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Duong, P.A.; Ryu, B.R.; Song, M.K.; Nguyen, H.V.; Nam, D.; Kang, H. Hazards of the Ammonia Bunkering Process. Encyclopedia. Available online: (accessed on 25 June 2024).
Duong PA, Ryu BR, Song MK, Nguyen HV, Nam D, Kang H. Hazards of the Ammonia Bunkering Process. Encyclopedia. Available at: Accessed June 25, 2024.
Duong, Phan Anh, Bo Rim Ryu, Mi Kyoung Song, Hong Van Nguyen, Dong Nam, Hokeun Kang. "Hazards of the Ammonia Bunkering Process" Encyclopedia, (accessed June 25, 2024).
Duong, P.A., Ryu, B.R., Song, M.K., Nguyen, H.V., Nam, D., & Kang, H. (2023, May 29). Hazards of the Ammonia Bunkering Process. In Encyclopedia.
Duong, Phan Anh, et al. "Hazards of the Ammonia Bunkering Process." Encyclopedia. Web. 29 May, 2023.
Hazards of the Ammonia Bunkering Process

Ammonia is thought to be a potential alternative for hydrogen storage in the future, allowing for CO2-free energy systems. Ammonia’s beneficial characteristics with regard to hydrogen storage include its high volumetric hydrogen density, low storage pressure, and long-term stability. However, ammonia is characterized by toxicity, flammability, and corrosiveness, making safety a challenge compared to other alternative fuels. In specific circumstances, leakage from ammonia bunkering can cause risks, dispersion, and unsafe areas due to its flammability and toxicity. To avoid dispersion, fire, and explosion hazards on ships, it is crucial to conduct thorough risk analyses.

ammonia marine vessels risk assessment

1. General Information and Physical Properties of Ammonia

Ammonia is composed of one nitrogen and three hydrogen atoms (NH3). The calorific value of ammonia is 22.5 MJ/kg [1]. Ammonia is a colorless gas with a pungent odor [2] that consists of 17.6% hydrogen by weight [3]. The average unit price of ammonia is about USD 250–300 [4]. The contribution of the ammonia production process to the total GHG emissions of the world has been estimated as about 1% [5]. Ammonia is known to have a variety of advantageous properties as fuel, making it appealing as a possible medium for hydrogen storage. The volumetric hydrogen density of ammonia is 45% greater than that of liquid hydrogen. This suggests that there is more hydrogen in liquid ammonia than there is in an equivalent volume of liquid hydrogen [6]. Compared to ethanol, methanol, liquid hydrogen, and gasoline, ammonia is a hydrogen carrier with a higher volumetric hydrogen density [7]. The storage of ammonia is simpler than the storage of hydrogen, the other carbon-free fuel. The storage of ammonia takes place either at room temperature at 10 bars or at 33 °C at 1 bar [2]. The basic properties of ammonia are presented in Table 1.
Table 1. Basic physical properties of ammonia [8][9][10].
Special safety precautions are necessary for the storage of ammonia given its toxic and corrosive nature. Compared to commonly used fuels such as methanol and diesel, the hazard level of ammonia is over three times higher [11]. The event of an ammonia leak into water can be harmful to aquatic life, but its natural degradation process and the nitrogen cycle can facilitate the regeneration of aquatic life. It should be noted that ammonia has a very low odor threshold (0.037 to 1.0 ppm), making it detectable by most individuals even in small amounts that do not pose a health risk.
Gaseous ammonia has a lower density than air (1.225 kg/m3 compared to 0.769 kg/m3 at STP), and under normal atmospheric conditions, it can quickly dissipate into the atmosphere, lowering the risk of explosion or fire in the event of a leak. In addition, compared to hydrogen, which has an auto-ignition temperature of 520 °C, ammonia’s higher auto-ignition temperature (650 °C) means a lower risk of fire. Liquid ammonia is highly toxic and has a vapor pressure relative to toxicity at atmospheric temperature that is roughly three orders of magnitude higher than those of gasoline and methanol.

2. Ammonia Bunkering Methods

Bunkering is a vital operation that supplies fuel to power the machinery of a ship. Ammonia bunkering, similar to that of alternative fuels such as LNG, LPG, and hydrogen, can be categorized into four main types: ship-to-ship (STS), terminal-to-ship (TTS), truck-to-ship (T-TS), and ammonia portable tank (APT). The suitable ammonia bunkering method is selected after considering the amount of ammonia bunkering required, operational circumstances, and time constraints. Figure 1 illustrates the three most common ammonia bunkering methods.
Figure 1. Ammonia bunkering methods.
A comparison of the advantages and disadvantages of each ammonia bunkering method is shown below in Table 2.
Table 2. Comparison of ammonia bunkering methods.


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