the moisture content at which the cargo first exhibits a flow state in the laboratory test. The 10% reduction from FMP to TML is the mandated safety margin, providing a buffer against sampling heterogeneity, laboratory variability, and the much more energetic cyclic loading that the cargo will experience in a ship at sea compared to the static test apparatus. For the Proctor-Fagerberg test, TML is determined from the compaction-saturation curve as the moisture content corresponding to 70% degree of saturation, a different but functionally equivalent threshold.

The loading rule is absolute. A Group A cargo must not be loaded when the actual moisture content equals or exceeds the TML. The shipper’s moisture certificate must show a moisture content strictly below the TML. A certificate showing moisture at 9.8% against a TML of 10.0% is technically compliant, but the 0.2 percentage-point margin is narrower than the typical measurement uncertainty of the moisture test and narrower than the variation that occurs between different portions of a large stockpile. P&I club practice recommends that masters treat any gap of less than 1 percentage point between declared moisture and TML as grounds for requesting independent survey.

Why the moisture can change between sampling and loading

The IMSBC Code requires moisture testing within seven days of the commencement of loading. For lead concentrate, moisture can change materially in that window because:

The cargo is typically stored in open or semi-open stockpiles. Rain falling on an uncovered stockpile raises the surface moisture within hours. The surface wets faster than the centre, and stockpile reclamation that draws material from multiple depths can blend high-moisture surface material with drier interior material, producing a cargo with variable moisture distribution. Rain at any point between sampling and loading invalidates the moisture certificate as a reliable predictor of actual moisture at loading.

Condensation within a warm stockpile shed during seasonal temperature changes can also raise interior moisture without obvious surface evidence. Shippers who sample the top of the stockpile and then load from the stockpile base may be presenting a moisture figure for a location that was not actually loaded. The IMSBC Code’s requirement for seven-day retesting after weather events addresses this directly, but enforcement depends on the shipper’s diligence and the master’s scrutiny of the certificate dates and any weather records for the port.

The MHB toxic classification

What MHB TX means

Lead concentrate carries the designation MHB TX (Material Hazardous in Bulk, Toxic) in the IMSBC Code schedule. This classification exists because the cargo presents a hazard not covered by the Group A (liquefaction) designation alone. Lead is a systemic heavy-metal toxin. Even brief exposure to lead dust at concentrations above occupational health limits causes measurable blood lead elevation. Chronic low-level exposure causes progressive neurological damage, anaemia, kidney damage, and reproductive toxicity. The health hazard from lead dust in a bulk-cargo context is real and documented: terminal workers and ship crew who handle lead concentrate without adequate controls have been found with elevated blood lead in occupational health surveys in multiple jurisdictions.

The MHB TX designation triggers a set of provisions in the IMSBC Code that are additional to the Group A requirements. These are not optional guidance. They are mandatory schedule requirements that bind the carrier and the terminal equally.

What the IMSBC Code requires for MHB TX cargoes

For lead concentrate loaded under the MHB TX designation, the Code requires:

The cargo declaration must include the MHB classification and the specific hazard information, including the nature of the toxicity, the exposure pathway (inhalation, ingestion, skin and eye contact), and the recommended precautions. This information must reach the master before loading begins.

Crew access to cargo holds and adjacent enclosed spaces must be restricted during loading, the voyage, and discharge. Any crew member who must enter a hold or enclosed space where lead dust may be present must use appropriate respiratory protection (a particulate respirator rated for lead dust, or a supplied-air respirator where concentrations may be high), protective gloves, and coveralls that are removed before entering accommodation spaces.

No eating, drinking, or smoking is permitted in areas where lead dust may be present, including on deck during loading at terminals where dust suppression is inadequate. Thorough washing of hands, face, and any exposed skin before meals and before entering accommodation is required.

The IMSBC Code also requires that wash-down water from hold cleaning after discharge be collected and disposed of appropriately, not pumped overboard. Lead ions in port water are regulated by national environmental standards in most jurisdictions; discharge of lead-contaminated wash water is a potential environmental offence.

