Deaths caused by electricity
Domestic and to a lesser extent the industrial
use of electricity cause a number of deaths annually. Most of these deaths are
the result of accidents, although suicide by electrocution is also seen.
The effect of the exposure of the body to an
electrical current will be influenced by a number of factors:
The type of current (alternating current [AC]
versus direct current [DC]). The human body is four to six times more susceptible to an alternating
current than to a direct current. It is especially low frequencies between 39
to 150 cycles per second (39±150 Hertz) which are dangerous. The higher the
frequency, the less dangerous the current. It is important to remember that
household electricity is usually 50 to 60 Hertz!
The strength of the current, measured in ampere. The higher the current, the more dangerous. A
current of 1 mA (milli-amperes) will only result in a sensation of shock, while
a current of 15,0 mA will result in contraction of the muscles and the person
will not be able to release the wire. As a matter of interest, the same
principle underlying the so-called pugilistic or boxer posture in charred
bodies plays a role in this situation: all themuscles in the body contract due
to the electrical stimulation, but the flexor muscles (because of their larger
mass and therefore power) will dominate. This results in closure of the hand,
and the wire is therefore tightly grasped. Death due to abnormal heart rhythm
will occur with exposure to a 70 mA current for 5 seconds, 300 mA for 0,3
seconds and 1 800 mA for 0,01 seconds.
The tension or voltage. High voltage is less dangerous than low
voltage. In the case of very high-tension currents, an electrical arc flame or
spark can cause burns even though the body is not in direct contact with the
wire. High-tension currents tend to throw the individual away from the current
(wire), which decreases the contact time.
The time exposed to the current. The longer the current flows through the body,
the more extensive the damage will be.
The resistance of the body. Water is a very good conductor of electricity.
Contact with an electric current with wet (eg sweaty) hands lowers the
resistance and therefore increases the amount of electricity flowing to the
body. It will also be increased if the person is earthed on a wet surface, for
instance standing barefoot on wet cement.
The route of the current through the body. An electrical current running parallel to the
electrical axis of the heart will most likely cause abnormal heart rhythms. The
electrical axis of the heart in the vertical plane is roughly from the right
shoulder to the left foot. Contact with the electrical current with the right
hand is therefore theoretically more dangerous than contact with the left hand,
and unfortunately, most of us are right-handed.
Underlying pathology. People with heart diseases are more vulnerable
to the effect of an electrical current than others. Ironically, electrical
energy is used in controlled conditions to treat abnormal heart rhythms.
Causes of death may either result in
instantaneous death or death at a later stage due to complications. It is
therefore possible that the person may survive initially and walk some distance
after having been exposed to an electrical current, but then collapses and dies
due to an abnormal heart rhythm.
Abnormal heart rhythm (arrhythmia), especially
ventricular fibrillation. In this condition the heart contracts in an unco-ordinated manner,
with no forward propulsion of blood. It therefore results in cardiac arrest.
Respiratory failure due to contraction of the
thoracic muscles (muscles of the chest) and diaphragm. This is due to stimulation of the muscle by the
electric current causing spasm, so that the person cannot inhale of exhale.
Paralysis of the brain stem and the vital
vital centres control respiration as well as the cardiovascular system. The
brain stem is especially vulnerable if the current flows through these centres,
in other words when the person's head comes into contact with the current or it
is in the way of the current as it passes through the body.
Other injuries include burns with high-tension
electricity currents, with the presence of arc burns, and head injuries, which
may occur when the person is thrown from a ladder after receiving an electrical
The post-mortem signs (excluding the burns and other
injuries which we already discussed) due to electrical current may be minimal
and can easily be overlooked, especially if they are in obscure places. In
cases where the resistance of the skin is very low, for instance due to being
wet, the contact wound may even be absent. The entrance or contact wound is
usually found on the hands, and the exit wounds on the soles of the feet.
The skin wounds are caused by heat production.
The epidermis resists the flow of the electrical current. The remainder of the body
tissue consists of water and electrolytes (salts), which are an ideal
conduction medium. Due to resistance to the flow of the electrical current, the
skin is heated, and this heat production creates a characteristic wound. The
epidermis becomes white and sometimes surrounds a vesicle containing fluid
caused by production of steam under the skin as it is heated by the current
flowing through the tissue with a high resistance (compare this with the
principle applying to a kettle). Histologically the cells of the basal layer of
the epidermis are distorted. This appearance is also known as Joule's wounds.
When the contact is less firm, small sparks may jump over the gap. This results
in a spark lesion consisting of a hard, brown nodule on the skin.
With special examination techniques the deposit
of metal particles (metalisa-tion) may be seen at the entrance wound.
Some authors have also noted that in an
individual previously exposed to electrical current, and who has survived,
calcifications may develop in the underlying tissue. This may be of importance
in cases of alleged torture with electricity.
In the case of lightning a powerful electrical
current acts over a very short period of time.
The post-mortem signs in a lightning victim may
include the following:
A fernlike or arborescent distribution of red or erythematous marks on
the body surface. Lightning usually occurs when the atmosphere is humid or
during rain storms. The wet body is drenched in water, which accumulates in the
body folds. It is along these ``paths'' of least resistance that the electrical
current will spread over the skin surface, with only slight burning of the
skin. This presents as arborising red lines.
More extreme burns and singed hair.
The shoes and clothes may be ripped from the body. This can raise
suspicion that the vicim was raped.
Rupture of the tympanum of the ear (ear drum) and injuries to the brain.
As a matter of interest, any metal objects on
the body, for instance the buckle of a belt or coins, can become magnetised and
act like a magnet.