ArticleIn this article, electrical engineer, Kenneth Kutchek, P.E. provides an introduction to electrocutions and electric shock injuries. His discussion includes the basic principles of electricity, including an explanation of circuits, typical ways that humans expose themselves to electrical current, and the consequences of electrical exposure.
The engineers at Robson Forensic frequently provide expert witness investigations involving electrocutions and electrical shock injuries related to consumer products, workplace exposures, and electrical utilities. Contact us to be connected with an expert whose background aligns with the disputed issues in your case.
Electrocutions & Electric Shock Injuries
An electric shock is the effect of an electric current flowing through the human body. Its effects can range from pain, muscular contractions, and difficulty in breathing, to burns, cardiac arrest, respiratory failure or death. The severity of injury is primarily based on three things:
- the amount of current,
- the duration of current and
- the path of current through the body.
It takes very little current to injure or kill a human being. The term “electrocution” is death by an electric shock.
Two Points of Contact
Electricity requires a complete path or circuit for current to flow. Two points of contact on the human body are required for current to enter and exit. In order for electrical current to flow there must be a voltage difference between these two points. Without two points of contact at different voltage levels, no shock will occur. This is why birds can safely rest on high-voltage utility wire without getting shocked. They make contact with the circuit at only one point; both feet are touching the same wire at the same voltage, so no shock occurs. A person’s hands, arms and feet are common points of contact in electric shock injuries.
Often, a person is standing on the ground when they contact a “live” or energized wire or object. One side of an electric power system is typically intentionally connected to earth ground. Therefore, the person is actually making two points of contact; the wire and earth ground. Normal footwear is not intended to protect someone from electric shock current through their feet. Typical shoe soles are too thin and not of the right material to provide adequate insulation. Also moisture, dirt, or body sweat in the soles will compromise the little insulating value the shoe may have had.
Amount of Shock Current
The amount of shock current is based on the voltage difference between the 2 points of contact divided by the resistance of the body between the 2 points of contact based on Ohm’s Law (V=I*R or I=V/R, where V=voltage, I=current and R=resistance). The greater the voltage, the greater the current, so there is greater danger from higher voltages. Shock currents as little as 1 mA (milliamperes) can cause tingling. Shock currents above 10 mA (milliamperes) can paralyze, hijack the control of, or “freeze” muscles, preventing a person from releasing a tool, a wire, or other object. As a comparison, a typical house circuit breaker trips at 15,000 mA or 20,000 mA (15 amps or 20 amps).
For more information on Voltage, Current, and Resistance, see our article on the Fundamentals of Electricity
Duration of Shock
The length of time of the shock greatly affects the severity of the injury. If the shock is short in duration, and the current is low enough, it may only be painful. If the same level of current flows through the same path and the shock lasts a few seconds, it could be fatal.
In cases where the causation or severity of injury is called to question, Robson Forensic can involve our own in-house biomechanical engineers to address these technical issues.
Shock Current Path
You often hear the saying “electricity takes the path of least resistance”. This statement is not entirely accurate. Electricity actually takes ALL available paths. A greater flow of electrical current will flow in the path of least resistance. A lesser flow of electrical current will occur in the other paths. Factors that influence the resistance of the body include: surface area of contact, moisture of the skin, contact pressure, and the conductivity of the various body parts (skin, blood, muscles, bones, joints, and other tissues/organs). Current through the heart can result in tissue damage, fibrillation or cardiac arrest. The current path through the body plays a significant role in the resulting injuries (see figure below).
Two points of contact are required on the body to complete the circuit for shock current to flow.
The three primary factors affect the injury severity of an electric shock: 1) the amount of current passing through the body 2) the duration of the current flow and 3) the current path through the body.
Investigating Electrocutions & Electrical Shock Injuries
The electrical engineers at Robson Forensic regularly investigate electrical shock injuries and electrocutions to determine their cause. These investigations typically include an evaluation of equipment installations in accordance with National Electrical Code (NEC), the National Electrical Safety Code (NESC), appliances, products, and equipment designs, maintenance and repair issues, presence of defects, and the adequacy of warnings and instructions.
For more information submit an inquiry or contact the author of this article.
Ken is an electrical engineer with more than 25 years of hands-on experience in electrical design, industrial automation, electrical controls, machinery and workplace safety. He applies his expertise to forensic casework involving electric shock injuries, fires of electrical origin, failure analysis as well as various issues involving electrical systems safety and performance.
Several members of the electrical engineering practice group regularly investigate electrical shock incidents. Please contact Robson Forensic to discuss your case and determine which of our experts is best qualified to assist with the specific issues in your case.