Page 93 - International safety guide for oil tankers and terminals

STATIC ELECTRICITY

Any earthing or bonding links used as a safeguard against the hazards of
static electricity associated with portable equipment must be connected
---ใช้เพื่อการศึกษาเท่านั้น---
whenever the equipment is set up and not disconnected until after the
equipment is no longer in use.

งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
3.2.3 Avoiding Loose Conductive Objects
Certain objects may be insulated during tanker operations, for example:

A metal object, such as a can, floating in a static accumulating liquid.
A loose metal object while it is falling in a tank during washing operations.
A metallic tool, lying on a piece of old lagging, left behind after
maintenance.

Every effort should be made to ensure that such objects are removed from the
tank since there is evidently no possibility of deliberately bonding them. This
necessitates careful inspection of tanks, particularly after shipyard repairs.

3.3 Other Sources of Electrostatic Hazards

3.3.1 Filters
Coarse (greater than or equal to 150 microns). ึ
Three classifications of filter may be used in tanker operations, as follows:

These do not generate a significant amount of charge, and require no
additional precautions provided that they are kept clean.

Fine (less than 150 microns, greater than 30 microns).
These can generate a significant amount of charge and therefore require
sufficient time for the charge to relax before the liquid reaches the tank. It is
essential that the liquid spends a minimum of 30 seconds (residence time) in
the piping downstream of the filter. Flow velocity should be controlled to ensure
that this residence time requirement is met.

Microfine (less than or equal to 30 microns).
To allow sufficient time for the charge to relax, the residence time after passing
through microfine filters must be a minimum of 100 seconds before the product
enters the tank. Flow velocity should be adjusted accordingly.

3.3.2 Fixed Equipment in Cargo Tanks

A metal probe, remote from any other tank structure but near a highly charged
liquid surface, will have a strong electrostatic field at the probe tip. Protrusions
of this type may be associated with equipment mounted from the top of a tank,
such as fixed washing machines or high level alarms. During the loading of
static accumulator oils, this strong electrostatic field may cause electrostatic
discharges to the approaching liquid surface.

Metal probes of the type described above can be avoided by installing the
equipment adjacent to a bulkhead or other tank structure to reduce the
electrostatic field at the probe tip. Alternatively, a support can be added
running from the lower end of the probe downward to the tank structure below,
so that the rising liquid meets the support at earth potential rather than the
insulated tip of a probe. Another possible solution, in some cases, is to
construct the probe-like device entirely of a non-conductive material. These

© ICS/OCIMF/IAPH 2006 59