Electricity is often referred to as a “silent killer” because it cannot be tasted, seen, heard, or smelled. It is essentially invisible. Electricity has long been recognized as a serious workplace hazard, exposing employees to electrical shock, which can result in electrocution, serious burns, or falls that result in other injuries or even death. We know that electricity is essential to our everyday life, both at home and on the job.
More importantly, we tend to overlook the hazards electricity poses and fail to treat it with the respect. There are several hundred electrocutions each year, all of which could have been prevented. Electricity respects no one; it can injure or kill a worker, manager, CEO, or office worker just as fast as it will an electrician.
The laws of physics for electricity apply to everyone. Some employees work with electricity as part of their everyday jobs while others work with it indirectly, primarily by the use of cord and plug connected equipment and tools. A basic understanding of the shock hazard effects on the human body is vital to an understanding of electrical safety.
Electrical shock occurs when a person’s body completes the current path between two wires of an electrical circuit or from the energized wire to a grounded surface or object. Shocks can result in anything from a slight tingle to immediate cardiac arrest.
The severity of the effect depends on several factors:
The following chart illustrates average values of current and the effects as taken from the published studies:
Current Effect mA = milliamp A= amp
1 mA Barely perceptible
1-3 mA Perception threshold (most cases)
3-9 mA Painful sensations
9-25 mA Muscular contractions (can’t let go)
25-60 mA Respiratory paralysis (may be fatal)
60 mA or more Ventricular fibrillation (probably fatal)
4 A or more Heart paralysis (fatal)
5 A or more Tissue burning (fatal if vital organ)
Although the majority of electrocutions are the result of ventricular fibrillation, burns are the most common shock-related injury. An electrical accident can result in an electrical burn, arc burn, thermal contact burn, or a combination of burns. Electrical burns are among the most serious burns and require immediate medical attention. They occur when electric current flows through tissues or bone, generating heat that causes tissue damage. The body cannot dissipate the heat generated by current flowing through the resistance of the tissue therefore, severe burns occur.
Most electrical accidents result from one of the following:
Unsafe equipment, installation, unsafe environment or Unsafe work practices and procedures. Some ways to prevent these accidents are through the use of insulation, guarding, grounding, electrical protective devices, and safe work practices.
Ground-fault circuit interrupters (GFCI’s) should always be used when working with cord and plug connected hand-held tools or other equipment, including extension cords.
GFCI’s, are used in wet locations, construction sites, and other high-risk areas. These devices interrupt the flow of electricity within as little as 1/40 of a second to prevent electrocution.
GFCI’s compare the amount of current going into electric equipment with the amount of current returning from it along the circuit conductors. If the difference exceeds 5 + 1 milliamperes, the device automatically turns off the power. Additionally, electrical accidents are largely preventable through safe work practices. Examples of these practices include the following:
A break in an electrical tool or machine insulation can cause its metal parts to become “hot” or energized, meaning they conduct electricity. Touching these energized parts can result in an electrical shock, burn, or electrocution. The best way to protect yourself when using electrical tools or machines is to establish a low-resistance path from the device’s metallic case to ground. This requires equipment grounding, a wire that directs unwanted current directly to the ground. A properly installed ground greatly reduces the amount of current that passes through your body. Equipment with a three-prong plug is a common example of equipment incorporating this ground conductor.
OSHA General Industry Standard 1910.334(a)(2) requires portable cord and plug connected equipment and flexible cord (extension cords) to be visually inspected before use on any shift for external defects and for evidence of possible internal damaged. If there is a defect or evidence of damage that might expose an employee to injury, the defective or damaged item shall be removed from service, and no employee may use it until repairs and tests necessary to render the equipment safe have been made.
Another form of protection is to use listed or labeled portable tools and appliances protected by an approved system of double insulation or its equivalent. Where such a system is employed, it must be marked distinctively to indicate that the tool or appliance uses an approved double insulation system.
A GFCI should be used with these tools and appliances in the event of equipment malfunctions or damage. The use of personal protective equipment, safe work practices, GFCI’s, and common sense will also help to prevent injuries and fatalities.
OSHA Standard 1910.332 requires all employees who work on, near, or with electrical circuits and equipment, energized at 50 volts or more, to be properly trained in electrical safety according to their respective job assignments. Electricity is a “silent killer” and must be respected.
For more information on this subject, go to http://www.osha.gov/index.html and read the following publication,
OSHA 3075 “Controlling Electrical Hazards”