Download The Effect of Electric Current on the Human Body

International Conference on Systems, Signal Processing and Electronics Engineering (ICSSEE'2012) December 26-27, 2012 Dubai (UAE)
The Effect of Electric Current on the Human
Body
A. Ouazani, A. Khellassi, I. Habi
Tetanizationmuscle: From 7to 8
mA muscles
contract. When the intensity reached 10-15mA, clenching of
the
hand (for
a
contact hand - hand
orhandfeet) on the seized items is such that it is possible to let go:
the tetanisation which may extend to the arms and legs.
For currents above 25 mA, the trajectory of current in the
body may include the respiratory muscles and result in death
from
asphyxiation. The
blocking of
the
chest can
harm the heart and therefore result in electrocution (fatal
accident).
-Fibrillation of
the
heart: Fibrillation
heart
is uncoordinated contraction of
muscle (cardiac arrhythmia cycle and loss of synchronism).
During fibrillation, the heart's electrical activity is disordered,
which prevents effective contraction of the heart.
Abstract—Two parts are considered in this study:
-In the first one the physiological effects are analyzed: the first
sensations due to electric current (the currents are not dangerous in
this case), the tetanisation which can have serious consequences
especially if the time of current flow is important, cardiac fibrillation
which is very dangerous and often results in electrocution and burns.
-The second part comprises a non-exhaustive study of the various
factors involved in the physiological effects of electric current such
as the current, the electrical impedance of the human body, the time
of passage of current, the trajectory of current through the human
body, the frequency of the current.
Keywords— accidents, burns, electric current, electric energy,
electric shock, fibrillation, frequency, voltage.
I. INTRODUCTION
When cardiac contractions are anarchic, the heart can no
longer fulfil its role of pump and the person becomes
unconscious and not
breathing. If
this
condition is
prolonged, irreversible damage appear followed by the death
of
the
victim.
-Electrical
burns: burns are
the most
common
consequence of accidents
due to
the electric
current.
The seriousness of electrical burns is related to all the physical
parameters of the accident: current, voltage and time of current
flow. Burns
due to high
voltages are
of particular gravity, because
in
addition
to local
burns, they appeared deep burns along the current flow in the
muscle
masses.
The arc burns are
due
to the
exposed
intense heat and concerns especially
parts (hands, face, eyes), but can reach a significant portion of
the skin surface and be aggravated by ignition of clothing.
Electrothermal burns are due to the passage of electric
current and related to the heat and their importance is directly
related
to the
law W = ITU.
In the mixed burns, electric arc and the passage of electric
current together result in superficial and deep burns.
E
LECTRICAL energy is today the form of energy most
commonly used. It is easy to transport and transform into
other forms of energy.
In any electrical installation the risk of electrocution (nonfatal accident), electrocution (leading to death) and fire are
real. When a person is in contact with two electrodes, it passes
through the body an electrical current. The intensity of this
current depends on several factors. The danger depends on
both the current, time of current flow through the body, the
trajectory followed by this current and many other factors
which are discussed partially.
The different physiological responses encountered when an
electric current passes through the human body are numerous
and require analysis not only electricians but also by medical
specialists (cardiologists, neurologists, occupational physicians
...).
II. PHYSIOLOGICAL EFFECTS
Perception-current: the
current
flow of
very
low
intensity is perceptible
by
a
tongue
by
giving a tangy sensation. Beyond and slightly
higher
intensities it becomes perceptible to the skin and causes a
tingling sensation, then pain.
III. FACTORS INVOLVED IN THE PHYSIOLOGICAL EFFECTS
OF ELECTRIC CURRENT
A. Ouazani,
is with the University of Boumerdes Algeria email:ouazani_abdellah@ yahoo.fr ).
A. Khellassi, is with the University of Boumerdes Algeria.
I. Habi , is with the University of Boumerdes Algeria (email:[email protected] ).
A. Current
The electrical currents based on their values provoke
different physiological actions on the human body. Some
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International Conference on Systems, Signal Processing and Electronics Engineering (ICSSEE'2012) December 26-27, 2012 Dubai (UAE)
C. Body impedance:
The impedance offered by the human body to the current
flow is not
linear.
Its value varies in
very
large proportions and the current through the human body
is obviously
a
function of
the impedance.
For the same person, the impedance varies with several
factors (contact points, the skin condition, the duration of
contact, the contact voltage ...).
values are interesting to know, what are the thresholds?
-Perception
thresholds:
To 0.45 mA current is
percept at
the tongue. Beyond and from 0.3
to 3mA
the
flow
of alternating current (50Hz) becomes noticeable at the skin
and
causes a
tingling
sensation and pain.
Experiments on 169
people showed
that the
sensation occurs on
average
for a
current of
1.086 mA from Dalziel [2].
For IEC
(International electrotechnical commission), the current
value perception is
0.5 mA [3,4].
Note that these are average values and depend on several
factors. Hence
from
Dalziel
the
value
of
current perception ranges
from 0.3
to
99.7 mA [2].
D. Time of current flow:
The danger is even greater than the time of passage of
current through the human body is big. So the danger is the
same for a current of 30mAfor 5 seconds and 300 mA for 0.5
seconds. Indeed during
time of
current
flow, the body
impedance decreases and the current through the body
increases.
