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How Electricity Can Kill

Working with electricity can be dangerous. Engineers, electricians, and other professionals work with electricity directly, including working on overhead lines, cable harnesses, and circuit assemblies. Others work with electricity indirectly and may also be exposed to electrical hazards.

As a source of energy, electricity is often used without much thought about the hazards it can cause. Because electricity is a familiar part of our lives, it often is not treated with enough caution.

Shocking statistics:

* Males comprised 93% of reported electrocutions.

* 46 of the electrocutions happened in occupational settings.

* Only 25% of the fatalities indicated lack of awareness on the victim’s part.

* Approximately 30 out of the 46 workplaces where an electrical fatality occurred did not have safe work procedures for the task involved.

* Nine electrocutions/electric shocks were reported between 1996-2003 in Ontario’s pulp and paper sector.

Effects of electrical energy

To determine how contact with an electrical source occurs, characteristics of the electrical source before the time of the accident must be evaluated (pre-event). For death to occur, the human body must become part of an active electrical circuit having a current capable of over-stimulating the nervous system or causing damage to internal organs. The extent of injuries received depends on the current’s magnitude (measured in amps), the pathway of the current through the body, and the duration of current flow through the body (event). The resulting damage to the human body and the emergency medical treatment ultimately determine the outcome of the energy exchange (post-event).

Electrical injuries may occur in various ways:

* Direct contact with electrical energy, injuries that occur when electricity arcs (an arc is a flow of electrons through a gas, such as air) to a victim at ground potential (supplying an alternative path to ground);

* Flash burns from the heat generated by an electrical arc; and

* Flame burns from the ignition of clothing or other combustible, non-electrical materials.

Direct contact and arcing injuries produce similar effects. Burns at the point of contact with electrical energy can be caused by arcing to the skin, heating at the point of contact by a high-resistance contact, or higher voltage currents. Contact with a source of electrical energy can cause external as well as internal burns. Exposure to higher voltages will normally result in burns at the sites where the electrical current enters and exits the human body. High voltage contact burns may display only small superficial injury; however, the danger of these deep burns destroying tissue exists. Additionally, internal blood vessels may clot, nerves in the area of the contact point may be damaged, and muscle contractions may cause skeletal fractures either directly or in association with falls from elevation. It is also possible to have a low-voltage electrocution without visible marks to the body of the victim.

Flash burns and flame burns are actually thermal burns. In these situations, electrical current does not flow through the victim and injuries are often confined to the skin.

Contact with electrical current could cause a muscular contraction or a startle reaction that could be hazardous if it leads to a fall from elevation (ladder, aerial bucket, etc.) or contact with dangerous equipment.

Voltages over 600 volts can rupture human skin, greatly reducing the resistance of the human body, allowing more current to flow and causing greater damage to internal organs. Estimated effects of 60 Hz AC currents that pass through the chest are shown below.

When current greater than the 16 mA “let go current” passes through the forearm, it stimulates involuntary contraction of both flexor and extensor muscles. When the stronger flexors dominate, victims may be unable to release the energized object they have grasped as long as the current flows. If current exceeding 20 mA continues to pass through the chest for an extended time, death could occur from respiratory paralysis. Currents of 100 mA or more, up to 2 amps, may cause ventricular fibrillation, probably the most common cause of death from electric shock. Ventricular fibrillation is the uneven pumping of the heart due to the uncoordinated contraction of the ventricular muscle fibres of the heart that leads quickly to death from lack of oxygen to the brain. Ventricular fibrillation is terminated by the use of a defibrillator, which provides a pulse shock to the chest to restore the heart rhythm. Cardiopulmonary resuscitation (CPR) is used as a temporary care measure to provide the circulation of some oxygenated blood to the brain until a defibrillator can be used.

The speed with which resuscitative measures are initiated has been found to be critical. Immediate defibrillation would be ideal; however, for victims of cardiopulmonary arrest, resuscitation has the greatest rate of success if CPR is initiated within four minutes and advanced cardiac life support is initiated within eight minutes.

The presence of moisture from environmental conditions such as standing water, wet clothing, high humidity, or perspiration increases the possibility of a low-voltage electrocution.

Prevention is crucial, as well as resuscitation, should an event occur. For Part II: How to prevent an electrical shock/electrocution, see next month’s article by Cindy Hunter.

Cindy Hunter is the Program/ Communications Specialist, Pulp and Paper Health and Safety Association (PPHSA).

PPHSA is a recognized leader in occupational health and safety in the pulp and paper and related industries. Visit them at www.pphsa.on.ca/

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Estimated Effects of 60 Hz AC Currents

1 mABarely perceptible

16 mAMaximum current an average man can grasp and “let go”

20 mAParalysis of respiratory muscles

100 mAVentricular fibrillation threshold

2 AmpsCardiac standstill and internal organ damage

15/20 AmpsCommon fuse or breaker opens circuit*

*Contact with 20 milliamps of current can be fatal. As a frame of reference, a common household circuit breaker may be rated at 15, 20, or 30 amps.