Page 243 - International safety guide for oil tankers and terminals

SHIPBOARD OPERATIONS
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11.8.2
11.8.2.1
11.8.2.2
As cargo compartments may be in a pressurised condition, the opening of
vapour lock valves, ullage ports or covers and the controlled release of
any pressure should only be undertaken by authorised personnel.
When measuring or sampling, care must be taken to avoid inhaling gas.
Personnel should therefore keep their heads well away from the issuing
gas and stand at right angles to the direction of the wind. Standing
immediately upwind of the ullage port might create a back eddy of
vapour towards the operator. In addition, depending on the nature of the
cargo being handled, consideration may have to be given to the use of
appropriate respiratory protective equipment (see Sections 10.8 and
11.8.4).
When open gauging procedures are being employed, the tank opening
should only be uncovered long enough to complete the operation.
Measuring and Sampling Non-Inerted Tanks
General
There is a possibility of electrostatic discharges whenever
equipment is lowered into non-inerted cargo tanks. The
discharges may come from charges on the equipment itself or
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from charges already present in the tank, such as in the liquid
contents, on water or oil mists. If there is any possibility of the
presence of a flammable mixture of hydrocarbon gas and air
mixture, precautions must be taken to avoid incendive discharges
throughout the system.
Precautions are necessary to deal with two distinct types of
hazard:
The introduction of equipment that may act as a spark
promoter into a tank that already contains charged materials.
The introduction of a charged object into a tank.
Each requires different mitigation measures.
Table 11.2 provides a summary of the precautions to be taken
against electrostatic hazards when ullaging and sampling
non-inerted cargo tanks.
Introduction of Equipment into a Tank
Measures to Avoid Introducing Spark Promoters
If any form of dipping, ullaging or sampling equipment is used in
a possibly flammable atmosphere where an electrostatic hazard
exists or can be created, precautions should be taken to ensure
that they do not act as an unearthed conductor at any time during
the operation. Metallic components of any equipment to be
lowered into a tank should be securely bonded together and to the
tank before the sampling device is introduced, and should remain
earthed until after removal. Bonding and earthing cables should
be metallic.
Equipment should be designed to facilitate earthing. For example,
the frame holding the wheel on which a metal measuring tape is
wound should be provided with a threaded stud to which a sturdy
© ICS/OCIMF/IAPH 2006 209