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Disposal of tank washings ,slops and dirty ballast - chemical tankers guideline

During normal operations of a chemical carrier, the main need to dispose of chemical residues, slops or water contaminated with cargo will arise during or immediately after tank cleaning. Final disposal of slops or washwater should be in accordance with the ship's P&A Manual. Tank washings and slops may be retained on board in a slop tank, or discharged ashore or into barges.



chemical tanker navigation at sea
Mandatory pre-wash water

Mandatory pre-wash procedures should be conducted strictly in accordance with the ship's P&A Manual, and the resulting contaminated wash water should always be discharged to shore. The intention of MARPOL is that this should happen immediately following the cargo discharge operations, and in the same port. However, occasions do arise when adequate shore reception facilities for the washings are not provided, and the ship must retain the washings on board until arrival at another port. MARPOL addresses this matter, and the P&A Manual will provide guidance on the correct procedures for a particular ship. During such a voyage, the slops and tank washings should be given the same safety and environmental care as the original cargo.


Dirty ballast

Dirty ballast, caused by ballasting into a cargo tank before the tank is cleaned, should be treated as slops, and must be disposed of in accordance with MARPOL and the ship's P&A Manual.

Safety precautions during discharge of cargo slops into the sea

When discharge overboard is permitted, it should only be undertaken when the ship is at sea normally be below the waterline through an underwater discharge outlet on the side of the ship away from essential water inlet valves. In the interests of safety, this procedure should be adopted even when it is not a mandatory requirement.

When any discharges are made above the waterline, care should be taken to avoid cargo vapour or liquid blowing back on board. If such a risk exists, discharge should be made below the waterline: if this is not possible, consideration should be given to altering the ship's course or speed to reduce the risk, and personnel on deck should wear appropriate protective clothing.

Management of slop tanks

Compatibility of various cargo and cleaning chemicals should be considered just as carefully when handling slops as when handling the cargoes themselves. Particular care is needed when washing several tanks which have contained dissimilar cargoes, and compatibility should be taken into account when selecting the destination tank for stripped wash water. The following should be avoided:

Mixing of slops from Annex I (oil) cargoes with slops from Annex 11 (chemical) cargoes.

Mixing of slops from incompatible cargoes.

Mixing of slops from vegetable oils or fats with chemical slops or petroleum oil slops.

If the ship's cargo tanks are used as slop tanks, care should be taken to avoid introducing slops from cargoes which are incompatible with the tank coating. In this regard, some cargoes which are themselves compatible may, when mixed with water, form acids and thus damage a coating, e.g. slops from hydrolytic cargoes in a zinc coated tank.


Recommendations

Desloping of any kind of slops to a shore reception facility is a costly affair. Therefore it is highly recommended that in the event of any slops generation following pre agreement / written communication is made with charterers Operator.







Related info:
  1. Fixed and portable tank cleaning equipments
    The installation of fixed tank washing machines within a cargo tank allows an inert atmosphere to be maintained during the washing operation, and thus permits cleaning in a closed mode in compliance with port regulations prohibiting release of noxious vapours. Their installation and use also reduces crew exposure to cargo vapours and inert gas.

  2. Tank cleaning and risk with cargo contact
    Different chemicals affect the human body in many different ways. A general information and some practical advice are available in Appendix,7, of "Medical first aid guide for use in accidents involving dangerous goods" published by IMO, WHO and ILO ref (36).

  3. Practical example of solving tank cleaning problems
    Cleaning of tanks is usually the responsibilty of the ship. Tank cleaning and the cleanliness involved have different standards depending upon the previous cargo and the cargo to be loaded. But the matter can be still more complicated, as cleanliness for one and the same product may vary, depending on who the receiver is and for what purpose the cargo is finally intended.

