Damage to the tissues due to the passage of electric current is called electrical injury. The injury is also commonly called as ‘electrocution’.
- The current enters at one point and leaves the body at an exit point.
- For electrocution to occur, there must be a pathway for electricity (or electrons) through the tissues.
- The pathway tends to take the shortest route between the entry and best exit
- Most dangerous pathway is entry through right hand and exit through left foot, because current passes obliquely along the heart axis.
Factors Affecting Electric Injury
Death is uncommon below 100V, domestic voltage is 220V, residential area mains are 11000V, power house mains have up to 100,000V.
- Low tension voltage = <500V
- High tension voltage = >1000 V
30mA can be tolerated by most people. 50-80mA across heart is fatal in a few seconds.
The major barrier to electric current is skin resistance. Skin resistance is decreased if wet. Due to high electric resistance of skin, heating up causes skin burns.
4. Duration of Contact
Low ampere current if passed through the body for a longer time is fatal.
5. Direction of Pathway of Current
Current follows the routes of least resistance which include blood filled vessels, and may thus reach the heart even though it does not lie in a straight line between the entrance and exit.
6. Anticipation of shock
There are more chances of death, if the person is not prepared for the shock encountered.
Causes of Death in Electrocution
1. Ventricular fibrillation is the most common mode of death in electric injury
2. Respiratory arrest due to spasm of muscles of respiration
3. Rarely brain stem arrest also occurs
- Due to fall from height
- Extensive burns
- Fractures due to muscle spasms
5. Hold on effect
If someone catches a live wire, spasm of flexor muscles occurs and person cannot get rid of the wire, due to extensive flexor spasm.
Types of Electrical Injuries
- Contact burns or Joule burns
- Spark burns
- Flash burns
- Grounding or exit injuries
Contact Burns or Joule Burns
- Skin lesions are the thermal burns due to tissue heating.
- Skin resistance heats up the tissue fluids and produces steam, leading to blister formation.
- When current ceases, the blister cools and collapses, thus producing the familiar lesion seen at autopsy.
- The mark of blister has raised grey or white edges, an area of blanching around it, which is pathognomic of electric injury. An outer hyperemic border is present.
- Fatal electrocution may occur without any skin mark.
There is no actual contact but electricity sparks to the skin through a narrow zone of air.
Temperature is very high which causes the keratin to melt over a small area, which gets the shape of a hard brownish nodule, usually raised above the surrounding skin surface. This is called spark lesion.
The surrounding area is blanced or pale.
These occur due to arcing (jumping) of current from high tension wires. All types of burns may occur.
Typical lesion is ‘crocodile skin’ lesion.
Grounding or Exit Injuries
These are not commonly seen. Exit injury may have a split or a lacerated appearance.
Gangrene of the affected limb occurs.
Convulsions (Muscle Spasms)
- Respiratory paralysis
- Associated injuries
- ‘Hold on’ effect
Post mortem Appearance
External Contact Marks/Burns
- Characteristic electric burns
- Pattern of the electrode
- Metallic burns
- Light green imprint with copper/brass
- Vaporized metal in skin may be visible to naked eye or detected on scanning electron microscopy.
- Chemical metal elusion tests
- Rigor mortis develops early
- Usually no significant findings
- Pulmonary edema or general signs of asphyxia may be present
- Cerebral edema may be present
- Perivascular hemorrhages may be found
- Injury to the bones may have occurred
- Generally accidental
- Occasionally suicidal
- Rarely homicidal or as a torture