Page 130 - International safety guide for oil tankers and terminals

INTERNATIONAL SAFETY GUIDE FOR OIL TANKERS AND TERMINALS

washing must be stopped until satisfactory conditions are restored (see
also Section 7.1.12).
---ใช้เพื่อการศึกษาเท่านั้น---

7.1.6.10 Purging
If the dilution method of purging is used, it should be carried out with theย์นาวี
When it is required to gas free a tank after washing, the tank should first
be purged with inert gas to reduce the hydrocarbon content to 2% or less
by volume. This is to ensure that, during the subsequent gas freeing
operation, no portion of the tank atmosphere is brought within the
flammable range.

The hydrocarbon content must be measured with an appropriate meter
designed to measure the percentage of hydrocarbon gas in an oxygen
7.1.6.12 Preparation for Tank Entry ย์ฝกพาณิช
deficient atmosphere. The usual flammable gas indicator is not suitable
for this purpose (see Section 2.4).

inert gas system set for maximum capacity to give maximum turbulence
within the tank. If the displacement method is used, the gas inlet velocity
should be lower to prevent undue turbulence (see Section 7.1.4).

7.1.6.11 Gas Freeing
Before starting to gas free, the tank should be isolated from other tanks.
ึ
When either portable fans or fixed fans connected to the cargo pipeline
system are used to introduce air into the tank, the inert gas inlet should
be isolated. If the inert gas system fan is employed to draw air into the
tank, both the line back to the inert gas source and the inert gas inlet into
งานห้องสมุด ศูน
each tank that is being kept inerted should be isolated.

To ensure the dilution of the toxic components of inert gas to below their
Threshold Limit Values (TLVs), gas freeing should continue until tests with
an oxygen analyser show a steady oxygen reading of 21% by volume and
tests with a flammable gas indicator show not more than 1% LFL.

If the presence of a toxic gas such as benzene or hydrogen sulphide is
suspected, gas freeing should be continued until tests indicate that its
concentration is below its TLV-TWA.

Positive fresh air ventilation should be maintained throughout the period
that personnel are in a tank, and frequent tests should be made of both
oxygen and hydrocarbon content of the tank atmosphere.

When other tanks in an inert condition are either adjacent or
interconnected (e.g. by a pipeline) to the tank being entered, personnel
should be alert to the possibility of inert gas leaking into the gas free tank
through, for example, bulkhead fractures or defective valves. The risk of
this occurring can be minimised by maintaining a small but positive inert
gas pressure. When a gas free tank is re-connected to the inert gas main,
it should immediately be re-inerted.

For general advice on entry into enclosed spaces see Chapter 10.

96 © ICS/OCIMF/IAPH 2006