Page 40 - International safety guide for oil tankers and terminals

INTERNATIONAL SAFETY GUIDE FOR OIL TANKERS AND TERMINALS

1.2.4 Tests for Flammability
---ใช้เพื่อการศึกษาเท่านั้น---
Since hydrocarbon gas/air mixtures are flammable within a comparatively
narrow range of concentrations of hydrocarbon gas in air, and concentration in
air is dependent upon vapour pressure, in principle, it should be possible to
evolve a test for flammability by measuring vapour pressure. In practice, the
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
very wide range of petroleum products, and the range of temperatures over
which they are handled, has prevented the development of one simple test for
this purpose.

Instead, the oil industry makes use of two standard methods. One is the Reid
Vapour Pressure test (see Section 1.1.2) and the other is the flashpoint test,
which measures flammability directly. However, with some residual fuel oils, it
has been shown that the flashpoint test will not always provide a direct
indication of flammability (see Section 2.7).

1.2.5 Flashpoint
In this test, a sample of the liquid is gradually heated in a special pot and a
small flame is repeatedly and momentarily applied to the surface of the liquid.
The flashpoint is the lowest liquid temperature at which the small flame
initiates a flash of flame across the surface of the liquid, thereby indicating the
presence of a flammable gas/air mixture above the liquid. For all oils, except
some residual fuel oils, this gas/air mixture corresponds closely to the Lower
ึ
Flammable Limit mixture.
There are many different forms of flashpoint apparatus but they fall into two
classes. In one, the surface of the liquid is permanently open to the
atmosphere as the liquid is heated and the result of such a test is known as an
‘open cup flashpoint’. In the other class, the space above the liquid is kept
closed except for brief moments when the initiating flame is introduced through
a small port. The result of this class of test is termed a ‘closed cup flashpoint’.

Because of the greater loss of gas to atmosphere in the open cup test, the
open cup flashpoint of a petroleum liquid is always a little higher (by about
6ºC) than its closed cup flashpoint. The restricted loss of gas in the closed cup
apparatus also leads to a much more consistent result than can be obtained in
open cup testing. For this reason, the closed cup method is now more
generally favoured and is used in this Guide when considering the
classification of petroleum. However, open cup test figures may still be found in
the legislation of various national administrations, in classification society rules
and other such documents.

1.2.6 Flammability Classification of Petroleum
There are many schemes for dividing the complete range of petroleum liquids
into different flammability classes based on flashpoint and vapour pressure
and there is a considerable variation in these schemes between countries.
Usually, the basic principle is to consider whether or not a flammable
equilibrium gas/air mixture can be formed in the space above the liquid when
the liquid is at ambient temperature.

Generally, in this Guide, it has been sufficient to group petroleum liquids into
two categories entitled non-volatile and volatile, defined in terms of flashpoint
as follows:

6 © ICS/OCIMF/IAPH 2006