  4. Tank cleaning fatality- case study & lessons learned
    In the trade practice onboard chemical tankers, it is not uncommon that the use of methanol or other chemical/detergents is undertaken to achieve the required standard of cleanliness inside the cargo tank, pipelines, cargo hoses, manifold adaptors/reducers, gauging equipment, etc. Industry publications clearly highlight and caution regarding their use due to their flammability and toxicity hazards.

  5. Pre-cleaning /washing of cargo tanks
    Washing between different grades of cargo is the most common reason for tank cleaning. In most cargo sequences on chemical tankers, this cleaning may consist of no more than a simple hot or cold seawater wash. A simple water wash will disperse many types of chemicals and has been found effective between clean petroleum products such as gas oil and kerosene.

  6. Final cleaning of cargo tanks prior loading
    Method of final cleaning to be used depends on both previous cargo and cargo to be loaded. As a general rule the tanks and piping shall be completely drained of water or residues before loading. The bottom of the tanks may have to be dried up with rags.

  7. Tank cleaning and posoning hazards
    Certain substances affect the tissues locally as an irritant (cashew nut shell oil) or cause grave damage to the eyes, skin or mucous membranes (e g strong acids and caustic). Other substances may be absorbed by contact to the skin without local effects (e g nitrobenzene, aniline).

  8. Testing of tanks and cargoes
    Most common tests and checks for oil and chemical cargoes include testing tank walls for cleanliness. Testing is normally carried out by independent surveyors who, according to local practice or a written agreement in the charter party, are accepted by shipper, receiver and owner.

  9. Practical tank cleaning methods for various noxious liquid cargo
    Tanks that may have contained monomer or drying oils should first be cleaned with sufficient cold water quantities to avoid polymerization of cargo residues. In some cases, it is necessary to employ tank cleaning chemicals, but their use is generally limited as it may be difficult to dispose of slops.

  10. Special tank cleaning method
    If a special method involving cleaning agents is to be used, it may create an additional hazard for the crew. Shipboard procedures should ensure that personnel are familiar with, and protected from, the health hazards associated with such a method. The cleaning agents may be added to the wash water or used alone. The cleaning procedures adopted should not entail the need for personnel to enter the tank.

  11. Determining proper tank cleaning by acid wash method
    The acid wash method is used if there is any suspicion that a cargo of aromatics may have been contaminated by a previous oil cargo. The method is also used as a check that a tank is sufficiently cleaned before loading aromatics.

  12. Supervision of all tank cleaning and gas freeing operations
    Tank cleaning is essential on-a chemical tanker, but it must be recognised as a potentially hazardous operation, and rigorous precautions should be observed throughout the process. Together with gas freeing, it is probably the most hazardous operation routinely undertaken on a chemical tanker.

  13. Disposal of tank washings, slops and dirty ballast - safe method
    During normal operations of a chemical carrier, the main need to dispose of chemical residues, slops or water contaminated with cargo will arise during or immediately after tank cleaning. Final disposal of slops or washwater should be in accordance with the ship's P&A Manual. Tank washings and slops may be retained on board in a slop tank, or discharged ashore or into barges.

  14. Cargo tank damage during pigging operations
    Blowing and pigging of pipelines at terminals poses inherent risks for the terminal and a chemical tanker. Frequent damages to tanks have occurred. If there are doubts about the shore operation or signs of problems ashore the OOW must immediately request clarification.

  15. Determining water contamination in chemical cargo
    Presence of free water in non water-soluble products can, very roughly be determined on board by warming a sample of the product in a test tube or in a bottle. Water will then collect at the bottom of the tube and can be seen after some time.

  16. Determining Sulphur contamination (sulphides) in chemical cargo
    Certain products, in particular "virgin naphta feedstock'' (petroleum naphta) are severely contaminated by minor amounts of sulphides (and also lead compounds), which poison catalysts in further processing. Previous heavy oils or dirty harbour ballast water may have left traces of sulphides in the cargo tanks.

