Barytes (Barite): IMSBC Group C Schedule and Carriage

Barytes is the Bulk Cargo Shipping Name the IMSBC Code gives to coarse barium sulphate ore, BaSO4, a Group C solid bulk cargo that is not liable to liquefy, and it is not the same entry as BARYTE, FLOTATION CHEMICAL GRADE, the Group A powder that amendment 07-23 introduced alongside it. The distinction is the whole of the classification problem on this cargo, because both entries describe the same mineral and their Bulk Cargo Shipping Names differ by one letter and a comma.

The schedule gives a bulk density of 2,941 kg/m3 against a stowage factor of 0.34 m3/t. A parcel therefore brings the ship to her marks while filling about a third of the hold by volume, so the operational problem is never finding room, it is keeping the tank top inside its limit. The trade exists because a drilling fluid needs weight: barite is the cheapest dense, inert, soft mineral available to supply it, and the U.S. Geological Survey reports that more than 90% of the barite sold in the United States is used as a weighting agent in fluids used in the drilling of oil and natural gas wells.

Dust is the only cargo-specific precaution the schedule carries. Seven of its fourteen fields read “No special requirements”, which means most of what a practitioner does with this cargo is trade practice and contract rather than Code obligation, and the article marks the boundary throughout.

What barytes is and how it is offered for carriage

Barite is barium sulphate, BaSO4, and its defining property is density. The NIOSH Pocket Guide to Chemical Hazards gives the mineral a specific gravity of 4.25 to 4.5 and a solubility of 0.0002% at 64 degrees F, and that near-total insolubility is what makes the cargo inert. It does not self-heat, does not emit gas, does not react with water and does not support combustion, which is why the IMSBC Code puts the coarse ore in Group C with no IMDG class, no UN number and no MHB classification.

The same insolubility is why ultrapure grades are swallowed. The USGS records barite as the contrast medium in X-ray and computed tomography examinations of the gastrointestinal tract, which is a useful thing for a chief officer to know when a stevedore asks whether the dust is poisonous.

Barytes, barite and baryte: one mineral, three spellings, two schedules

In ordinary trade English the three spellings are interchangeable. In the IMSBC Code they are not, and this is the trap.

The Code’s Bulk Cargo Shipping Name for the coarse ore is BARYTES. The US and drilling-industry spelling is barite, which is what the USGS and the American Petroleum Institute write. The mineralogical name is baryte, and that singular form is also the first word of a different Bulk Cargo Shipping Name in a different group. A parcel described commercially as “barite” or “barium sulphate” is not described in the Code’s terms at all.

The Appendix 4 index gives the master no help here. It carries three baryte-adjacent entries, all in capitals, meaning all three are Bulk Cargo Shipping Names in their own right with no cross-reference: BARYTE, FLOTATION CHEMICAL GRADE at Group A, BARYTES at Group C, and BARIUM NITRATE UN 1446 at Group B. There is no lower-case secondary entry for Barite, Baryte, Barium sulphate or Heavy spar anywhere in the index. Compare “Barley malt pellets”, two lines above, which is lower case and carries “see SEED CAKE”. So the only two strings that resolve are the two that differ by a letter and a comma, and the commercial name resolves to nothing.

The drilling fluid weighting role

A drilling fluid carries cuttings up the annulus, cools and lubricates the bit, seals the borehole wall with a filter cake, and exerts a hydrostatic column pressure that holds back the formation. That last job is the weighting agent’s. The column of weighted mud is the primary barrier against a kick or blowout, which is the connection between this cargo and offshore drilling .

USGS Minerals Yearbook 2021 records that barite is a component of almost all drilling fluids and can make up more than 40% by weight of a heavyweight oil-based mud, against about 10% of a lightweight one. Demand is close to inelastic because there is no cheap substitute at scale. MCS 2026 puts it flatly: owing to technical and economic factors, there are no large-scale alternatives to barite in oil- and gas-drilling fluids. Calcium carbonate, hematite, ilmenite and manganese tetroxide are the most common alternatives in specific circumstances, and celestite, iron carbonate and strontium carbonate appear in technical literature and patents without being widely used.

The API grades, and what the ship does with them

Drilling-grade barite is held to API Specification 13A, Drilling Fluid Materials, 19th Edition, October 2019, as amended by Addendum 2 of June 2022. The standard does not use the words “specific gravity” that the trade uses; it sets a minimum density in grams per millilitre and names the two grades by that number.

Other than density the two grades carry identical test specifications. The 4.1 grade was added because the 4.2 material was running short: USGS Minerals Yearbook 2021 records that the API issued the lower-density specification effective 1 August 2010 in response to concerns about dwindling reserves of 4.20 specific gravity barite, and MCS 2026 notes the consequence for reserves reporting, which now counts only material developed since that standard was adopted. The ISO twin is ISO 13500:2008 with Amendment 1:2010, titled “Barite 4,1”.

The grading matters commercially and not at all operationally. Whether a parcel is 4.1 or 4.2, the marine handling problem is identical, and neither API 13A nor ISO 13500 is incorporated by reference into any flag or port state regulation that touches carriage. What the grade decides is what the receiver tests against, which is the ground most barytes cargo claims are fought on.

The two particle-size caps in the table are worth reading together. A weighting agent that settles out of the circulating fluid is useless, and one ground too fine drives the mud viscosity up, so the specification brackets the product from both ends. That is why the parcel reaching a drilling region is often coarse ore destined for a shore mill rather than finished product.

Filler, brake pad and shielding grades

The non-drilling fraction is small and varied, and it explains why some parcels move to chemical and industrial receivers rather than to oilfield service terminals. The USGS lists barite as a filler, extender or weighting agent in paints, plastics and rubber, including automobile brake and clutch pads and automobile paint primer, as the aggregate in high-density radiation-shielding concrete around X-ray units, nuclear powerplants and university nuclear research facilities, in the cement jacket around underwater petroleum pipelines, and in mold-release compounds in metal casting. A separate chemical route converts barite into barium carbonate, barium chloride and precipitated barium sulphate.

A receiver expecting chemical-grade or filler-grade material holds the parcel to whiteness and purity limits that a drilling-grade parcel is not held to. What that grade expectation does not do is change the schedule, and the reason is not the one intuition suggests: a fine chemical-grade parcel produced by flotation is a different Bulk Cargo Shipping Name in a different group, covered in the next section.

