Changes to the IMSBC Code: Ammonium Nitrate based Fertilizers

When pure ammonium nitrate is heated strongly (by a hot flame or similar) it will decompose, giving off various gases. The addition of some chemicals will make this worse, whereas other chemicals can reduce the effect.

Self-sustaining decomposition (SSD)

Certain fertilizers can exhibit self-sustaining decomposition (SSD) which means decomposition continues even when the heat source is removed. SSD is more likely when there is a higher concentration of ammonium nitrate in the fertilizer. The likelihood is also increased with higher concentrations of chlorides. Therefore, the 2022 edition of the IMSBC Code will place new limits on the ammonium nitrate and chloride concentration found in the cargo.

If SSD starts, firefighting techniques that aim to starve the fire of oxygen (for example smothering with CO₂ or by shutting down the hold ventilation) do not prevent spreading of the decomposition and heating. Cooling (e.g., with lots of water) is the only effective response.

The trough test

To assess the risk of SSD in a cargo, the trough test has been used as laid out in the IMSBC Code Appendix 2.

However, a limitation of the trough test is that a relatively small quantity (a few kilograms) of the fertilizer is tested. When compared to the very large quantities carried on a bulk carrier which can retain heat, the trough test sample can more readily lose heat to the atmosphere.

Changes to the IMSBC Code

Previous editions of the IMSBC Code had several entries for ammonium nitrate and ammonium nitrate based fertilizers (ANBF) to control the hazards that may arise during their transport.

The existing schedule for AMMONIUM NITRATE BASED FERTILIZER (non-hazardous) has been removed from the 2022 edition of the IMSBC Code, the carriage of which has been at the centre of some high-profile incidents, most famously the MV CHESHIRE, where apparent SSD took place due to a suspected constant heat source being applied to the cargo on passage. The ANBF on board the MV Cheshire had passed the trough test prior to loading.

For the 2022 edition, this schedule is now replaced by two new schedules:

AMMONIUM NITRATE BASED FERTILIZER – GROUP C: straight nitrogen-based fertilisers or compound fertilizers that are within specified composition limits.

AMMONIUM NITRATE BASED FERTILIZER MHB – GROUP B: classified as a material hazardous in bulk (MHB) but is not assigned a UN number.

**Note that Ammonium Nitrate (UN 1942) is a separate material and should not be confused with ANBF**

Shipper’s obligations

The shipper is responsible for the testing of the cargo to determine its properties. In this respect there are some changes to the way in which the cargoes are classified.

Any AMMONIUM NITRATE BASED FERTILIZER – GROUP C cargo must:

• be within the limits as specified in the schedule for certain straight nitrogen or a compound NPK/NK/NP fertilizer containing less than 2% chlorides and less than 20% ammonium nitrate
• be confirmed as not meeting any of the criteria for hazardous goods or materials hazardous in bulk in accordance with sections 9.2.2 and 9.2.3.
• have the shipper declare the ammonium nitrate and chloride content for compound fertilizers in accordance with section 4.2 of the Code.
• require a negative trough test (a positive test could show an increased danger of chemical decomposition when heated which continues when the heat is removed). This is in accordance with the UN manual of tests and criteria Part III, section 29. If this test finds the cargo to be Class 9, this schedule cannot apply and cannot be considered as a Group C cargo.

Any AMMONIUM NITRATE BASED FERTILIZER MHB – GROUP B cargo must:

• be within the content limits contained in the schedule for uniform mixtures of nitrogen with or without potash or phosphate.
• have the shipper declare the ammonium nitrate and the chloride content in accordance with section 4.2 of the Code.
• require a negative trough test (a positive test could show an increased danger of chemical decomposition when heated which continues when the heat is removed). This is in accordance with the UN manual of tests and criteria Part III, section 29. If this test finds the cargo to be Class 9, this schedule cannot apply and cannot be considered as a Group B (MHB) cargo.

Master’s vigilance

Masters should ensure that they are fully aware of the new schedules’ contents when these changes take effect.

Initially, it is important that the Master receives a full declaration in advance of loading, and that the declaration is scrutinised, not just simply accepted as received. Pay particular attention to the declared Bulk Cargo Shipping Name (BCSN): it should no longer be Ammonium Nitrate Based Fertilizers (Non-Hazardous). If declared as this, it is a possible indicator that the shipper is unaware of the Code changes and the new requirements.

Getting the declaration as early as possible allows for clarifications to be sought in good time, therefore preventing delays. The requirements on testing and cargo composition should also be confirmed as complete and correct.

The hold(s) must be cleaned to the satisfaction of all parties. Pay particular attention to the presence of previous cargo residues such as grain or other organic materials.

Despite being assigned Group C, the schedule for AMMONIUM NITRATE BASED FERTILIZER – GROUP C comes with the following warning:

“When this cargo is heated strongly, it will decompose and give off toxic gases with the risk of toxic fumes in the cargo hold, adjacent spaces and on deck……”

Crew should not relax whenever the cargo is on board just because this is a Group C cargo. Ensure heat sources (and potential heat sources) are removed from the holds, such as restricting hot work activities and isolating hold lighting.

Carriage risks

The ongoing risks are the same as for loading. Crew should monitor the cargo including the AMMONIUM NITRATE BASED FERTILIZER – GROUP C, and especially any MHB cargo on passage for some or all of the following:

• A drop in the oxygen level
• A rise in the carbon monoxide levels
• A rise in the methane levels
• Unusual smells from the hold
• Pressurisation within the hold (notable when the sampling port is opened)
• Any water dripping out of the sampling port when opened
• Small amounts of dust escaping from the sampling ports when opened.
• A rise in hold temperature, although temperature changes may well not be noted until chemical decomposition is well under way.

These can all be signs of chemical decomposition. Seek expert help and keep accurate records of the sampling and testing carried out on passage.

Other considerations.

Note that Group B cargoes should be individually listed on the vessel’s Document of Compliance (DoC) to allow carriage. Therefore, Members should check to see if their vessels’ DOCs require amending to include the new Group B cargo, AMMONIUM NITRATE BASED FERTILIZER MHB.

Remember the date!

The 2022 edition of the IMSBC Code takes effect on a voluntary basis from the 1 January 2023. It will come into force fully on the 1 December 2023.

As such, there is the possibility of seeing declarations and the use of BCSNs based on the old and new schedules, dependent on the region in which vessel is loading the cargo.

With thanks to CWA International for their assistance with this article.