  17. Chloride contamination in chemical cargo - how to resolve?
    Certain cargoes are very senstive to chloride contamination, in particular glycols, methanol, ethanol . The tanks should be finally washed with fresh water. However, chlorides (salt) may still be present and a check might be useful. The greatest risk for salt deposits is on horizontal surfaces.

  18. APHA (Hazen) method for determining color of very light chemical products
    A method called APHA (Hazen) is often used for very light products, defined in ASTM D-1209, viz aromatics, ketones. This colour scale is defined with an origin in 100 cc distilled water (value 0) to succesively higher values (max 500) by adding APHA-solution (a platinum-cobolt salt solution).

  19. Loading, discharging & care of Phenol - Safety guideline
    PHENOL is carried at sea in a generally pure state. As a result, it has a high freezing point of approximately 40~ 41deg C. PHENOL is also extremely dangerous when it comes into contact with the eyes or skin and can be fatal.

  20. Hazards of Phenol - safe handling of Phenol on chemical tankers.
    Phenol must be carried at temperatures within charterers instructions, typically between +50 and + 60 degrees C. Heating instructions of the Shipper or Owners must be followed to avoid protests and delays in the port of discharge. Overheating can damage this cargo. A full cargo heating log must be maintained.

  21. Handling benzene & methanol safety precautions
    Benzene is known as a strong carcinogen and known to cause leukaemia. When handling cargoes with more than Benzene concentration of 0.5%, the Master is to ensure that all personnel involved are aware of the long term hazards.

  22. Personal protective equipments for carcinogens & cyanide-like cargoes onboard chemical tankers
    A carcinogen is a substance that may cause cancer by contact or by inhalation. It is therefore essential that the highest safety precautions are taken when handling these cargoes. Access to deck areas must be restricted to duty personnel only. All accommodation doors and ports must be closed and ventilation put on recirculation. Any member of crews involved in cargo operations must wear chemical protective suits and breathing apparatus

  23. Handling ACRYLONITRILE safety precautions
    ACRYLONITRILE are high value and require sophisticated handling for safety, health and loss prevention reasons. They need careful consideration prior loading , tank coating compatibility, cross compatibility with other cargoes carried, environmental controls if required (inerting).

  24. handling ISOCYANATES safety precautions
    Product safety data sheets may be available from various sources. For safety preparation, until the specific product safety data sheet can be obtained, Chemical Data Guide for Bulk Shipment by Water (U.S. DoT), should be used.

  25. Loading, carrying & discharging of Sulphuric acid - regulatory requirements & special handling methods
    IBC code compatibility chart strictly prohibits water in adjacent compartment to Sulphuric acid as you are aware if both come in contact with each other will generate a violent reaction. It is therefore recommended that the during loading of sulphuric acid adjacent ballast tanks to be always stripped dry to the maximum efficiency of the deballasting equipment used.



Cargo compatibility and reactivity of various chemical cargo

Poisoning and required first aid treatment onboard

Procedure for slop disposal onboard chemical tankers

Determining presence of contaminants in chemical cargo

Checklist for handling dangerous liquid chemicals in bulk

Defining three main categories of noxious liquid chemicals at sea

Cargo handling equipments for handling noxious liquid substances in bulk

Cargo handling safe practices onboard modern chemical tankers

IMO codes guideline for modern chemical tankers

Controlling the atmosphere in cargo tanks with nitrogen supplied from shore

How to determine the level of a liquid in a chemical tank

Poisoning and required first aid treatment onboard

After tank cleaning gas freeing safety guideline for chemical tankers

Draegar safety tube prior entering enclosed spaces

Preparations prior allowing personnel into cargo tanks / enclosed spaces

How to rescue injured or unconscious person from enclosed spaces

Preparations for hot work and safety precautions

Total flooding method for seagoing chemical tankers

Water extinguishing method for fire protection

Foam extinguishing method for chemical tankers

Dry powder fire extinguishing method





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