Page 62 - International safety guide for oil tankers and terminals

INTERNATIONAL SAFETY GUIDE FOR OIL TANKERS AND TERMINALS

along the tube and the length of discoloration, which is a measure of the
gas concentration, is read off a scale integral to the tube.
---ใช้เพื่อการศึกษาเท่านั้น---
In some versions of these instruments, a hand operated injection syringe
is used instead of a bellows pump.
The tubes are designed and intended to measure concentrations of gasย์นาวี
It is important that all the components used for any measurement should
be from the same manufacturer. It is not permissible to use a tube from
one manufacturer with a hand pump from another manufacturer. It is also
important that the manufacturer’s operating instructions are carefully
observed.

Since the measurement depends on passing a fixed volume of gas
งานห้องสมุด ศูนย์ฝกพาณิช
through the glass tube, any use of extension hoses should be in strict
accordance with the manufacturer’s instructions.

in the air. As a result, measurements made in a ventilated tank, in
preparation for tank entry, should be reliable.

For each type of tube, the manufacturers must guarantee the standards
of accuracy laid down in national standards. Tanker operators should
consult the ship’s flag administration for guidance on acceptable
equipment.
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2.4.7.2 Electrochemical Sensors
Electrochemical sensors are based on the fact that cells can be
constructed that react with the measured gas and generate an electric
current. This current can be measured and the amount of gas
determined. The sensors are low cost and are small enough to allow
several to be incorporated into the same instrument, making them
suitable for use in multi-gas detectors.

There are numerous electrochemical sensors available covering a
number of gases which may be present in the shipboard environment,
such as ammonia, hydrogen sulphide, carbon monoxide, carbon dioxide
and sulphur dioxide.

Electrochemical sensors can be used in stand-alone instruments, which
may provide a warning at a predetermined concentration of vapour, or
they can be fitted in a multi-sensor instrument to provide a reading of the
concentration of the vapour, usually in parts per million (ppm).

These sensors may give erroneous readings due to cross-sensitivity. This
occurs, for example, when measuring toxic gases with hydrocarbon gases
present, for example H 2 S in the presence of nitric oxide and sulphur
dioxide.

2.4.8 Fixed Gas Detection Installations
Fixed gas detection installations are used on some petroleum tankers to
monitor the flammability of the atmosphere in spaces such as double hull
spaces, pumprooms and pipe tunnels in double bottoms.
Three general arrangements have been developed for fixed monitoring
installations, as follows:

28 © ICS/OCIMF/IAPH 2006