Several authors have developed empirical formulas for
the current fibrillation versus time of passage through the
human body (8.9). Thus according to Dalziel and C.E.I.:
Non-threshold drop
For currents
above
the current perception,
sensation becomes unpleasant
and reached
all
the hand (touch hand or hand to foot) and can lead to muscle
contraction.
The threshold of release is not defined by the IEC as
the maximum current that can be tolerated by a person.
The
threshold
for non-release depends
on
several
factors. Among these factors include time since the electrical
impedance of the human body decreases, implying a contact
voltage for a defined increase in the intensity of the current
through the
human
body and lead to death within a
few minutes.
For example the current value of non-release is set at
10 mA by
the
IEC [3]
and
at 16 mA
by Folliot and Dollin [6,7].
-Threshold of
ventricular
fibrillation:
The threshold for cardiac fibrillation depends mainly on the
value of the current, time of current flow in the body
and the current
trip.
For a time of passage of current greater than the cardiac
cycle(approximately one second), most authors consider that
the fibrillation is between 25 mA and 100 mA [3, 4,5].
Towards 25-30 mA, if
the circuit
cut occurs quickly, the
danger of electric shock is unlikely. This explains the
choice of this
threshold by
lawmakers
and manufacturers of protective
relays acting quickly
on
the switchgear.
Ih=
165
√t
and
Ih= 10 +
10
t
The values for the currents fibrillation are very different,
which
can be
explained
by the
different
experiences of different models in different conditions.
E. Time of current flow:
The current trajectrory has a great influence on the
danger, the electric current circulates through the
highest conductance of the human body. These are the
trajectories that can harm the heart that induce ventricular
fibrillation. Thus according to the IEC the danger to
the trajectory from hand to foot is 3.8 times larger than
that from hand to hand.
F. frequency:
The
vast majority
of common household
and
industrial distributed at a frequency of 50-60Hz which are
the most
dangerous
frenquencies.
For frequencies above 50Hz, the current becomes less
dangerous. At
1000Hz the
values of
current
perception, the not release and
fibrillation are 2.1
times, 6.68 times and 14 times higher than for a frequency
of 50Hz.
B. Voltage:
The value
of
the
voltage does
not
represent
the danger criterion, the criterion being the current through
depends
on
the
contact
the body and the current
voltage and the value of the electrical impedance of the human
body.
Thus the means of protection do not refer to the current
that is not easily measurable, but the value of touch voltage.
The IEC believes that voltages lower than 50V are not
dangerous [3,8].
G.Other influences:
They are very numerous. Among them are:
-age,
-Health,
-the physical,
-the size,
-the psychological state,
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International Conference on Systems, Signal Processing and Electronics Engineering (ICSSEE'2012) December 26-27, 2012 Dubai (UAE)
[5]
[6]
-room temperature
-the ambient atmosphere,
the moisture-,
-Elevation .......
[7]
[8]
[9]
Table I : Summary
curre
nt
(mA)
0,045
0.5 to
1
6-8
10
15,5
20
30
50
70 to
100
>500
Effects of electric current
Sensory level language
Perception threshold depending on the state of
the skin, light
muscle contractions
Perception skin shock to the touch
Electrical shock, muscle contraction,
Threshold defined by the non-release C.E.I.
Impossibility of self-liberation of the current
Electric shock, tetanization of the
thorax, possibility
On ventilatory asphyxiation if t is greater than
3 minutes if the current path of interest to
the diaphragm (contact by hand)
Electric shock, tetanization of the thorax,
possibility of ventricular fibrillation if t is greater
than one minute
Possibility of ventricular fibrillation with a
probability greater than 50% and if t is greater
than 1.5 of the cardiac cycle
Ventricular fibrillation with a probability
greater than 50% if t is less than 0.75 of the
cardiac cycle; burns
Nerve centers destroyed; internal chemical
composition, burns veryimportant; almost
immediate death
IV. CONCLUSION:
The
statistics of accidents show
that
the
percentage of accidents due to electric current is very
low, where as those of deadly accident is much higher.
The widespread
use of
electricity leads
to many accidents that can be very serious and a sizeable
percentage results
in
death.
The study of the effects of electric current on the human
body and that of the electrical impedance of the human
organism are
essential.
A non-exhaustive part has been studied in the present work.
REFERENCES
[1]
[2]
[3]
[4]
A. Ouazani, Théorie et pratique pour l’amélioration de la sécurité dans
les installations électriques.Thèse de doctorat, Moscou 1990.
C.F. Dalziel, Electric shock hazard. IEEE Spectrum, 1972.vol.6 N2.
Effets du courant passant par le corps humain ». Commission
électrotechnique internationale, rapports de la C.E.I, publication 479.1,
1984.
C. Remond, Les effets du courant électrique traversant le corps humain
JEEE N538 ,1986.
209
Ray Frisch, All about electric shock. Radio electronic, 1985, vol.35 N8.
P. K. Dolin, La sécurité dans les installations électriques. Moscou,
Energoatomizdat, 1984.
D. Folliot, La connaissance des risques : physiopathologie des
électrisations, JEEE, N462 ,1980.
Effets du courant passant par le corps humain . C.E.I, rapports de la
C.E.I, publication 479, 1974..
C.F. Dalziel, Lethal electric current. IEEE Spectrum 1968, vol.6 N2.