International Conference on Electrical, Electronics and Communication Engineering (ICEECE'2014) Oct. 9-10, 2014 Antalya (Turkey)
Electricity and Risks for the Human Body
A. Ouazani, and I.Habi
-Peception-current :it is the minimal current that an individual
can detect.
This threshold varies 1onsiderably among individuals.
-Let-go current :fot highter levels of current,nerves and
muscles are vigrously stimulated, and pain and fatigue
eventually result.
Involuntary contractions of muscles results.
Abstract--- In this paper two parts are considered:
---Analyse
of
physiological
effects:
(sensations, tetanisation, fibrillation) and no exhaustive study of
differents factors involved in the physiological effects of electric
current(current ,impedance of human body,time of passage of
current,trajectory of current through he human body.....)
----Analyse of the electrical impedance of the human body :
this impedance depend of several factors .In our study we analysed
the way of non exhaustive factors that affect significant way on the
electrical impedance.
The let-go current is definlted as the minimal current at which
subject can withdraw voluntary.
The minimal threshold for the let-go current is 6.mA
-Tetanization-muscle(1,2,3) From 7
to 8
mA ,muscles
contract. When the intensity reached 10-15mA, clenching of
the hand (for a contact hand - hand or hand - feet) 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: the hearth is susceptible to electric
current in a special way that makes some current particulary
dangerous .
Part of the current passing through the shest flows through the
heart.
If the magnitude of the current is sufficient to excite only
part of the hearth muscle,then the normal propagation of
electric activity in the hearth muscle is disrupted .
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
intense heat and concerns especially
exposed
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.
Keywords-----electric current, fibrillation, voltage, impedance,
human body.
I .INTRODUCTION
E
LECTRICITY has been one of the greatest benefits to
mankind.It has contributed to all major advances that we
enjoy.At the same time,electricity can also be one of the
most dangerous risks to our health and safety.
In any electrical installation the risk of electrisation (no fatal
accident) or electrocution(death) and fire are real.
When a person is on contact with two electrodes,it passes
through the body an electrical current.
The dangers of this electrical current depend of several
factors. The electrical intensity that circulates around the
human body because of an accidental contact,will exclusively
depend only of the impedance that is offeres to the passage of
the current.
II. EFFECTS OF ELECTRIC CURRENT
A. Physiological effects:
Electrical hazards are caused by –
the improper use of machinery, apparatur,outlets,or electrical
equipments,
-The improper maintenance of apparaturs , outlets and
electrical equipments.
Dangers of electricity include a variety of hazards include
electric shock, physiological damage, physical burns,
neurological damage and ventricular fibrillation resulting in
death.
A.Ouazani: University of Boumerdes Algeria (corresponding author phone:
213 55247835; e-mail: ouazani_abdellah@yahoo.fr).
I.Habi University of Boumerdes Algeria (corresponding author e-mail:
ouazani_abdellah@yahoo.fr).
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International Conference on Electrical, Electronics and Communication Engineering (ICEECE'2014) Oct. 9-10, 2014 Antalya (Turkey)
the body and the current
depends
on
the
contact
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).
Neurological effects:current can causes interference with
nervous control, especially over the hearth and lungs.
Repeated or severe electric shock whitch does not lead to
death has been shown to cause neuropathy
Recent reshearch has found functional differences in neutral
activation during spatial working memory and implicit
learning oculamotor tasks have been identified in electrical
shock victims.
Body impedance:
B. Factors involved in the physiological effects of electric
current
Current:
The electrical current based on their values, provoke
different physiological actions on the human body. Some
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
floor
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 electro technical 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).
-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.
Voltage:
The value
of
the
voltage does
not
represent
the danger criterion, the criterion being the current through
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 ...).
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.:
The values for the currents fibrillation are very different,
which can be explained by the different
experiences of different models in different conditions.
Current path:
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.
Frequency:
The
vast majority
of common household
and
industrial distributed at a frequency of 50-60Hz which are
the most
dangerous
frequencies.
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.
Other influences:
They
are
very
-age,
-Health,
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numerous. Among
them are:
International Conference on Electrical, Electronics and Communication Engineering (ICEECE'2014) Oct. 9-10, 2014 Antalya (Turkey)
-the physical,
-the size,
-the psychological state,
-room temperature
-the ambient atmosphere, the moisture-,
-Elevation .......
Zi-can be considered mainly resistive and is virtually constant.
Zp-depend of voltage contact, frequency, the surface of the
electrodes, the contact pressure of the moisture from the skin
etc. It varies with in very wide limits (even for one and the
same person) .
For voltages below 50V,the skin impedance varies widely.
The total impedance varies in the same way. For higher
voltage,, the total impedance less dependent of the impedance
of the skin and its value is close, after puncturing the skin
from that of the internal impedance Zi.
Statistical extrapolation of the result of measurement of
body impedance carried out on corpses and living persons.
“The values of table were measured for a current path handhand [5]-[8]. Values are measured on 50 living persons at U =
15V, on 100 living persons at U = 25V and at one person at
200V after 0,03s.
For voltages below 25V, the measured values with contact
surfaces wetted with normal water are lower 10-25%
compared to dry conditions.
