IMDG Class 6: Toxic and Infectious Substances

IMDG Class 6 divides into two divisions that share a class number but are operationally, scientifically, and regulatorily almost independent of one another. Division 6.1 Toxic Substances are non-living chemicals that cause death, serious injury, or acute harm to human health when swallowed, absorbed through skin, or inhaled. Division 6.2 Infectious Substances contain or are reasonably expected to contain viable pathogens capable of causing disease in humans or animals. The IMDG packing group calculator implements the full Division 6.1 decision tree for oral, dermal, and inhalation routes.

The 2022 Edition of the IMDG Code (Amendment 41-22, mandatory from 1 January 2024 under SOLAS Chapter VII) consolidated these rules after decades of incremental amendment. The Class 6 chapter in IMDG 41-22 runs from 2.6.1 (scope) through 2.6.3.2.3 (Category B exemptions). This article works through Division 6.1 classification, the packing-group threshold table, the inhalation hazard zone system, Division 6.2 categorisation and packaging instructions P620 and P650, stowage and segregation, the emergency schedules, and documentation requirements. For the general IMDG framework, maritime legal basis, and the other seven IMDG classes, see SOLAS Chapter VII: Carriage of Dangerous Goods and the sibling class articles linked throughout.

Why Class 6 carries two operationally distinct divisions

The Class 6.1 harm mechanism is dose-dependent chemical toxicology. A substance is Class 6.1 because its LD50 or LC50 falls within the specified numeric range; the hazard exists whether the material is alive or dead. Packaging keeps the dose below the exposure threshold.

Division 6.2 harm doesn’t follow classical dose-response kinetics. A single viable Ebola virion cannot guarantee infection, but the replication dynamic once infection is established means the effective hazard is bounded differently from a fixed-concentration chemical. Packaging philosophy for 6.2 is therefore containment under failure rather than quantity limitation; a broken P620 package is an event, not simply a changed concentration.

These different physics produce different rules. Class 6.1 uses the standard IMDG performance-tested drum, IBC, and tank container framework, with quantity limits and packing-group-graded packaging standards. Class 6.2 uses triple packaging specified to fixed mechanical test standards (9-metre drop for Category A, 1.2-metre drop for Category B) regardless of quantity, because the quantity doesn’t change the biological event.

Division 6.1: classification criteria and packing groups

The three toxicity routes and their test endpoints

IMDG Code 41-22 Chapter 2.6.2 assigns packing groups to Division 6.1 substances using three independent toxicity routes:

Oral toxicity: LD50 oral in the rat, expressed in mg/kg body weight. The standard OECD Test Guideline 401/423 protocol involves gavage administration to groups of five male and five female rats; the LD50 is the dose causing 50% mortality within 14 days. Sodium cyanide (UN 1689) has an oral rat LD50 of approximately 6.4 mg/kg, placing it firmly in the PG I range.

Dermal toxicity: LD50 dermal in the rat or rabbit, expressed in mg/kg body weight. OECD TG 402 applies four-hour dermal exposure under occlusion. This route matters most for substances absorbed efficiently through intact skin, including many organophosphate insecticides. Parathion has a dermal LD50 in rabbits of approximately 21 mg/kg, PG I territory.

Inhalation toxicity: LC50 in the rat over a 4-hour exposure period, expressed as mg/L for aerosols, dusts, and mists, or as mL/m3 (ppm v/v) for vapours and gases. The distinction between vapour and aerosol/dust/mist is operationally important: substances that volatilize under ambient conditions get vapour-phase treatment, while non-volatile solids get the dust/mist table. Hydrogen cyanide gas (UN 1051) has a vapour LC50 of approximately 140 mL/m3 in rats over 1 hour, extrapolated to a 4-hour LC50 of about 40 mL/m3, placing it in PG I Hazard Zone A.

The packing group is the most stringent result across all three routes. A substance can be PG I by inhalation and PG III by oral without changing the packing group assignment: PG I governs.

The packing group threshold table for Division 6.1

The vapour-phase LC50 cutoffs are more complex than the table suggests. IMDG 41-22 Chapter 2.6.2.2 introduces a vapour-versus-saturated-concentration check: if the saturated vapour concentration at 20°C (Vsat) is at or below the LC50, the substance cannot achieve LC50 conditions in air under ambient handling conditions, and the oral/dermal routes govern packing group placement instead. Vsat is calculated from vapour pressure using the ideal gas relationship: $V_{sat} = \frac{P_{vap}}{P_{total}} \times 10^6$ mL/m3.

