Ventilation Procedures for Cargo Tanks

General Informations:

• Cargo residue of substances with a vapour pressure greater than 5kPa at 20 degrees Celcius may be removed from a cargo tank by Ventilation.

• Before the cargo residues of NLS are ventilated from a tank the safety hazards relating to cargo flammability and toxicity shall be considered.

• With regards to the safety aspects, the operational requirements for openings in cargo tanks shall be amended.

• Port authorities may also have regulations on cargo tank ventilation.

Procedures:

• The procedures for ventilation of cargo residues from a tank are as follows:
• The pipelines shall be drained and further cleared of liquid by means of ventilation equipment.
• The list and trim shall be adjusted to the minimum levels possible so that evaporation of residues in the tank is enhanced.
• Ventilation equipment producing an air jet that can reach the tank bottom shall be used.
• The following figure shall be used to evaluate the adequacy of ventilation equipment used for ventilating a tank of a given depth.  

• The ventilation equipment shall be placed in the tank opening closest to the tank sump or suction point.
• The ventilation equipment shall, when practicable, be positioned so that the air jet is directed at the tank sump or suction point and impingement of the air jet on tank structural members is to be avoided as much as possible.
• The ventilation shall continue until no visible remains of liquid can be observed in the tank. This shall be verified by a visual examination or an equivalent method.

Reference: IMO Publications & Documents - International Conventions - MARPOL - Annex II - Appendix 7