How to prepare a DB fuel oil tank for a survey/inspection?

Double bottom (DB) tank survey preparation:

 DB tank survey is necessary to ascertain the condition of double bottom. Before opening DB tank manhole for survey, following procedure must be followed:

• Carry out risk assessment.
• Arrange all tools
• Sounding of DB tank and the tank in which remaining fuel oil is to be transferred must be taken.
• Make sure that there is same fuel in the other tank in which oil from tank to be inspected is to be transferred.
• If it is not possible then make sure that both oil are compatible.
• Empty the oil, strip with portable pumps if required
• Clean the tank with sea water and pump it out through the oily water separator
• Ventilate the tank(s) with a blower specially provided for the purpose, always cross ventilate i.e. there should be at least two openings, each for entry and exit for the air
• Check the space for explosive gases at various points suitably, more sampling should be carried out at the corners at the bottom most part of the tank

  FIG.: Dragger