How much electric current can pass through the human body?

Question

Yes, and please specify what kind of power source I should use. Is a 9-volt battery enough? How about three button cells?

I am supposed to make an open circuit and let the current pass through the body in order to close it. I do not know which is appropriate: 9-volt battery powering a buzzer OR three button cells powering LEDs.

I am afraid of giving myself an electric shock though; I do wish to be careful at least.

Answer 1

I think you are saying the current through your body will power the buzzer or LEDs. That's never going to happen. The current required to power those devices would kill you (but you'll never get that current from low voltage batteries). Your experiment won't hurt you, but it also won't buzz the buzzer or light the LEDs.

Answer 2

Current Passing Through Human Body

Answer 3

Yes, as with birds landing on one of the High Tension wires between pylons. With no connection to earth (ground), the electricity takes the path of least resistance ..i.e, the wire...NOT the bird. The same applies to a human...

Answer 4

As any other material human body has a resistance so, try with low voltages first and then go up... but do not use 110v... Use a regulated power supply... good luck...

Answer 5

you will have to increase the voltage to shock yourself

Answer 6

Resistance

Resistance of the human body has been likened to that of a leather bag filled with an electrolyte fluid, with high resistance on the outside and lower inside. Skin resistance also varies depending on moisture content, thickness, and cleanliness. Resistance offered by the callused palm may reach 1,000,000 ohms/cm2, while the average resistance of dry normal skin is 5000 ohms/cm2. This resistance may decrease to 1000 ohms/cm2 if hands are wet. Skin resistance is encountered primarily in the stratum corneum that serves as an insulator for the body. The voltage gradient in skin cannot be increased indefinitely and breaks down at low voltages. Exposure of the skin to 50 volts for 6-7 seconds results in blisters that have a considerably diminished resistance.

The dermis offers low resistance, as do almost all internal tissues except bone, which is a poor conductor of electricity. Other factors that affect the flow of electrons are the nature and size of the substance through which it passes. If the atomic structure of the material is such that the force of attraction between its nucleus and outer electrons is small, little force is required to cause electron loss. These substances (eg, copper, silver) in which electrons are loosely bound are termed conductors, because they readily permit the flow of electrons. Materials such as porcelain and glass are composed of atoms that have powerful bonds between their nuclei and the outer electrons. These materials are termed insulators because electron flow is restricted.

Resistance is a measure of how difficult it is for electrons to pass through a material and is expressed in a unit of measurement termed an ohm. The resistance offered to the flow of electricity by any material is directly proportional to its length and inversely proportional to its cross-sectional area. Electricity is transmitted by a high-voltage system, because it allows the same amount of energy to be carried at lower current, which reduces electrical loss through leakage and heating. The relationship between current flow (amperage), pressure (voltage), and resistance is described in Ohm's law, which states that the amount of current flowing through a conductor is directly proportional to voltage and inversely related to resistance.

Current (I) = Voltage (E)/Resistance (R)

Electrons set in motion by the current force (voltage) may collide with each other and generate heat. The amount of heat developed by a conductor varies directly with its resistance. Power (watts) lost as a result of the current's passage through a material provides a measure of the amount of heat generated and can be determined by Joule's law.

Power (P) = Voltage (E) x Current (I)

Because E = I x R (resistance), the above equation becomes P = I(squared) R. Consequently, the heat produced is proportional to the resistance and the square of the current. Commercial electric currents usually are generated with a cyclic reversal of the direction of electric pressure (voltage). Pressure in the line first pushes and then pulls electrons, resulting in alternating current. Frequency of current in hertz (Hz) or cycles per second is the number of complete cycles of positive and negative pressure in 1 second. The usual wall outlet (120 volts) provides a current with 120 reversals of the direction of flow occurring each second and is termed 60-cycle current. Frequency of alternating current can be increased to a range of millions of cycles per second. In direct current, electron travel is always in the same direction.

