Page 123 - International safety guide for oil tankers and terminals

Chapter 7

SHIPBOARD

งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
SYSTEMS

This Chapter describes the principal ship systems that are used during cargo and
ballast operations in port.

7.1 7.1.1 Generalารศึกษาเท่านั้น---
Fixed Inert Gas Systems

This Section describes, in general terms, the operation of a fixed inert gas (IG) system
that is used to maintain a safe atmosphere within a ship’s cargo tanks. It also covers
the precautions to be taken to avoid hazards to health resulting from the risks
associated with operating IG plants.

Reference should be made to the ship’s operations manual and the manufacturer’s
instructions and installation drawings, as appropriate, for details on the operation of a
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particular system. The IMO publication ‘Guidelines for Inert Gas Systems’ should be
consulted for a more comprehensive explanation of the design and operating principles
---ใช้เพื่อก
and practices for typical inert gas systems.

Hydrocarbon gas normally encountered in petroleum tankers cannot burn in an
atmosphere containing less than approximately 11% oxygen by volume.
Accordingly, one way to provide protection against fire or explosion in the
vapour space of cargo tanks is to keep the oxygen level below that figure. This
is usually achieved by using a fixed piping arrangement to blow inert gas into
each cargo tank in order to reduce the air content, and hence the oxygen
content, and render the tank atmosphere non-flammable.

See Section 1.2.3 and Figure 1.1 for detailed information on the effect of inert
gas on flammability.

7.1.2 Sources of Inert Gas

Possible sources of inert gas on tankers and combination carriers are:
Uptake gas from the ship’s main and auxiliary boilers.
An independent inert gas generator.

A gas turbine plant when equipped with an afterburner.

7.1.3 Composition and Quality of Inert Gas

The International Convention for the Safety of Life at Sea (SOLAS 1974),as
amended, requires that inert gas systems be capable of delivering inert gas
with an oxygen content in the inert gas main of not more than 5% by volume at
any required rate of flow; and of maintaining a positive pressure in the cargo

© ICS/OCIMF/IAPH 2006 89