Inhalation hazard zones A, B, C, D

IMDG Code 41-22 Chapter 2.6.2.2.4 assigns an inhalation hazard zone to Division 6.1 substances that are PG I by vapour inhalation. The zone determines the supplementary marking requirement and, for some intermodal movements, the tunnel restriction category under ADR.

Hazard Zone A: LC50 (vapour, 4h) at or below 200 mL/m3, and saturated vapour concentration at or above 500 times the LC50. Hydrogen cyanide (UN 1051, LC50 approximately 40 mL/m3) and hydrogen fluoride anhydrous (UN 1052, LC50 approximately 966 mL/m3) are representative entries. Zone A is the most stringent: “Inhalation Hazard” marking is mandatory on packages and cargo transport units.

Hazard Zone B: LC50 at or below 1,000 mL/m3, and saturated vapour concentration at or above 10 times the LC50. Tetraethyl lead (UN 1649, PG I, Motor fuel anti-knock mixture) falls here. Zone B also triggers the “Inhalation Hazard” marking.

Hazard Zone C: LC50 at or below 3,000 mL/m3, and saturated vapour concentration at or above the LC50. No mandatory supplementary marking, but the classification record must note Zone C.

Hazard Zone D: LC50 at or below 5,000 mL/m3, and saturated vapour concentration at or above 0.2 times the LC50. Zone D is the least stringent within the PG I inhalation zone system; no supplementary marking.

Hazard Zones C and D are relevant primarily for the inland-transport (ADR) tunnel restriction coding, where they map to Tunnel Category D. They don’t generate additional IMDG-specific obligations beyond the base PG I requirements.

Boundary cases: Class 6.1 versus adjacent classes

Several substance types require a deliberate classification decision at the Class 6 boundary.

Class 6.1 versus Class 2.3 Toxic Gases: A substance that is gaseous at 20°C and 101.3 kPa is Class 2, not Class 6.1, even if it meets the Division 6.1 toxicity thresholds. Chlorine (UN 1017) is Class 2.3 (Toxic Gas) despite being acutely toxic by inhalation. Hydrogen cyanide (UN 1051) is Class 6.1 because it liquefies at approximately 25.6°C at standard pressure; it’s transported as a liquid and becomes vapour on release. The distinction matters for packaging: Class 2 cylinders versus Class 6.1 drums.

Class 6.1 versus Class 8: A substance causing harm primarily through systemic toxicity after absorption is Class 6.1; one causing harm primarily through corrosive attack on skin or mucous membranes is Class 8. Phenol (UN 1671) is classified Class 6.1 with a subsidiary Class 8 hazard: it penetrates skin rapidly and the systemic effect (hepatotoxicity, nephrotoxicity) is the primary classification driver, but it also burns skin. Sulphuric acid (UN 1830) is Class 8 with no Class 6.1 subsidiary; the corrosive action so dominates that the systemic toxicity from swallowing a diluted quantity is not the classification hazard.

Class 6.1 versus Class 3 Flammable Liquids: A flammable toxic liquid is classified by the primary hazard. Acrylonitrile (UN 1093) is Class 3 with a Class 6.1 subsidiary because its flash point of -1°C places flammability as the fire risk dominating the transport hazard. Methanol (UN 1230) is Class 3 with a Class 6.1 subsidiary (PG II, oral LD50 approximately 5,600 mg/kg in rats, but significant toxicity via inhalation and dermal routes over extended exposure). Where the two hazards are genuinely co-equal, IMDG 41-22 Chapter 2.0.3 specifies the precedence rule.

Common Division 6.1 entries by chemical family

Cyanides and nitriles. Sodium cyanide (UN 1689, PG I) and potassium cyanide (UN 1680, PG I) are the dominant bulk industrial cyanides, transported in gold-leach operations primarily from chemical producers in Germany, Japan, and the United States to mining operations in West Africa, Latin America, and Central Asia. Acute oral LD50 values in rats are in the 6 to 10 mg/kg range for both. Hydrogen cyanide stabilised (UN 1051) ships as a liquid in dedicated pressure-rated tank containers with inhibitor; its vapour is Hazard Zone A. Acetone cyanohydrin (UN 1541, PG I) is a cyanide precursor shipped in organic synthesis supply chains. Any cyanide entry in the presence of Class 8 inorganic acids (even traces from a leaking co-load) generates hydrogen cyanide gas; the segregation requirement ‘separated longitudinally by a complete compartment or hold from’ between cyanides and acids exists specifically for this reaction.