The IMSBC schedule for barytes

The BARYTES schedule in Appendix 1 of the Code classifies the cargo in Group C with no IMDG class, no subsidiary hazard and no MHB classification, and carries exactly two substantive fields out of fourteen. The Code became mandatory under SOLAS chapter VI regulation VI/1-2 on 1 January 2011, through the amendments in resolution MSC.269(85). The text below is the entry as it stands in amendment 07-23 , adopted by resolution MSC.539(107) on 8 June 2023 and mandatory since 1 January 2025.

Two details of that table are worth pausing on because they are commonly reproduced wrongly. Moisture sits inside the Description field, not as a characteristic of its own, and a Group C schedule has no UN number cell at all: the hazard classification block has exactly four, being Class, Subsidiary hazard(s), MHB and Group. There is also no Emergency procedures block, which is the clean marker of a Group C entry.

Which fields bind, and which are guidance

This is the distinction that decides how much of any barytes article is regulation and how much is trade practice, and it is the one most often skipped.

Section 1.4.2 makes the Description, the Characteristics other than the hazard classification block, the Hazard field and the Emergency procedures recommendatory or informative. Section 1.2.1 puts it beyond doubt: the schedules’ properties “are given only for guidance. Consequently, before loading, it is essential to obtain current valid information from the shipper.”

So the 2,941 kg/m3 and the 0.34 m3/t are informative. The mandatory cells are Class, Subsidiary hazard(s), MHB and Group, together with the Loading and Precautions text. A loading plan is built on the density the shipper declares for the actual parcel, never on the schedule figure.

Seven fields read “No special requirements”: stowage and segregation, hold cleanliness, weather precautions, ventilation, carriage, discharge and clean-up. Everything this article says about hold standards, weather, ventilation, voyage routine, discharge method and cleanup is therefore contract, charterparty or good seamanship. The article marks the boundary each time.

The Loading field, which is the most important text in the schedule

The Loading field is one of the two that bind, and it states the cargo’s central hazard in the Code’s own words:

“Trim in accordance with the relevant provisions required under sections 4 and 5 of this Code. As the density of the cargo is extremely high, the tank top may be overstressed unless the cargo is evenly spread across the tank top to equalize the weight distribution. Due consideration shall be given to ensure that the tank top is not overstressed during the voyage and during loading by a pile of the cargo.”

That clause is not boilerplate. About two dozen schedules carry a conditional variant reading “When the stowage factor of this cargo is equal to or less than 0.56 m3/t, the tank top may be overstressed unless…”, which applies to cargoes whose density range straddles the threshold. BARYTES gets the unconditional form because its single value of 0.34 m3/t is never above it.

The Precautions field, in full

The other binding field carries four requirements, of which most published summaries reproduce only the first and the last:

“Appropriate precautions shall be taken to protect machinery and accommodation spaces from the dust of the cargo. Bilge wells of the cargo spaces shall be protected from ingress of the cargo. Due consideration shall be given to protect equipment from the dust of the cargo. Persons who may be exposed to the dust of the cargo shall wear protective clothing, goggles or other equivalent dust eye-protection and dust filter masks, as necessary.”

The second sentence is a Code obligation, not prudent practice, and it is a loading duty rather than a discharge one. The third covers deck machinery, cranes and external navigational aids.

Why the angle of repose reads “Not applicable”

The intuitive answer is that a cargo of 101.6 mm lumps is too coarse for a slump angle to mean anything. That is not the Code’s reasoning, and getting it wrong leads a reader to the wrong trimming rules.

BARYTES is absent from the Appendix 3 paragraph 1.1 list of cargoes that are non-cohesive when dry. Paragraph 1.3 then governs: “All cargoes, other than those listed in this appendix, are cohesive, and the use of the angle of repose is, therefore, not appropriate. Cargoes not listed should be treated as cohesive until otherwise shown.” Section 5.3.2 completes it: the angle of repose “is not an indicator of the stability of a cohesive bulk cargo and it is not included in the individual schedules for cohesive cargoes.”

So the cell is blank because the Code’s default classifies barytes as cohesive. The practical consequence is that section 5.4 and its numerical levelness ladder do not apply, and no numerical limit on unevenness binds a barytes stow. Trimming is governed instead by the general provisions in 5.1 and by the schedule’s own tank top clause.

Two things sharpen this. Section 5.4.1 leaves the door open, since a cargo not listed may still be shown to exhibit non-cohesive properties, so the silence is a default rather than a prohibition. And the Code’s own test cannot be run on this cargo: section 6.2.1 limits the tilting box method to “non-cohesive granular materials with a grain size not greater than 10 mm”, which excludes four fifths of a barytes parcel by mass.

A related error is worth naming. The coarse size distribution is not why barytes is Group C. Group C is purely residual under section 1.7, being cargoes classified as neither Group A nor Group B, and the next section is the counterexample: the same mineral, finely ground, is Group A.

What governs a fixture today

Amendment 07-23 is in force and mandatory and governs every voyage to 31 December 2026. Amendment 08-25, resolution MSC.575(110) adopted 26 June 2025, may be applied voluntarily and becomes mandatory on 1 January 2027. MSC.575(110) does not touch either baryte schedule, so the entry below is identical in the 2023 and 2025 editions and will still be identical when 08-25 bites.

The schedule has been remarkably stable. In eight amendment sets since MSC.268(85) adopted the Code on 4 December 2008, the only edit ever made to BARYTES was editorial: amendment 04-17, resolution MSC.426(98) item 33, replaced the words “of the Code” with “of this Code” in the first sentence of Loading. The characteristics, the group, the hazard and the substance of both binding fields are as adopted in 2008.

The two baryte entries in the Code, and the declaration trap

Amendment 07-23 put two baryte cargoes in the IMSBC Code in different groups: BARYTES is a coarse Group C ore that is not liable to liquefy, and BARYTE, FLOTATION CHEMICAL GRADE is a Group A powder ground to 75 micrometres that is liable to liquefy above its transportable moisture limit. Both were introduced in the same amendment set, they sit on consecutive pages of Appendix 1, and they share the identical tank top clause in their Loading fields.

Compiled from the individual Appendix 1 schedules under amendment 07-23, resolution MSC.539(107).

