Static Electricity 2000 Edition

4.3 Discharge of Static Electricity and Ignition Mechanisms.
4.3.1 General.
As electric charge accumulates through sepa-
ration, there will be an increase in the electrical forces trying
to restore a neutral condition by reuniting those charges in
the form of a static electric discharge. Many types of dis-
charges can occur, and these are illustrated broadly in Figure
4.3.1. For a static electric discharge to be a source of ignition,
the following four conditions must be met:
(1) An effective means of separating charge must be present.
(2) A means of accumulating the separated charges and
maintaining a difference of electrical potential must be
available.
(3) A discharge of the static electricity of adequate energy
must occur.
(4) The discharge must occur in an ignitible mixture.
C
Q
V
----
=
Liquid
flow
+
+
+
+
+
+
+
+
+
+
+
+ + + + +
Earthed
storage tank
(a) Charge accumulation on
low conductivity liquids
(b) Charge accumulation on
an insulated conductor
(c) Charge accumulation on
a person on an insulating
floor or wearing insulating
footwear
+
+
+
+
+
(d) Charge accumulation on
insulating solids (e.g.,
rubbing an insulating pipe)
Bonding
wire not
connected
Streaming
current
+
+
+
+
+
+
+ +
+
+
+
+
+ +
+
+
+
+
+
i
+
+ +
+
– – – –
Q
t
Q
0
t
τ
⁄
–
=
τ
RC
=
τ
ρεε
0
=

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