Lead dust and enclosed-space hazards

Galena and associated iron sulphide minerals in the concentrate can oxidise slowly in the presence of oxygen and moisture. While lead concentrate is not typically classified as self-heating, the sulphide mineral fraction means that the hold atmosphere during a long voyage may contain traces of sulphur dioxide from oxidation of pyrite and other iron sulphides. Confined-space entry protocols require atmosphere testing for oxygen depletion, toxic gases (sulphur dioxide, hydrogen sulphide), and flammable vapours before any person enters a cargo hold.

The oxygen content risk in lead concentrate holds is lower than in pure sulphide concentrates with high pyrite content, but it is not zero. The Code’s general confined-space provisions under the IMSBC Code Section 3 and under SOLAS apply to all bulk carrier cargo holds, and lead concentrate holds specifically require atmosphere testing before entry given the MHB designation.

Bulk density, structural loading, and tanktop stress

Why density matters for structural loading

A bulk carrier’s tanktop is designed to a specific allowable load in tonnes per square metre. The tanktop loadline for a Handysize bulk carrier of approximately 28,000 DWT is typically in the range of 10 to 15 t/m² depending on class and ship design. At a bulk density of 3.5 t/m³, lead concentrate fills only 2.9 to 4.3 metres depth before reaching the tanktop limit. This is shallow relative to the full hold depth, which on a typical Handysize ranges from 12 to 16 metres. Loading a full hold of lead concentrate is structurally impossible on most vessels; the tanktop would be overloaded before the hold is half full.

In practice, masters and operators plan lead concentrate loading with a maximum cargo depth per hold, calculated as:

where $d_{\max}$ is the maximum cargo depth in metres, $q_{\text{allow}}$ is the tanktop allowable load in t/m², and $\rho_{\text{bulk}}$ is the bulk density of the cargo in t/m³. For a tanktop rated at 12 t/m² and lead concentrate at 3.5 t/m³, this gives $d_{\max} = 3.4$ m. Loading deeper than this value risks permanent tanktop deformation and potential structural failure.

The IMSBC Code requires the master to verify that the cargo distribution does not exceed the hold structural limits stated in the ship’s loading manual. For lead concentrate, this check is not a formality. On ships designed for general bulk cargo trade, the tanktop is the binding constraint, not the overall deadweight. A charterer who presents a full cargo of lead concentrate for a vessel rated at 12 t/m² without advance planning is presenting a structural problem, not merely a loading sequence question.

Distribution across multiple holds

Because no single hold can carry a deep load of lead concentrate without risking tanktop overload, the cargo is typically spread across all available holds at a controlled depth. This creates a different planning problem: the vessel’s trim, list, and longitudinal bending moment are all affected by the distribution. On a five-hold Handysize, a uniform shallow layer across all five holds is usually the starting point, with adjustments for the vessel’s baseline trim and any stability requirements.

The longitudinal strength of a bulk carrier is sized for normal cargo distributions. A very dense cargo loaded shallow in all holds loads the double-bottom structure and tanktop heavily while leaving the upper hold structure lightly stressed. This reverses the normal bending stress pattern relative to homogeneous cargoes that fill the hold depth. While modern ships’ loading computers handle these calculations in real time, the master and chief officer should verify that the bending moment envelope stays within the permitted limits at all times during loading, not only at completion.

Trimming requirements under the IMSBC Code

The IMSBC Code requires Group A cargoes to be trimmed so the height difference between peaks and troughs in the cargo surface does not exceed 5% of the ship’s breadth. For a Handysize with a moulded breadth of 32 m, this is a maximum surface relief of 1.6 m. Lead concentrate at a loading depth of 3 to 4 m can develop surface irregularities from the fall of the spout stream, which need to be levelled before the hatches are closed.

Mechanical trimming with a bulldozer or front-end loader working in the hold is common at major concentrate terminals. Any crew member supervising or assisting trimming operations in a lead concentrate hold must comply with all MHB TX personal protection requirements: respiratory protection, coveralls, and hygiene measures apply to hold entry regardless of the reason for entry.

