Static Electricity 2000 Edition

7.12.3 Steam Cleaning.
Steam cleaning can create very large
charge densities with correspondingly large space charge
potentials that increase with the size of the tank. Therefore,
the following precautions are recommended:
(1) Tanks larger than 4 m
3
should be inerted before steam
cleaning.
(2) All components of the steaming system should be con-
ductive and grounded.
(3) All conductive components of the tank should be bonded
and grounded.
7.12.4 Internal Grit Blasting.
Where possible, tanks and pro-
cess vessels should be clean and free of ignitible materials (no
more than 10 percent of LFL). Hose used for grit blasting
should be grounded and the resistance to ground from any
part of the hose assembly, especially the nozzle, should not
exceed 10
6
ohms. (See A.7.4.3.)
7.13 Portable Tanks, Intermediate Bulk Containers (IBCs),
and Containers.
The following practices are recommended
to reduce static electricity hazards during filling and emptying
of portable tanks, IBCs, and containers.
7.13.1 Metal Portable Tanks and IBCs.
Metal portable tanks
and IBCs should be bottom-filled, if possible. Where used for
nonconductive flammable liquids, filters should be placed at
least 30 seconds upstream, as recommended in 7.4.5. The por-
table tank or IBC should be bonded to the fill system prior to
opening and should be closed before being disconnected
from the bond. Filling rates should be similar to those nor-
mally used for drum filling, about 225 L/min or less, unless
the container is inerted. If the fill pipe does not extend close
to the bottom and the vessel is not inerted, a slow start velocity
of 1 m/sec or less should be used until the fill pipe is sub-
merged to about 150 mm. Portable tanks and IBCs with non-
conductive linings present hazards somewhat more severe
than with drums, due to the larger capacity and the greater
energy that can be stored for equal charge densities.