Page 54 - International safety guide for oil tankers and terminals

INTERNATIONAL SAFETY GUIDE FOR OIL TANKERS AND TERMINALS

An atmosphere containing less than 5% oxygen by volume causes immediate
unconsciousness with no warning other than a gasp for air. If resuscitation is
---ใช้เพื่อการศึกษาเท่านั้น---
delayed for more than a few minutes, irreversible damage is done to the brain,
even if life is subsequently saved.

งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี

2.4 Gas Measurement

2.4.1 Introduction

This Section describes the principles, uses and limitations of portable
instruments for measuring concentrations of hydrocarbon gas (in inerted and
non-inerted atmospheres), other toxic gases and oxygen. Certain fixed
installations are also described. For detailed information on the use of all
instruments, reference should always be made to the manufacturer’s
instructions.

It is essential that any instrument used is:
Suitable for the test required.
Sufficiently accurate for the test required.
Of an approved type.

Correctly maintained.
ึ
Frequently checked against standard samples.

2.4.2 Measurement of Hydrocarbon Concentration

The measurement of hydrocarbon vapours on tankers and at terminals falls
into two categories:

1. The measurement of hydrocarbon gas in air at concentrations below the
Lower Flammable Limit (LFL).

This is to detect the presence of flammable (and potentially explosive)
vapours and to detect concentrations of hydrocarbon vapour that may be
harmful to personnel. These readings are expressed as a percentage of
the Lower Flammable Limit (LFL) and are usually recorded as % LFL. The
instruments used to measure % LFL are Catalytic Filament Combustible
Gas (CFCG) Indicators, which are usually referred to as Flammable Gas
Monitors or Explosimeters. A CFCG Indicator should not be used for
measuring hydrocarbon gas in inert atmospheres.

2. The measurement of hydrocarbon gas as a percentage by volume of the
total atmosphere being measured.

On board a tanker, this is usually carried out to measure the percentage of
hydrocarbon vapour in an oxygen deficient (inerted) atmosphere.
Instruments used to measure hydrocarbon vapours in an inert gas
atmosphere are specially developed for this purpose. The readings
obtained are expressed as the percentage of hydrocarbon vapour by
volume and are recorded as % Vol.

The instruments used to measure percentage hydrocarbon vapours in inert
gas are the Non-Catalytic Heated Filament Gas Indicators (usually referred
to as Tankscopes) and Refractive Index Meters. Modern developments in
gas detection technology have resulted in the introduction of electronic

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