Test methods for TML determination

Flow table test

The flow table test, prescribed in IMSBC Code Appendix 2, is the original standard method for finely ground mineral concentrates. A weighed sample is placed in a brass mould on the flow table and compacted with a spring-loaded tamper. The mould is removed and the table is operated through a series of drops from a height of 12.5 mm, repeated 25 times. The spread of the sample is measured. The test is repeated at progressively higher moisture levels until the sample spreads by more than the reference threshold, indicating the flow state. The moisture at which flow first appears is the FMP; TML is 90% of FMP.

The flow table test is suitable for concentrates with maximum grain size up to 1 mm, and in some implementations up to 7 mm for coarser fractions. Lead concentrate, ground to 50 to 150 micrometres by flotation milling, sits well within this range. The main limitation is operator subjectivity in judging the onset of flow; the Code acknowledges this and requires accredited, experienced laboratories.

Penetration test

The penetration test eliminates the subjectivity of the flow table method by replacing visual judgement of flow with a measurable penetration depth. The sample is placed in a cylindrical vessel on a vibrating platform. Brass weights on the sample surface are observed as moisture is progressively increased. The FMP is the average moisture between the run where weights penetrate more than 50 mm and the preceding run where they did not. Like the flow table test, TML = 0.9 × FMP. The penetration test is applicable up to 25 mm top size, making it versatile for coarser concentrates, but for flotation-milled lead concentrate the results from flow table and penetration tests are generally consistent.

Proctor-Fagerberg test

The Proctor-Fagerberg test was developed specifically for ore concentrates and is the most commonly used method for sulphide concentrates in Australia, Peru, and other major producing countries. The sample is compacted in a cylindrical mould at a series of moisture levels. Dry density and moisture content at each compaction point generate a compaction curve and a saturation line. The TML is the moisture content on the compaction curve corresponding to 70% degree of saturation in the voids. No FMP is directly determined; the test uses the full compaction-saturation relationship.

The Proctor-Fagerberg test is applicable to concentrates with maximum particle size up to 5 mm, which covers all flotation-milled lead concentrates. It requires more careful sample preparation and data processing than the flow table test but produces a TML that does not depend on a subjective visual observation. For a shipper whose concentrate is tested regularly by the same accredited laboratory, the Proctor-Fagerberg method provides consistent, reproducible results. P&I club analyses have documented cases where different laboratories using different methods produced TML values differing by 2 to 3 percentage points on the same cargo batch, an error large enough to shift a borderline cargo from compliant to prohibited.

Which method applies to lead concentrate

The IMSBC Code does not mandate a single test method for lead concentrate as a category; the schedule does not restrict the choice among Appendix 2 methods. In practice, the Proctor-Fagerberg test dominates in Australia and Peru. The flow table test is more common in Asian testing laboratories with a history of coal testing. Any method may be used provided the laboratory is accredited and the cargo’s particle size falls within the method’s stated applicability range. A TML certificate must state the method used, the test date, and the accreditation of the laboratory. Masters should verify the certificate explicitly on all three points before accepting the cargo.

Cargo declaration and pre-loading documentation

Mandatory documents before loading

IMSBC Code Section 4 and SOLAS Regulation XII/10 require the following documents from the shipper before the first tonne of lead concentrate is loaded:

A cargo declaration stating the Bulk Cargo Shipping Name (LEAD CONCENTRATE), the cargo group (Group A and B), the full chemical composition including lead, zinc, silver, and sulphur percentages, the declared moisture content on a wet mass basis, and the bulk density. The bulk density declaration requirement became mandatory under Amendment 07-23 (MSC.539(107), in force from 1 January 2025), addressing a gap that P&I clubs had flagged for years. For a cargo with bulk density of 3.5 t/m³, an estimate based on a generic concentrate range of 2.0 to 3.5 t/m³ can produce a stability calculation error large enough to invalidate the vessel’s approved loading condition.

A TML certificate from an accredited laboratory, valid within six months of the loading date, stating the TML value, the method used, and the laboratory accreditation reference.

A moisture content certificate, confirming measurement within seven days of the commencement of loading and showing a result strictly below the TML. If rain, snow, or other moisture input reaches the stockpile between the sampling date and loading, the shipper must retest and issue a new certificate.