The Group A entry, in its own terms

BARYTE, FLOTATION CHEMICAL GRADE is described in the Code as a product from naturally occurring low-grade baryte ore made by flotation, with barium sulphate at 97 per cent and trace silicon dioxide, iron oxide, aluminium oxide, strontium sulphate and calcium carbonate. It is an odourless white or off-white powder.

Its hazard field reads: “This cargo may liquefy if shipped at a moisture content in excess of its transportable moisture limit (TML). See sections 7 and 8 of this Code.” That single sentence engages the whole Group A apparatus: TML certification, the section 8 test procedures, and the five-limb weather regime of section 7.3.2 restricting handling in precipitation.

Its carriage field goes further than most: “The appearance of the surface of this cargo shall be checked regularly during the voyage. If free water above the cargo or fluid state of the cargo is observed during the voyage, the master shall take appropriate actions to prevent cargo shifting and potential capsize of the ship and give consideration to seeking emergency entry into a place of refuge .”

Telling them apart at the hatch

Four tells, in increasing order of reliability.

Size is the obvious one. BARYTES arrives as crushed ore with visible stone up to 101.6 mm and a fines fraction; the flotation grade is a uniform powder with no lump in it at all. Colour helps: the ore carries its mineral colouring, while the flotation grade is specified white or off-white. Behaviour under the spout is a third, since a cohesive coarse ore will not run out to the hold boundaries while a powder heaping at 46.3 degrees will build a cone.

The paperwork tell is the decisive one, and it beats all three. A Group A parcel arrives with a moisture content certificate and a transportable moisture limit certificate. A Group C parcel does not, because IMSBC 4.2.2.10 requires those documents only “in the case of a group A cargo”. A visual doubt about which cargo is alongside is a reason to stop loading and resolve the declaration, not a reason to proceed carefully.

What changes operationally

Declaring the flotation grade switches on obligations that BARYTES does not carry at all: moisture and TML certification before loading, the can test as a supplementary shipboard check, restrictions on handling during precipitation, a prohibition on ventilating the cargo spaces during the voyage rather than merely no requirement to ventilate, regular checking of the cargo surface through the passage, the master’s duty to act on free water or a fluid state, and a clean-up duty to clear bilge wells and scuppers.

The trimming regime inverts too, which is a neat illustration of how far apart the two sit. Because BARYTES is cohesive it falls under the general provisions of section 5.1 with no numerical levelness limit. Because the flotation grade is on the non-cohesive list with a repose angle of 46.3 degrees, it routes to section 5.4.5, where the difference between the highest and lowest levels of the cargo surface shall not exceed B/10, with a maximum of 2 metres. Same mineral, opposite rule.

Why the coarse ore is the denser of the two

At 2,941 against 2,637 kg/m3 the crushed ore is denser than the 97 per cent concentrate, which is counterintuitive to anyone expecting a purer product to be heavier. The explanation is packing rather than chemistry: a graded distribution of lumps with a fines fraction filling the voids between them packs closer to the mineral’s own specific gravity than a uniform fine powder does. Bulk density is a property of the stow, not of the mineral.

The Code’s index will not help you

A parcel offered commercially as “barite”, “barium sulphate” or “heavy spar” resolves to nothing in the Code. The Appendix 4 index carries only three baryte-adjacent entries, all capitalised Bulk Cargo Shipping Names with no cross-reference: BARYTE, FLOTATION CHEMICAL GRADE at Group A, BARYTES at Group C, and BARIUM NITRATE UN 1446 at Group B. There is no lower-case secondary entry for any of the trade names, unlike the ordinary index pattern where “Barley malt pellets”, two rows above, carries “see SEED CAKE”.

So the only two strings that resolve differ by a single letter and a comma, and the commercial name a broker or forwarder uses resolves to neither.

Barium nitrate is a different cargo entirely

The third barium entry is not a grade question at all. BARIUM NITRATE UN 1446 is Group B, IMDG Class 5.1 with a subsidiary hazard of 6.1, described in the Code as glossy white crystals or powder, soluble in water. Its hazard field reads: “Toxic if swallowed or by dust inhalation. If involved in a fire the mixture with combustible materials is readily ignited and may burn fiercely.”

The distinction that matters is solubility, not the element. Barium sulphate is effectively insoluble, which is why it is inert and why it is swallowed as a radiological contrast medium. Soluble barium salts are toxic. A cargo described only as “a barium cargo” tells the master nothing useful, and the Class 5.1 oxidiser regime shares no part of its handling with the inert sulphate.

Barytes as a high density solid bulk cargo

Section 1.7 of the Code defines a high density solid bulk cargo as one with a stowage factor of 0.56 m3/t or less. Barytes at 0.34 m3/t is well inside that definition, which is the cleanest classification statement available about this cargo and the reason the whole structural regime engages.

Section 2.1.2 supplies the comparison that makes the number mean something. A general cargo ship “is normally constructed to carry cargoes in the range of 1.39 to 1.67 cubic metres per tonne when loaded to full bale and deadweight capacities”. Barytes is between four and five times denser than that design point. The Code then requires that “particular attention shall be given to the distribution of weights to avoid excessive stresses, taking into account that the loading conditions may be different from those found normally and that improper distribution of such cargo may be capable of stressing either the structure under the load or the entire hull.”

The Code stops there, deliberately: “To set out exact rules for the distribution of loading is not practicable for all ships because the structural arrangements of each vessel may vary greatly. The information on proper distribution of cargo may be provided in the ship’s stability information booklet or may be obtained by the use of loading calculators, if available.”

There is therefore no IMSBC formula for a permissible tank top load. The Code states a duty and routes the number to the ship’s own approved documents. SOLAS regulation VI/7 requires the cargo loading manual and prescribes its contents, which include the maximum allowable load per unit surface area of tank top plating and the maximum allowable load per hold. Section 13.2.13 of the Code, its own reference table for avoidance of excessive stresses, points to SOLAS chapter XII regulations 5, 6 and 11, to the BLU Code at resolution A.862(20), and to MSC.1/Circ.1357.

The tank top check is a hold mass curve, not a load per square metre

This is the part most often stated loosely, and for barytes the loose version is misleading.

IACS Unified Requirement S1A requires the loading manual of a bulk carrier of 150 m and above to state the “maximum allowable tank top loading together with specification of the nature of the cargo for cargoes other than bulk cargoes”. The tonnes per square metre figure is expressly qualified away from bulk cargo. What UR S1A requires for a bulk cargo instead is the hold mass curve , the maximum allowable and minimum required mass of cargo and double bottom contents for each hold as a function of the draught at mid-hold position, and the same for any two adjacent holds against the mean draught in way of them. The loading instrument is required to check both.

