LEE Hongku, KIM Jongmin
KR System Safety Research Team

  1. Introduction

Recently, there has been active progress in utilizing ammonia as an eco-friendly alternative fuel for ships. However, regulations and procedures for safely performing ship-to-ship (STS) ammonia bunkering are not yet fully established. Furthermore, as the ordering and construction of ammonia carriers and ammonia-fueled propulsion ships continue, there will be a need for safe bunkering procedures for these vessels. In particular, since ammonia is highly toxic and can cause serious risks to human life and the environment if leaked, thorough safety management is essential. For safety management, it is necessary to designate and control safety management zones.

The safety management zone is established based on the dispersion distance corresponding to a specific concentration determined through leak analysis. However, there is currently limited data on dispersion distance calculations for potential ammonia leakage incidents during ship to ship bunkering operations. Existing studies indicate that ammonia shows longer dispersion distances compared to other alternative fuels such as LNG, in some cases even exceeding the full length of the vessel. Therefore, in this paper, we assumed a domestic port where future ship to ship ammonia bunkering operations are expected to take place and calculated the dispersion distance of ammonia leakage accidents using the commercial software PHAST. Based on this, we estimated the approximate dispersion distances that may occur during bunkering related leakage scenarios. In addition, we reviewed relevant regulations on personal protective equipment (PPE) essential for safe operations during leakage accidents and proposed appropriate protective equipment.

  2. Dispersion Distance Analysis

During ship-to-ship bunkering operations, leakage accidents were assumed under two scenarios to calculate the dispersion distance.

• Case 1: Leakage begins due to damage at the hose connection (e.g., gasket, fitting), and continues until the emergency shutdown (ESD) valve is activated, which is assumed to take 1 minute.
• Case 2: Leakage occurs due to damage to the hose itself, with the same assumption that ESD activation requires 1 minute.

In both scenarios, it is further assumed that residual ammonia inside the hose continues to leak even after ESD activation. The size of the damage to the hose and fittings was referenced from the SGMF LNG bunkering guidelines. ¹⁾

Table 1 shows the sizes of the leakage openings. The supplying and receiving vessels involved in the bunkering operation were not specified, and the bunkering specifications were referenced from other research institute reports and academic papers. ²⁾

Table 1. size of leak opening

The meteorological conditions were based on the 2024 weather data for the relevant area, applying an annual average temperature of 15.5 ℃, wind speed of 2.1 m/s, relative humidity of 67%, and cloud cover of 50%. For the calculation of ammonia dispersion distance, the endpoint concentrations were set as 300 ppm, corresponding to the workplace acute health hazard concentration (IDLH) defined by the U.S. National Institute for Occupational Safety and Health (NIOSH), and 1,600ppm, corresponding to the acute exposure guideline level (AEGL-3) established by the U.S. Environmental Protection Agency (EPA).

The calculated dispersion distances ranged from 73 to 259 m at 1,600 ppm and from 145 to 920 m at 300 ppm. From a conservative perspective, the distances can be considered as approximately 259 m at 1,600 ppm and 920 m at 300 ppm. Under the assumed conditions, the analysis indicates that the dispersion distance of an ammonia leak during ship to ship bunkering approximately exceeds the overall length (L) of the vessel. This implies that all personnel on board could potentially be within the affected area. Furthermore, the results suggest that the safety distance required to prevent toxic exposure to ammonia is significantly greater than the safety distances for flammable fuels such as LNG, which primarily focus on explosion and fire prevention. Therefore, a higher level of caution is required along the entire length of the vessel during ammonia bunkering operations.

  3. Response Measures for Leakage: Personal Protective Equipment

As reviewed above, the dispersion distance of ammonia leakage can extend across the entire length of a vessel. Therefore, workers handling ammonia must be equipped with appropriate personal protective equipment (PPE). Regulations and guidelines on PPE required for ammonia handling and leakage response have been examined from both domestic and international organizations, including IMO/IBC Code, Domestic law, Classification Society, and SGMF. The findings are summarized in the following table 2.

Table 2. Domestic and International Regulations for PPE

Based on the review of the above regulations and the current use of PPE during actual ammonia bunkering operations, the PPE requirements for ammonia bunkering personnel are proposed according to the type of bunkering activity, as summarized in Table 3 below.

  4. Conclusion

In this study, ammonia dispersion distances were analyzed under the assumption of a leakage accident during ship to ship (STS) ammonia bunkering operations, and corresponding response measures were examined. The analysis showed that the dispersion range of ammonia could exceed the overall length of the vessel, indicating that the impact may not be limited to the bunkering work area but could extend throughout the entire ship. This highlights the need for a different safety distance approach compared to flammable fuels such as LNG, given the toxic characteristics of ammonia.

In addition, a review of domestic and international regulations, along with current on site practices, revealed that personal protective equipment (PPE) for ammonia bunkering personnel should be applied differentially depending on the type of task and associated risk level. In particular, higher level protective equipment - such as supplied air respirators or self contained breathing apparatus - was identified as essential for responding to leakage incidents.

For the future implementation of ammonia bunkering, it will be necessary to conduct dispersion analyses that reflect actual port conditions and weather factors, establish safety management zones tailored to the properties of ammonia, and develop detailed PPE requirements and emergency response procedures for each operational stage.