Page 231 - International safety guide for oil tankers and terminals

SHIPBOARD OPERATIONS
11.4.3
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Procedures and Precautions
The following recommendations apply to gas freeing generally:
A Responsible Officer must supervise all gas freeing operations.
All personnel on board should be notified that gas freeing is about to
All tank openings should be kept closed until actual ventilation of the์นาวี
begin.
Appropriate ‘No Smoking’ regulations should be enforced.
Instruments to be used for gas measurement should be calibrated and
tested in accordance with the manufacturer’s instructions before
starting operations.
Sampling lines should, in all respects, be suitable for use with, and
impervious to, the gases present.
individual compartment is about to commence.
Venting of flammable gas should be by the ship’s approved method.
Where gas freeing involves the escape of gas at deck level or through
hatch openings, the degree of ventilation and number of openings
should be controlled to produce an exit velocity sufficient to carry the
gas clear of the deck.
Intakes of central air conditioning or mechanical ventilation systems
should be adjusted, if possible, to prevent the entry of petroleum gas,
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by recirculating air within the spaces. (See Section 4.1.)
If at any time it is suspected that gas is being drawn into the
accommodation, central air conditioning and mechanical ventilation
systems should be stopped and the intakes covered or closed.
Window type air conditioning units which are not certified as safe for
use in the presence of flammable gas, or which draw in air from
outside the superstructure, must be electrically disconnected and any
external vents or intakes closed.
Gas vent riser drains should be cleared of water, rust and sediment,
and any steam smothering connections tested and proved satisfactory.
If several tanks are connected by a common venting system, each
tank should be isolated to prevent the transfer of gas to or from other
tanks.
If petroleum vapours persist on deck in high concentrations, gas
freeing should be stopped.
If wind conditions cause funnel sparks to fall on deck, gas freeing
should be stopped.
Tank openings within enclosed or partially enclosed spaces, such as
under forecastles or in centrecastles, should not be opened until the
compartment has been sufficiently ventilated by means of openings in
the tank that are outside these spaces. When the gas level within the
tank has fallen to 25% of the LFL or less, openings in enclosed or
partially enclosed spaces may be opened to complete the ventilation.
Such enclosed or partially enclosed spaces should also be tested for
gas during this subsequent ventilation.
When undertaking gas freeing in port, the following should be observed:
As a general rule, gas freeing should not take place concurrently with
cargo handling. If for any reason this is necessary, there should be
close consultation with, and agreement from, both the Terminal
Representative and the port authority.
© ICS/OCIMF/IAPH 2006 197