Static Electricity 2000 Edition

7.10.6 Agitation.
When solids are dissolved or dispersed into
nonconductive liquids, the rate of charge generation can be
large depending on factors such as solids loading, particle size,
and agitation rate. Dissipation of the charge is frequently
achieved by raising the conductivity of the continuous phase
by reformulation with conductive solvents or by the addition
of antistatic additives. Ignition hazards can alternatively be
controlled by inerting.
7.10.7 Nonconductive Process Vessels.
In general, noncon-
ductive process vessels should not be used with flammable liq-
uids. They present external ignition risks if their outer
surfaces become charged. If a nonconductive tank is to be
used and the possibility exists that the atmosphere around the
tank or in the vapor space could be ignitible, the following
should be incorporated to ensure the safe dissipation of
charge and to prevent discharges:
(a) All conductive components (e.g., a metal rim and
hatch cover) should be bonded together and grounded.
(b) Where used to store nonconductive liquids, an enclos-
ing, grounded conductive shield should be provided to pre-
vent external discharges. This shield can be in the form of a
wire mesh buried in the tank wall, provided it is grounded.
The shield should enclose all external surfaces.
(c) Where used to store nonconductive liquids, the tank
should have a metal plate with a surface area not less than 0.05
cm
2
/m
3
of tank volume located at the bottom of the tank and
bonded to ground. This plate provides an electrical path
between the liquid contents and ground through which the
charge can dissipate.
(d) Where used to store conductive liquids, a grounded fill
line extending to the bottom of the tank or an internal
grounding cable extending from the top to the bottom of the
tank and connected to ground should be provided. A
grounded fill line that enters at the bottom and does not intro-
duce a spark promoter fulfills this recommendation.