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Preparation for discharging various liquid chemical cargo

Technical readiness: A chemical carrier's cargo containment and handling systems are carefully designed, and constructed under strict supervision, to comply with the requirements of the IMO Codes and the SOLAS and MARPOL Conventions, in order to transport and handle safely the chemicals that the ship is certified to carry. There are large variations in the design of cargo containment and cargo handling systems, and specific instructions should always be prepared for inclusion in the ship's cargo handling manual.

chemical tanker navigation at sea
The following measures have to be taken prior to discharging operations commencing, with particular attention being paid when the cargo is highly toxic, flammable or both:
  1. Ensure Cargo Temperature(s) correct (High Viscosity and solidifying substances) Continue/reduce/close tank heating on relevant tanks
  2. Switch on High – Level alarms and test
  3. Prepare the Level gauging system
  4. Check if P/V valves are working and PV line clear.
  5. Prepare the vapour return line-if required.
  6. Prepare manifold, drip tray and cargo line system.
  7. Manifold - reducer-ASA/Din
  8. Prepare ballasting system
  9. Prepare / check jumper hoses or fixed connections.

  10. Chemical tanker ginga leopard at sea

  11. Check Nitrogen system
  12. Check if all is ready for closed discharging
  13. Set Decontamination shower and eye-wash in operational position
  14. Check if relevant instruments are ready for use.
  15. Prepare / post cargo description
  16. Prepare discharge plan
  17. It is essential that the accommodation is kept under positive pressure to prevent the entry of Hydrocarbon Vapours – the Operation of sanitary and galley extraction fans will cause a vacuum and therefore the air conditioning system intakes must not be kept fully closed. The accommodation air conditioning system should be maintained on partial recirculation during cargo operation.
  18. Ensure that all gas detection equipment (both fixed and portable) is in operation and calibrated with the required gases. It may, in some circumstances when loading / discharging toxic / flammable cargoes, be necessary to organise gas checks of some deck areas at regular intervals with portable gas detection equipment. Check that sufficient Toxic gas detectors are on board
  19. Key cargo instrumentation, such as temperature, pressure gauges and portable gauging equipment in use, are calibrated as applicable.
  20. Ensure that cargo tank vent systems are drained and empty
  21. Ensure that cargo line systems are free from blockage and cargo
  22. Check for any solidification / sedimentation in cargo tanks (especially with Veg Oil and animal oils.
  23. Test cargo pumps and purge cofferdams of submerged cargo Pumps
  24. PPE & Antidotes ready
  25. Squeezing gears & lights for vegetable oil ready
  26. Tank cleaning equipment & gear ready


Post stowage plan, cargo operation forms and chemical hazard data sheet/MSDS. Brief crew on the following:
  • Risk level of the cargo to be discharged
  • Appropriate chemical protective clothing is to be worn at all times during cargo operations
  • Fire fighting equipment to be used
  • What to be done in case of spillage, exposure
  • Additional medical equipment
  • Restricting access to deck areas of non-essential personnel during some cargo operations
  • The possibility that some cargoes which emit highly toxic imperceptible vapours may have perceptible additives introduced.

    Chemical tanker cargo handling gears

    Ullaging and sampling

    The cargo surveyor will check together with the chief-officer the ullages of the tanks to be discharged. Cargo sampling by the surveyor must be conducted in presence of an officer. The method used for calculating specific density at the disport must be the same as the method used in the load port.

    When sampling, ensure the sampling cans, bottles, ropes and closed sampler are thoroughly cleaned, prior sampling.

    Pre- discharge meeting

    This procedure describes the main points to be discussed on arrival before discharging operations can start. The complexity of discharging operations on chemical tankers makes it necessary to plan all activities in which vessel and terminal are involved. Parties:
    • Terminal Loading master
    • Vessel Master/Chief Officer
    • Expert Surveyor.
    If for any reason it is assumed that any party is planning to file a claim of any kind against the vessel the cargo samples from the loading port are to be retained on board. They may only be given to persons stipulated after consultation with the management office.

    Vessel –terminal agreements

    The Master/Chief Officer should present the Notice of Readiness (NOR) to the loading master for his signature. The loading master is the addressee for all protests in connection with the discharging.