Arsenic compounds. Arsenic trioxide (UN 1561, PG II) is the dominant arsenic entry; it’s an intermediate in copper smelting and a feedstock for wood preservative (CCA) manufacture. Rat oral LD50 is approximately 15 mg/kg, solidly PG II. Arsenic compound, solid, n.o.s. (UN 1557) covers a wide range of organic and inorganic arsenic species at PG I, II, or III depending on the individual compound. Arsenical dust (UN 1562, PG I) covers fine particulate material from smelter baghouse operations. These entries are marine pollutants under MARPOL Annex III in virtually all cases; see MARPOL Annex III: Harmful Substances in Packaged Form for the marking and stowage overlay.

Mercury compounds. Mercuric chloride (UN 1624, PG II) remains in transit in thermometer manufacturing and pharmaceutical supply chains. Mercury compounds, liquid, n.o.s. (UN 2024) covers organomercury compounds used in laboratory synthesis. All mercury compounds with a marine pollutant designation require the MP mark; virtually all mercury entries carry it. Mercury itself (elemental, UN 2809) is Class 8 with Class 6.1 subsidiary, not a primary Class 6.1 entry.

Organophosphorus pesticides. Organophosphorus pesticide, solid, toxic (UN 2783) and its liquid equivalent (UN 3018) are PG I or II depending on the specific active ingredient. Parathion (oral LD50 approximately 2 mg/kg in rats) and methyl parathion (oral LD50 approximately 14 mg/kg) are PG I. Chlorpyrifos (oral LD50 approximately 135 mg/kg) is PG III. The dominant trade lane is from Chinese and Indian formulators to South/Southeast Asian and African agricultural markets. Nearly all organophosphate entries are marine pollutants; the technical name of the active ingredient(s) must appear parenthetically in the proper shipping name on the dangerous goods declaration.

Organochlorine pesticides. Organochlorine pesticide, solid, toxic (UN 2761) covers legacy entries including lindane (gamma-HCH), endosulfan, and DDT. The Stockholm Convention on Persistent Organic Pollutants (POPs) has eliminated or restricted most of these in regular agricultural use, but transport continues for legacy disposal shipments moving from stockpile to high-temperature incineration facilities, particularly under Basel Convention trans-boundary waste movement permits. The regulatory status at departure port versus destination port must be confirmed before loading.

Carbamate pesticides. Aldicarb (oral LD50 approximately 0.93 mg/kg in rats, PG I) is one of the most acutely toxic registered pesticides; it’s shipped under UN 2757 (solid). Carbofuran (oral LD50 approximately 8 mg/kg, PG I) and methomyl (oral LD50 approximately 17 mg/kg, PG II) follow similar routes.

Nicotine and alkaloids. Nicotine (UN 1654, PG II, oral LD50 approximately 50 mg/kg in rats but extremely toxic to humans via dermal absorption with a dermal LD50 approximately 50 mg/kg placing it firmly PG II by that route) is a growing entry volume driven by nicotine-pouch and e-cigarette liquid manufacturing. It’s shipped as freebase nicotine in dark-glass or steel drums from tobacco-processing countries (China, India, Brazil) to consumer product manufacturers.

Aniline and aromatic amines. Aniline (UN 1547, PG II) is an industrial intermediate for dyes, rubber processing chemicals, and pharmaceuticals; it’s shipped in bulk liquid tanks (T7 portable tanks). Its oral LD50 is approximately 440 mg/kg in rats (PG III) but its inhalation toxicity (NIOSH REL 2 ppm, LC50 below 2 mg/L over 4h in rats) places it PG II overall.

The IMDG dangerous goods finder lets you look up any of these UN numbers to verify class, packing group, EmS code, and special provisions. The IMDG packing group calculator implements the three-route decision tree with the volatility correction.

Division 6.1 stowage, segregation, and marine pollutant rules

Stowage

IMDG Code 41-22 Chapter 7.1 gives the stowage categories for Division 6.1 entries. Most entries carry stowage category A (on deck or under deck) or B (on deck or under deck, shielded from accommodation). PG I entries, particularly Hazard Zone A and B vapour-toxic entries, carry the additional restriction that they must not be stowed in the same compartment or hold as crew-accessible spaces.

The master segregation table at IMDG 41-22 Chapter 7.2 provides the Class-versus-Class matrix. For Division 6.1 the key pairs are:

From Class 3 Flammable Liquids: ‘separated from’ for most combinations. For flammable liquids co-loaded with Class 6.1 pesticides, the 2014 IMDG amendment (IMDG 36-12) introduced a ‘separated by complete compartment or hold from’ requirement for specific high-volatility pesticide categories because a fire in the flammable liquid container could aerosolize the pesticide and create a toxic vapour cloud.

