Page 230 - International safety guide for oil tankers and terminals

INTERNATIONAL SAFETY GUIDE FOR OIL TANKERS AND TERMINALS

Equipment to be used for further tank cleaning operations, such
as the removal of solid residues or products in tanks which have
---ใช้เพื่อการศึกษาเท่านั้น---
been gas freed, should be so designed and constructed, and the
construction materials so chosen, that no risk of ignition is
introduced.
As far as possible, tank cleaning, particularly in the initial stages,ย์นาวี
11.3.6.11 Cleaning of Contaminated Ballast Spaces

Where leakage has occurred from a cargo tank into a ballast tank,
it will be necessary to clean the tank for both MARPOL
compliance and to effect repairs.

This task is difficult when the contamination is due to crude or
งานห้องสมุด ศูนย์ฝกพาณิช
black oils and particularly difficult if it occurs in a double hull or
double bottom space.

should be carried out by methods other than hand hosing. Such
methods may include, but not be limited to, using portable
machines, the use of detergents, or washing the bottom of the
tank with water and detergent. Hand hosing should only be
permitted for small areas of contamination or for final cleaning.
Whichever method is used, the tank washings must always be
handled in accordance with MARPOL regulations.
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After a machine or detergent wash, prior to entry for final hand
hosing, the tank must be ventilated in accordance with the
procedures referred to in Section 11.4.7, until readings at each
sampling point indicate that the atmosphere meets the ‘safe for
entry’ criteria in Chapter 10. Suitable control measures should be
implemented to protect the safety and health of personnel
entering the space.

11.4 Gas Freeing

11.4.1 General

It is generally recognised that gas freeing is one of the most hazardous
periods of tanker operations. This is true whether gas freeing for entry, for
Hot Work or for cargo quality control. The cargo vapours that are being
displaced during gas freeing are highly flammable, so good planning and
firm overall control are essential. The additional risk from the toxic effect
of petroleum gas during this period cannot be over emphasised and must
be impressed on all concerned. It is therefore essential that the greatest
possible care is exercised in all operations connected with gas freeing.

11.4.2 Gas Free for Entry Without Breathing Apparatus

In order to be gas free for entry without breathing apparatus, a tank or
space must be ventilated until tests confirm that the hydrocarbon gas
concentration throughout the compartment is less than 1% of the LFL,
that the oxygen content is 21% by volume, and that there are no hydrogen
sulphide, benzene or other toxic gases present, as appropriate (see
Section 10.3).

196 © ICS/OCIMF/IAPH 2006