    The Chief-Officer and loading master will discuss the discharge programme. All relevant items, in the ‘Ship/Shore Safety Checklist’, as provided by the terminal, are to be completed by the Terminal Representative and the Chief Officer.

    If no safety checklist is provided by the terminal, or it is not to the same standard as that contained within ISGOTT, the ISGOTT (5th Edition) Ship/Shore Safety Checklist, including Part C Bulk Liquid Chemicals, must be used. After agreeing, both must sign. Occasionally, the loading master will ask for the C.O.F. and/or hose certificates. Any defect to the cargo pumps requiring use of portable pump to be discussed.

    For chemicals which, according to MARPOL Annex II, are subject to the prewash obligation the washing programme and slop disposal are to be agreed upon and Port MARPOL Inspector notified. Discharging sequence and grades to be discharged agreed.

    Vessel - Surveyor agreements

    The surveyor has to discuss with the Chief Officer the discharging and sampling programme, especially if the cargo is kept under a nitrogen blanket. The surveyor receives the cargo samples destined for the receiver from the port of loading in exchange for a receipt.

    Related Info:

    Preparations for cargo operations
    Before any cargo transfer starts, the responsible officer should be satisfied that the applicable precautions are being observed. The use of safety checklists, appropriately adapted for the specific ship, is strongly recommended. ....

    Voyage planning and related considerations
    Prior commencement of a voyage a ship master is by law and in practice ultimately responsible for the correct stowage of the cargo. He must take all parameters such as, ....

    Cargo sampling safety precautions
    Cargo samples are evidence of the condition of the product during the various phases of transport (storage at terminal, arriving on board, loading, passage, discharging).....

    Preparing a cargo tank atmosphere
    For some cargoes the IBC Code requires vapour spaces within cargo tanks to have specially controlled atmospheres, ....

    Cargo unloading operation safety precautions
    Just prior to commencing discharge the responsible officer should check that the cargo pipeline system is set correctly, that correct valves are open, that valves not being used are closed, and that the cargo venting system is appropriate for the cargo operation. .....

    How to avoid solidification in cargo tanks ?
    Solidification in the cargo tanks can occur when solidifying cargoes are stowed adjacent to “cold cargoes” or cold ballast water in adjacent spaces. .....

    Cargo line clearance requirement for chemical tankers
    The lines used for cargo operations must be cleared and the pressure released to prevent solidification, polymerisation, reaction, pitting and danger to personnel connecting and disconnecting hoses or taking samples. .....

    How to arrange disposal of tank cleaning waste ?
    All processing and discharging of slops on tankers which are carrying a cargo of noxious liquid substances in bulk is to be in strict compliance with the requirements of Annex II of MARPOL 73/78 and procedures described in the approved ship specific Procedure and Arrangements Manual (P & A Manual). ....
    Restrictions on discharge cargo residue into sea
    The growing importance of environmental care demands that the crews of chemical tankers have a clear understanding of the pollution regulations. ....

    Retention of slops on chemical tankers
    If tank washing or slops are to be transferred to a barge alongside the Ship to Ship Transfer Guide is to be followed, and it must be ensured that the necessary hose connections are properly made.....

    Vapour emission control requirement for chemical tankers
    Where required, VEC is to be used and operated in accordance with IBC Code, local regulations, and instructions contained in the vessel’s VEC System Operation Manual and in conjunction with the requirements and provisions of the shore installation. .....

    What is closed unloading operation ?
    Chemical cargo closed unloading means discharging with securely closed ullage, sounding and sighting ports. Additionally the venting must be controlled. For gauging e.g. ullaging, sounding closed devices must be used. The level alarm systems must be operated during the entire closed cargo operation. .....
    Cargo hose disconnection - Benzene cargo fatality
    Hose disconnection and checks of the line must be carried out with extra awareness, especially when handing toxic chemical cargoes. Crew training in cargo hose disconnection is important including – Personal Safety on Chemical Tankers. ....
    Cargo discharging safety precautions
    Particular attention should be paid to ship’s cargo discharge equipment, such as pump, pump room ventilation etc. The following precautions should be observed: .....
    Cargo unloading safe practice
    Many cargoes carried under nitrogen cover must be discharged using vapour-return-lines. The tank pressure must be in excess of atmospheric pressure throughout the whole discharge period to prevent ingress of air i.e. oxygen.....

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