From Class 5.1 Oxidising Substances: ‘separated from’. Oxidiser contact with cyanides forms cyanogen and cyanogen halides; contact with organophosphates accelerates thermal decomposition.

From Class 8 Corrosives: For inorganic cyanides specifically, IMDG 41-22 applies ‘separated longitudinally by a complete compartment or hold from’ for combination with Class 8 inorganic acids. This is the cyanide-acid HCN generation rule. The segregation applies even if both are in sealed containers, because a container breach from any cause during the voyage brings the pair into the same micro-environment.

From foodstuffs: Division 6.1 is subject to the ‘separated from’ requirement relative to foodstuffs in most combinations. PG I entries require ‘separated by complete compartment or hold from’ foodstuffs, medicines, and animal feed. This applies even when the foodstuff is also a dangerous good (e.g., Class 3 ethanol for beverages).

From Class 6.2: ‘separated from’. The decontamination chemistry for a cyanide spill (alkaline oxidant) is incompatible with the biological decontamination (dilute bleach, formaldehyde vapour) required for a Class 6.2 event; keeping the two divisions separated simplifies emergency response.

Marine pollutant overlay under MARPOL Annex III

Many Division 6.1 entries carry a marine pollutant (MP) or severe marine pollutant (SMP) designation. The IMDG Code’s dangerous goods list column 4 notes “P” (pollutant) or “PP” (severe pollutant) for each entry. Pesticides in particular are almost universally marine pollutants; cyanides, arsenic compounds, and mercury compounds are too.

When an entry is a marine pollutant, the shipper must:

• Mark each package or IBC with the marine pollutant mark (stylized fish and tree, at least 100 mm at the longest dimension for packages of 500 L or more, or in proportion for smaller packages per IMDG 41-22 Part 5).
• Note the marine pollutant designation on the Dangerous Goods Declaration / Multimodal Dangerous Goods Form.
• Apply the MARPOL Annex III stowage requirements in addition to the IMDG stowage requirements: for SMP entries this means specific distance requirements from the hull and from sea-water overboard lines.

The MARPOL Annex III marine pollutant lookup calculator returns the MP status for a given UN number directly from the IMDG dangerous goods list.

Division 6.2: infectious substances

The Category A versus Category B distinction

IMDG Code 41-22 Chapter 2.6.3 defines the two categories. Category A is a substance that, in the form transported, is capable of causing permanent disability, life-threatening or fatal disease in otherwise healthy humans or animals when exposure occurs. The code’s language is specific: “otherwise healthy” means immuno-compromised individuals are out of scope for classification; the criterion is a worst-case healthy adult exposure.

Category A is further sub-divided by host species:

UN 2814 Infectious substance, affecting humans. Covers pathogens capable of causing disease in humans, including pathogens that also affect animals. Representative entries from the indicative list in IMDG 41-22 Appendix 2.6 include: Ebola virus, Marburg virus, Lassa fever virus, Crimean-Congo haemorrhagic fever virus, variola virus (smallpox), monkeypox virus (clade I, from African endemic regions), severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), Nipah virus, Hendra virus, and Yersinia pestis (plague bacillus). This list is indicative, not exhaustive; the consignor must apply the Category A definition to any pathogen not named.

UN 2900 Infectious substance, affecting animals only. Covers pathogens not known to cause human disease that are capable of causing significant disease in animals. Representative entries include: foot-and-mouth disease virus (FMDV), classical swine fever virus (CSFV), peste des petits ruminants virus (PPR), African swine fever virus (ASFV), and Newcastle disease virus (NDV). These move primarily between national veterinary reference laboratories, between academic research facilities, and from field collection sites to diagnostic laboratories during outbreak investigations.

Category B is the residual category: any infectious substance not meeting the Category A definition. All Category B substances use UN 3373 with the proper shipping name “Biological substance, Category B.” This single UN number covers an enormous practical range:

• Diagnostic specimens (patient blood, urine, sputum, swabs, biopsy tissue) being shipped from clinic to laboratory for routine diagnostic analysis.
• Freeze-dried reference strains being shipped between accredited culture collections.
• Environmental samples suspected to contain biological agents during outbreak investigation.
• Attenuated or inactivated microorganisms where the inactivation has been validated and the risk of reversion is negligible.

A separate entry covers substances that don’t meet either division definition:

UN 3291 Regulated medical waste, n.o.s. (or Clinical waste, unspecified, n.o.s.). Covers waste arising from medical, veterinary, or research activities that may contain pathogens but is packaged in a way that makes Category A exposure implausible (e.g., sealed sharps containers, incineration bags). This is the UN number used for large-volume clinical waste shipments moving by sea to high-temperature incineration facilities.

