Dangers of Working With Electrical Currents
Dangers Of Working With Electrical Currents
Electrical current passing through the body
The degree of risk posed by electrical energy not only depends on the level of the electrical current generated from the voltage, but also the exposure time, frequency and route that the current takes when passing through the human body.
NOTE: Remaining in the direct vicinity of an activated electric machine or high-voltage system can impair the function of electronic life-support systems.
These include:
- Internal analgesic pumps
- Brain pacemakers
- Implanted defibrillators
- Cardiac pacemakers
- Insulin pumps
- Hearing aids
Employees wearing these or similar devices on or inside the body are not permitted to perform work on high-voltage vehicles.
In this regard, current that flows through the heart is particularly dangerous, even more so when the heart attempts to follow the frequency of the alternating current. Cardiac fibrillations that can occur even after momentary exposure and at low currents are the direct consequence. The pumping capacity of the heart decreases to zero. A lack of oxygen leads to a loss of consciousness and death within a very short time.
The maximum permitted voltage that people can come into contact with is therefore different for direct and alternating currents. The maximum voltage is 50 V for alternating currents and 120 V for direct currents. On electrical systems that operate with higher voltages, safety measures prevent currents from flowing through the body or switch off the system within a specific time (e.g. < 0.2 s).
Bodily reactions
Sensitivity to the electrical currents depends entirely on the individual. While the perception threshold is usually 0.5 mA, some people claim to feel nothing when exposed to much higher currents. Sensitive individuals and children, however, are able to sense much weaker currents due to the physiological condition of the individual. The following are directly responsible for sensations and the actual flow of current:
- Level of the voltage supplied
- Resistance at the points of entry and exit
- Individual resistance of the body tissue
- Sensitivity of the affected area of the body
The effects of the current flow on people depend heavily on the length of time the current is applied. While exposure to currents below 10 mA does not generally have a damaging effect, even for prolonged periods, currents >200 mA have a harmful effect and cause serious physical reactions if the exposure time exceeds 10 ms.
As a result, maximum release times (e.g. < 0.2 s) are defined for protective measures. The electric shock can then definitely be felt and will be painful, but will not cause permanent damage if the person has a healthy constitution.
The effects are classified as follows:
NOTE: Effects may manifest themselves several hours after the accident. Therefore always seek medical attention after accidents involving electricity.
The occurrence of the effects listed depends on the level of the current. Chemical effects occur primarily after accidents involving direct currents. In the case of tissue decomposition, symptoms of poisoning often emerge several hours after the accident, even if the victim initially has no symptoms.
Bodily resistance
The level of the current flow from a specific voltage depends on the degree of resistance (Ohm's law). Protective measures are designed based on an assumed bodily resistance of 1000 ohms. Under the assumption that contact with live components is typically made with the hands (housing) and feet (ground) or the left hand and right hand, the 1000 ohms are calculated by adding the individual resistances of the extremities. The resistance of the skin is crucial here. The resistance of the inside of the body is negligibly small.
According to Ohm's law, a voltage of 288 V (high-voltage battery) produces a current flow of 288 mA at 1000 ohms(288 V/1000 ohms).
The level of the effective current flow is often significantly lower than a calculated value because the body connects with the contact resistances "in series" (gloves, surface paint, footwear, entire surface of hand does not touch component, etc.).
According to the laws of series connection, "poor" contact with the location of the fault reduces the contact voltage.
Arcing effect
Electrical currents can be dangerous even if they do not flow through the body. The energy stored in the high-voltage system is capable of generating electric arcs that can reach temperatures well in excess of 7200° F. (4,000° C.).
Electric arcs are generated by:
- poor connections, e.g. loose or oxidised contacts, damage caused by overtightening screws
- isolation faults
- the use of incorrect electric cables or connections (wrong size, shape, material)
- Moisture/Dirt (conductive dust)
- Foreign objects, falling metal components and small parts
If an individual is the cause of the electric arc or is standing in the immediate vicinity, the following effects can be expected.
Acoustic effects
- Trauma from acoustic shock
Thermal effects
- 1st to 4th degree burns
- Blindness or flash burn of the eyes from exposure to electric arcs
- Fire, melting of metal
Toxic effects
- Poisoning by gases or dust produced from ozone or decomposition products from the affected materials, for example
Electrodynamic forces
- Pressure waves
- Injuries from moving parts
- Spraying of liquid metal
- Bursting of housings
Secondary accidents
Subsequent defence or shock reactions can also cause secondary accidents:
- Injury caused by stumbling, falling or slipping
- Cutting, crushing, stab and graze injuries
- Injury caused by falling components