The Group B hazard information document, covering the MHB TX classification, the specific health hazard (lead toxicity via inhalation and ingestion), the required personal protective equipment, and the emergency procedures for crew exposure. This document must be provided to the master and, by the terminal, to all personnel handling the cargo.

The master’s review obligation

Accepting these documents is not a clerical task. The master or chief officer should check:

First, that the TML certificate is dated within six months, that it names the specific cargo (not a generic concentrate certificate issued for a different batch), and that it identifies an accredited laboratory. Second, that the moisture content certificate is dated within seven days, that the declared moisture is below, not at, the TML, and that the sampling method is described. A sample taken from the top of the stockpile may not represent the deeper material that will actually be loaded. Third, that the bulk density declared is plausible for lead concentrate (anything below 2.5 t/m³ should raise questions) and has been entered into the vessel’s loading computer to generate a structural check.

The IMSBC Code gives the master the authority to refuse loading if documents are absent or unsatisfactory. That authority is also a duty: accepting a non-compliant cargo is a regulatory violation and a potential insurance liability, not merely a commercial inconvenience.

Loading operations

Pre-loading hold inspection

Before accepting lead concentrate, the master should confirm that bilge suction systems for the intended cargo holds are tested and clear. Fine concentrate particles can block bilge suction strainers if they migrate into the bilge well during loading. A suction cover of coarse burlap or canvas placed over the bilge well strainer before loading reduces blockage risk. Bilge well sounding rods and pump capacities should be checked. Any moisture that migrates from the cargo during the voyage needs to be recoverable; a blocked suction system is both a safety risk and a potential cause of hold flooding.

Hatch cover condition is the other critical pre-loading check. A hatch cover with damaged compression bars, worn rubber seals, or misaligned hold-down cleats will admit rainwater during the voyage. For a Group A cargo this matters because rainwater ingress after the hatches are closed raises the cargo moisture progressively and can push it above the TML before the vessel reaches the discharge port. Lead concentrate’s MHB classification adds a further consideration: any moisture that leaves the hold carrying fine lead particles must be treated as contaminated effluent, not ordinary bilge water.

Hold cleanliness is especially important for lead concentrate. The previous cargo must be swept clean and the hold washed. Residues of fertiliser, salt, or other hygroscopic cargoes alter the effective moisture balance. Any residue of a previous cargo that contains organic material can react with the sulphide minerals in the lead concentrate; the hold should be confirmed clean and dry before accepting the first cargo.

The can test during loading

The IMSBC Code Section 8 can test is a shipboard screening procedure that the master and officers can use during loading to detect obvious moisture excess. The procedure for lead concentrate is the standard Section 8 method: fill a metal container of 0.5 to 1 litre with a representative sample from the loading stream, then bring it down sharply onto a solid surface from approximately 0.2 metres height, repeating 25 times at one- to two-second intervals. Examine the surface for free moisture.

For lead concentrate, the can test should be performed at the start of loading in each hold, at each change of cargo source (when the terminal switches from one stockpile section to another), and after any rainfall event during loading. Because lead concentrate carries the MHB TX classification, the officer performing the can test should wear gloves and avoid touching face or eyes during the procedure.

A positive result (free moisture visible on the cargo surface) requires immediate loading suspension and notification to the charterer. An independent surveyor should take fresh samples for laboratory moisture determination before any decision is made to resume. A negative result does not confirm the cargo is below TML; the can test catches gross failures, not marginal ones.

Loading suspension in rain

The IMSBC Code requires that loading of Group A cargoes stop during precipitation. For lead concentrate, this rule has an additional practical dimension: rain that falls into an open hatch onto a partially loaded hold creates a surface layer of lead-contaminated water that will eventually accumulate in the bilge. The bilge water must be pumped ashore for disposal, not overboard, even in port. Terminal protocols for rainfall suspension should specify the rain intensity threshold for loading halt, the inspection interval after rain ceases, and whether re-sampling is required before loading resumes. P&I club guidance consistently supports erring toward early halt rather than waiting for rain to intensify.