If the surfaces are wet contact with conductive solutions,
the measured values decrease up to half of the values with dry
conditions.
Summary table:
current
(mA)
0,045
0.5 to 1
6-8
10
15,5
20
30
50
70 to100
>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
TABLE I
VALUES OF IMPEDANCE HUMAN BODY
Touch
voltage(v
)
25
30
75
100
220
700
2000
5% OF
50% of the
population
1750
1450
1250
1200
1000
750
660
3250
2625
2200
1875
1 350
1 100
1100
THE
POPULATION
95% of the
population
6100
4375
3500
3200
2125
1550
1500
The current path influences the value of the impedance of
the human body.
As the example: the impedance from a current- path one
hand to Both feet is 75%, and the impedance from Both Hands
to both Feet 50% , and from Both Hands to the trunk of the
body 25 % of the impedance hand-hand (100% ).
As far as the effect of frequency is concerned, the
impedance of the skin decreases when the frequency
increases.
ZT decreases sharply for frequencies of up to 500 Hz ,then
the decrease is less pronounced and from 5kHz essentially
constant.
Other factors affecting the value of impedance of the human
body.
-Contact surface of the electrodes S: more surface area and the
less is the value of ZT. And ZT axes of 6 times when S
increases from 3 cm2 to 24 cm2 at a frequency of 50 Hz.
-The temperature experiments [14] have made summers in
Tajikistan from living people using a touch voltage equal to
15V and have resulted in the relationship
Z (kΩ) = 4.85 - 0.057 T(°C)
III. ANALYSIS OF ELECTRIC IMPEDANCE HUMAN BODY
Different parts of the human body, such as skin, blood,
muscles, and other tissues and joints-have for current electric
some impedance.
The value of the impedance depends of very important
number factors especially the current path, the contact voltage,
duration of current flow, the moisture condition of the skin,
the surface of touch, temperature etc..
This study examines the dependence of ZT as a function of
several factors [8,10,12,13].
The impedance consists of three parts. The two impedances
of skin at the electrodes ZP and the internal impedance Zi.
The vector sum of the internal impedance of the human body
and the skin impedance is called total impedance of the human
body which is shown in figure 1.
Thus for T=0°C, Z = 4.85kΩ and for T=40°C, Z = 2.57
kΩ.
-Altitude: Z decreases with altitude [15] and at 850 m Z =
Fig. 1 Circuit-diagram for the impedance of the human body
Measurement seems to indicate that the internal impedance
also has a small capacitive component.
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International Conference on Electrical, Electronics and Communication Engineering (ICEECE'2014) Oct. 9-10, 2014 Antalya (Turkey)
4.45 kΩ and at 3700m Z = 4.07 kΩ, for contact voltage equal
to 12V.
-Other factors: size, weight, sex, psychological conditions etc .
IV. CONCLUSIONS
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.
The danger of electric current to humans is dependent of
the intensity of the current flowing there through. This
intensity is difficult to measure in the human body. It is
defined as the ratio of the contact voltage and electrical
impedance of the human body.
This impedance is non linear and depends of a very
important number of factors some of which were analyzed in
this work, in particular the action of the contact voltage and
the current path in the human body.
REFERENCES
[1]
Ouazani A.
« Théorie et pratique pour l’amélioration de la sécurité dans les
installations électriques » .Thèse de doctorat, Moscou 1990.
[2] Dalziel C.F.
« Electric shock hazard. IEEE Spectrum »,1972.vol.6 N2. »
[3] « Effets du courant passant par le corps humain ». Commission
électrotechnique internationale, rapports de la C.E.I, publication 479.1,
1984.
[4] Remond C.
«Les effets du courant électrique traversant le corps humain » JEEE
N538 ,1986.
[5] Ray Frisch
«All about electric shock. Radio electronic », 1985, vol.35 N8.
[6] Dolin P. K.
«La sécurité dans les installations électriques ». Moscou,
Energoatomizdat, 1984.
[7] Folliot D.
«La connaissance des risques : physiopathologie des électrisations »,
JEEE, N462 ,1980.
[8] Dalziel C.F.”«Lethal electric current. IEEE Spectrum » 1968, vol.6 N2.
[9] Muller, “la mise a la terre du point neutre a la terre des réseaux
triphasés a basse tension”. Revue générale de l’electricité.tom 36 N 10 ,
193O.
[10] G. Biegelleier, “L’impédance electrique du corps humain”. Revue
gennérale de l’électricité N 11, 1985.
[11] G. Biegelmeier, “Uber den einflub der korper-impédanz des menschen”
E.u M ,vol97,1980.
[12 ] A. Ouazani, “Résistance électrique du corps humain”. V.I.N.I.T.I,N
7175.B88 ,Moscou ,1988.
[13] A. Ouazani, “Nouvelle représentation de la résistance électrique du
corps humain”. V.I.N.T.I.,N 2251.B88, Moscou,1989.
[14] K. M. Usmanov,“Elektritcheski soprotivlenia tela tchelovieka”.
Dnepropetrovsk,1975.
[15] M. Y. Khakel, “Elektritcheski soprotivlenia tela tchelovieka v uslovia
srednii asii”. Dnepropetrovsk, 1975.
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