Page 176 - International safety guide for oil tankers and terminals

INTERNATIONAL SAFETY GUIDE FOR OIL TANKERS AND TERMINALS

When preparing for entry into a ballast tank or void space where
hydrocarbon vapours may not normally be present, it is prudent to test
---ใช้เพื่อการศึกษาเท่านั้น---
the space for hydrocarbon vapour or H 2 S if the space is adjacent to a
cargo or bunker tank. This is particularly important if entry is being made
to investigate the possibility of bulkhead defects.
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี

10.2.2 Respiratory Hazards
Respiratory hazards from a number of sources could be present in an
enclosed space. These could include one or more of the following:
Hydrocarbon vapours, such as butane and propane.
Toxic contaminants associated with organic vapours, such as aromatic
hydrocarbons, benzene, toluene etc.
Toxic gases, such as benzene, hydrogen sulphide and mercaptans.
Oxygen deficiency caused by the presence of inert gas, oxidation
(rusting) of bare steel surfaces, or by microbial activity.
Solid residues from inert gas and particulates, such as those from
asbestos, welding operations and paint mists.

10.2.3 Hydrocarbon Vapours
spaces for the following reasons: ึ
During the carriage and after the discharge of hydrocarbons, the
presence of hydrocarbon vapour should always be suspected in enclosed

Cargo may have leaked into compartments, including pumprooms,
cofferdams, permanent ballast tanks and tanks adjacent to those that
have carried cargo.
Cargo residues may remain on the internal surfaces of tanks, even
after cleaning and ventilation.

Sludge and scale in a tank that has been declared gas free may give
off further hydrocarbon vapour if disturbed or subjected to a rise in
temperature.
Residues may remain in cargo or ballast pipelines and pumps.

The presence of gas should also be suspected in empty tanks or
compartments if non-volatile cargoes have been loaded into non-gas free
tanks or if there is a common ventilation system which could allow the
free passage of vapours from one tank to another.

Toxic contaminants could be present in the space as residues from
previous cargoes, such as benzene or hydrogen sulphide.

To be considered safe for entry, whether for inspection, Cold Work or Hot
Work, a reading of less than 1% LFL must be obtained on suitable
monitoring equipment.

142 © ICS/OCIMF/IAPH 2006