Trimming and levelling

Concentrate loaded through a spout or shiploader forms a conical pile centred on the fall point. The IMSBC Code’s 5% of breadth limit on surface relief applies. Mechanical trimming with a bulldozer working in the hold is standard at major concentrate terminals. When a trimming machine or front-end loader is used, the operator should be aware of the tanktop depth constraint described above; the bulldozer must not compact the surface layer to a point where the load is concentrated on a small area, and the post-trim depth must be checked before the hatch is closed.

All personnel entering the lead concentrate hold during trimming must comply with MHB TX requirements: half-face or full-face respirator appropriate for lead dust, disposable coveralls and gloves, and decontamination before entering accommodation or mess areas.

Closing hatches and departure

Before departure, the master should confirm the final cargo moisture from the loading certificates, record the bilge sounding in each loaded hold as a departure baseline, and verify the stability condition using the declared bulk density. The loading computer should reflect the actual fill heights, not approximate weights converted from voyage estimates. Any discrepancy between the certified cargo weight and the scale weights from the loading terminal should be investigated; weight differences above 2 to 3% may reflect moisture or density errors in the shipper’s declaration.

The master’s right and duty to refuse

SOLAS Chapter VI Regulation 2 requires the shipper to provide information about the cargo before loading. IMSBC Code Section 4.3 specifies that the master may refuse any cargo for which the required information is absent or unsatisfactory. For lead concentrate, the documents required are the TML certificate, the moisture content certificate, the bulk density declaration, and the Group B hazard information. If any of these is missing, the master must not begin loading.

The duty to refuse extends to the case where loading has begun and conditions change. If the can test becomes positive during loading, if rain is not suspended when required, or if the declared moisture is shown by independent survey to be understated, the master has both the right and the duty to stop loading and to notify the operator in writing.

Commercially, refusing to load can trigger demurrage claims or charter-party disputes. The master’s basis for refusal is strongest when the documentary evidence is clear: an outdated certificate, a declared moisture within 1 percentage point of the TML, a can test failure, or a rain event not followed by re-sampling. The master should document every step, including the specific documents reviewed, the can tests performed (with times and results), any weather events during loading, and the written communication to the charterer and shipper. A P&I correspondent at the loading port should be contacted before or at the time of any formal refusal, so that independent survey can be arranged promptly.

The regulatory and insurance exposure for the master who loads non-compliant lead concentrate is real. If a vessel develops a severe list from liquefied lead concentrate at sea, the investigation will examine the loading documents in detail. A master who accepted a moisture certificate showing 9.9% against a TML of 10.0% and did not request independent survey will face scrutiny. A master who loaded without receiving the Group B hazard document will face a separate regulatory compliance question. The IMSBC Code’s documentation requirements are not bureaucratic formalities; they are the evidentiary chain that establishes whether the loading was legally authorised.

Specially fitted ships and the Section 7 exemption

IMSBC Code Section 7 provides for ships specially constructed or fitted to carry Group A cargoes above the TML. Such ships are rare in the lead concentrate trade. They must have double-bottom structure and tanktops reinforced for hydrostatic loads from partially liquefied cargo, bilge systems capable of removing large volumes of fluid concentrate mixture, and stability assessments prepared specifically for the partially liquefied condition. Flag state or class approval covering carriage of wet concentrate is required. No standard Handysize, Supramax, Ultramax, or Panamax bulk carrier meets these requirements without specific modification and documentation.

The practical consequence is straightforward: when a shipper cannot certify that the cargo moisture is below the TML, there is no standard commercial bulk carrier that can legally carry it. The cargo must remain in storage until it dries, or be blended with drier material, or be further filtered. Business pressure to ship on schedule is the most important human factor in concentrate liquefaction incidents, and it does not create a legal exception to the Section 7 rule.

Discharge and hold cleaning

Lead concentrate is typically discharged by grab crane into a receiving hopper, with water sprays on the hopper and in the hold to suppress airborne dust. The receiving terminal controls the environmental and occupational health aspects of the discharge environment; the vessel’s obligation is to ensure that hold ventilation during discharge does not create an escape path for dust into accommodation or work areas where crew are present without protection.

