This safety talk will cover GFCI (also known as ground fault circuit interrupters);
OSHA says regarding Ground-Fault Circuit Interrupters: All 120-volt, single-phase 15- and 20- amp receptacle outlets on construction sites, which are not a part of the permanent wiring of the building or structure and which are in use by employees, shall have approved ground-fault circuit interrupters for personnel protection. To make the job as safe as possible GFCI should be used whenever one is using electric tools.
HOW GFCIs WORK:
GFCI is designed to prevent fatal electric shock. A shock is felt when electricity uses your body as path-to-ground. A “ground-fault” occurs when there is a break in the ground path from a tool or electrical system. Ground-fault is the MOST COMMON electrical shock hazard. Ground-faults occur as a result of “leaking” electricity. Leakage current occurs when an electrical current escapes from its intended path. When the body provides this “path to ground” burns, injury and death can occur. The GFCI compares the amount of current going to and returning from equipment along the circuit conductors. The GFCI senses any loss of current. If a loss of current is sensed by the GFCI, it quickly shuts off the power. Takes a fraction of a second – a shock may still be felt, but the continuous current will be shutdown. All GFCIs have a built-in test circuit, with test and reset buttons that trigger an artificial ground-fault to verify protection. Test portable GFCIs each time they are used. Generally, to test your GFCI, simply press the “TEST" button in. You will hear a snap sound that trips the outlet and cuts power off to the plugin connections. Follow the manufacturer’s guidelines for specific testing procedures. A GFCI that trips is indicative of an electrical grounding problem. The GFCI will not protect you from line contact hazards (i.e. a person holding two "hot" wires, a hot and a neutral wire in each hand, or contacting an overhead power line). there are several types of GFCIs available - The Receptacle Type, Portable Type and Cord-Connected Type.
THE DANGERS OF ELECTRIC SHOCK:
The severity of an injury depends on the amount of electrical current and the length of time the current passes through the body. Example: One-tenth of an amp passing through the body for 2 seconds can cause death. Currents over 10 mA (milliamps) can cause muscle freezing, and in many cases can cause a tighter grip on tools. This continued grasping of an electrified tool can cause paralysis of the lungs. This “freezing” is what makes shocks through handheld tools so dangerous. If you can’t let go of the tool, the amperage will continue to flow through the body. Heart paralysis can occur at 4 amps and tissue is burned at greater than 5 amps. Voltage over 600 volts causes internal hemorrhage & violent muscle contractions. Remember that when working at height an electrical shock can also result in a dangerous fall.