There are large variations in the design of cargo containment and cargo handling systems of modern chemical tankers, and specific ship require special precautions for discharging various grade noxious liquid substances in bulk. Particular attention should be paid to ship’s cargo discharge equipment, such as pump, pump room ventilation etc. The following precautions should be observed:

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A pre-discharge conference with responsible terminal personnel which should include

• Characteristics of cargoes to be discharged
• Sequence of cargoes to be discharge
• Temperature of cargoes to be discharged
• Quantities of cargoes to be discharged
• Pumping rates and pressure
• Emergency shutdown procedure
• Mode of communications
• Careful monitoring of discharge temperature to ensure cargoes are not damaged due to over heating or lack of heat and to comply with MARPOL Annex II requirements for category Y high viscosity and solidifying cargoes.

Prior commencing discharge the responsible officer must ensure that the entire discharge system, including pumps and vents, are secured and ready.

After completion of discharge, including stripping and line clearing to shore (never allow shore to drain lines and hoses back into a ship tank) and hoses are disconnected. Personnel engaged in hose disconnection must wear proper personal protective equipment. All tank openings to be closed and secured.


Discharging agreements

Prior to discharge the ship / shore checklist has to be completed by the chief officer and the loading master. Thereafter they have to agree on the discharge plan. This discharge plan must be completed in writing and approved by the Master.

As a minimum the discharge plan must at least contain the following information:

1. Manifold connection to be used for each cargo
2. Which tanks are to be discharged
3. Maximum discharge rate and/or back-pressure
4. Discharge sequence and procedure for changing grades

The chief officer and the Loading Master shall both sign the discharge plan. Should the loading master refuse to sign, a letter of protest must be issued. The loading master will receive one copy of the discharging plan.

a) Commencement and execution of the discharge

Before commencement of discharge the following to be carried out:

1. Cargo pump emergency stop trips are to be tested.
2. The Chief Officer is once again to personally check that the correct line up of valves has been made and that all required isolations by spools or spectacles are made.

Discharge should start at slow speed. During this phase the cargo line(s) and off shore manifold should be examined for signs of any leakage.

After confirmation from shore the discharge rate can be increased up to the agreed maximum or maximum backpressure.

When several tanks containing the same cargo are connected i.e. by jumper hoses the risk of causing an overflow due to wrong setting of the valves is increased. In this case the level of the other connected tanks should be continuously monitored. Level alarms must be switched on.

The officer on duty must be available throughout the cargo operation. One watchman is to be on deck in the vicinity of the manifold throughout the entire operation in order that any potential risk is identified immediately and the required steps are taken to promptly control or remedy the risks, such as but not limited to informing the officer on duty etc.

The discharge must be conducted in accordance with the agreement made between the Chief Officer and the Loading master as well as additional instructions / standing orders given by the Chief Officer.