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Low Voltage Electrocution - 1 - M Bikson A review of hazards associated with exposure to low voltages Dr. Marom Bikson Low Voltage Electrocution
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M Bikson
A review of hazards associated with exposure to low voltages

Dr. Marom Bikson
Department of Biomedical Engineering, City College of New York of the City University of New
York
The Graduate School and University Center of the City University of New York
New York, N.Y

O
VERVIEW


This review summarizes peer reviewed papers,
government reports, and regulatory group
recommendations on hazards from electricity. A
goal of this report is to determine a
safe voltage
level below which these hazards will not occur; the
review emphasis is, therefore, on extremely-low
voltage (<50 V
RMS
or 71 V
PEAK
) exposure. This
report is divided into five main sections dealing with
human exposure. S
ECTION
I addresses the basic
mechanisms by which electric current can affect
biological tissue in a hazardous manner. S
ECTION
II
summarizes experimental research studies involving
application of electric current to human subjects.
S
ECTION
III reviews the epidemiology and case
reports of human electrocution. S
ECTION
IV
includes a summary of previous electrical safety
standards. S
ECTION
V includes the review
conclusions for human exposure. An A
PPENDIX
deals with the electrocution of dogs.

Review Scope

This review and its summary conclusions
relate only to adverse effects of transdermal current
exposure
1
. This review is not concerned with
electric shocks that cause no long-term hazardous
effects (e.g. sensory sensations such as noxious
stimulation and phosphenes). Moreover, this review
does not include injuries that result from humans
being startled by otherwise non-hazardous electrical
current (e.g. falls) or interference with medical
devices. This review only includes scientific reports
which: 1) appeared in scientific journals; 2) include
recommendations by a (inter)nationally recognized

1
When electricity enters the body subdermally, as for
example through two needles inserted into the heart,
voltages as low as 20 V and currents as low as 100 µA
can cause fibrillation (Camps et al. 1976). With
electrodes placed directly on the heart, ventricular
fibrillation is usually achieved with voltages of ~0.2 V
and current flow of 80-600 µA (Kugelberg 1976;
Webster 1998).
scientific organization; or 3) were sponsored by a
government agency. This review does not address
resuscitative measures, forensic diagnosis, or electric
safety measures. Lightning strikes, high-voltage
arcs, and electrical fires/explosions are not
considered.

S
ECTION
I:

B
ASIC MECHANISMS BY WHICH
ELECTRIC CURRENTS AFFECT BIOLOGICAL TISSUE


Electrically Excitable Tissue / Burns

The human body will conduct electricity. If
the body makes contact with an electrically
energized surface while simultaneously making
contact with anther surface at a different potential
(or ground) then an electric current will flow
through the body, entering the body at one contact
point, traversing the body, and exiting at the other
contact point. The magnitude of this current will
increase as the voltage difference across the contact
points increases. This section introduces potential
hazards associated with such currents.
Certain tissues in the body have
traditionally been considered most sensitive to
electricity because they normally use bio-electric
signals. Cells in the central and peripheral nervous
system (neurons) use bio-electrical signals to rapidly
process and communicate information. Neurons
regulate the contraction of cardiac cells, diaphragm
muscle cells (inducing lung inspiration), and
peripheral muscle cells (controlling movement).
Cardiac and muscle cells, in turn, also use bio-
electric signals to trigger their contraction. These
cells are collectively referred to as electrically
excitable cells (Hille 2001) Electric stimulation, or electrical
shock, results when a portion of the current
conducted by the body passes through/polarizes
excitable cell membranes. Theoretical and forensic
studies examining the effects of electricity on
biological tissue have thus focused on systems
containing or regulated by excitable cells. For
example, electric shock can lead to activation of Low Voltage Electrocution
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M Bikson
neurons/muscles involved in respiration or cardiac
pacing. Electric shocks can acutely affect cell
function without necessarily damaging these cells.
Electric currents may also heat external and
internal tissue sufficiently to induce structural
damage through
electrical burns. Electrical burns
affect human health through actions on both
excitable (e.g. cardiac, nervous) and non-excitable
(e.g. skin, blood vessels) tissues.
Electroporation refers to changes in cell
membrane permeability by electric fields.
Electroporation affects both excitable and non-
excitable cell function and can lead to irreversible
cell damage (Chilbert 1998). The role of irreversible
electroporation in transdermal electrical accidents
remains unclear and is thought to be limited to high
voltages/currents (>200 mA; Reilly 1998).
Electrocution refers to fatalities resulting
directly from lethal current flow through the body.

Conventions, Metrics, and Cellular Models

The theory governing the interaction of
electric current with excitable cells (electric shocks)
has been well characterized by my group (Durand
and Bikson 2001; Bikson et al. 2004) and others
(Reilly 1998; Rattay 1999; McIntyre and Grill 1999).
The consensus of these reports is that the effects of
electric currents can be directly calculated using
information about the detailed cell geometry/
biophysical properties and detailed information
about the electrical potential (induced by current
flow) along this geometry; all with micrometer
resolution
2
. Unfortunately, this combined
physiological/electric-potential data is not available
for human exposure. Moreover, theoretical
consideration of the detailed electric potential
induced under various exposure conditions and their
effects on every excitable cell in the body is
intractable (but see Reilly 1998, p334).
Therefore, the approach taken by previous
research reports and regulatory groups has been to
assume a (quasi-) uniform electric field (E in
volts/meter) across the tissue of interest (but see
Reilly and Diamont 2003).
3
This assumption may

2
Specifically, information about the second derivative
of the extracellular potential in space can be related to
the excitation strength, the amount of current moving
across a cell membrane.
3
Note that this assumption ignores a central concept
that it is the second special derivative of voltage (i.e.
be grossly valid for currents passing across the entire
body. It significantly simplifies the analysis of
electric current effects because it allows
standardization across disparate experimental studies
where similar uniform fields were used. In
addition,
this
assumption
facilitates
the
establishment of safe exposure levels using a single
number, such as the uniform electric field strength.
Electric field (E in units of V/m) can be
related to current density (J in A m
-2
) by: E = J·
where a homogenous volume resistivity ( in ·m)
is assumed. Current density can, in turn, be related
to current (I in A) across the entire tissue through
knowledge of the tissue geometry, notably cross-
sectional area (A
cs
in m
2
), and current entry/exit
locations. The voltage (V in V) across the entire
tissue can be theoretically related to current I
through a tissue with a total path resistance R by V =
I·R. Finally, for a cylindrical block, total path
resistance R, can be related directly to uniform
resistivity by R = ·d/ A
cs
where d is the path
length (in meters).
Stray voltage refers to unintended
electrical potentials between contact points that may
be encountered by humans or animals. Accidental
electrocution can result when stray voltages exceed a
safe threshold voltage level. This report focuses on
determining this safe voltage level as stray voltages
are readily measurable during quality assurance
(Con Edison 2004). The internal electric field will
depend not only on the contact voltage magnitude
but also on contact geometry/tissue properties; safe
voltage levels may thus vary depending on
exposure/subject
conditions.

Additional
consideration must be exercised in considering safe
voltage levels (as opposed to safe current levels);
note that an individual wearing electrically
insulating gear (e.g. rubber g