Alternating current

Alternating current has almost entirely superseded direct current, since it is cheaper and can be transformed easily into any required voltage. Most machines in industry and appliances in the home use alternating currents; therefore, workers and consumers are mainly at risk from this current. Direct current usage is primarily restricted to the chemical and metallurgical industries, ships, streetcar systems, and some underground train systems.

Electric arc

Contact with high-voltage current may be associated with an arc or light flash. An electric arc is formed between two bodies of sufficiently different potential (high-voltage power source and the body, which is grounded). The arc has an intense, pale-violet light and consists of ionized particles that are driven by the voltage pressure between the two bodies and are present in the space between them. Temperature of the ionized particles and immediately surrounding gases of the arc can be as high as 4000°C (7232°F) and can melt bone and volatilize metal. As a general guide, arcing amounts to several centimeters for each 10,000 volts. Burns occur where portions of the arc strike the patient. The electric arc remains the cause of most high-voltage electrical burn injuries. Because of its high frequency, the electric arc has become the basis for many standard safety precautions.

Effects of electricity on the body

Effects of electricity on the body are determined by 7 factors: (1) type of current, (2) amount of current, (3) pathway of current, (4) duration of contact, (5) area of contact, (6) resistance of the body, and (7) voltage. Low-voltage electric currents that pass through the body have well-defined physiologic effects that are usually reversible. For a 1-second contact time, a current of 1 milliampere (mA) is the threshold of perception, a current of 10-15 mA causes sustained muscular contraction, a current of 50-100 mA results in respiratory paralysis and ventricular fibrillation, and a current of more than 1000 mA leads to sustained myocardial contractions.

Humans are sensitive to very small electric currents because of their highly developed nervous system. The tongue is the most sensitive part of the body. Using pure direct current and 60-cycle alternating current, the first sensations are those of taste, which are detected at 45 microamperes. When subjected to 60-cycle alternating current, the threshold of perception in the hands of men and women, which is usually a tingling sensation, is approximately 1.1 mA. Using pure direct current applied to hands, the first sensations are those of warmth in contrast to tingling, detected at 5.2 mA.

Skin offers greater resistance to direct current than alternating current, thus 3-4 times more direct current is required to produce the same biologic effect elicited by alternating current. With increasing alternating current, sensations of tingling give way to contractions of muscles. The magnitude of the muscular contractions enhances as the current is increased. Finally, a level of alternating current is reached for which the subject cannot release the grasp of the conductor. The maximum current a person can tolerate when holding a conductor in one hand and still let go of the conductor using the muscles directly stimulated by the current is termed the “let-go” current. This tetanizing effect on voluntary muscles is most pronounced in the frequency range of 15-150 Hz.

Such strong muscular reactions may cause fractures and/or dislocations. Numerous reports of bilateral scapular fractures and shoulder dislocations and fractures in electric accidents attest to this occurrence. As the frequency increases above 150 Hz, the potential for this sustained contraction is lessened. At frequencies from 0.5-1 megacycle, these high-frequency currents do not elicit sustained contractions of the skeletal muscles. For 60-cycle alternating current, the let-go threshold for men and women is 15.87 mA and 10.5 mA, respectively. The lower value for women may result from their generally somewhat poorer muscular development compared to men.

Electrical accidents involving power frequency (50-60 Hz) and a relatively low voltage (150 V/cm) occasionally can result in massive trauma to the victim. Skeletal muscle and peripheral nerve tissue are especially susceptible to injury. Historically, Joule heating, or heating by electrical current, was viewed as the only mechanism of tissue damage in electrical trauma. Yet in some instances, Joule heating does not adequately describe the pattern of injury observed distant to the sites of contact with the electrical source. These victims exhibit minimal external signs of thermal damage to the skin, while demonstrating extensive muscle and nerve injury.

Recently, electroporation of skeletal muscle and nerve cells was suggested as an additional mechanism of injury in electrical burns. This mechanism is different from Joule heating, even though it is influenced by temperature. It is the enlargement of cellular-membrane molecular-scale defects that results when electrical forces drive polar water molecules into such defects. Experimental studies have documented that electroporation effects can mediate significant skeletal muscle necrosis without visible thermal changes.