UN 3245 Genetically modified microorganisms (GMMOs) or genetically modified organisms (GMOs). Covers organisms that don’t meet the Category A or B definition but that pose a risk through their genetic modification rather than through natural pathogenicity. Agricultural GMOs for seed or research transit most commonly under this number.

Exempt patient specimens and exempt clinical waste

IMDG Code 41-22 Chapter 2.6.3.2.3 creates an exemption from all Division 6.2 requirements for specimens shipped when “there is a minimum likelihood that pathogens are present.” The practical test is the clinical assessment: if a physician or veterinarian has evaluated the patient and determined that the likelihood of a specific listed pathogen is negligible (routine blood chemistry, normal diagnostic panel, no fever of unknown origin, no haemorrhagic signs), the specimen may be transported outside the Division 6.2 framework.

This exemption is legally significant. Hospital laboratories regularly ship exempt patient specimens by courier without UN 3373 packaging when the clinical context excludes Category A and Category B pathogen risk. The exemption doesn’t apply when there’s any reasonable basis to suspect an infectious etiology for the clinical presentation. Getting this wrong in either direction creates problems: over-classification wastes expensive P650 packaging; under-classification for a genuinely infectious specimen is a regulatory violation and a public-health risk.

Packaging instructions P620 and P650

The triple-packaging system is the defining feature of Division 6.2 transport. Both P620 (Category A) and P650 (Category B) require three nested containment layers, but the mechanical performance requirements differ substantially.

Packing Instruction P620 applies to UN 2814 and UN 2900. The inner primary receptacle must be watertight and leak-proof; for liquids, absorbent material sufficient to absorb the entire liquid contents must be placed between the primary and the secondary. The secondary packaging must be watertight, leak-proof, and must itself be cushioned in the outer packaging. The outer packaging must pass:

• A 9-metre drop test in the fully packed condition on concrete without any of the three layers failing or leaking.
• A puncture test (a 7 kg steel bar dropped from 1 metre onto the top of the package).
• A stack test (24-hour load equal to the total weight of packages stacked 3 metres above).

P620 packaging is manufactured by specialist producers certified to the testing standard. Individual packages carry the UN test mark and typically a manufacturer-assigned batch and date code. The maximum volumes permitted per primary receptacle are 50 mL for liquids and 50 g for solids/powders. Total net mass of infectious substance per outer packaging is limited to 4 kg for solids and 4 L for liquids, with special exemption for larger volumes under certain conditions where the outer packaging meets an enhanced test standard.

Packing Instruction P650 applies to UN 3373. The three-layer structure is identical in concept, but the outer packaging needs to pass only a 1.2-metre drop test. P650 outer packaging is widely commercially available; the major integrator courier networks supply branded compliant boxes (branded examples include Saf-T-Pak, and the major medical courier services offer compliant options through their clinical packaging programmes). Maximum volume per outer packaging is 4 L for liquids and 4 kg for solids.

For both P620 and P650, the package must remain intact over the temperature range encountered in the transport chain. For Category B diagnostic specimens and Category A cultures requiring cold-chain maintenance, dry ice (UN 1845, Class 9) or liquid nitrogen (UN 1977, Class 2.2) may be packed as a refrigerant inside the outer packaging; the documentation must cover both the infectious substance and the refrigerant separately. Dry ice, when used, requires adequate ventilation (a perforated inner liner so CO2 can escape without pressure build-up) and must be noted on the documentation because of the asphyxiation hazard in confined spaces.

Category A and B packaging comparison

WHO and ICAO alignment

The IMDG P620/P650 system is deliberately harmonised with ICAO Technical Instructions Packing Instructions 620 and 650, and with WHO’s biennial “Guidance on regulations for the transport of infectious substances.” This harmonisation matters in practice because the overwhelming majority of Category A and Category B shipments are multimodal: a culture of Marburg virus leaving a high-containment biosafety-level-4 facility in Germany will travel by road, then by air, then possibly by sea to reach its destination laboratory. The packaging that meets IMDG P620 meets ICAO PI 620; the consignor doesn’t build a different package for each transport mode.

WHO’s biennial guidance (current edition WHO/WPE/CPI/2023.1) provides the “Annex 2” decision tree for classifying a pathogen as Category A or Category B when the substance is a named strain with known epidemiology. For novel or poorly characterised pathogens, WHO guidance defaults to Category A until evidence supports a downgrade. This precautionary default drove the UN 2814 classification of early SARS-CoV-2 cultures in early 2020 before the clinical case-fatality rate in healthy adults was established.

