How environmental factors affect the outcome of electrical injuries
Environmental factors significantly influence the outcome of electrical injuries. Temperatures and humidity rise, electrical hazard. An increase in temperature and humidity causes not only a decrease in the body's electrical resistance, but also decreases the body's overall resistance to electrical current.
The risk of injury decreases as the ambient air pressure increases and increases as the pressure decreases.
The degree of danger of injury is also affected by the partial composition of air. An increased content of oxygen in the air reduces the body's sensitivity to electric current, and a reduced one increases it. Content carbon dioxide has the opposite effect on the body's sensitivity to electric current.
By the nature of the environment, the following production rooms: normal — dry rooms where there are no traces of hot and dusty rooms with chemically active or organic environment; dry — relative air humidity no more than 60%; wet — steam or condensation temporarily and in small quantities moisture is released, relative air humidity exceeds 60%, but does not exceed 75%; raw - relative air humidity exceeds 75% for a long time; particularly humid — relative humidity close to 100%, the walls, floor, ceiling and objects are covered with moisture; hot - the air temperature constantly or periodically (a period of more than 1 day) exceeds 35 °C; dusty - the emitted dust settles on the wires and falls into the machines, devices, etc., the rooms can have conductive and non-conductive dust; with a chemically active or organic environment — permanently or for a long time contains aggressive vapors, gases, liquids, deposits or mold, has a destructive effect on the insulation and parts of the equipment under voltage.
According to the risk of electric shock for people, they are divided into rooms without increased danger, with increased danger and especially dangerous:
1. Premises without increased danger are distinguished by the absence of conditions that create increased or special danger.
2. Premises with increased danger are characterized by the presence of one of the following conditions:
a) humidity - the relative humidity of the air exceeds 75% for a long time;
b) conductive dust — metal or coal;
c) conductive floors - metal, earth, reinforced concrete, bricks, etc.;
d) high temperature — the air temperature is constant or periodically (period over 1 day) exceeds 35 °C;
e) the probability of simultaneous contact of a person with those who have a connection to the ground for metal structures of buildings, technological devices, mechanisms on the one hand and to metal boxes of electrical equipment — on the other.
3. Particularly dangerous premises are characterized by the presence of one of the following conditions:
a) special humidity - the relative humidity of the air is close to 100%, the ceiling, walls, floor and objects in the room are covered with moisture;
b) chemically active or organic environment — indoors permanently or for a long time contains aggressive vapors, gases, liquids, deposits or mold, which have a destructive effect on the insulation and live parts of electrical equipment;
c) two or more conditions of increased danger at the same time. Territories for the placement of external electrical installations are equated to particularly dangerous premises.
Electrical resistance of the human body
The human body is a conductor of electricity. Conductivity of living tissue in contrast to conventional conductors due not only to its physical properties, but also to the most complex inherent only biochemical and biophysical processes living matter. Therefore, the resistance of the human body is a variable that has a non-linear dependence on many factors, including the condition of the skin, electrical circuit parameters, physiological factors and environmental conditions.
Electrical resistance of different tissues of the human body is not the same: skin, bones, fatty tissue, tendons and cartilage have relatively high resistance and muscle tissue, blood, lymph and especially the spinal cord and brain — low resistance.For example, the resistance of dry skin is 3 x 103 — 2 x 104 Ohm x m, and blood 1 — 2 Ohm x m.
From these data it follows that the skin has a very large amount of resistance, which is the main factor determining the resistance of the human body as a whole.
The value of the impedance of the human body depends on a number of factors: the condition of the skin, the parameters of the electric circuit, the place where the electrodes are applied to the human body, the applied values of the current, voltage, type and frequency of the current, the area of the electrodes, the duration of the impact, physiological factors of environment.
Calculated electrical resistance of the human body alternating current with a frequency of 50 Hz in the analysis of the risk of injury, the human current is assumed equal to 1 kOhm.