How far can an electric spark travel?

2. The dangers of electric current

The dangers of electrical current can basically be divided into three areas:

  1. Accidents by Flow of electric current over the human body (Flow accident)
  2. Burns from exposure to electric arcs (Arcs are so-called electrical breakdowns) through the air, combined with the formation of high-energy sparks, flame arcs or plasma
  3. Fire caused by short circuits, excessive heating of electrical equipment (e.g. cables, coils, etc.) or electrical devices overheating

2.1 The flow accident

Flow accidents (electric shock) are the most common electrical accidents. A flow accident can occur when the human body becomes part of a closed circuit (Fig. 1).

Fig. 1: Body perfusion hand => feet (scheme)

The severity of a flow accident (e.g. flow from hand to foot or from hand to hand) depends essentially on the strength of the current flowing through the human body, the path of the current through the human body and the exposure time.

The electric current also follows Ohm's law when flowing through the human body. After that, the current intensity depends on the applied voltage and the resistance of the circuit. The greater the voltage, the greater the amperage.

Above 50 V AC voltage (contrary to popular belief), a fatal outcome must be expected from the flow.

A bridging of the human body with the usual mains voltage of 230 V to earth in accordance with Ohm's law (I = U / R) requires a current of 230 mA through the person with a body resistance of 1000 Ohm (assumed in simplified terms). A perfusion accident under these conditions leads to ventricular fibrillation and will be fatal if effective first aid is not provided as soon as possible (Chapter 9).


A flow of 230 V alternating current through the body can be fatal!

2.2 The secondary accident

Even a small current flow below the "release limit" (<15 mA) can be dangerous due to the associated startle reactions and a resulting secondary accident. Secondary accidents are triggered by electrical reflexes and uncontrolled movements of the body. This means that comparatively small values ​​of the contact voltage, far below the limit value of 50 V AC, are also relevant. This can lead to ladders falling, the hand slipping, reaching into moving machine parts or the like.


Even a "harmless power wiper" can lead to dangerous "secondary accidents"!

Table 1: Effect of the current on the human body as a function of the current strength

Amperage

Effect on the human body

<5 mA (milliamps)

Only minor effects (tingling, light blow)

5 - 15 mA

Muscle cramp, but still possible to let go

> 15 mA

Muscle cramps, no longer able to let go of your own accord

> 25 mA

Increase in blood pressure, heart irregularity, cardiac arrest with resumption of heart activity

> 50 mA

unconsciousness

> 80 mA

Ventricular fibrillation (acute danger to life)

> 3000 mA

Internal and external burns, cardiac arrest


2.3 Fire originating from electrical equipment

The evaluation of fire incidents shows that the cause of fires is often a small electrical device such as a defective kettle or a defective coffee machine. If one takes a closer look at the various fire cause statistics, it can be assumed that "electricity" is the cause of every third fire.

Often short circuits and excessive heating of electrical equipment (e.g. cables, coils, etc.) or other overheating of electrical equipment are the cause.