The reason the limit moves with draught is buoyancy. IACS Recommendation No. 46 puts it directly: the net vertical load on the double bottom “is the difference between the vertical downward weight of the cargo and water ballast in the double bottom and the hopper ballast tanks in way of the cargo hold and the upward buoyancy force which is dependent on the ship’s draught”, so “there is a reduction in the cargo carrying capacity of a hold with a reduction in the mean draught”. Ballast still sitting in the double bottom and hopper wing tanks in way of the hold is deducted from the allowable cargo weight.

For barytes that turns the usual assumption inside out. The cargo brings the ship to her marks with the holds about a third full, so the ship reaches each draught mark with comparatively little cargo aboard. The exposure is therefore not the departure condition, which is comfortable, but the intermediate stage: a heavy pour into one hold while the ship is still light, the buoyancy under that hold small, and ballast not yet out from beneath it. That is the moment the hold mass curve is tightest and the pour is heaviest.

The arithmetic that does hold

Where the loading manual states a uniform distributed load for the tank top, the check is the simple product of density and stow height.

At the schedule’s bulk density of 2.941 t/m3, an evenly spread layer imposes 2.94 t/m2 for every metre of depth. So a 4 metre layer reaches 11.8 t/m2, a 5 metre layer 14.7, and a 6 metre layer 17.6. Inverting gives the permissible stow height directly: a manual figure of 15 t/m2 permits 5.10 m of barytes, and 18 t/m2 permits 6.12 m.

Those numbers are arithmetic on the schedule figure and need no ship. The permissible value itself is always the specific ship’s class-approved figure from its loading manual, and no generic band substitutes for it.

The failure mode is a local peak rather than an average. Spread the parcel evenly and the load is the layer depth times 2.941. Leave it in a pile and the pressure directly beneath the apex is the pile height times 2.941, so a 10 metre pile presses at about 29 t/m2 on plating that an even stow would have loaded at half that. This is exactly what the schedule’s Loading field warns of when it requires that the tank top not be overstressed “during loading by a pile of the cargo”, and it is why a cohesive coarse ore that will not run out to the boundaries needs active trimming rather than a longer pour.

The corresponding class rule reduces to the same thing. The Common Structural Rules give the static cargo pressure on the inner bottom as density times gravity times height, with a shape factor that equals one where the panel is horizontal. The operational rule of thumb is the class rule with the panel angle set to zero.

One caution on that. The structural calculation carries an assumed angle of repose, taken as 30 degrees in general, and the schedule’s “Angle of repose: Not applicable” says nothing about it. The Code’s blank cell reflects a cohesion default, not an absence of slope in the structural model, and the two must not be read across.

Alternate hold loading, and the statute that can forbid it

Loading a dense cargo into alternate holds raises the ship’s centre of gravity and eases the rolling motion, which is a real and documented motive. IACS Recommendation No. 46 states it and then states the price: “When high density cargo is stowed in alternate holds, the weight of cargo carried in each hold is approximately double that carried in a homogeneous load distribution”, and “the holds which remain empty, with this type of cargo distribution, have not been reinforced for the carriage of heavy cargoes with a non-homogeneous distribution”. Its conclusion is unqualified: ships not approved for the practice by their classification society must not adopt it.

The approval is a class matter, recorded as the additional service feature BC-A, written in the form “BC-A (holds a, b, … may be empty)” and defined in the Common Structural Rules. IMSBC 5.1.2 adds that “alternate hold loading restrictions, as required by SOLAS chapter XII, may also need to be taken into account”.

Those restrictions can be absolute. SOLAS regulation XII/14 provides that a single side skin bulk carrier of 150 m in length and upwards, carrying cargoes of density 1,780 kg/m3 and above, which does not meet the structural standards of regulation XII/5.1 and resolution MSC.168(79), shall not sail with any hold loaded to less than 10 per cent of that hold’s maximum allowable cargo weight in the full load condition, after reaching 10 years of age. Barytes at 2,941 kg/m3 is far above the trigger. Where such a restriction applies it is recorded in the loading booklet under regulation XII/8.2 and marked on the ship’s side under XII/8.3 with a solid equilateral triangle of 500 mm sides, apex 300 mm below the deck line, port and starboard at midships. A triangle on the side shell is a visible sign that alternate hold loading of this cargo may be barred.

The loading instrument does not see an asymmetric stow

A point worth more than it costs to state. IACS Recommendation No. 46 records that still water shear force and bending moments calculated by an onboard loading instrument “do not consider the torsional loads acting on the hull girder resulting from asymmetrical cargo or ballast loading”, and that the double bottom, cross deck and transverse bulkhead structures are designed on the basis of a trimmed cargo distributed symmetrically. It adds that heavy cargo poured at one end of a hold raises the lateral pressure on the transverse bulkhead and the transverse compressive stress in the cross deck.

So a green loading instrument on a lopsided barytes stow is reporting a calculation that assumes the stow is not lopsided. Cargo is stowed symmetrically in the longitudinal direction and trimmed, as far as practicable, for that reason and not merely for tidiness.

Stability: a stiff ship with a short roll period

A barytes cargo sits low and shallow on the tank top, which places the cargo’s centre of gravity well below the ship’s, raises the metacentric height and produces a short natural roll period with high angular accelerations for the whole passage. That is safe in the capsize sense and punishing in a seaway.

The 2008 IS Code, resolution MSC.267(85), addresses it directly at Part B paragraph 5.1.6: “The stability criteria contained in part A chapter 2 set minimum values, but no maximum values are recommended. It is advisable to avoid excessive values of metacentric height, since these might lead to acceleration forces which could be prejudicial to the ship, its complement, its equipment and to safe carriage of the cargo. Slack tanks may, in exceptional cases, be used as a means of reducing excessive values of metacentric height. In such cases, due consideration should be given to sloshing effects.”

Three things follow. The Code names the three exposures precisely: the ship’s structure, the crew, and the securing of the cargo. It sets no maximum GM, so there is no threshold to fail. And it does name one mitigation, slack tanks in exceptional cases, so it is not true that nothing can be done. Part B of the IS Code is recommendatory; only Part A is mandatory, so all of this is advice rather than requirement.

