Page 177 - International safety guide for oil tankers and terminals
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ENCLOSED SPACES
10.2.4 Toxic Gases
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10.2.4.1 Benzene
See Section 2.3.5 for a description of the hazards associated with
in some products in varying concentrations. Where theิชย์นาวี
benzene. Checks for benzene vapour should be made prior to
entering any compartment in which a cargo that may have
contained benzene has recently been carried. Entry should not be
permitted without appropriate personal protective equipment, if
statutory or recommended TLV-TWAs are likely to be exceeded
(see Section 2.3.3.2). Tests for benzene vapours can only be
undertaken using appropriate detector equipment, such as
detector tubes. Detector equipment should be provided on board
all ships likely to carry cargoes in which benzene may be present.
งานห้องสมุด ศูนย์ฝกพาณ
10.2.4.2 Hydrogen Sulphide
See Section 2.3.6 for a description of the hazards associated with
Hydrogen Sulphide (H 2 S). H 2 S is present in some crude oils and
concentration is high, the oil is often referred to as being ‘sour’.
H 2 S is very soluble in water. General practice and experience
indicates that washing a tank with water after carrying a cargo
containing H 2 S should eliminate the hydrogen sulphide vapour
within the space. ึ
However, prior to entry into an enclosed space which has
previously carried oil containing H 2 S, or where the presence of
H 2 S vapour may be expected, the space should be ventilated to a
reading of less than 1% LFL on a combustible gas indicator and
tested for the presence of H 2 S using a gas detector tube. Care
should be taken not to rely on the use of catalytic H 2 S sensors
which may have a cross-sensitivity with hydrocarbon vapour.
Since H 2 S is heavier than air, it is very important that the bottom
of any space is thoroughly tested.
When carrying a cargo containing H S, particular attention should
2
be given to the possibility of the presence of H S in locations
2
such as pumprooms, deck stores and in ballast tanks. There is a
high probability of the presence of H S in ballast tanks due to the
2
gas being drawn into the tank when deballasting during the
loading operation.
10.2.4.3 Mercaptans
See Section 2.3.7 for a description of the hazards associated with
Mercaptans. Mercaptans are present in the vapours of pentane
plus cargoes and in some crude oils. They may also be present
where oil residues have been in contact with water for extended
periods.
The presence of Mercaptans can be detected by the use of
chemical detector tubes. Their concentration should be reduced to
0.5 ppm to avoid discomfort to personnel and nuisance smells.
© ICS/OCIMF/IAPH 2006 143
