Overcoming ammonia’s toxicity challenge: a technical perspective

by | 5th October 2023 | Research & Education, The Naval Architect

Home News Overcoming ammonia’s toxicity challenge: a technical perspective

Source: Korean Register

Both innovation and caution are key to overcoming the hazards of ammonia and enabling its use as a marine fuel, according to South Korean classification society KR

As the maritime industry pivots toward more environmentally friendly solutions, ammonia has emerged as a promising alternative fuel under the International Maritime Organization’s (IMO) Global Greenhouse Gas (GHG) Strategy. While ammonia’s carbon-neutral profile offers a clean option, it also introduces a new set of complications, notably its toxic nature.


Regulatory landscape and safety concerns

Traditionally, maritime fuel regulations primarily address flammability. With ammonia, toxicity becomes an equally crucial parameter. According to the existing International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code) and MARPOL Annex VI/18, the use of toxic substances like ammonia as a fuel is currently prohibited.

CHOI Wooseok, principal surveyor of the Korean Register (KR) Machinery Rule Development Team, states: “The maritime industry has not yet seen a toxic gas like ammonia being used as a primary fuel. Its toxicity makes it a subject of numerous safety and health regulations. This creates an entirely new set of challenges that the existing frameworks don’t currently address.”

The use of ammonia as a fuel presents the industry with two main questions: Can ammonia leaks be effectively controlled within the maritime environment? If control measures fail, how can we safeguard crew members from harmful exposure?


The unique maritime environment

The maritime industry can glean insights from ammonia’s use in land-based applications and its transport as cargo on ships. However, the maritime context presents several unique challenges that distinguish it from terrestrial applications where ammonia is used:

  • Limited Space: The confined space on a ship complicates immediate remedial action and limits escape routes and evacuation measures in case of a leak.
  • Lack of External Support: Unlike land-based scenarios, ships often cannot rely on quick external assistance for rapid incident management, placing the onus of safety solely on the onboard crew.
  • System Integration: During maritime operation, ammonia is not merely stored; it is actively transported to the engine room for combustion, increasing exposure risks for the crew.


Risk assessment: the first step

Before ammonia can be considered a viable maritime fuel, comprehensive risk assessments must be conducted. These should include identification of all potential leak points and failure scenarios. CHOI Wooseok advises that: “The safe adoption of ammonia as a maritime fuel is dependent on comprehensive risk assessments and multi-layered safety measures. These assessments should go beyond individual ship systems to include a systemic view of potential risks.”


Exposure limits and alarm systems

In the design phase for ammonia engines and fuel supply systems, manufacturers propose concepts that closely align with those for low flash-point fuels. This foundational design allows for the identification of all potential leakage scenarios, which must be addressed by implementing safety measures based on two key factors: concentration for toxicity and concentration for flammability, also known as the lower explosive limit (LEL).

To establish a safe environment onboard, it’s crucial to determine the permissible exposure limit (PEL), a concentration level that poses no health risks, considering both the frequency and duration of exposure. While there are established concentration reference values for various terrestrial conditions, these existing guidelines for toxic substances in industrial environments provide some direction for maritime applications. CHOI Wooseok notes: “”While land-based guidelines offer a starting point, we need marine-specific standards that consider the unique challenges of the sea.”

One value under consideration for maritime applications is the PEL-time weighted average (PEL-TWA) of 25 parts per million (ppm), as defined by the National Institute for Occupational Safety and Health (NIOSH). This is a concentration level deemed to have no serious health impacts after repeated exposure over an eight-hour period. Additionally, it’s crucial to identify the concentration that could cause serious health effects even during short-term exposure. A reasonable figure for this IDLH concentration is 300ppm as also defined by NIOSH.

So, how can a maritime environment ensure avoidance of long-term exposure to an ammonia concentration of 25ppm and short-term exposure to 300ppm? The straightforward solution involves the strategic placement of gas detectors in areas where hazardous gases may be present. These detectors would be configured to trigger an alarm system, calibrated to the identified limits, and emergency protocols can include gas treatment and shutdown systems set to trigger at predetermined concentrations, such as the suggested IDLH concentration of 300ppm.


Design safeguards

The design specifications can provide insights into various aspects of each potential leakage scenario, including the quantity of leaked material. To ensure the safety of seafarers, specific safety measures can be implemented for key sources of leakage, as detailed below:

  • Machinery Space: Following the International Code of Safety for Ships Using Gases or Other Low-flashpoint Fuels (IGF Code), the machinery space can be designed as a gas-safe area. Gas detectors within double-walled pipes would be set to sound an alarm at an ammonia concentration of 25ppm and to shut down fuel systems at 300ppm.
  • Fuel Preparation and Tank Connection Space: Gas detectors in these areas would trigger an alarm at an ammonia concentration of 25ppm. At 300ppm, they would shut down fuel systems and activate gas treatment systems, thereby controlling gas levels within the space as well as in the ventilation discharging to the open deck.
  • During Bunkering: Entry to the area surrounding the bunkering station would be restricted. Gas detectors near the bunkering manifold would sound an alarm at 25ppm, initiate gas treatment systems to control the concentration, and halt bunkering operations at 300ppm.
  • Purging of Fuel Pipes: The ammonia treatment systems should ensure that ammonia leakage into the air during fuel pipe purging is capped at 300ppm.

For normal operating conditions, existing gas treatment systems are capable of reducing ammonia gas concentrations to permissible exposure limits. However, emergency scenarios — such as a tank pressure relief valve opening due to fire or collision — could result in substantial leakage. To mitigate this risk, tanks should be safeguarded against impacts and fires. Additionally, robust gas treatment systems and comprehensive emergency response plans should be in place. Specifically including contingency to demarcate toxic zones around all sources of gas release. The gas-safe area should be spatially separated from these toxic zones to prevent the inflow of ammonia gas. The upper limit for defining an ammonia toxic zone should be set at 25ppm.


Regulatory developments

The IMO has accelerated the development of safety provisions for ammonia fuel, targeting completion by 2024 and the adoption of interim guidelines by 2025. These provisions are likely to form the basis for future regulations for ammonia cargo used as fuel under the IGC Code.

CHOI Wooseok emphasises the need for collaborative efforts: “Effective regulations will only emerge from a multi-disciplinary approach involving ammonia chemists, ship operators, builders, and safety experts.”


Beyond regulation: human factors and emergency planning

Besides technological and regulatory advances, human factors play a pivotal role in safety. Crew training, proper maintenance, and detailed operational manuals are paramount. In emergencies involving leaks, fires, or collisions, the ship must have a well-co-ordinated emergency response strategy.


Conclusion and future outlook

Ammonia’s potential as a marine fuel is significant but not without obstacles. Rigorous safety measures, guided by exhaustive risk assessments and informed by collaborative multi-disciplinary insights, are essential. As CHOI Wooseok concludes: “The era of ammonia-fuelled ships is closer than we might think, but reaching that point safely is a complex journey that requires both innovation and caution.”

As regulatory bodies, engineers, and safety experts continue to work together, the development of a comprehensive safety framework for ammonia as a marine fuel is in sight. The roadmap for achieving this lies in detailed risk assessments, safety-centric design modifications, stringent regulation, and proactive emergency planning and crew training.

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