Aeration of cargo tanks on board an LNG carrier is the final step in preparing the vessel for its upcoming dry dock. In this process, the inert gas generator onboard is operated in dry air mode. Dry air with a low dew point of -45°C is introduced into the tank from the top, while the heavier inert gas is extracted from the bottom of the tank and released into the atmosphere. This process, known as the displacement of inert gas with dry air, ensures that the cargo tank is safe for manned entry and subsequent inspections or repairs. This operation can also be carried out while the vessel is at sea.
Exercise Overview:
- Initial Steps:
- The exercise begins with the prerequisites for performing aeration inside the tank.
- Portable multi-gas detectors and dew point meters are used to monitor the atmosphere during the process.
- The correct lineup of valves and connection of school pieces is carried out.
- The inert gas generator is prepared in dry air mode, ensuring that the power generators are operating efficiently.
- Assessment Process:
- The assessment begins when the dry air is introduced into the tank from the inert gas generator.
- Continuous monitoring is required, using various sampling points and gas detectors, to ensure that the air is effectively replacing the inert gas inside the tank.
- The user must also ensure that the tanks are within the prescribed pressure range.
- Completion Criteria:
- The exercise is considered complete when the following criteria are met:
- Oxygen content: Greater than 20% by volume
- Methane content: Less than 0.2% by volume
- Carbon dioxide content: Less than 0.5% by volume
- Carbon monoxide content: Less than 50 ppm
- The final evaluation occurs when the required dew point has been achieved, and the gas measurements confirm that the tank is ready for manned entry.
- Evaluation:
- The user will be evaluated on their ability to navigate the process, including responding to various remarks, alarms, and cautions throughout the exercise.
- Successful completion will depend on the user’s ability to follow the procedure efficiently and maintain safety standards throughout the exercise.