The roll period, quantified

Part A paragraph 2.3.4, inside the severe wind and rolling criterion, supplies an approximate relation for use where sufficient information is absent:

with \(C = 0.373 + 0.023 (B/d) - 0.043 (L_{WL}/100)\), where \(B\) is moulded breadth in metres, \(d\) the mean moulded draught, and \(L_{WL}\) the waterline length. Its purpose in the Code is to feed a factor in the weather criterion, not to require anyone to compute a roll period.

The useful consequence is the inverse square root. A stow that doubles GM shortens the natural roll period by a factor of one over the square root of two, about 29 per cent. That is the difference between a comfortable motion and one that throws people about, and it is why the passage is planned around heading and speed in beam and quartering seas to avoid synchronous rolling rather than around softening the stability.

The modern treatment of the same phenomenon is MSC.1/Circ.1627 of 10 December 2020, the interim guidelines on the second generation intact stability criteria , which address five dynamic stability failure modes of which excessive acceleration is one. The guidelines are interim, non-mandatory and complementary to the 2008 IS Code.

No free surface, no liquefaction, on this entry

Because BARYTES does not liquefy, the free-surface effect that destroys the stability of a Group A cargo does not arise, and neither does dynamic separation . There is no fluidised mass and no slumping surface to erode GM on passage, so the intact stability condition and the trim and list check computed at departure hold for the voyage, subject only to consumption changing the displacement.

That statement is about this entry. It is not true of BARYTE, FLOTATION CHEMICAL GRADE, which is Group A and carries the full liquefaction regime.

Shipper declaration, documentation and the master’s authority

The shipper must give the master cargo information before loading under SOLAS regulation VI/2, and the Code lists what it must contain. Of the eighteen items in IMSBC 4.2.2, a Group C barytes parcel engages the Bulk Cargo Shipping Name at .1, the group at .2, the total quantity at .5, the stowage factor at .6, the bulk density at .7, the need for trimming and the trimming procedures at .8, the harmful to the marine environment status under MARPOL Annex V Appendix I at .17, and any national requirements at .18.

It is relieved of item .10 entirely, which requires the moisture content and the transportable moisture limit certificate only “in the case of a group A cargo”. So no TML certificate, no flow moisture point and no declared moisture content is required for barytes, and the arrival of those documents alongside a parcel described as baryte is a signal to check which schedule is being declared.

Secondary names may be used in addition to the Bulk Cargo Shipping Name, not instead of it, so “barite” on a mate’s receipt is unobjectionable next to BARYTES and useless on its own.

The density declaration applies only at 150 metres and above

Item .7 of the list reads “bulk density (as required by SOLAS regulation XII/10)”, and the parenthesis carries the whole of its scope. SOLAS regulation XII/10.1 requires the shipper to declare the density of the cargo before loading on bulk carriers of 150 m in length and upwards, length being Load Line length rather than length overall. The Code does not create a free-standing density duty; it imports the SOLAS regulation and its threshold.

Below 150 m neither the SOLAS duty nor the Code item bites, and the schedule’s informative 2,941 kg/m3 is the only density figure the ship has. That is a live limitation rather than a technicality, because a fair part of the barytes trade runs on tonnage under that mark.

The separate verification duty in XII/10.2, requiring an accredited testing organization to verify a declared density, applies only where the declared figure falls within the range 1,250 to 1,780 kg/m3. Barytes is above the band, so no verification is triggered.

The master’s authority, stated accurately

There is no general refusal power in section 4 of the Code. What exists, and is directly useful on this cargo, is IMSBC 5.1.3: “The master has the right to require that the cargo be trimmed level, where there is any concern regarding stability based upon the information available, taking into account the characteristics of the ship and the intended voyage.” Since the hazard the schedule names is tank top overstress from an uneven stow, that is the operative authority.

Alongside it sit the right under SOLAS regulation VI/7 to suspend loading where the ship’s structural limits would be exceeded, with notification to the port State, the general obligation in SOLAS VI/1-2, the contract of carriage, and the master’s overriding authority under paragraph 5.2 of the ISM Code. The right to refuse a cargo in the broader sense is built from those, not from the schedule.

Hold preparation, where the standard is contractual

The BARYTES schedule sets no hold cleanliness requirement. The field reads “No special requirements”, so the standard a barytes parcel is loaded to is fixed by the charterparty and by the receiver’s grade specification, not by the Code. That is a different thing from saying the normal clean condition applies, and a chief officer arguing a cleanliness dispute is arguing contract, not regulation. The grade ladder itself is set out in the cargo hold preparation standards , and the certificate side in hold cleanliness inspection .

What the receiver expects drives the real standard. A drilling-grade parcel bound for a shore mill tolerates a good deal; a chemical-grade or filler-grade parcel held to whiteness limits will not tolerate rust streaks or residual coal dust, and a stained parcel becomes a contamination claim rather than a cleanliness argument.

Bilge wells, which is a Code duty

The one preparation item the Code does impose is the bilge wells, and it imposes it twice. The schedule’s Precautions field requires that “bilge wells of the cargo spaces shall be protected from ingress of the cargo”, and section 2.2.2 gives the general rule that “due consideration shall be given to bilge wells and strainer plates, for which special preparation is necessary, to facilitate drainage and to prevent entry of the cargoes into the bilge system”.

The Code prescribes the outcome and never the method, so burlap, mesh and purpose-made covers are all trade practice. The reason it matters more here than on a coarse cargo alone would suggest is the fines fraction: material below 6.4 mm flows into every gap and packs, and a dense packed fines plug in a bilge suction is not cleared at sea. See bilge well preparation for the methods.

Section 2.2.4 adds a detection step the article’s readers will not find in most summaries: “Because of the velocity at which some high-density solid bulk cargoes are loaded, special care may be necessary to protect cargo space fittings from damage. To sound bilges after the completion of loading may be effective to detect damage on cargo space fittings.” For a dense lump cargo poured onto a bare tank top, the first pour is the one that breaks fittings, and a bilge sounding after loading is how it is found.

Moisture, and what wet barytes means

The schedule’s description gives a moisture content of 1% to 6%. That is well below anything approaching a liquefaction condition on this entry, and there is no transportable moisture limit to test against. The Weather precautions field reads “No special requirements”, so there is no Code restriction on loading barytes in the rain, and the duty to keep it dry is commercial rather than statutory.

