Procedure Onboard Chemical Tankers

The use of Nitrogen onboard chemical tankers requires a very strict procedure that must be followed with extreme precision. The lack of precision during such operations will result in casualty and or damages to the ship and cargo.

It is therefore extremely important to have a prior meeting with all personnel involved in the operation to ensure proper knowledge and understanding of these procedures and of the way the operation will be carried out. The following must be discussed with the terminal, and all crew members and personnel involved should be aware:

• The number of tanks that will require purging or padding.
• The quantity of the gas required.
• The maximum flow rate to be used by the terminal.
• The nitrogen supply arrangement ashore.
• The pipe diameter and pressure.

Additionally, prior to the commencement of the operation, the following paperwork must be completed:

• Ship to Shore Safety Checklist.
• Ship to Shore Agreement.
• Cargo Operation Plan.

A toolbox meeting should be carried out in addition to the meeting with the terminal, in order to ensure that all the ship’s personnel involved in the operation are well aware of the agreed procedure to be followed for the intended operations and the use of nitrogen. The following steps will then be followed:

• An inspection and check of the conditions of the PV Valves will be carried out.
• The piping systems are ensured to be lined up correctly and the valve positions are checked.
• If entry into a cargo tank for inspection is required, the enclosed space entry procedure must be strictly followed.
• The nitrogen purging line must be confirmed as isolated by blanking or other permanent means. (It is important to note, that isolation by means of closing the valves is not considered adequate and therefore, does not meet the requirements). The loading master must be advised accordingly.
• No personnel or loose material should be left inside the cargo tank. A roll call may be carried out in order to do a proper headcount.
• A Lock-Out or Tag Out system is used to identify the inerted tanks and the tanks inspected and ready for inerting.
• Communications with the terminal are properly established and used at all times.
• Warning placards are hung at various locations such as, at the hatch, on the manifold valve, and near the Pressure Vacuum (PV) Valve.
• The attention of all crew members and personnel is drawn by means of the (PA) Public Address System.
• The Pressure and Vacuum monitoring systems must be checked and confirmed as working.
• Crew should be ready at the manifold and valve stand in order to be ready to divert the nitrogen to the next designated tank or to stop the supply of nitrogen to a specific tank as necessary.
• A Personal Gas Analyser must be worn by all deck crew during such operations. Additionally, this equipment must be tested before use.
• The atmosphere on the deck must be continuously checked during the operation.
• When venting through the PV (Pressure Vacuum Valve) system, the rate must be conforming to the designed capacity of the PV Valve. A due allowance to the liquid loading rate at a factor of 1.25 is given for both the vapour growth and the vapour density.
• Located on the catwalk in the vicinity of the tank, must be 2 SCBA (Self Contained Breathing Apparatus) and 1 oxygen resuscitator in case of an emergency.

Upon completion of the operation,

• Complete gas tightness of all openings to the tank must be confirmed.
• The tank pressure and oxygen content of the individual tanks must be recorded.
• Placards must be displayed at the tank hatch after completion, clearly marking the presence of nitrogen inside and the lack of oxygen.
• Pressure Vacuum Valves (PV) must be set in the correct position.