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Tank cleaning and slop disposal for noxious liquid substances on chemical tankers

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). The above regulations (the latest amended version) must be available on board, and consulted before the loading of any noxious cargo is considered.

Consideration must always be given to coating compatibility and for the stowage of Slop of incompatible cargoes. The retention of viscous and vegetable oil Slops in zinc coated tanks must be avoided.

All operations with respect to a Noxious liquid substance which take place on board the vessel, including discharge into the sea or removal by ventilation of residues, is to be properly recorded in the Cargo Record Book for Ships Carrying NLS in Bulk.

Substances posing harm to the environment are categorised by MARPOL 73/78 Annex II into four Categories – X, Y, Z and OS. Category X substances are those posing the greatest threat to the Marine Environment, whilst Category Z substances are those posing the smallest threat. Water contaminated with chemical cargo (e.g. tank washings) may be required to be discharged ashore, into barges and, under certain circumstances, into the sea always in compliance with Marpol Annex II.

When washing tanks, which contained incompatible cargoes, each tank to be washed separately and the washings pumped independently to the shore, barge or sea as per Marpol Annex II. Do not collect incompatible cargo slops into same tank. Always take coating compatibility into account.

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. Barge personnel must be acquainted with the nature of the hazards and with the safety precautions, which must be observed in the interest of both parties.

Under no circumstances must water with noxious cargo be discharged overboard into port or enclosed waters, without the express permission of the appropriate authority. At sea, tank washings must only be discharged overboard when absolutely necessary, and in strict compliance with Annex II of MARPOL 73/78 and ship’s P&A Manual.

When chemical tankers are carrying a cargo or part cargo of oil in bulk they must Marpol Annex I regulations for discharge of Annex I cargo slops.


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







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Ship to ship transfer guideline using VEC systems

Cargo unloading operation safety precautions

Liaison between ship and shore

Preparation for cargo operation

Preparing a cargo tank atmosphere

Controlling the atmosphere in cargo tanks with nitrogen supplied from shore

Ship shore safety checklist while alongside a terminal

Cargo handling safe practice for chemical products

Cargo compatibility and reactivity of various chemical cargo

Poisoning and required first aid treatment onboard

Determining presence of contaminants in chemical cargo

Checklist for handling dangerous liquid chemicals in bulk

Ship shore safety checklist while alongside a terminal

Isolation of cargo tanks and piping systems

Ship shore cargo connection safe method

Venting of cargo tanks safety procedure

Ship to ship transfer operation

Controlling the atmosphere in cargo tanks with nitrogen supplied from shore



Effects of Tugs and other craft alongside chemical tankers

Primary means of cargo connection between ship and shore

Means of access (gangways or accommodation ladders) safety precautions

Ship/Shore Safety Checklist

How to prepare a cargo loading / discharge plan ?

Technical readiness prior loading operations

Voyage planning and related considerations

Cargo sampling safety precautions

Cargo calculation

Signing a bill of lading and related guideline

Preparation for cargo operation

Preparing a cargo tank atmosphere

Cargo unloading operation safety precautions

Liaison between ship and shore

How to prevent cargo pipeline leakage

Ship shore safety checklist while alongside a terminal


Reference publications

  1. IBC Code / BCH code
  2. International Safety Guide for Oil Tankers and Terminals (ISGOTT)
  3. ICS Chemical Tanker Safety Guide
  4. Ship’s “Procedure and Arrangements Manual” (Approved by Class)
  5. Certificate of Fitness for the Carriage of Dangerous Chemicals in Bulk
  6. Ship’s “VEC System Operational Manual” (Approved by Class)
  7. Ship to Ship Transfer Guide (Petroleum)
  8. Tank Cleaning Manual




Other Info:

Voyage planning and related considerations

Preparation for cargo operation

Preparing a cargo tank atmosphere

Cargo unloading operation safety precautions

Liaison between ship and shore

Cargo line leakage countermeasures

Checklist for handling dangerous liquid chemicals in bulk

Recommended temperature monitoring equipments onboard

Practical example of solving tank cleaning problems

Pre-cleaning /washing of cargo tanks

Risk & hazards of chemical contamination onboard

Cargo compatibility and reactivity of various chemical cargo

Poisoning and required first aid treatment onboard

Chemical tanker safe mooring practice

Determining presence of contaminants in chemical cargo

How to avoid solidification in cargo tanks ?

Cargo segregation requirement for chemical tankers

How to arrange disposal of tank cleaning waste ?

Restrictions on discharge cargo residue into sea

Retention of slops on chemical tankers

Vapour emission control requirement for chemical tankers

Handling self reactive chemicals

Handling of toxic chemical cargoes

Pre-loading meeting safety consideration

How to determine chemical cargo temperatures at different level ?

How to take cargo samples ?

How to avoid solidification in cargo tanks ?

Cargo line clearance requirement for chemical tankers

How to arrange disposal of tank cleaning waste ?

Care of cargo pums - risk of pump overload or underload


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