ITOPF: Consequences of an ammonia spill in the marine environment
ITOPF has published a report highlighting the distinct nature of claims arising from ammonia spills compared to traditional oil spills, focusing on the unique impacts associated with ammonia’s toxicity and reactivity.
As explained in the “Fate, Behaviour and Potential Damage & Liabilities Arising From a Spill of Ammonia Into the Marine Environment” report, the Standard European Behaviour Classification (SEBC) categorises ammonia as a gas/dissolver (GD). During an incident, ammonia’s hazards will guide the first actions and emergency response, followed by specific actions linked to its behaviour classification. Some of ammonia’s key properties that influence its hazards, fate, and behaviour when spilled are listed in Table 1.
Table 1: Summary of key ammonia properties dictating its hazards, fate and behaviour
| Properties | Behaviour |
|---|---|
| Boiling Point | -33.3 °C (Ammonia is a gas at ambient conditions). |
| Liquid Specific Gravity (@ -33 °C) | 0.682 (Ammonia is less dense than water and will float if spilled on water). |
| Vapour Specific Gravity (@ -33 °C in presence of water vapour) | >1.0 (Ammonia vapour forms a dense white cloud above the ground/sea surface). |
| Vapour Specific Gravity (@ 20 °C) | 0.597 (Vapours at ambient conditions are lighter than air and will easily disperse in open or well-ventilated areas). |
| Solubility (@ 20 °C) | 529 kg/m³ (Ammonia is highly soluble in water). |
| Flammability Range | 15.5 – 27 (v/v) % (Ammonia is flammable only within this range). |
When spilled into the marine environment above the waterline, part of the liquid ammonia rapidly boils, releasing ammonia vapours. The ammonia that comes in contact with water will dissolve, with part of it also evaporating. For large surface spills, approximately 60% of the spilled volume would dissolve, with the remaining ammonia evaporating. This evaporation/dissolution ratio remains consistent when spilled underwater at shallow depths. However, if the spill occurs at depths less than 2 meters, the quantity of vapours produced and lost to the atmosphere may decrease to between 5% and 15% of the spill volume.
When spilled in large quantities, ammonia vapours will absorb moisture from the air, forming a dense white cloud of ammonium hydroxide (NH4OH) that can travel laterally for several hundred meters, particularly in high wind conditions. As ammonia vapour temperatures increase to ambient conditions, they become less dense than air and will dissipate into the atmosphere.
Ammonia that dissolves in seawater will form a corrosive, caustic solution of NH4OH, which is less dense than seawater and will form a layer on the water’s surface. The violent reaction between ammonia and water is exothermic, leading to a localized temperature increase on the water surface. The NH4OH concentrations and elevated temperatures will decrease with distance from the incident location. The rate at which the NH4OH plume disperses depends on the intensity of mixing in the aquatic environment, which is influenced by tidal currents and wind-induced wave action. A release in high-energy open water will disperse more rapidly than one in a sheltered port or inland waterway.
Hazards of ammonia spilled in the environment
Ammonia’s hazards can lead to direct impacts on health and safety, primarily through its toxicity and reactivity. The ecotoxicity of ammonia can cause damage over a more extended period compared to health and safety impacts.
Toxicity
Ammonia is toxic and corrosive, and it is hygroscopic, meaning it has a high affinity for water. When spilled into the atmosphere, it will react with water from nearby sources, including the human body, to form a caustic, corrosive solution (NH4OH) with a pH greater than 11.5. This makes the eyes, lungs, and skin particularly vulnerable due to their high moisture content. Exposure to high concentrations of ammonia can lead to permanent injury or death. The odour threshold for ammonia is around 20 ppm, while life-threatening health effects or death can occur with exposure to 3,800 ppm for five minutes. The low odour threshold allows for early detection of a release.
