Preparation For Discharging Various Liquid Chemical Cargo


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.

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.
    1. Check Nitrogen system
    2. Check if all is ready for closed discharging
    3. Set Decontamination shower and eye-wash in operational position
    4. Check if relevant instruments are ready for use.
    5. Prepare / post cargo description
    6. Prepare discharge plan
    7. 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.
    8. 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
    9. Key cargo instrumentation, such as temperature, pressure gauges and portable gauging equipment in use, are calibrated as applicable.
    10. Ensure that cargo tank vent systems are drained and empty
    11. Ensure that cargo line systems are free from blockage and cargo
    12. Check for any solidification / sedimentation in cargo tanks (especially with Veg Oil and animal oils.
    13. Test cargo pumps and purge cofferdams of submerged cargo Pumps
    14. PPE & Antidotes ready
    15. Squeezing gears & lights for vegetable oil ready
    16. 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.

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.

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Source: Chemicaltanker