Pump rooms on tankers are required to be mechanically ventilated. The ventilation system must be of the exhaust type and designed to prevent the accumulation of flammable vapors. To ensure this, the system needs to have a minimum capacity of 20 air changes per hour based on the gross volume of the space. The exhaust fans must be a non-sparking type, and the air ducts should be arranged to provide effective ventilation throughout the entire space. The discharge from the exhaust fans must be led to a safe location on the open deck.

Cargo Tank Ventilation

Cargo tanks are ventilated to make them "gas free," which means removing flammable or toxic vapors. This can be achieved using portable fans or blowers. These fans must be constructed to prevent incendiary sparking, for example, if the impeller were to touch the casing. The fans must also have sufficient capacity and penetration to quickly gas-free the entire tank atmosphere.

Alternatively, on tankers equipped with an Inert Gas System (IGS), the system itself can be used for ventilation. To do this, the connection from the scrubber tower is closed, an air inlet from the atmosphere is opened, and the IGS blowers are started. This process effectively ventilates the cargo tanks by drawing in fresh air and pushing out the existing atmosphere.

The primary problem with carrying LNG is maintaining its extremely low temperature of approximately -160°C. Despite the insulated tanks, a small amount of the LNG will inevitably vaporize, a phenomenon known as "boil-off." This boil-off must be managed, as it poses a safety risk and represents a loss of cargo. The process of managing this boil-off is critical and consumes a significant amount of power if the gas is to be reliquefied.

Several methods are used to handle boil-off gas on board LNG carriers:

• Reliquefaction: Heavy-duty compressors are used to compress the boil-off gas, converting it back into a liquid state and returning it to the cargo tanks.
• Mixed Refrigeration: A refrigeration process that uses a mixture of different refrigerants to cool and reliquefy the boil-off gas.
• Expander Cycle: A method that uses an expander to cool the boil-off gas, causing it to reliquefy.
• Using it as Fuel: The boil-off gas can be used as fuel for the ship's engines, either completely or as a partial fuel in a dual-fuel combustion system. This turns a potential problem into a source of power for the vessel.