Ecotoxicity
Ammonia is considered non-persistent in the environment and does not accumulate in the tissues of organisms. However, it can be acutely toxic to aquatic organisms, affecting the central nervous system and leading to convulsions or death. Sublethal concentrations can reduce hatching success, growth rates, and cause pathologic changes in organ tissues. Additionally, the NH4OH plume resulting from ammonia reacting with water forms a caustic solution with a pH above 11, which can damage the tissues, exoskeletons, and shells of aquatic organisms. Ammonia’s breakdown into nitrates can lead to nutrient imbalances, causing algal blooms that result in hypoxic or anoxic conditions affecting marine organisms.
Ammonia exists in two forms in water: unionised ammonia (NH3) and ammonium (NH4+). NH3 is more toxic because it can cross the membranes of aquatic organisms more readily. The proportion of NH3 and NH4+ depends on pH, with higher pH and temperature favouring the more toxic NH3 form. Therefore, aquatic organisms in warmer, more alkaline waters are more vulnerable to ammonia toxicity.
Reactivity
Ammonia is highly reactive with various substances, including copper, brass, zinc, and other alloys. In the presence of moisture, it corrodes these materials, forming a greenish/blue colour. This reactivity could lead to hazards when incompatible materials or chemical cargoes are carried aboard ammonia-fuelled vessels, potentially causing violent or explosive reactions.
Flammability
Ammonia has a relatively narrow flammability range of 15.5 to 27 (v/v)%. Outside this range, the vapour mixture is not flammable. Additionally, ammonia requires a relatively high ignition energy to ignite, and without a catalyst or the presence of combustible materials, it is difficult to ignite. These properties reduce fire risks, especially in open air. If liquid ammonia were spilled and ignited, a pool fire could result, continuing until all the fuel is consumed. The height of the flames and spread of the pool depend on the rate of the spill and metocean conditions. If ammonia vapours come into contact with an ignition source, a flash fire may occur, typically short in duration. If a fire starts onboard, ammonia decomposes at temperatures above 450 °C, forming hydrogen, which is highly flammable.
Explosivity
Ammonia could undergo a boiling liquid expanding vapour explosion (BLEVE) under certain conditions. This type of explosion happens when a pressurized liquid tank ruptures after reaching a temperature above its boiling point, in ammonia’s case, -33 °C. This could occur if the tank temperature rises and gas release systems fail.
Temperature
The low temperature at which liquid ammonia can be stored can freeze tissue (both plant and animal) upon contact and cause materials to become brittle, losing their strength or functionality.
Key points for consideration
#1 Ammonia’s environmental impact and toxicity
Ammonia’s short residence time in the marine environment, combined with its high toxicity and reactivity, leads to significant differences in the types of claims compared to conventional persistent hydrocarbon oil spills. These claims would primarily arise from the incident’s unique characteristics and the necessary mitigation measures.
#2 Claims from clean-up and preventive measures
Claims resulting from ammonia-related incidents are expected to focus on clean-up measures and preventive actions. These may include source control, monitoring using expert modeling or sensors mounted on UAVs/ROVs, and potential bunker fuel removal. Traditional clean-up methods will not be applicable for ammonia spills, so claims from prolonged clean-up operations are unlikely.
#3 Personal injury and loss of life
Despite the lack of a long clean-up period, personal injury and loss of life claims could be significant. Ammonia exposure poses serious risks, including respiratory damage, and could potentially lead to death or life-altering injuries for crew members, passengers, nearby operators, and the public.
#4 Environmental damage and geographic confines
Environmental damage from ammonia spills is expected to be geographically limited in comparison to the widespread damage caused by oil spills. Post-spill studies may be conducted to assess the extent and severity of environmental damage, but restoration measures are likely to be minimal and localized.
#5 Property damage claims
Instead of traditional property damage claims, which typically involve cleaning and cosmetic repairs for oil spills, ammonia spills may lead to claims for corrosive damage or potential fire/explosion risks. These claims may require more costly and time-consuming structural repairs or replacements.
#6 Economic losses from ammonia spills
Economic loss claims may arise from the release of toxic ammonia vapors or a fire/explosion. These losses could include port closures, disruption costs, damage to property, local aquaculture losses from stock mortality, and losses related to fishing bans. Additionally, impacts on commercial water intakes and tourism may contribute to economic damages.
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