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Hazards of tank cleaning onboard chemical tankers - supervision and preparations

Chemical tankers safety procedure

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.

The additional risk created by cargo gases expelled from the tanks cannot be overemphasised. Depending on the most recent cargo carried in tanks that are to be cleaned, vapours that are toxic, flammable and corrosive should be expected to be released onto and around the cargo deck area. It is therefore of utmost; importance that every possible care is exercised during all operations connected with tank cleaning and gas freeing, and that the operations are carried out using the approved procedures and arrangements for the ship.

Personnel involved should be fully aware of the dangers and take necessary precautions, because the consequences of an inadvertent error can be very serious and far reaching.

All ships certified to carry noxious liquid substances in bulk must be provided with a Procedures and Arrangements (P&A) Manual, approved by the flag administration, which addresses the marine environmental aspects of removal and disposal of residues from cargo tanks, and describes how to perform those operations. The Manual should be adhered to in all respects, including the performance of mandatory pre-wash requirements in accordance with MARPOL 73/78 Annex II.


Preparatory guideline for tank cleaning operation

A responsible officer should supervise all tank cleaning and gas freeing operations. All stages of the operation should be performed in a safe manner appropriate to each individual chemical's physical characteristics, such as toxicity, corrosiveness and reactivity.

A pre-cleaning meeting under the leadership of the responsible officer should be held prior to any tank cleaning or gas freeing operation. Other crew members involved should be identified by the responsible officer, and their role explained. It is to clarify that all personnel involved fully understand their duties during the forthcoming tank cleaning operation.

The meeting should confirm:

i) The tanks to be cleaned, and the cleaning sequence.
ii) The type of cargo to be cleaned from each tank, and its characteristics. Cargo information sheets should be available so that personnel involved are familiar with the hazards.
iii) The major risks during cleaning, such as toxicity, flammability, corrosiveness and reactivity.
iv) The safety equipment and personal protective equipment to be available and ready for use throughout the operation and during connecting and disconnecting of hoses at the cargo manifold.
v) The cleaning instructions to be followed in each case.
vi) The means of disposal of any cargo, residues and the contaminated cleaning water. The relevant slop tank must be specified in each case.
vii) The precautions necessary to confirm that the cargo deck area is free from cargo vapours during tank washing and gas freeing operations.
viii) That at regular intervals throughout the operation, checks will be made to ensure that tank washings containing cargo are not inadvertently being discharged into the sea.

A written tank cleaning schedule should be drawn up and made available for reference by all personnel participating in the operations.

Chemical tanker tank cleaning machine

Fig:Chemical tanker tank cleaning machine

Preparations

Before any tank cleaning or gas freeing operations begin, the responsible officer should confirm that all necessary equipment is available, and that adequate checks are made to establish that all equipment to be used is in good working condition. Both before and during tank cleaning and gas freeing operations, the responsible officer should be satisfied that the appropriate precautions are being observed. All personnel on board should be notified that tank cleaning or gas freeing is about to begin, and only those personnel involved in the operations should be allowed into the cargo tank area.




If other craft are alongside the tanker, their personnel should be notified that tank cleaning operations are about to commence, and their compliance with all appropriate safety measures should be confirmed.

When gas freeing or tank cleaning while alongside at a terminal, the precautions for cargo handling should be observed where appropriate. Before starting, the permission of the port authority and terminal operator should be obtained, and the appropriate personnel ashore should be consulted to confirm that conditions on the jetty do not present a hazard, and to obtain agreement that operations can start.

The following checks should be made before operations commence:

i) That essential protective clothing and respiratory protection equipment are being worn if so required.
ii) That fresh water shower and eyewash arrangements are ready for immediate use in the event of contamination of personnel.
iii) That work not related to cargo operations, and not otherwise essential, is avoided in the cargo area during tank cleaning operations.
iv) That cargo pipelines serving a set of cargo tanks are isolated from the tanks to be cleaned or gas freed, unless all tanks in that set are to be cleaned.
v) That tanks served by a common vent system are properly isolated.
vi) That cargo tank lids, tank washing openings, ullage openings and sighting ports in uncleaned tanks are kept closed until they are to be cleaned.
vii) That all sea and overboard discharge valves connected to the cargo and ballast systems are shut and secured when not in use.
viii) That pump-room precautions are being observed and will continue to be observed throughout tank cleaning and gas freeing operations.
ix) That fire fighting equipment is ready for immediate use.





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Following reference publications provide useful guidance and international regulations for carrying hazardous chemicals at sea.



Our detail pages contain somewhat larger lists of resources where you may find more useful information.


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