Page 67 - International safety guide for oil tankers and terminals

HAZARDS OF PETROLEUM

Water traps are often used in modern gas measurement instruments.
These utilise a Polytetrafluoroethylene (PTFE) membrane that prevents
่อการศึกษาเท่านั้น---
liquid and moisture passing onto the sensors.

The use of water-retaining filters is essential with oxygen meters,
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
particularly of the paramagnetic type, because the presence of water
vapour in the sample can damage the measuring cell. Only
manufacturer’s recommended filters should be used.

2.5 Hydrocarbon Gas Evolution and Dispersion

2.5.1 Introduction

During many cargo handling and associated operations, petroleum gas is
expelled from cargo tank vents in sufficient quantity to give rise to flammable
gas mixtures in the atmosphere outside the tanks. In this Guide, a major
objective is to avoid such a flammable gas mixture being exposed to a source
of ignition. In many cases, this is achieved either by eliminating the source of
ignition or by ensuring that there are barriers, such as closed doors and ports,
between the gas and unavoidable potential sources of ignition.

However, it is impossible to cover every possibility of human error and every
combination of circumstances. An additional safeguard is introduced if
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operations can be arranged so that petroleum gas issuing from vents is
dispersed sufficiently well to prevent flammable gas mixtures reaching those
areas where sources of ignition may exist.

There can be a flammability problem from gas concentrations external to cargo
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tanks in the case of high vapour pressure volatile cargoes, the main types of
which are:
Crude oil.

Motor and aviation gasolines.
Natural gasolines.
Light Distillate Feedstocks (LDFs) and naphthas.

The gases from these petroleum liquids are denser than air and this has an
important bearing on how they behave, both inside and outside the tanks (see
Section 1.3).

The gas which is vented is formed within the tanks and the way in which it is
formed affects both the concentration when vented and the length of time
during which a high concentration is vented. Situations which lead to gas
evolution include loading, standing of cargo in full or part filled tanks (including
slop tanks), evaporation of tank residues after discharge, and crude oil
washing.

The initial tank atmosphere, whether air or inert gas, has no bearing on gas
evolution or venting.

© ICS/OCIMF/IAPH 2006 33