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Operational Hazards
There are various operational hazards when nitrogen is used onboard chemical tankers, the most common include tank structure damage due to pressure and exposure of crew to liquid or gas on deck, which also occurs due to pressure.
A chemical tanker underway. Photo - Jörgen Språng.
Tank Structure Damage due to Pressure
Tanks onboard chemical tankers are designed to withstand a specific amount of pressure as required by the IBC/BCH Code. A pressure vacuum relief valve is provided in order to prevent the tanks from being exposed to their designed pressure. Additionally, the second means of pressure and vacuum monitoring system is also available onboard as required by the regulations, and in most cases includes the use of pressure sensors.
When a cargo tank is exposed to a pressure greater than its designed pressure, the tank structure is damaged. This may lead to various disastrous consequences and a chain of events, such as fire, explosions, and even worse damage to life, ship, cargo, and the environment.
When clearing of the cargo lines by using a compressed gas and pipeline pig is carried out by the terminal, there is also the risk of over-pressurization of tanks. In order to avoid this, it is important to ensure that the tank vapour pressure is continuously monitored.
Exposing the Crew to Liquid or Gas on Deck
When the hatches to tanks are left open, in weather conditions where not much wind turbulence is present, if the nitrogen is vented through the tank hatch or tank cleaning hatch, an oxygen-deficient atmosphere may develop in the vicinity. Crew members should be knowledgeable enough to recognise such risks and ensure proper precautions are taken when walking on deck if such operations are underway.
During the padding of cargo tanks, exposure of personnel to liquids or gas may also occur, if the operation is not carried out in a controlled manner. When padding is carried out in a loaded tank, after completion of loading of a low pour point cargo, it may lead to the blockage of pipe vents and valves. Additionally, it may lead to spillages on deck which if undetected by crew members, can result in serious injury or even death.