Section 8.5: Fertilizer Cargoes (Ammonium Nitrate based, Corrosive Properties)

Fertilizers are essential agricultural inputs transported globally in vast quantities, often as solid bulk cargoes. While many fertilizers are relatively benign, some types, particularly those based on Ammonium Nitrate (AN), possess significant chemical hazards, including the potential for self-sustaining decomposition, fire, and even explosion under certain conditions. Additionally, many fertilizers are hygroscopic (absorb moisture) and can be corrosive to steel, or can cake and harden if not handled correctly. The IMSBC Code provides specific schedules and detailed guidance for various fertilizer cargoes, and strict adherence to these provisions is paramount for safety.

1. Common Types of Fertilizer Cargoes Carried in Bulk:

The term “fertilizer” covers a wide range of chemical compounds designed to enhance soil fertility. Common types carried in bulk include:

Ammonium Nitrate Based Fertilizers (ANBF):

Ammonium Nitrate (AN) itself (UN 1942): A strong oxidizing agent. Pure AN or AN with high concentrations is classified as a dangerous good (IMO Class 5.1 – Oxidizing substances) and has very strict carriage requirements, often prohibiting bulk carriage on general cargo ships or requiring specialized vessels. Its carriage in bulk is highly regulated and may be restricted.

Ammonium Nitrate Based Fertilizer UN 2067: This refers to mixtures containing ammonium nitrate with other inert materials or certain types of phosphate or potash, where the AN content and other factors meet specific criteria to be classified under this UN number (often still Class 5.1, or Class 9 – Miscellaneous dangerous goods, depending on composition and test results for self-sustaining decomposition).

Ammonium Nitrate Based Fertilizer UN 2071 (Type B): Typically NPK/NP/NK fertilizers containing ammonium nitrate with not more than 70% AN and not more than 0.4% total combustible/organic material, or not more than 45% AN with unrestricted combustible material. These are usually Group C under IMSBC, provided they show no self-sustaining decomposition properties when tested.

Calcium Ammonium Nitrate (CAN): A mixture of ammonium nitrate and calcium carbonate/dolomite. Generally considered less hazardous than pure AN but still requires careful handling.

Urea: A common nitrogenous fertilizer. Generally a Group C cargo, but can be hygroscopic, may emit ammonia fumes if wet or contaminated, and can be corrosive to some metals.

Sulphate of Ammonia (Ammonium Sulphate): Group C. Can be corrosive when wet.

Potash (Potassium Chloride / Muriate of Potash – MOP): Group C. Hygroscopic, can cake, and is corrosive to steel when wet.

Superphosphate (Single – SSP, Triple – TSP): Group C. Can be dusty and may have some corrosive properties, especially if acidic.

Diammonium Phosphate (DAP) / Monoammonium Phosphate (MAP): Group C. Can emit ammonia fumes, especially if wet or warm. Can be corrosive.

NPK/NP/NK Compound Fertilizers: Mixtures containing Nitrogen (N), Phosphorus (P), and/or Potassium (K) in various proportions. Their properties and IMSBC Code classification depend heavily on their exact composition, particularly the presence and concentration of ammonium nitrate.

2. IMSBC Code Classification and Key Considerations for Fertilizers:

The IMSBC Code has numerous individual schedules for different types of fertilizers. It is essential to identify the correct Bulk Cargo Shipping Name (BCSN) and consult the specific schedule.

Key Classifications:

Group A: Some fertilizers, if they have a high moisture content and suitable particle size, could theoretically be prone to liquefaction, though this is less common than for mineral ores. The specific schedule should be checked.

Group B (MHB – Materials Hazardous only in Bulk): This is where most hazardous fertilizers fall, particularly ANBFs. Hazards include:

Self-sustaining decomposition (SSD): Some ANBFs, if heated sufficiently (e.g., by an external fire, welding, or contamination with heat-generating substances), can undergo SSD. This is an exothermic decomposition that, once initiated, can propagate through the mass of the cargo even if the initial heat source is removed. It produces large volumes of toxic gases (oxides of nitrogen, ammonia) and heat.

Oxidizing properties (for AN-rich types): Can intensify fires in other combustible materials.

Fire/Explosion risk (especially for high AN content): While pure AN requires specific conditions to detonate, contamination or involvement in a large fire can lead to explosion risks. The MV Grandcamp (Texas City, 1947) and MV Tianjin Dongjiang (Tianjin, 2015) explosions involved ammonium nitrate, highlighting its devastating potential.

Group C: Many common fertilizers (e.g., Urea, Potash, Superphosphate, DAP/MAP, and some NPKs with low or no AN content and no SSD properties) are Group C. Their main issues are usually hygroscopicity, caking, dustiness, and corrosivity.