Hold cleaning after discharge is a controlled operation. The IMSBC Code’s MHB requirements mean that lead-contaminated residues, the sweepings from the hold after the main cargo is out and any bilge water that contains fine particles, must be disposed of as hazardous waste. Wash-down water must be collected and transferred to shore for disposal; pumping overboard is not permitted and will be a violation of environmental regulations in virtually every discharge port jurisdiction. The quantity of lead-contaminated residue from a single concentrate voyage is small, typically a few hundred kilograms of sweepings and a few tonnes of wash water, but it is classified as hazardous under national chemical waste legislation in most countries.

After wash-down, the hold should be inspected to confirm that no lead concentrate residue remains before loading the next cargo. If the next cargo is food, grain, or a cargo with strict contamination limits, the hold cleanliness standard is higher still.

Comparison with zinc and copper concentrates

Physical properties

Lead concentrate differs from zinc concentrate and copper concentrate primarily in bulk density. The table below shows the key values for comparison:

Lead concentrate’s exceptional density means that the same hold volume that holds 500 tonnes of copper concentrate holds up to 900 tonnes of lead concentrate. The structural loading implication is proportional: ships that carry copper concentrate comfortably may be tanktop-limited before reaching hold capacity on lead concentrate.

Hazard classification

All three are Group A cargoes with liquefaction risk. The MHB toxic classification is specific to lead concentrate; copper and zinc concentrates can carry MHB SH (self-heating) or MHB CR (corrosive) sub-classifications depending on sulphide content and chemistry, but are not generally MHB TX. The specific toxicity hazard of lead makes the personal protection requirements for lead concentrate more stringent than for most copper and zinc concentrate cargoes.

Trade volumes

Copper concentrate trade at roughly 25 to 30 Mt/year dwarfs lead concentrate trade at roughly 4 to 6 Mt/year and zinc concentrate trade at roughly 8 to 12 Mt/year (estimates based on publicly available trade flow data). In vessel selection, copper concentrate is a routine large-volume cargo for Supramax and Ultramax vessels; lead concentrate, with its density constraints, is more commonly carried in Handysize vessels in partial-cargo configurations or in vessels purpose-selected for dense-cargo service.

Limitations

This article reflects the IMSBC Code as amended by Resolution MSC.539(107) (Amendment 07-23, mandatory from 1 January 2025). The official published text of the IMSBC Code as adopted by IMO is the definitive authority; this article does not reproduce schedule tables verbatim.

TML values and bulk density ranges given here are the indicative ranges from the IMSBC Code schedule and from the published literature on lead concentrate composition. The actual TML and bulk density for any specific shipment depend on the mineralogy, grind size, clay content, and processing history of that batch. The only reliable values for a given cargo are those determined by an accredited laboratory on a representative sample of that specific batch within the validity window.

Tanktop load calculations and loading depth limits cited here are illustrative. The actual allowable tanktop load for any specific vessel is stated in that vessel’s loading manual approved by the classification society. Masters must use their vessel’s actual figures, not the illustrative values in this article.

Occupational exposure limits for lead dust vary by jurisdiction. The general principle of minimising dust exposure through engineering controls and personal protective equipment applies universally, but the specific blood-lead action levels, air monitoring requirements, and medical surveillance obligations for crew on lead concentrate vessels are governed by the flag state’s occupational health regulations and, at the discharge port, by the port state authority’s environmental and health rules.

The information on global trade volumes for lead, zinc, and copper concentrates is based on publicly available industry estimates and is subject to year-to-year variation. It is provided for context, not as a source for commercial or financial analysis.

See also

• IMSBC Code
• IMSBC Group A cargoes: Cargoes that may liquefy
• Cargo Liquefaction: TML, FMP, and Group A Controls
• Mineral Concentrates: IMSBC Code Schedule
• Zinc Concentrate: IMSBC Code Schedule and Carriage
• Copper Concentrate: IMSBC Code Schedule and Carriage
• Iron Ore Concentrate: IMSBC Code Schedule and Carriage

Related calculators:

• IMSBC Lead Concentrate
• IMSBC TML Moisture Check
• IMSBC Group A/B/C Classification
• IMSBC Bulk Cargo Finder
• IMSBC Zinc Concentrate
• IMSBC Copper Concentrate