Page 65 - International safety guide for oil tankers and terminals

HAZARDS OF PETROLEUM

reference point (nitrogen or carbon dioxide). (See also Sections 8.2.6
and 8.2.7.)
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2.4.11 Multi-gas Instruments
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
Multi-gas instruments are now widely used and are usually capable of housing
four different sensors. A typical configuration would comprise sensors for
measuring:

Hydrocarbon vapour as a % LFL (explosimeter function using a pellistor
sensor).

Hydrocarbon vapour in inert gas as a % Volume (tankscope function using
an infra-red sensor).
Oxygen (using an electrochemical sensor).

Hydrogen Sulphide (using an electrochemical sensor).

Multi-gas instruments should be tested at regular intervals in accordance with
the manufacturer’s instructions.

Multi-gas instruments may be supplied for gas measurement use and be fitted
with a data logging capability, but without an alarm function.
Care should be taken when using multi-gas instruments to check for
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hydrocarbons in an inerted atmosphere under pressure as the pellistor within
the instrument could be damaged if subjected to pressure (see Section
2.4.3.2).

2.4.12 Personal Gas Monitors
Multi-gas instruments may be supplied as compact units fitted with an alarm
function for personal protective use during tank entry. These personal monitors
are capable of continuously measuring the content of the atmosphere by
diffusion. They usually employ up to four electrochemical sensors and should
automatically provide an audible and visual alarm when the atmosphere
becomes unsafe, thereby giving the wearer adequate warning of unsafe
conditions.

Disposable personal gas monitors are now available. They usually provide
protection against a single gas and are available for low oxygen level, and high
concentrations of hydrocarbons and other toxic vapours. The units should
provide both audible and visual warning at specified levels of vapour
concentration, which should be at or below the TLV-TWA for the monitored
vapour. These monitors typically weigh less than 100 grams and have a life of
about 2 years.

2.4.13 Gas Sample Lines and Sampling Procedures

2.4.13.1 Gas Sample Lines

The material and condition of sample lines can affect the accuracy of gas
measurements.

Metal tubes are unsuited to most cargo tank gas measurements and
flexible lines should be used.

© ICS/OCIMF/IAPH 2006 31