Critical Information from Shipper: For fertilizers, especially ANBFs, the shipper’s declaration is vital and must include:

Correct BCSN and UN Number (if applicable).

IMO Class (if applicable).

Composition (especially % of Ammonium Nitrate, % of combustible material, % of chloride).

Results of tests for self-sustaining decomposition (e.g., Trough Test – UN N.4, or other tests specified in the ANBF schedules). A fertilizer that shows SSD properties is highly hazardous.

Any other specific hazards and precautions.

3. Key Hazards and Precautions Associated with Fertilizer Cargoes:

A. Self-Sustaining Decomposition (SSD) and Fire/Explosion (Primarily ANBFs):

Mechanism of SSD: Initiated by heating. The decomposition reaction itself generates more heat, causing it to spread. Produces voluminous toxic fumes (brown/yellowish NOx, white ammonia).

Initiation Sources: External fires, welding/cutting operations near cargo, contact with hot surfaces (steam pipes, heated bulkheads), contamination with substances that can react and generate heat (e.g., acids, some metals, organic materials).

Prevention (Critical):

Strict “No Smoking” and Hot Work Prohibitions: Near holds containing ANBFs. Hot work permits must be meticulously managed, and areas must be certified gas-free and free of cargo residues.

Avoid Contamination: Ensure holds are scrupulously clean and free from any combustible materials, oils, grease, acids, alkalis, chlorides (from previous cargoes like salt or potash if not thoroughly cleaned), sulphur, or finely divided metals.

Temperature Control: Do not load ANBFs if their temperature is elevated (e.g., >55°C, or as specified). Avoid stowage near heated bunker tanks or engine room bulkheads unless properly insulated and temperature-monitored.

Electrical Equipment: Ensure electrical fittings in or near cargo spaces are suitable for the environment and well-maintained to prevent sparks.

Emergency Response for SSD/Fire:

Boundary Cooling: The primary response is often intensive cooling of the affected hold boundaries with water to try and halt the spread of decomposition.

Water Application to Cargo (with extreme caution): For some ANBFs, the IMSBC Code may advise application of large quantities of water directly onto the seat of decomposition/fire. However, this can also generate more steam and potentially spread contamination if not done correctly. The specific IMSBC Code schedule for the cargo must be consulted for emergency procedures. For high AN content fertilizers, water can sometimes worsen the situation or create run-off pollution.

Use of Fixed CO₂ is generally NOT effective for SSD of ANBFs, as the decomposition can be self-sustaining even without external oxygen. CO₂ may also react with AN at high temperatures.

SCBAs are essential for any personnel involved in fire-fighting or approaching affected areas due to toxic fumes.

Prepare for potential evacuation if the situation cannot be controlled.

B. Oxidizing Properties (AN-rich Fertilizers):

These will not burn themselves but will readily yield oxygen to support and intensify the combustion of other materials.

Segregation: Must be segregated from combustible materials, flammable liquids/gases, acids, and other incompatible substances as per IMSBC and IMDG Code requirements if applicable.

C. Corrosivity:

Many fertilizers (e.g., Ammonium Sulphate, Potash, Superphosphate, DAP/MAP, and ANBFs if wet) are corrosive to steel, especially in the presence of moisture.

Prevention:

Holds must be clean and dry.

Good quality, intact paint coatings on hold surfaces provide protection.

Minimize water ingress during voyage (weathertight hatches).

Thoroughly wash holds after discharging corrosive fertilizers to remove residues.

Some fertilizers can also corrode other metals like zinc (galvanizing) or aluminum.

D. Hygroscopicity and Caking:

Many fertilizers (e.g., Urea, Potash, ANBFs, CAN) are hygroscopic, meaning they readily absorb moisture from the atmosphere.

Consequences:

Caking/Hardening: Absorbed moisture can cause the fertilizer particles to bind together, forming hard cakes or even a solid mass in the hold. This can make discharge extremely difficult and costly (requiring jackhammers or specialized equipment).

Quality Degradation: Excess moisture can reduce the fertilizer’s effectiveness or alter its physical properties.

Increased Corrosivity: Wet fertilizer is often more corrosive.

Prevention:

Load only dry cargo.

Ensure holds are dry before loading.

Maintain weathertight integrity of hatch covers during the voyage.

Ventilation: This is complex for hygroscopic cargoes. Generally, ventilation should only be carried out if the dew point of the ambient air is lower than the dew point of the air in the hold (or the temperature of the cargo, if that’s the controlling factor for condensation). Introducing moist air can worsen caking. Often, keeping holds sealed is the best approach unless specific conditions warrant ventilation. The IMSBC Code schedule for the specific fertilizer should provide guidance.

E. Dust:

Many fertilizers are prilled, granulated, or crystalline, but handling can still generate dust.

Health Hazard: Inhalation of fertilizer dust can cause respiratory irritation. Some fertilizer dusts can be toxic or allergenic. PPE (dust masks/respirators, goggles) is essential.