Wetting degrades a parcel commercially without creating a safety hazard. The practical concern is that water reaching the tank top under a densely packed cargo does not drain out again, which is the second reason bilge protection at the load port earns its time. Hatch covers are weathertight tested before the voyage in the ordinary way, covered in hatch cover weathertightness testing .

Loading and trimming

Barytes is trimmed for structural reasons rather than stability ones: the object is to spread the dense cargo evenly across the full tank top area so that no local pile exceeds the inner bottom loading limit, not to control an angle of repose the schedule declares inapplicable.

The controlling document is the loading plan, which sequences the holds so that the still water bending moment, shear force and hold mass limits are respected at every intermediate stage and not merely in the final condition. The plan and its sequencing are covered in the bulk carrier loading plan , and the hull girder side in longitudinal bending .

What the Code requires, and what is practice

The requirement is section 5.1.2: “Cargo spaces shall be as full as practicable without resulting in excessive loading on the bottom structure or ’tween deck to prevent sliding of a solid bulk cargo. Due consideration shall be given to the amount of a solid bulk cargo in each cargo space, taking into account the possibility of shifting and longitudinal moments and forces of the ship. Cargo shall be spread as widely as practicable to the boundary of the cargo space.” Section 5.1.1 adds that cargoes “shall be trimmed reasonably level, as necessary”, and section 2.1.3.3 that high density cargoes shall as far as practicable be loaded in the lower holds in preference to ’tween decks.

Everything else is method, and the Code prescribes none of it. Moving the spout across the hold during the pour, and levelling afterwards by bulldozer or trimming machine, are how the outcome is achieved rather than obligations in themselves. A self-trimming bulk carrier does not solve the problem here, because self-trimming hull forms are shaped to make a free-flowing cargo settle level and barytes is cohesive and coarse: it will not run out to the boundaries on its own.

Loading rate and deballasting

The pour rate is coupled to the ship’s ballast pumping capacity, not merely to the terminal’s shiploader capability. IACS Recommendation No. 46 puts the constraint plainly: high cargo loading rates may create problems with the ballasting operation where the ship’s pumping capacity is low relative to the loading rate, in which case the cargo operation must be stopped or the loading rate adjusted to synchronise with the pumping capacity. UR S1A requires the loading manual to state the maximum rate of ballast change, with the advice that the load plan be agreed with the terminal on the basis of achievable rates.

Because barytes brings the ship to her marks at a shallow cargo depth, each draught mark arrives with comparatively little cargo aboard, and the deballasting has to keep pace with a pour that is heavy in tonnes but small in volume.

The ship to shore interface is the BLU Code, resolution A.862(20) of 27 November 1997, with its companion BLU Manual. It defines a pour as “the quantity of cargo poured through one hatch opening as one step in the loading plan”, requires the agreed plan to state the order of holds, the weight of each pour and the total in each hold, and requires that the plan “be prepared so as to ensure that all ballast pumping rates and loading rates are considered carefully to avoid overstressing the hull”. In European Union terminals Directive 2001/96/EC gives the BLU Code legal force regardless of the ship’s flag.

Dust: the one live precaution

Dust is the only cargo-specific precaution the BARYTES schedule carries, and it is one of the two binding fields. It requires protective clothing, dust eye protection and filter masks for exposed personnel, protection of machinery and accommodation spaces, and due consideration to protecting equipment.

The Code’s general provisions carry more of the load than most operators realise, and they are requirements rather than good practice. Section 2.2.5: “As far as practicable, ventilation systems shall be shut down or screened and air conditioning systems placed on recirculation during loading or discharge, to minimize dust ingress into the living quarters or other interior spaces.” Section 2.2.6: “Due consideration shall be given to minimize the extent to which dust may come into contact with moving parts of deck machinery and external navigational aids.” Section 3.5.5 requires ventilation such that escaping dust cannot enter accommodation. And section 3.3, on health hazards due to dust, requires a high standard of personal hygiene with “appropriate breathing protection, protective clothing, protective skin creams, adequate personal washing and laundering of outer clothing”, as necessary.

Is barite dust toxic?

No, in the sense the question is usually asked, and the reason is solubility rather than the element.

Barium sulphate is effectively insoluble, at 0.0002% in water at 64 degrees F per the NIOSH Pocket Guide to Chemical Hazards, and regulators treat it separately from soluble barium compounds. Under the US occupational limits at 29 CFR 1910.1000 Table Z-1, barium sulphate carries 15 mg/m3 for total dust and 5 mg/m3 respirable, while barium in soluble compounds carries 0.5 mg/m3, a difference of a factor of thirty. NIOSH recommends 10 mg/m3 total and 5 mg/m3 respirable. The ACGIH threshold limit value is 5 mg/m3 inhalable, expressed for material containing no asbestos and less than 1 per cent crystalline silica; ACGIH is a professional body rather than a regulator and its values carry no legal force by themselves. There is no European Union wide binding or indicative limit for barium sulphate. All of these are named national or regional overlays on an IMO baseline that sets no numerical exposure limit at all.

The documented occupational effect is not poisoning. The ATSDR toxicological profile for barium reports a benign pneumoconiosis, baritosis, observed in workers exposed to barium sulphate, with other studies finding no barium-related respiratory alteration, and ATSDR derived no inhalation minimal risk level for barium because the human data were inadequate to establish the exposure concentrations associated with adverse effects. Baritosis is radiodense, so it shows on a chest film, which historically is how it was found.

The real shipboard hazard is physical. The dust is dense and abrasive, it works into bearings, ventilation intakes and electrical equipment, and because of its density it settles and stays rather than blowing off the deck.

Crystalline silica, stated at its proper width

Barite ore carries quartz as a common gangue mineral. USGS Minerals Yearbook 2021 records that lower quality barite typically contained higher levels of more abrasive impurities such as iron oxides and quartz, and notes the same association with lower specific gravity material. That matters because the 4.1 g/mL API grade admits ore the 4.2 grade would reject.

Where a dust contains 1 per cent or more crystalline silica the ACGIH value for barium sulphate does not apply on its own terms, and the respirable silica limit governs instead. In the European Union that limit is binding: Directive 2004/37/EC, as consolidated on 9 April 2024, lists “work involving exposure to respirable crystalline silica dust generated by a work process” in Annex I and sets a limit value of 0,1 mg/m3 over an eight hour reference period in Annex III. The Annex I wording attaches to a process that generates the dust, so a grab discharge into a hopper is within it.