Division 6.2 stowage and segregation

IMDG Code 41-22 specifies that Division 6.2 packages must be stowed so as to avoid crushing, and that the integrity of the packaging is preserved throughout the voyage. Category A packages must be accessible for emergency inspection during the voyage; they must not be buried in a heavily loaded container. Reefer transport at the temperature required by the consignor’s cold-chain specification is mandatory for specimens requiring refrigeration.

The segregation requirements for Division 6.2 in the IMDG master table:

• From Division 6.1: ‘separated from’. The chemical-decontamination procedures used after a Class 6.1 spill can destroy evidence and compromise the biological integrity of an adjacent Class 6.2 package; and the biological-decontamination agent for a 6.2 event (typically dilute hypochlorite or formaldehyde vapour) can react with many Class 6.1 chemicals.
• From foodstuffs: ‘separated by complete compartment or hold from’, regardless of Category A or B classification.
• From live animals: ‘separated by complete compartment from’, because stress in the live animals can worsen the infection risk from any containment breach.

Division 6.2 EmS and incident response

IMDG Code 41-22 assigns EmS code F-A (standard fire schedule) and S-A (standard spillage schedule) to Category B (UN 3373). Category A (UN 2814 and UN 2900) also begins with F-A/S-A but the MFAG (Medical First Aid Guide, IMO publication) provides supplementary guidance for Category A breaches.

A Category A package breach on a vessel is a notifiable event under most flag-state regimes regardless of apparent severity. The response protocol:

1. Cordon the area and prevent any personnel who had contact with the released material from leaving the vessel.
2. Contact the consignor’s 24-hour emergency contact (a biosafety officer or national public-health authority, as documented on the dangerous goods declaration).
3. Notify the master, who notifies the flag-state authority and, under SOLAS Chapter VII Part A.2, the competent authority of the nearest port state.
4. The flag-state authority will coordinate with WHO’s Global Outbreak Alert and Response Network (GOARN) if the pathogen is a listed Category A organism.

A Category B breach (typical example: a cracked blood-specimen vial inside a compliant P650 package, contained by the absorbent layer) is treated as a standard biohazard spill: personal protective equipment, absorbent material decontaminated with dilute bleach, notification to the vessel operator’s designated quarantine contact.

Stowage category summary for Class 6

IMDG Code 41-22 Part 7 assigns stowage categories to individual UN number entries in the dangerous goods list. The default categories for Class 6 entries are:

Documentation requirements

Dangerous Goods Declaration for Division 6.1

The Multimodal Dangerous Goods Form (MDGF) for a Division 6.1 shipment must contain:

• UN number in the form “UN XXXX” (e.g., “UN 1689”).
• Proper shipping name in full (e.g., “Sodium cyanide”). For entries with a technical name requirement (all pesticides, all n.o.s. entries), the technical name of the active ingredient(s) follows in parentheses (e.g., “Organophosphorus pesticide, liquid, toxic (chlorpyrifos)”).
• Class and division: “6.1” for the primary class; subsidiary hazard class listed separately if applicable (e.g., “3” for a flammable toxic).
• Packing group: “I”, “II”, or “III”. Must match the IMDG dangerous goods list entry or a classification approved by the competent authority.
• Hazard Zone: “Hazard Zone A”, “B”, “C”, or “D” for inhalation-toxic PG I entries. Required where the IMDG dangerous goods list specifies it or where the consignor has determined it from measured data.
• Marine pollutant indicator: “MARINE POLLUTANT” or “SEVERE MARINE POLLUTANT” if applicable.
• Number and type of packages and total quantity: by net mass (liquids also by volume).
• EmS reference: typically “F-A, S-A”; specific EmS codes differ for specialty entries.
• 24-hour emergency contact: a phone number at which a person knowledgeable about the substance is reachable continuously during the voyage.

Dangerous Goods Declaration for Division 6.2

For UN 2814 and UN 2900 (Category A):

• UN number, proper shipping name including “Category A”, and the technical name of the pathogen in parentheses (e.g., “Infectious substance, affecting humans (Ebola virus)”).
• Reference to packing instruction P620 used.
• Quantity: number of packages and volume or mass of infectious substance per package.
• 24-hour emergency contact: must identify the biosafety officer or the designated public-health authority with jurisdiction over the pathogen.
• Consignor’s and consignee’s full name, address, and emergency phone.