Nuisance/Environmental: Dust can spread to accommodation and surrounding areas.

Explosion Risk (Rare for most fertilizers, but possible for very fine organic dusts or if mixed with other combustible dusts).

F. Ammonia Emission (e.g., from Urea, DAP, MAP, decomposing ANBFs):

Ammonia (NH₃) is a pungent, irritant, and toxic gas.

Can be released if these fertilizers become wet, are stored at high temperatures, or are contaminated.

Precautions: Adequate ventilation if ammonia odor is detected. Avoid entry into spaces with high ammonia concentrations without SCBA.

G. Shifting:

While not as prone to catastrophic shifts as grain or some mineral fines, granulated or prilled fertilizers can still shift if not properly trimmed, especially if the angle of repose is low.

Trimming reasonably level as per IMSBC Code Section 5 is generally required.

4. Pre-Loading Preparations:

Hold Cleanliness: CRITICAL. Holds must be scrupulously clean, dry, and free of any residues from previous cargoes, especially combustible materials, oils, grease, acids, alkalis, chlorides, sulphur, or metals that could react with or contaminate the fertilizer. For ANBFs, this is a paramount safety requirement.

Bilge Wells: Clean, dry, strum boxes in place, suctions tested. Ensure bilge wells are protected from cargo ingress but can still drain any minor condensation.

IMSBC Code and Shipper’s Declaration: Obtain and meticulously review all documentation, especially for ANBFs (UN number, composition, SSD test results).

Stowage Plan: Consider segregation requirements (from bunkers, other cargoes), avoidance of heat sources, and even distribution of weight.

Fire-Fighting Equipment: Ensure all FFA is ready. For ANBFs, confirm availability of copious amounts of water for boundary cooling/direct application if permitted by the Code schedule. SCBAs must be ready.

No Hot Work: Ensure no hot work is planned in or near cargo spaces during loading or voyage without extreme precautions and formal permission.

5. Loading Operations:

No Smoking/Naked Lights: Strict enforcement.

Avoid Contamination: Ensure loading equipment is clean. Prevent foreign objects from entering the cargo.

Temperature of Cargo: Do not load fertilizers if they are excessively hot.

Weather: Avoid loading hygroscopic fertilizers during rain. If rain occurs, ensure hatch covers are closed immediately.

Dust Control: Implement measures to minimize dust.

Trimming: Trim as required by the IMSBC Code.

Segregation: Maintain required segregation distances if loading different types of fertilizers or other cargoes.

6. Precautions During Voyage:

Temperature Monitoring (for ANBFs or those prone to self-heating): If required by the IMSBC Code schedule, monitor cargo temperatures regularly.

Ventilation: Follow specific IMSBC Code guidance for the fertilizer being carried. Often, for hygroscopic fertilizers, holds are kept sealed to prevent moisture ingress unless specific conditions (dew point comparison) favor ventilation. For ANBFs, ventilation requirements vary greatly depending on the type and potential for gas emission or decomposition; some may require surface ventilation, others no ventilation. Always refer to the specific schedule.

Regular Inspections (where safe and possible): Check for any signs of caking, wetness, or unusual odors from hold vents.

Weathertightness: Ensure hatch covers remain weathertight.

7. Discharge Operations:

Dust Control: Manage dust.

Avoid Damage to Ship: Supervise grab operations to prevent damage, as caked fertilizer can be hard to dig out.

Hold Cleaning After Discharge: Thoroughly clean holds after discharging fertilizers, especially corrosive types or ANBFs, to remove all residues. Washings must be disposed of according to MARPOL Annex V, considering that fertilizer residues are often HME or contain HME cleaning agents.

8. Master’s Key Responsibilities Specific to Fertilizers:

Absolute Vigilance on ANBFs: Understand the specific hazards (SSD, fire, explosion) and ensure all precautions related to cleanliness, contamination avoidance, and temperature control are rigorously followed.

Correct Identification and IMSBC Code Schedule Application: Ensure the cargo is correctly identified by its BCSN and that the requirements of the correct individual schedule are applied. There are many different fertilizer schedules.

Strict Control over Hot Work and Ignition Sources.

Understanding Ventilation Requirements: This can be complex and cargo-specific.

Emergency Preparedness for ANBF Incidents: Ensure the crew is drilled on responding to SSD or fire involving ANBFs, as per Code guidance (which may differ from typical shipboard fire-fighting).

The carriage of fertilizer cargoes, while essential for global agriculture, demands a high degree of caution, knowledge, and adherence to the IMSBC Code, particularly for ammonium nitrate based varieties. The potential for severe incidents makes it imperative for the Master and crew to be fully conversant with the specific risks and the prescribed safety measures for the particular type of fertilizer being transported.