The daily operation of oil tankers involved many hazards. There are many check items that should be complied with to ensure a safe working atmosphere. The Chief Officer shall manage cargo oil and carry out related operations.
Water And Cargo Oil Measurement
As following the Charterer’s instructions, measure water contained in the cargo and the quantity of cargo oil in each tank during voyage in calm waters.
Every day, during the loaded passage, the Levels (Ullage) and Temperatures (in case of heated cargo) of cargo shall be measured and recorded. Any unexpected change in such levels shall be reported. This check is to monitor for any increase or decrease and inflow of oil into other tanks due to valve leakage.
When evolution of cargo vapors is significant in case of gassy / volatile cargoes, confirm complete maintaining of closure of openings. and normal operation of breather valves, and spray water over the deck for cooling as required to prevent vapor loss.
Topping Up Operation : On the contrary, when the pressure in tanks in negative to such the air, put Inert Gas into tanks to keep a proper internal pressure.
Throughout the loaded passage, until the discharge port, keep continuous record monitoring of the fixed IGS pressure recorder, in addition to wheel house record book. This record book can provide some pressure control and behavior estimation for further management of the cargo vapor control. Ambient atmospheric temperature and sea water temperature variations can differ.
Cargo Oil Heating
Heat tanks properly according to the Charterer’s instructions, if any.
The Chief Officer is responsible for monitoring the temperatures and will liaise with the Chief Engineer for the operation of the cargo heating system.
The Chief Engineer is responsible for the correct operation and adjustment / maintenance of the cargo heating system. The boiler cascade tank shall be monitored regularly and alarms where fitted should be in good operational condition.
Chief Engineer also should consider extra Fuel Consumption for heating cargo.
Cargo heating Plan
1). Prepare a suitable heating plan & maintain/monitor heating record.
2). Consider the following factors when preparing the heating plan :
Adjacent Cargo / Ballast tank temperatures and condition (loaded/empty).
Ambient air temperature, sea condition & spray on deck, causing cooling effect on heated cargoes.
(3). Condition & technical limitations of steam coils / lines with respect to :
Steam trap blockages.
Limitation of machinery & equipment design.
Selection of first discharging tanks.
(4). Adjustment of steam valves based on daily cargo tank temperature record.
(5). Steam Main Line Pressure and the number / degree of opening of steam valve to cargo tanks (recorded in “Heating Record”).
(6) Additionally when high cargo temperatures are to be attained:
i. Design & structural limitations and capability of cargo steam heating system.
ii. In case of vapor segregation, rapid rise in temperature could lead to high I.G/vapor pressure build up inside tanks (Limitation – IN PORT).
Inform the company / operator promptly in case of such temperature discrepancy.
Line Pressure Test
Conduct a pressure test of cargo lines, COW lines and cargo valves using cargo oil before entering port to check for leak.
Double Hull (D/H) Operation / Oil Tank (COT) Monitring Records.
Monitoring of Ballast tanks for Hydro carbon / H2S and Leakage / Ingress of Oil is to be carried out after loading- for three continuous days and thereafter, weekly.
Tank Explosion Countermeasures
An explosion in a cargo tank is one of the most serious situations that any Emergency Organisation can be called upon to fight. In the loaded condition there will probably be little that the Emergency Party can achieve, and the saving of life is of paramount importance.
In the ballast condition there may be a greater chance of taking some effective action. The following points must be considered by the Master following such an explosion :
Possible isolation of the resultant fire by the Emergency Party putting up a “water wall” around the periphery of the fire.
Arresting the transfer of heat into adjacent accommodation spaces by spraying the poop front bulkheads etc.
Bringing foam-making equipment into action.
Evacuation of non-essential personnel.
Adjusting the vessel’s course and speed as necessary to minimise fire spread and reduce further structural damage.
The release of the fixed gas fire extinguishing medium into the cargo pumproom to inert that space in order to prevent the spread of fire from the cargo tank or hold.
Before releasing the fixed gas extinguishing system in the pumproom the Master must be satisfied that there is no chance of an explosion in the pumproom (an explosimeter reading must not exceed 40% LEL). It must be remembered that electrostatic charge separation may occur at the CO2 nozzles. This produces a possible source of ignition in the form of charged frozen particles of C02 in the pumproom.
Any possible action is to be dictated by circumstances (the ability to provide water on deck etc) but it is the duty of the Master and the Emergency Organisation to do all in their power to combat the situation, even after the non-essential personnel have left the ship.
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