Electrical injuries

Published on 14/03/2015 by admin

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Last modified 14/03/2015

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Chapter 31 Electrical injuries

In a two-year period from 2002, 1493 people in Australia were hospitalised as a result of an electrical injury, including 77 from lightning strikes. Of the 1493, 209 were aged 0–14 years, with 18 of those sustaining injury from high voltage lines.

In a four-year period (2001–2004), there were 162 deaths attributable to electrical injury (93% male), with seven from lightning strikes (all male).

Electrical injuries are more common among males, and mostly occur in the young adult and adult years. The most common locations for injury were, in order, the home and the workplace.

Despite the relative infrequency of these injuries, it is important that health providers be familiar with the types of presentation seen and aware of optimum management techniques.

The sources of electrical injury may be divided into three broad subgroups, with important differences in assessment and management of patients relevant to each. For example, cardiac arrest, as provoked by an electrical current, will more commonly be asystole from a lightning strike and ventricular fibrillation (VF) from a household AC current. The three subgroups, therefore, are:

PHYSICS

Electricity is the flow of electrons from higher to lower potential. Direct current (DC), from sources such as car batteries or defibrillators, flows in one direction. Domestic alternating current (AC) switches to and fro at 50–60 cycles per second (hertz) as this confers advantages in terms of current generation and transmission. Ironically, human muscular tissue is sensitive to frequencies in this range, with tetany of peripheral and VF arrest of cardiac muscles a risk during contact with household electricity. Domestic voltage in Australia is 240 V.

Lightning contains around 10 × 106 V and a current of 10,000–200,000 amperes. However, as a result of the incredibly brief duration (microseconds to milliseconds) of a lightning strike, the final amount of current delivered is much less than expected. It is the electrical current that is important in terms of human morbidity and mortality, and this basic electrical injury potential rests with two laws:

Ohm’s law

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Joule’s law

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So, while dry, thick calloused skin may be more resistant to injury by virtue of its very high resistance (up to 100,000 ohms), the resistance of moist skin is only 1000 ohms. It is therefore of vital importance to preach good electrical safety, especially in the home and workplace, and especially relating to moisture and electrical appliances and the installation of circuit breakers.

Similarly, it is the role of all health professionals to educate the public about safety during electrical storms. Those who enjoy outdoor recreation, such as golfers and hikers, are the major group of people affected by lightning strike. Solo people who are struck make up 70% of the recorded mortality. Most fatalities (about 70%) are recorded between midday and 6 pm.

Deaths occur five times more frequently in the country than in urban areas. The summer storm season is associated with the highest mortality. The annual mortality is decreasing in all recording countries.

Three major predictors of mortality are: cardiac arrest at the time of injury, cranial burns (5-fold increase) and leg burns.

In order to avoid lightning there are some simple measures which should be followed:

It is important to note that, contrary to popular belief, lightning does strike twice or more in the same spot.

Wide-band magnetic direction finders are increasingly used to warn of incoming lightning storms.

Lightning injuries can be markedly decreased by taking measures to avoid becoming a conductor, and by not being near an obvious conductor. Piloerection during an electrical storm can mean that a lightning strike is imminent, and immediate evasive measures along the lines of those described above should be taken.