For UN 3373 (Category B):

• Proper shipping name: “Biological substance, Category B”.
• Reference to packing instruction P650.
• Full consignor and consignee details with emergency contact.
• Optional but advisable: a notation of the specimen type to assist emergency responders (e.g., “human diagnostic blood samples, HIV-negative patient cohort”).

Marking and placarding

Package marking for Division 6.1 uses the skull-and-crossbones label (square-on-point diamond, black symbol and border on white background, with the numeral “6” in the lower triangle). Hazard Zone A and B entries additionally require the “Inhalation Hazard” text marking on the package. Marine pollutant entries require the marine pollutant mark as well. The IMDG marking, labelling and placarding guide covers the dimension, placement, and CTU placard requirements in detail.

For Division 6.2 Category A (UN 2814 / UN 2900), the label is the biohazard trefoil on white, square-on-point diamond, with the proper shipping name in the lower band. Category B (UN 3373) does not use a diamond label; it uses the square-on-point “UN 3373” marking only, a white-on-black or black-on-white square tilted 45 degrees with “UN 3373” and “BIOLOGICAL SUBSTANCE, CATEGORY B” text. No cargo transport unit placard is required for UN 3373 below 4 L or 4 kg per package when limited to a single package per CTU.

Emergency schedules

IMDG Code 41-22 assigns emergency schedule (EmS) codes to each entry in the dangerous goods list. Division 6.1 entries predominantly use:

F-A (Fire schedule, toxic substances): Water spray is the primary extinguishing agent at safe stand-off distance. All personnel involved in fire-fighting wear self-contained breathing apparatus regardless of apparent fire severity; toxic combustion products from virtually any Class 6.1 entry (cyanogen from cyanides, phosphorus oxides from organophosphates, arsenic trioxide from arsenicals) present inhalation hazard levels the first-arriving crew can’t assess without instrumentation.

S-A (Spillage schedule, toxic substances): Stop the leak if possible only with full respiratory protection. Bund the spill to prevent run-off to bilges or overboard. Absorb with inert material (sand, earth, vermiculite). Recover into salvage drum. Chemistry-specific decontamination: alkaline hydrogen peroxide for cyanides, lime or calcium hydroxide for organophosphates (hydrolysis), calcium polysulphide for arsenic compounds, sulphur powder for mercury compounds. The specific guidance is in the EmS guide; the IMDG EmS lookup calculator returns the correct EmS pair for any UN number.

Some Class 6.1 entries use modified schedules:

F-E: Applied to some Class 6.1 entries where conventional water may spread the hazard or react adversely. Specific guidance is entry-level in the EmS guide.

S-G: Applied to entries where the spillage creates a secondary reactive hazard. Cyanide fires, for instance, where alkaline water spray is specified to convert vapour-phase HCN into less volatile cyanide salt aerosol.

Division 6.2 entries use EmS F-A / S-A (Category B) and F-A / S-A supplemented by MFAG Category A pathogen-specific advice. The MFAG (IMO Medical First Aid Guide for use in accidents involving dangerous goods, current edition) has a dedicated section for Category A incidents covering isolation, decontamination, and emergency notification chains.

Class 6 and the IMDG regulatory framework under SOLAS Chapter VII

SOLAS Chapter VII Part A (Carriage of packaged dangerous goods) makes compliance with the IMDG Code mandatory for ships on international voyages. The IMDG Code 41-22 (Amendment 41-22 entered force 1 January 2024) is the current mandatory version; its predecessor IMDG 40-20 remained in effect during the transitional period that closed 31 December 2023. For the full SOLAS/IMDG legal basis see SOLAS Chapter VII: Carriage of Dangerous Goods.

The UN Model Regulations (UN TDG, 23rd revised edition, 2023) are the upstream source for Class 6 criteria; the IMDG Code adopts them with mode-specific adjustments. The GHS (Globally Harmonised System of Classification and Labelling of Chemicals, 10th revised edition, 2023) aligns the acute toxicity categories with the UN Model Regulations categories, so GHS Category 1 (oral LD50 at or below 5 mg/kg) maps directly to IMDG PG I. Shippers who have GHS classification data for a new substance can derive the IMDG packing group directly from it without a separate IMDG classification exercise, provided the GHS test data conform to the endpoint requirements of the UN Manual of Tests and Criteria Part III.

Passenger ships carrying Class 6.1 cargo are subject to additional restrictions. IMDG Code 41-22 Chapter 7.1 lists entries that are prohibited on passenger ships (most PG I liquids, Hazard Zone A entries). A separate list covers entries permitted on passenger ships in limited quantities only. The IMDG segregation calculator flags passenger-ship prohibition status.

