Page 229 - International safety guide for oil tankers and terminals

SHIPBOARD OPERATIONS
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11.3.6.9
11.3.6.10
maximum charge levels is also very much less. Furthermore,
although a tank may be almost free of hydrocarbon gas at the
start of steaming, the heat and disturbance will often release
gases, and pockets of flammability may build-up.
Steaming may only be carried out in tanks that have been either
inerted or water washed and gas freed. The concentration of
flammable gas should not exceed 10% of the LFL prior to
steaming. Precautions should be taken to avoid the build-up of
steam pressure within the tank.
Strict observance of the static electricity precautions contained in
Chapter 3 is essential.
Use of Chemicals in Tank Cleaning Wash Water
Constraints on the use of chemicals in tank cleaning wash water,
will depend on the type of tank atmosphere (see Section 11.3.5.2).
If tank cleaning chemicals are to be used, it is important to
recognise that certain products may introduce a toxicity or
flammability hazard. Personnel should be made aware of the
Threshold Limit Value (TLV) of the product. Detector tubes are
particularly useful for detecting the presence of specific gases
and vapours in tanks. Tank cleaning chemicals capable of
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producing a flammable atmosphere should normally only be used
when the tank has been inerted.
Use of Chemicals for Local Cleaning of Tanks
Some products may be used for the local cleaning of tank
bulkheads and blind spots by hand wiping, provided the amount of
tank cleaning chemical used is small and the personnel entering
the tank observe all enclosed space entry requirements.
In addition to the above, any manufacturer’s instructions or
recommendations for the use of these products should be
observed. Where these operations take place in port, local
authorities may impose additional requirements.
A Material Safety Data Sheet (MSDS) for tank cleaning chemicals
should be on board the ship before they are used and the advice
of any precautions to be taken should be followed.
Leaded Gasoline
Whereas shore tanks may contain leaded gasoline for long
periods and therefore present a hazard from Tetraethyl Lead
(TEL) and Tetramethyl Lead (TML), ships’ tanks normally alternate
between different products and thus present very little risk.
However, ships employed in the regular carriage of leaded
gasoline should flush the bottom of the tanks with water after
every cargo discharge.
Removal of Sludge, Scale and Sediment
Before the removal by hand of sludge, scale and sediment, the
tank atmosphere must be confirmed as safe for entry, with
appropriate control measures implemented to protect the safety
and health of personnel entering the space. The precautions
described in Section 10.9 should be maintained throughout the
period of work.
© ICS/OCIMF/IAPH 2006 195