Electrocution
Dr A McLeod



This mini-article explores electrocution as a cause of death - how it kills and what the autopsy findings are. This info is largely referenced from Knights Forensic Pathology with additional information from the US CDC

How electrocution
occurs

There are several components to an electric 'shock'
More on Voltage, current and resistance:
To calculate voltage (V) in volts: put your finger over V,this leaves you with I R, so the equation is V = I x R
To calculate current (I) in amperes: put your finger over I, this leaves you with V over R, so the equation is I = V/R. Note that damaging currents are in the milliampere range rather than amperes!
To calculate resistance (R) in ohms: put your finger over R, this leaves you with V over I, so the equation is R = V/I

It is the current that causes tissue damage.
You can see that (I=V/R) as either voltage increases, or resistance decreases the amout of current goes up - causing more damage.
V=IR

Effects of Electrical Current on the Body (from CDC)
Current Reaction
1 milliamp (mA) Just a faint tingle.
5 mA Slight shock felt. Disturbing, but not painful. Most people can "let go." However, strong involuntary movements can cause injuries.
6-25 mA (women)
9-30 mA (men)
Painful shock. Muscular control is lost. This is the range where "freezing currents" start. It may not be possible to "let go."
50-150 mA Extremely painful shock, respiratory arrest (breathing stops), severe muscle contractions. Flexor muscles may cause holding on; extensor muscles may cause intense pushing away. Death is possible.
1,000-4,300  Ventricular fibrillation (heart pumping action not rhythmic) occurs. Muscles contract; nerve damage occurs. Death is likely. 3A is the smallest fuse in common usage.
10 amps (A) Cardiac arrest and severe burns occur. Death is probable.
13 A  The typical current at which the fuse blows in an item like a hairdryer or electric drill!


The flow of current through the body after bypassing the skin is fairly easy - it is well conducted by the (low elecrical resistance) organs and fluids of the body in a fairly straight line from point of entry to the earthing point. Certain entry and exit points are known to be more dangerous than others.


Mode of death

Circumstances of death


Indicators of electrocution as a mode of death

These can be very subtle - the best indicator is the circumstances surrounding the death. These may prompt the search for specific signs.

Typically electrical burns or blisters are confined to the site at which current enters the body - the earth point is usually lesion free but burns here may be seen sometimes.

There are two main type of electrical lesions:
It is very important to look for these lesions - hands, feet and head must be carefully examined. Lesions may be concealed by the clasped fingers of rigor mortis and if necessary the tendons must be cut to release fingers for a proper examination.

Other important areas to check for lesions are:

Electrocution in water:
This provides special problems - the entry point may be over a wide area and at low resistance - there may simply not be any electrical burn lesions. Here the context may be the only clue to electrocution as cause of death.

Severe burns:
These may result from either massive currents or lower currants over a long time. Even the current from an electrically powered vehicle may cause severe burns over the course of hours (see pic right).
Severe electrical burn



PATHOLOGYPHARMACOLOGYMAIN PAGELINKSiBSc

Created February 2010