Limitations

The classification criteria in this article are drawn from IMDG Code 41-22 and the UN Model Regulations 23rd revised edition. Classification of a specific substance not on the IMDG dangerous goods list (an n.o.s. entry) requires measured toxicological data; literature values for LD50 and LC50 have inter-laboratory variability of one to two packing group steps in some cases. A substance with a published LD50 near a packing group boundary (e.g., oral LD50 of 49 mg/kg, near the PG I/II boundary at 50 mg/kg) should be classified PG I as the conservative choice unless the shipper holds a specific competent authority approval for PG II.

The Category A pathogen list in IMDG 41-22 is indicative, not exhaustive. Novel pathogens (new zoonoses, laboratory-created chimeric organisms) require evaluation against the Category A definition by the consignor; WHO technical guidance should be consulted. Following the WHO default to Category A for uncharacterised pathogens is the legally defensible position.

Division 6.2 regulations for sea transport are formally governed by the IMDG Code, but in practice the dominant compliance framework for most Category A and B movements is the ICAO Technical Instructions (air) and WHO guidance, because air is the dominant mode for time-sensitive infectious materials. Shippers who are expert in the air-transport regime but less experienced with the sea-transport framework should note that IMDG quantity limits per outer packaging and per vessel differ from ICAO limits; the IMDG Code permits larger volumes per outer package under certain conditions for sea transport.

MARPOL Annex III obligations overlay but do not substitute for IMDG Class 6.1 requirements. A Class 6.1 entry with a marine pollutant designation must meet both the IMDG packaging standard for its packing group and the MARPOL Annex III stowage requirements. The stowage requirement with the greater physical separation governs. For severe marine pollutants (SMP), MARPOL Annex III Regulation 6 imposes proximity-to-shell-plating restrictions that may in some vessel configurations require specific hold selection even when the IMDG stowage category would permit broader placement.

The IMDG 41-22 text is the authoritative source; this article is a reference guide and should not be used as a substitute for consulting the Code directly for a specific shipment.

See also

• IMDG Class 1: Explosives for the explosives framework and segregation principles that apply when Class 6.1 cyanides and Class 1 detonators share a vessel.
• IMDG Class 2: Gases for Division 2.3 Toxic Gases; several Hazard Zone A volatile entries are Class 2.3 rather than Class 6.1.
• IMDG Class 3: Flammable Liquids for the primary-hazard precedence rule that governs flammable toxic liquids.
• IMDG Class 4: Flammable Solids for the segregation between Class 4.2 pyrophoric materials and Class 6.1 toxic solids.
• IMDG Class 5: Oxidisers and Organic Peroxides for the cyanide-oxidiser segregation case and the MSC Flaminia pesticide fire.
• IMDG Class 8: Corrosive Substances for the Class 8 acid / cyanide contact hazard and the boundary classification of phenol and sulphuric acid.
• IMDG Class 9: Miscellaneous Dangerous Goods for dry ice (UN 1845, Class 9) used as a refrigerant in Division 6.2 cold-chain packages.
• IMDG Marking, Labelling and Placarding for skull-and-crossbones label dimensions, the biohazard trefoil label, the UN 3373 square mark, and the “Inhalation Hazard” supplementary text.
• SOLAS Chapter VII: Carriage of Dangerous Goods for the treaty basis of the IMDG Code’s mandatory status.
• MARPOL Annex III: Harmful Substances in Packaged Form for the marine pollutant marking, stowage, and SMP restrictions that overlay Class 6.1 entries.
• IMSBC Code for the parallel framework that governs some Class 6.1 substances (such as copper concentrate and cyanide-bearing tailings) when shipped in bulk rather than in packages.

Related calculators:

• IMDG packing group calculator: three-route oral/dermal/inhalation decision tree with volatility correction.
• IMDG dangerous goods finder: UN number to class, packing group, EmS, special provisions.
• IMDG segregation calculator: Class-versus-Class master table with passenger-ship flags.
• IMDG EmS lookup: fire and spillage schedule by UN number.
• IMDG limited quantity calculator: LQ exemption check.
• Container IMDG class lookup: container-level placard verification.
• IMDG tank container T-code calculator: T-code selection for Class 6.1 bulk-liquid tank containers.
• MARPOL Annex III marine pollutant lookup: P or PP status from the IMDG dangerous goods list.
• MARPOL Annex III packaged harmful substances calculator: stowage and marking checks for marine pollutant entries.
• IMDG packing group screening (flash point method): quick PG screen for flammable toxic liquids.