Electrical Safety II - Unit 2: Effects of Current on the Human Body

Flashcards covering the definition of electrical risk, types of contact, physiological thresholds (perception, reaction, let-go, fibrillation), and the standardized current-time zones for AC and DC according to IEC and AEA regulations.

Riesgo eléctrico

The probability of an accident occurring due to exposure to electrical energy, which can cause damage to living beings, the environment, or property.

Contacto directo

Occurs when a part of the human body comes into contact with a live part of an electrical circuit, such as touching a copper bar in an energized electrical panel.

Contacto indirecto

Occurs when a part of the human body comes into contact with an electrical mass (an conductive element not normally part of the circuit) that has become live due to an insulation failure.

Masa eléctrica

A conductive element that is not part of the electrical circuit but can become part of it when an insulation failure occurs.

Choque eléctrico (IEC 60050)

The physiological effect resulting from the passage of an electric current through the human or animal body.

High Voltage (AT) effects

Effects produced by tensions > 1\,kV, causing electrical currents of several Amperes (e.g., $7,6\,A$ for $13.200\,V$) that primarily result in burns to the skin and tissues.

Low Voltage (BT) effects

Effects produced by tensions < 1\,kV, causing currents of some milliamperes (e.g., $220\,mA$ for $220\,V$) that primarily damage the heart and nervous system through ventricular fibrillation or cardiorespiratory arrest.

Umbral de percepción

The minimum value of contact current that causes a sensation in the person through whom it passes.

Umbral de reacción

The minimum current value that causes an involuntary muscular contraction; in alternating current (AC), a value of $0,5\,mA$ is considered the threshold regardless of time.

Tetanización eléctrica

The maximum muscular contraction of the human body caused by the passage of an electric current.

Inmovilización

The effect of electric current that influences the human body or a part of it in a way that prevents voluntary movement, affecting muscles or associated brain nerves.

Umbral de soltar o no soltar

The maximum value of contact current at which a person gripping an electrode can release it; in AC, this is considered to be $5\,mA$.

Umbral de fibrilación ventricular

The minimum value of contact current that, when passing through the body, causes ventricular fibrillation, depending on physiological conditions and current characteristics.

Período vulnerable del corazón

A relatively short part of the cardiac cycle representing about $10\%$ of the cycle (the first part of the T-wave in an ECG) during which the heart fibers are in a non-homogeneous state of excitability.

AC-1 Zone

A current-time zone for AC ($15\,Hz$ to $100\,Hz$) up to $0,5\,mA$ where perception is possible but usually no reaction occurs.

AC-2 Zone

A zone ranging from $0,5\,mA$ to curve b characterized by perception and eventual involuntary muscle contractions but usually no harmful physiological effects.

AC-3 Zone

A zone ranging from curve b to c1 characterized by strong involuntary muscle contractions, breathing difficulties, and reversible heart function disturbances; immobilization can occur.

AC-4 Zone

A zone above curve c1 where pathophysiological effects such as cardiac arrest, respiratory arrest, and severe burns occur, with increasing probability of ventricular fibrillation ($AC-4.1$ up to $5\%$, $AC-4.2$ up to $50\%$, and $AC-4.3$ above $50\%$).

DC-1 Zone

The perception threshold for direct current (DC), defined as current up to $2\,mA$, causing a slight tingling sensation.

30 mA

The designated current limit for an indefinite time in AC ($15\,Hz$ to $100\,Hz$) that can circulate without causing irreversible damage; also the nominal current for differential switches used for human protection.

150 mA

The current limit for an indefinite time in DC considered to be the threshold for ventricular fibrillation, which is $5$ times higher than the AC limit.

Total Body Impedance ($Z_T$)

Modeled as the sum of skin impedance ($Z_s$) and internal impedance ($Z_i$), influenced by factors such as contact voltage, frequency, humidity, and contact surface.

Factor de corriente del corazón ($F$)

A factor used to relate a current path ($I_h$) to the reference path of the left hand to both feet ($I_{ref}$), calculated as $I_{ref} = I_h \times F$.