Published: 1 October 2018

Despite being categorised as ‘non-hazardous’, incidents involving the carriage of ammonium nitrate-based fertilizer (non-hazardous) (anbf(nh)) on board PURPLE BEACH (2015) and CHESHIRE (2017) have highlighted the potential hazards of this cargo. the cargo is liable to decomposition which is where toxic gases containing ammonia and nitrogen are created and the cargo may ultimately explode.

In response to these incidents, the International Maritime Organisation (IMO) issued circular CCC.1/Circ.4 in September 2017. This highlighted some of the key issues and the precautions to be taken when carrying such cargoes.

The circular notes that even for ANBF(nh) cargoes classified as Group C (non-hazardous), the relevant precautions in appendix 1 of the International Maritime Solid Bulk Cargoes (IMSBC) Code should be applied carefully. It also sets out a number of specific actions that should be taken in the event of cargo decomposition; including opening cargo hatches as soon as decomposition is found in order to prevent the buildup of pressure and to help cool the cargo, thereby stopping or slowing down the process of decomposition.

The circular also draws attention to the information available in the guidance document issued by Fertilizers Europe Guidance advising on the sea transport of ANBF

The final casualty investigation report into the CHESHIRE accident was published by the Isle of Man Ship Registry

The report highlights a number of issues and gives advice on precautions to take when carrying ANBF(nh):

  • Although the ANBF(nh) cargo on CHESHIRE was categorised as ‘non-hazardous’ and ‘non-self-sustaining’, the cargo still experienced a catastrophic thermal decomposition. This

ultimately led to the ship being declared a constructive total loss despite various efforts to respond to the situation.

  • Regular monitoring of ANBF(nh) cargoes, including the review of relevant trend data, is crucial throughout a voyage to detect possible signs of initial decomposition. This should include monitoring for:

– any significant abnormal fluctuations in temperature

– the presence of water, as ANBF(nh) cargoes normally contain very little moisture when manufactured (<0.5%)

– reduced oxygen content by volume compared to other holds, as oxygen is displaced by the gases generated during decomposition

– a foul smell (possibly due to oxides of nitrogen and ammonia generated as part of the chemical reaction)

  • Members’ SMS should provide readily available safety information for the carriage of ANBF(nh) cargoes, including:

– Information on warning signs of possible decomposition (such as oxygen depletion, water accumulations, visible vapours, temperature increases and a smell of ammonia – discernible and detectable at low concentrations)

– What steps should be taken to ensure an effective arrest of any decomposition process (including maximum ventilation, hotspot location identification and specifically directed cooling)

  • It is essential to contact the cargo manufacturer as soon as there is any suspicion that cargo decomposition is in progress. The manufacturer should have full knowledge of the cargo’s chemical composition and how it will be expected to behave and can therefore provide the best advice, based on feedback and experience.
  • The decomposition process may result in the formation of a ‘matrix’ at the reaction front which can assist the decomposition process by retaining heat energy needed for the reaction to continue; therefore steps should be taken, as far as possible, to prevent the formation of such a matrix.
  • The decomposition process may lead to the emission of a toxic gas cloud. Human exposure to any affected areas during an incident should therefore be avoided. If crew are required to operate in such areas then Self-Contained Breathing Apparatus (SCBA) and appropriate protective clothing (PPE) must be worn during such periods of exposure.
  • Any decomposition products drawn into the engine room ventilation system may lead to fouling of the turbocharger filters causing air starvation and exhaust temperature imbalance, which could ultimately lead to the engines tripping.

– All efforts should be made to manoeuvre the ship safely in order to minimise, as far as possible, the exposure to the toxic gases and decomposition products

– Additional counter measures may be required to prevent the ingress of the toxic gases into accommodation spaces through gas tight openings

– Should the turbocharger filters become fouled, these will need to be cleaned manually or removed by crew wearing suitable PPE/SCBAs

  • Although not a statutory requirement, operators of ships carrying ANBF(nh) cargoes may wish to consider the carriage of additional specialist equipment to assist with the detection of and response to any decomposition event. Such equipment could include, inter alia:

– thermal detection equipment, reflected infra-red thermometers, or infra-red camera/analysis equipment

– high pressure water lances (commonly referred to as ‘Victor Lances’)

– additional SCBA

As for all hazardous situations, prevention is the best cure. As noted in the IMO circular, awareness of the decomposition process to allow its identification at the earliest possible stage is key. Although by no means a simple process, a decomposition event can be brought under control if tackled quickly and appropriately. Regular monitoring of the cargo throughout the voyage is therefore crucial to detect the beginning of a possible decomposition and allow early action to be taken to prevent the situation deteriorating.