What cannot be said is that barytes dust is a silicosis risk. No source gives a silica content for a typical marine parcel, and the schedule imposes nothing on this account. The honest statement is the association, the threshold at which the governing limit changes, and the fact that the ship does not know the parcel’s silica content unless someone measures it.

Controlling the dust in practice

Control starts at the terminal, with enclosed transfer points, chutes that reach down into the hold to cut the fall height, and water spray at the loader head, covered in dust suppression . On the ship, ventilation intakes on the working side are closed or screened and air conditioning is put on recirculation under section 2.2.5, accommodation doors and ports are shut, non-essential personnel are kept clear, and deck machinery and exposed fittings are protected under 2.2.6.

Discharge is dustier than loading, because a grab drops the cargo through air repeatedly, so the precautions bind harder at the discharge port than at the load port even though the schedule’s Discharge field asks for nothing.

Settled barite dust is its own maintenance problem afterwards. It is heavy, so it does not blow off the deck the way a lighter mineral dust does; it works into hatch coaming drain channels, cleat threads and hatch cover tracks, where it grits the bearing surfaces and can foul the rubber to steel seal that keeps the next cargo dry.

Ventilation, carriage and cargo condition

The BARYTES schedule imposes no ventilation requirement and no carriage requirement. Both fields read “No special requirements”, because the cargo does not self-heat, emit gas or liquefy.

“No requirement” is not the same regulatory state as “prohibited”, and the distinction matters on this cargo precisely because its Group A sibling carries the prohibition. Barytes may be ventilated, and any ventilation is a condensation decision taken on the usual dew point comparison between hold air and outside air rather than a duty owed to the cargo. See cargo hold ventilation .

The voyage routine is therefore short: hatch covers kept weathertight and the seals checked after heavy weather, bilges sounded on the standard schedule and any water investigated rather than simply pumped, since water on the tank top under barytes points to a hatch or ballast line leak. None of that is a schedule obligation.

One thing the absence of a chemical hazard does not remove. Section 3.2.2 records that any cargo space may be oxygen depleted and that a space closed for some time may have insufficient oxygen to support life, so a hold inspection on a benign Group C cargo is still an enclosed space entry .

Discharge

Barytes discharges by grab into hoppers at oilfield service terminals, chemical receivers and general bulk berths. The Discharge and Clean-up fields both read “No special requirements”, so everything in this section is trade practice and the only Code text that follows the cargo ashore is the dust precaution, which is not discharge specific but applies wherever persons may be exposed.

Grab work suits the cargo because coarse lumps up to 101.6 mm and a very high density are outside what a pneumatic unloader handles. It is efficient by weight and slow at the end, because the fines pack into the tank top margin and the bilge hat covers and resist both the grab and the sweep. A dense cargo of a given tonnage sits in a shallower, more tightly packed heel than a lighter one of the same weight, which is why the cleanup takes longer than the tonnage suggests. Grabs and bulk handling attachments covers the equipment.

Structural damage on discharge

This is a designed-for hazard rather than an accident. SOLAS regulation XII/6.4.1, for bulk carriers of 150 m and upwards carrying cargoes of 1,000 kg/m3 and above constructed on or after 1 July 2006, requires that “the structure of cargo holds shall be such that all contemplated cargoes can be loaded and discharged by standard loading/discharge equipment and procedures without damage which may compromise the safety of the structure”. Barytes is far above that density trigger.

Class carries the same idea as a notation. Under the Common Structural Rules the GRAB [X] notation is mandatory for ships with the BC-A or BC-B service features, and IACS Recommendation No. 46 gives the design grab masses: 35 tonnes for ships over 250 m, 30 tonnes between 200 and 250 m, and 20 tonnes for smaller vessels, which is the figure that applies to the Handysize and Supramax tonnage that carries most barytes.

The mechanism worth understanding is where the damage shows up. Recommendation No. 46 records that “impact damage to the inner bottom plating or the hopper sloping plating will result in the breakdown of coatings in the adjacent water ballast tanks, thereby intensifying the rate of structural deterioration”. The corrosion consequence of a tank top impact is on the other side of the plate, in the ballast tank, which is why an indentation is a survey finding rather than a cosmetic one. Hydraulic hammers and bulldozers used to free cargo can chip and buckle side frames at their lower connections, and Recommendation No. 46 asks that holds be inspected by the ship’s officers on completion of discharge and that damage affecting hull integrity be reported to the classification society.

Hold washing and residues

Wash water carrying fine barite is handled under the ship’s cargo residues and hold washings procedures and the MARPOL Annex V regime, covered in Annex V garbage discharge . Barium sulphate is inert and insoluble, so the constraint is the Annex V hold washing rules and their distance from land conditions rather than any chemical spill regime.

Whether the residues are harmful to the marine environment is the shipper’s declaration, not a property of the mineral. IMSBC 4.2.2.17 puts the determination on the shipper against the criteria in MARPOL Annex V Appendix I, with the implementation guidance in resolution MEPC.295(71) of 7 July 2017. An article cannot declare a parcel non-HME on the shipper’s behalf.

Quantity, contamination and cargo claims

Quantity on a barytes parcel is settled by draught survey against the shore weightometer or the bill of lading figure. The survey resolves cargo weight from a displacement difference, so its sensitivity in tonnes per centimetre of draught is a property of the ship’s waterplane and not of the cargo. What the cargo changes is the consequence: barytes is deadweight limited and valuable per tonne, so the same absolute survey error carries a larger money value than it would on a light cargo, and disputes with the shore weightometer are correspondingly sharper.

The trim, list, hog and sag corrections and the water density correction apply in the ordinary way. A shallow even layer is easier to draught survey than a deep one and harder to grab clean, which is the trade the discharge port makes.

Claims on this cargo are more often about grade than damage. A drilling grade parcel is tested against API 13A density and screen residue; a chemical or filler grade parcel is tested against whiteness and purity limits that a rust streaked or previously coal laden hold will fail. That puts most barytes disputes in the contamination category rather than the shortage one, and the hold preparation standard that was contractual at the load port becomes the evidence at the discharge port. Cargo claim time bars apply as for any cargo under the Hague-Visby Rules , and the slow final heel can put pressure on laytime and into demurrage .

