The Global Center for Maritime Decarbonization (GCMD) has published a guide to inform interested parties of the dangers of ammonia when it is released at sea.
What happens when liquefied ammonia comes into contact with water?
As GCMD explains, release of liquefied ammonia (-33°C) below the waterline forms ammonium hydroxide (NH₄OH). Ammonium hydroxide solutions are lighter than water, floating on top and slowly diffusing into the water column. As aqueous ammonium hydroxide is colourless up to 30% concentration in water, visual observations of floating or dissolved plumes during spills are difficult. Factors affecting ammonia dissolution in water:
- Rate and extent of ammonia vaporisation
- Heat generated from ammonia dissolving in seawater
- Reactions of ammonium hydroxide with seawater impurities
- Solubility of ammonium hydroxide at the specific sea temperature Previous tests of ammonia release into water have shown that 55-60% of the ammonia dissolved in water.
Therefore, the vapour above remains pungent, stinging, and irritating. A dissolved ammonia plume in seawater can continuously release ammonia vapour depending on current and wind conditions.
“Thirty minutes of exposure to ammonia with a concentration of 1,600 parts per million can be lethal. Ammonia also forms ammonium hydroxide upon contact with water, and this can be corrosive. An accidental release of ammonia therefore poses challenges that are very different from those caused by an oil spill,” explains GCMD CEO, Prof Lynn Loo.
What happens when liquefied ammonia comes into contact with air?
NH₃ Release of liquefied ammonia (-33°C) causes rapid expansion into gas, creating a cooling effect in the surrounding area. This cooling effect condenses moisture in air, forming a dense, visible ammonia cloud. Some of the ammonia reacts with atmospheric moisture to form ammonium hydroxide (NH₄OH).
Weather conditions affecting dispersion:
Temperature:
- Ammonia boils at -33°C at atmospheric pressure. Temperatures greater than the boiling point of ammonia will cause it to vaporise.
- Cold ammonia vapour tends to stay close to the release level, which can increase the risk of exposure to humans.
- Ammonia is more volatile at warmer temperatures, leading to quicker dispersion in the atmosphere. This dispersion can increase the propensity of ammonia vapour reacting with other atmospheric pollutants, forming secondary pollutants, like PM2.5.
Humidity:
- In dry conditions, ammonia remains in its gaseous form, potentially increasing the risk of respiratory problems for exposed individuals.
- High humidity facilitates the formation of ammonium aerosols, contributing to air pollution.
Wind speed:
- In calm conditions, ammonia can accumulate in the release area, increasing local exposure risk.
- Strong winds can disperse ammonia quickly over a large area, reducing local concentrations but potentially affecting a wider region.
“When airborne, ammonia vaporises to form a dense and visible cloud that can pose immediate and significant health risks to those aboard vessels and in nearby communities,” said Prof Lynn Loo.
To remind, a recent study supported by the MIT Climate and Sustainability Consortium indicates that, under current legislation, switching the global fleet to ammonia fuel could cause up to 600,000 additional premature deaths each year.
Download GCMD Ammonia ERP here!
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Source: GCMD
