“Electricity is really just organized lightning.” That’s the way electricity was described by the late George Carlin. When you think of it like that, it makes sense that when the “lightning” becomes “disorderly,” bad things can and will happen.
Almost 3 million workers in the United States are at risk every day from uncontrolled energy when servicing equipment. There are roughly 3,600 disabling injuries and 4,000 non-disabling electrical contact injuries every year. Electrical hazards include electrocution, electric shock, burns, and falls. According to the BLS, electrocution is the fifth leading cause of work place fatalities in the US. When you consider these statistics with the relatively low number of workers that perform electrical work as a normal function of their job, it is clear that electrical safety is a concern for all employees, in every workplace.
Electric shock occurs in one of three ways. Individuals, while in contact with the ground, must come in contact with:
1. Both wires of the electric circuit
2. One wire on an energized circuit and the ground
3. A metallic part that has become “hot” by contact with an energized conductor
Because the skin offers most of the body’s electrical resistance, the point of electrical contact with the skin will determine the amount of shock received. The condition of the skin also affects resistance to electricity. Resistance is increased if electricity contacts in an area that has thick or callused skin or if the skin is dry. Resistance is decreased if the electricity contacts thin, wet or sweaty, or broken skin.
The presence of moisture from standing water, wet clothing, high humidity, or perspiration decreases resistance. Under dry conditions, the resistance offered by the human body may be as high as 100,000 ohms. Wet or broken skin may drop the body’s resistance to 1,000 ohms.
The level of current passing through the body is directly related to the resistance of its path through the body. Wet conditions, therefore, increase the possibility of a low-voltage electrocution.
People have different levels of resistance to electric shock because every human body is built differently. This is why a similar voltage shock can feel minor to one person and be deadly to another. Of course, there are other considerations than just resistance. For example, one person might have a heart that is more sensitive to ventricular fibrillation (twitching heart).
The three most basic units in electricity are voltage (V), current (I, uppercase “i”) and resistance (r). Voltage is measured in volts, current is measured in amps and resistance is measured in ohms. There is a basic equation in electrical engineering that states how the three terms relate. It says that the current is equal to the voltage divided by the resistance.
A neat analogy to help understand these terms is a system of plumbing pipes. The voltage is equivalent to the water pressure, the current (amperage) is equivalent to the flow rate, and the resistance is like the pipe size.
An electric circuit is formed when a conductive path is created to allow free electrons to continuously move. This continuous movement of free electrons through the conductors of a circuit is the current, and it is often referred to in terms of “flow,” just like the flow of a liquid through a hollow pipe in the analogy above.
The force motivating electrons to “flow” in a circuit is called voltage. Voltage is a specific measure of potential energy that is always relative between two points. When we speak of a certain amount of voltage being present in a circuit, we are referring to the measurement of how much potential energy exists to move electrons from one particular point in that circuit to another particular point. Without reference to two particular points, the term “voltage” has no meaning.
Remember that on a given circuit, voltage is consistent, but the resistance changes, which in turn changes the amps. As resistance goes up, amps decrease, and if the resistance goes down, amps will increase. When resistance is greater, fewer amps will be received, which lowers the chances of a harmful shock.
Here’s an example: Let’s say we’re dealing with a 120-volt circuit, and let’s assume a body has 2,000 ohms of resistance.
Using a formula for determining amps, we calculate that that 120 volts divided by a resistance of 2,000 ohms equals 0.06 amps. Because 1,000 milliamps (mA) equals 1 amp, 0.06 amps equals 60 milliamps. Therefore, an average person can be exposed to 60 milliamps with a typical home voltage of 120.
Here’s how different levels of exposure to electricity could affect people:
- Exposure Level = 2-10 mA
Impact on Body: Minor shock is possible.
Other Potential Outcomes: If working from an elevation, could cause a person to fall
- Exposure Level = 10-25 mA
Impact on Body: May lose muscle control and may not be able to release or let go of the circuit
Other Potential Outcomes: Rescuer may receive shock trying to assist a victim.
- Exposure Level = 25-75 mA
Impact on the Body: Painful and may lead to collapse or even death
Other Potential Outcomes: The longer the person is exposed to this electrical current, the more likely death will occur.
- Exposure Level = 75-300 mA
Impact on the Body: Even for a quarter of a second, this exposure is almost always immediately fatal.
Other Potential Outcomes: Causes ventricular fibrillation (the rhythmic pumping action of the heart ceases)
Even low voltage electrical shock has been shown to cause sustained “invisible” injury that manifests itself over the course of the days or weeks following the initial event. The injuries can take the form of numbness, muscle weakness, general or localized fatigue, and cognitive dysfunction, including memory change or loss, concentration issues, and post-traumatic stress, among others. These side effects of shock have only recently become the subject research so that the medical community can begin to understand this phenomenon.
Now that we have a general understanding of electricity and the danger associated with it, tomorrow’s follow-up article will discuss the various electrical emergencies one may encounter in the workplace, and how to respond.
- Use Digital Multimeters to Check Amps, Ohms and Volts (b2bbusinessnews.wordpress.com)
- How lightning kills and injures victims (washingtonpost.com)
- Glossary of Home Electrical Terms (freediyhomeimprovement.com)
- How Electricity Works (howstuffworks.com)
- Controlling Electrical Hazards (osha.gov)