Page 240 - International safety guide for oil tankers and terminals

INTERNATIONAL SAFETY GUIDE FOR OIL TANKERS AND TERMINALS

11.7 Cargo Leakage into Double Hull Tanks
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11.7.1 Action to be Taken

This Section addresses the actions to be taken in the event of a leak of
which can be considered to maintain the tank atmosphere in a safeิชย์นาวี
hydrocarbons into a double hull or double bottom tank.

If a hydrocarbon leak is discovered, the first step should be to check the
atmosphere in the tank to establish the hydrocarbon content. It should be
noted that the atmosphere in the tank could be above the Upper
Flammable Limit (UFL), within the flammable range, or below the Lower
Flammable Limit (LFL). Regardless of the number of samples taken, any
or all of these conditions may exist in different locations within the tank,
due to the complexity of the structure. It is therefore essential that gas
readings are taken at different levels, at as many points as possible, in
งานห้องสมุด ศูนย์ฝกพาณ
order to establish the profile of the tank atmosphere.
If hydrocarbon gas is detected in a tank, there are a number of options

condition:
Continuous ventilation of the tank.
Inerting the tank.
Filling or partially filling the tank with ballast.
ึ
Securing the tank with flame screens in place at the vents.
A combination of the above.

The option chosen will depend upon a number of factors, especially the
degree of confidence in the hydrocarbon content of the atmosphere,
bearing in mind the potential problems identified above.

It is strongly recommended that operators develop guidelines, taking into
account the tank structure and any limitations of the available
atmosphere monitoring system, which will assist ship’s personnel to
select the appropriate method of rendering the atmosphere safe.

Filling or partially filling the tank with ballast in order to render the
atmosphere safe and/or stop any further leakage of cargo into the tank
must take into account prevailing stress, trim, stability and loadline
factors. It must also be borne in mind that all ballast loaded into a tank
after a leak has been found, and all tank washings associated with
cleaning the tank, will be classed as ‘dirty ballast’ as defined by the
MARPOL regulations and must be processed in accordance with those
regulations. This means that they must either be transferred directly to a
cargo or slop tank for further processing in accordance with the
requirements or, if discharged directly to sea, passed via the oil content
monitor. The spool piece used to connect the ballast system to the cargo
system should be clearly identified and stowed close to its working
position and it should not be used for any other purpose.

If the tank is ventilated or inerted in lieu of filling, it should be sounded
regularly to ascertain the rate of liquid build-up and thus of leakage.

If the quantity of cargo leaking into the space is determined to be
pumpable, it should be transferred to another cargo tank via the
emergency ballast/cargo spool piece connection (see above), or other
emergency transfer method, in order to minimise contamination of the
space and to facilitate subsequent cleaning and gas freeing operations.

206 © ICS/OCIMF/IAPH 2006