Page 226 - International safety guide for oil tankers and terminals

INTERNATIONAL SAFETY GUIDE FOR OIL TANKERS AND TERMINALS

To Control the ‘Sources of Ignition’ in the Tank
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a) Individual tank washing machines should not have a
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throughput greater than 60 m /h.
b) The total water throughput per cargo tank should be kept as
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งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
low as practicable and must not exceed 180 m /hr.
c) Different washing methods give rise to differing risks and the
following should be followed for tank washing in non-inert
conditions:
Recirculated wash water MUST NOT be used.
Heated wash water may be utilised, but use should be
discontinued if the gas concentration reaches 35% of the
LFL. A hot wash for a low flashpoint product should ONLY
take place following a full (i.e. top to bottom) cold wash
cycle.
If the hot wash water temperature is above 60ºC,
monitoring of the gas concentration level should be at an
increased frequency.

Chemical additives may only be considered if the
temperature of the wash water DOES NOT exceed 60ºC.

Steam must never be injected into the tank when tank
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washing in non-inert conditions and MUST NOT be
considered until the tank has been verified as gas free (see
Section 3.1.2 and Definitions).
d) The tank should be kept drained during washing. Washing
should be stopped to clear any build-up of wash water.
e) At all times, the discharge into the wash water reception/slop
tank should be below the liquid level in that tank.

f) If portable washing machines are used, all hose connections
should be made up and tested for electrical continuity before
the washing machine is introduced into the tank.
Portable washing machines should not be introduced into the
tank until the LFL level is 10% or less.

Connections should not be broken until after the machine has
been removed from the tank. To drain the hose, a coupling may
be partially opened (but not broken) and then re-tightened
before the machine is removed.

g) The introduction of sounding rods and other equipment into
the tank should be made utilising a full depth sounding pipe. If
a full depth sounding pipe is not fitted, it is essential that any
metallic components of the sounding rod or other equipment
are bonded and securely earthed to the ship before
introduction into the tank, and remain earthed until removed.

This precaution should be observed during washing and for
five hours thereafter to allow sufficient time for any mist
carrying a static charge to dissipate. If, however, the tank is
continuously mechanically ventilated after washing, this period
can be reduced to one hour. During this period:
An interface detector of metallic construction may be used
if earthed to the ship by means of a clamp or bolted metal
connection.

192 © ICS/OCIMF/IAPH 2006