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Purging nitrogen - required safety guides for chemical tankers

Nitrogen is used on Chemical Tankers as the primary Inert Gas for cargo quality control and / or for safety reasons. The requirements for the use of nitrogen, in respect to cargo handling, are either dictated by the IBC/BCH Codes for tank environment control or when the cargo quality / customers require it.

Prior to loading certain chemical cargoes, it may be necessary to purge the tank(s) with Nitrogen, either to reduce the O2 level or in order to displace vapours from the previous cargo(s). Extensive structural damage can, and has, occurred to cargo tanks due to shore nitrogen being supplied at too high a flow rate or at too great a pressure. Great caution is therefore necessary.



chemical tanker navigation at sea
The following are the general procedures for carrying out this operation, however some differences may exist depending on the number of tanks to be purged onboard and the Terminal and its facilities.

A ship specific Critical Operations checklist is to be created for such an operation on board.

Reference Publications :



Related Info:
  1. Purging requirement of chemical tank(s) with Nitrogen - safe method
    Prior to loading certain chemical cargoes, it may be necessary to purge the tank(s) with Nitrogen, either to reduce the O2 level or in order to displace vapours from the previous cargo(s).

  2. Nitrogen blanketing - safety method
    Nitrogen Blanketing or Padding is used to establish a positive pressure on a tank which has already been filled with product in order to prevent the ingress of air or water as the tank cools and thus prevent a possible dangerous reaction / damage between the cargo and water/air.

  3. Supply of Nitrogen from shore - safety guideline
    The nitrogen may be supplied at high pressure (up to 10 bar) and at a high flow rate. Agreement on the procedure for handling the nitrogen is paramount, and should be part of the pre-loading checklist between ship and shore, with emphasis on a clear understanding of the transfer rate and pressure

  4. Failure prevention and maintenance guideline for inert gas systems onboard
    Continuous availability of inert gas and its correct use is highly important for chemical tankers. To ensure its availability it must be operated, tested, and maintained at regular intervals, and in accordance with the manufacturer’s instructions and the vessel’s Planned Maintenance System.

  5. Gas freeing safety precautions for chemical tankers
    A space is considered as “gas free” when the concentration of flammable gases in its atmosphere is less than 0% LEL, the concentration of toxic gases (including IG components) is less than the TLV and the Oxygen concentration is not less than 20.8%.

  6. Poisoning and required first aid treatment onboard
    The poison is a very toxic substance which when absorbed into the human body by ingestion, skin absorption, or inhalation produces a serious or fatal effect. Poison may enter the human body orally, by inhalation, or by skin contact. After being absorbed by the body it may affect certain organs or give a general poisonous effect. Lately the cancerogene effects of some industrial chemicals have been noticed. This has led to significant reductions of hereto accepted TLV- values in many countries.

  7. How to test a tank environment prior entry ?
    Entry into an enclosed space that is not in normal daily use, great care should be taken to create and maintain safe working conditions, even if the duration of the work is to be short. Many fatalities in enclosed spaces have resulted from entering such spaces without proper supervision or adherence to agreed procedures. In almost every case the fatality would have been avoided if the simple guidance in this section had been followed.



More Info:

Isolation of cargo tanks and piping systems

Ship shore cargo connection safe method

Venting of cargo tanks safety procedure

Ship to ship transfer operation

Ship to ship transfer guideline using VEC systems

Gas freeing safety precautions for chemical tankers

Poisoning and required first aid treatment onboard

How to test a tank environment prior entry ?

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