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Chemical cargo closed unloading safety procedure for chemical tankers

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.

Closed cargo operations must be stopped as soon as any essential system for safe loading or discharging becomes inoperative. Sampling will be closed by sampler where possible.

Vessels equipped with a system such as Skarpenord (pressure gauges in the tanks) or radar ullage systems shall at all times carry out closed unloading procedures for all cargoes except when cargo system is defective and approved by Management Office and agreed by Terminal.

The Master has overall responsibility for compliance with closed unloading procedures. Closed loading has to be carried out as a requirement of the:
Gauging, sounding and sampling

A closed gauging device penetrates the cargo tank, but is part of a closed system and prevents the cargo or its vapour being released. Examples are the float-type systems, radar systems, electronic probe, magnetic probe and protected sight-glass.

For sampling and sounding the Dovianus or Hermetic portable gauging and sampling systems may be used. It is important that sufficient of these devices are carried onboard and maintained in a fully operational and certified calibrated condition.

Vapour locks, where fitted, are to be calibrated and certified by a recognised cargo inspection company which will also approve the datum level corrections including list and trim corrections for tank volumes. The approval certificate is to be readily available during cargo surveys.





Cargo tank venting

Controlled venting must be established if closed cargo operations are required. A controlled tank venting system is a system with pressure and vacuum-relief valves (P/V valve) fitted on each tank in order to limit the pressure or vacuum in the tank. The P/V valve should operate in such a manner that neither pressure nor vacuum is created in the cargo tank during cargo operations that exceed the tank design parameters.

Continuously monitor the secondary venting system onboard to prevent damage from under pressurization.


Vapour return

Vapour return should be used in accordance with local, terminal or customer’s requirements. VECS manual to be complied with. Vapour returned to be used as per IBC code.


Customers’ requirements

Specific closed cargo operations may be required by the customer under the Charter Party or Contract of Affreightment (COA). The management office will inform the Master when such requirements exit.



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




Related Info:

Preparation for chemical cargo loading

Voyage planning and related considerations

Cargo sampling safety precautions

Preparing a cargo tank atmosphere

Cargo unloading operation safety precautions

Liaison between ship and shore

Cargo care during transit

Ship shore safety checklist while alongside a terminal

Cargo calculation

Signing a bill of lading and related guideline

Preparation for cargo operation

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

Handling various grade liquid chemicals during loading

How to prepare a cargo loading or discharge program ?

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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