Port state control

A port state control officer boarding a barytes fixture checks the same items as on any solid bulk cargo, and the Group C classification removes none of them: the cargo information under SOLAS VI/2 and IMSBC 4.2, the declared bulk density where SOLAS XII/10 applies, the approved loading manual and loading instrument, the agreed loading plan under SOLAS VI/7, the stability booklet, and evidence that the tank top and hold mass limits were respected. Where a regulation XII/14 restriction applies, the side shell triangle and the entry in the loading booklet are both visible checks.

The current procedures instrument is resolution A.1206(34), adopted 3 December 2025, which revoked A.1185(33). Regional regimes add their own overlay through the Paris and Tokyo memoranda.

One United States point, because it is a common misreading. Title 46 CFR 148.8 incorporates the IMSBC Code, and part 148 addresses hazardous materials and Potentially Dangerous Materials. A Group C cargo with no class, no UN number and no MHB classification falls outside part 148, so no part 148 obligation attaches to barytes.

The seaborne barytes trade

World barite mine production was an estimated 8,700 thousand metric tons in 2025 according to the USGS Mineral Commodity Summaries 2026, up from 8,000 in 2024, and the tonnage no longer moves with the rig count.

Thousand metric tons, from USGS Mineral Commodity Summaries 2026. United States production is withheld to avoid disclosing company proprietary data.

The United States mined barite through three companies at four operations in Nevada in 2025 and remains a net importer, with import reliance above 75 per cent of apparent consumption in every year from 2021 to 2025. Its import sources over 2021 to 2024 were India at 39 per cent, China at 21, Morocco at 19, Mexico at 14 and others at 7, which traces the principal seaborne routes into the US Gulf. The USGS notes that offshore and onshore drilling operations outside the producing regions primarily used imported barite because of the higher cost of rail and truck transport compared with ocean freight, which is the economic reason this trade exists at all rather than moving Nevada material to the coast overland.

What drives barite tonnage, and why it is not the rig count

The rig count is the traditional proxy and the USGS has now qualified it. MCS 2026 states that rig counts “are often used as an indicator of barite consumption”, then explains why the link has weakened: “barite use per rig has been increasing owing to deeper oil and gas wells that require fewer rigs for oil and gas production.”

The 2025 figures make the point better than the explanation does. Through October 2025 the world average rig count excluding the United States was 1,258 against 1,349 over the same period of 2024, and the domestic average was 564 against 599. Both series fell, and barite sales were estimated to have increased. A deeper well consumes more weighting agent per rig, so tonnage can rise on a shrinking rig fleet.

The practical consequence for anyone forecasting barytes freight is that a rig count series is a lagging and increasingly loose proxy. Well depth and completion intensity carry information the rig count no longer does.

Limitations

This article describes the BARYTES schedule and its operational consequences. It does not replace the in-force IMSBC Code text, the ship’s approved loading manual, or the shipper’s cargo declaration, all of which govern an actual shipment.

The schedule figures are informative, not mandatory. Under IMSBC section 1.4.2 the description and the characteristics other than the hazard classification block are recommendatory, and section 1.2.1 requires current valid information to be obtained from the shipper before loading. The bulk density of a particular parcel varies with grade, moisture and compaction, and on a bulk carrier of 150 m and upwards it is the shipper’s declared figure under SOLAS regulation XII/10, not the schedule’s 2,941 kg/m3, that a loading plan is built on. Below 150 m no declaration is required and the ship may have nothing better than the schedule value.

Structural limits are ship specific. Permissible tank top loads, hold mass curves, bending moment and shear force envelopes and any alternate hold permission are the individual ship’s class approved figures, stated in its loading manual. No generic band substitutes for them, and this article publishes none. The arithmetic given for stow height against a uniform distributed load is arithmetic on the schedule density alone.

The two baryte entries are separate cargoes and this article covers one of them. BARYTE, FLOTATION CHEMICAL GRADE is Group A, liable to liquefy above its transportable moisture limit, and carries a ventilation prohibition, a voyage monitoring duty and a place of refuge clause that nothing here describes. Where a parcel is barium nitrate, UN 1446, IMDG Class 5.1 with a subsidiary hazard of 6.1, an entirely different and hazardous schedule applies.

Exposure limits are regional overlays, not an IMO baseline. The Code sets no numerical dust exposure limit. The OSHA, NIOSH, ACGIH and European Union values cited here apply in their own jurisdictions and to shore workplaces in the first instance, and their application to a ship’s crew depends on the flag and the port. No source consulted gives a crystalline silica content for a typical barytes marine parcel, so the silica discussion states an association and a governing threshold and stops there.

The mined ore is not treated as radioactive material. The schedule assigns no class, and the barium sulphate naturally occurring radioactive material literature concerns scale precipitated from oilfield produced water downstream of production, not the ore. IMSBC 4.2.2.16 requires the shipper to declare radioactive properties if applicable, and a parcel above the relevant threshold would be a different Bulk Cargo Shipping Name entirely.

On sources not fully resolved. The current consolidated edition of the Common Structural Rules was not opened for this article, so the CSR is cited by part and chapter rather than by an edition specific paragraph. The sub paragraph numbering within SOLAS regulation VI/7 for the master’s right to suspend loading is cited to the regulation rather than to a sub item.

Related Articles

• IMSBC Code : the parent mandatory instrument and its structure
• IMSBC Group C cargoes : the classification barytes belongs to
• IMSBC individual cargo schedule : how a schedule is laid out and which fields bind
• High density solid bulk cargo : the 0.56 m3/t threshold barytes sits well inside
• Tank top strength and loading limits : the structure the schedule warns about
• Cargo liquefaction : the Group A hazard the flotation grade carries and this cargo does not
• Bulk carrier : the ship type and its hull girder limits
• SOLAS chapter XII regulation 10 : the density declaration and its 150 m threshold
• Shipper’s cargo declaration : the eighteen items of IMSBC 4.2.2
• BLU Code and BLU Manual : the ship to shore loading interface
• Angle of repose for solid bulk cargoes : why the cell reads not applicable here
• Iron ore: IMSBC Code schedule : the dense cargo barytes is usually compared against
• Chrome ore: IMSBC Code schedule : another heavy mineral with the same tank top problem
• Alumina: IMSBC Code schedule : the sibling schedule with its own declaration trap
• Offshore drilling and wells : where the cargo goes and why the trade exists