Basic Electrical Safety
The concepts discussed herein are intended to provide explanation and clarification of basic electrical safety for individuals who have little or limited training or familiarity with the field of electricity. An understanding of these principles is essential for comprehension of OSHA's Electrical Safety Standards.
contents:
Theory of Electricity ...................................... 1
Hazards of Electricity .................................... 25
Effects of Electricity on the Human Body .................... 28
Common Workplace Circuits .............................. 33
Electrical Protective Devices ............................... 35
Grounding ............................................. 40
Ground Fault Circuit Interrupters ........................... 46
Reversed Polarity
There are three basic electrical hazards that cause injury and death: shock, arc-flash, and arc-blast.
Shock Current can pass through the human body’s nervous or vascular systems, and across the surface of the body. The current required to light a 71/2 W, 120 V lamp, passing through the chest, can cause death. Of those killed while working on voltages below 600 V, half were intentionally working on "hot" energized equipment. Most electrocutions can be avoided with proper training, planning, job preparation, procedures, and equipment.
Arc-flash (extremely high temperature conductive plasma and gases resulting from an arc fault incident). As many as 80 percent of all electrical injuries are burns resulting from an arc-flash contact and ignition of flammable clothing. Arc temperatures can reach 35,000 F four times hotter than the sun’s surface. Arc-flash can cause second and third degree burns.
Arc-blast (pressure wave caused by the rapid expansion of gases and conducting material with high flying molten materials and shrapnel). An arc-blast may result in a violent explosion of circuit components and thrown shrapnel. The blast can destroy structures, and knock workers from ladders or across a room. The blast can rupture eardrums and collapse lungs.
Training, planning, and writing procedures
Provide training. Obviously, an important aspect of electrical safety is training. To be qualified, workers need training on the tasks and procedures (such as lockout/tagout procedures) that are essential to conducting their work in a safe manner.
Plan every job. Take the time to prepare a work plan that considers all possible eventualities. Before starting the job, think about each step and try to visualize the potential for hazards.
Anticipate unexpected results. When thinking about a job, break each task into small steps. Understand that plans can change, so be ready to modify the plan. Make sure that everyone involved in the job is working according to the same plan. Whenever work is required near an electrical hazard, a written plan is needed to outline the scope of the job.
Use procedures as tools. Procedures are the best way to help you prepare, execute, and complete a job. Like any tools, make sure procedures are maintained.
Identify the hazard. After your work plan is complete, review each step. Consider that the equipment might be perfectly safe under normal conditions and very unsafe when systems are not working properly. Also consider potential hazards that may be unrelated to electrical energy.
Assess people’s abilities. Any person assigned to tasks associated with electrical energy must be qualified and trained for the job at hand. He or she must be able to identify electrical hazards, avoid exposure to those hazards, and understand the potential results of all action taken.
Providing an electrically safe work condition
Use the right tool for the job. Use the appropriate tools for the job at hand, keep them accessible and in good working condition. Using a screwdriver for a job that requires a fuse puller is an invitation to an accident.
Isolate the equipment. The best way to avoid an accident is to reduce exposure to the hazards present. Keep doors closed. Keep barricades in place. Install temporary voltage-rated blankets covering exposed live parts. Put the equipment in a safe working condition prior to performing maintenance. Lock out the disconnect.
Protect the person. Use the proper personal protection equipment for the job. This may include safety glasses or goggles, head protection, voltage-rated gloves, safety belts and harnesses, or flame-resistant clothing.
Minimize the hazard. If it is impossible to establish an electrically safe work environment, be sure to shut down every possible energy source. Understand that sometimes a de-energized circuit can become re-energized and do something to lessen the risk.
Audit these principles. A principle is something you believe in enough to be willing to do. Review these principles often; add to them as needed.
Lockout/Tagout
The Lockout/Tagout Standard was created to help reduce the death and injury rate caused by the unexpected energization or start-up of machines or the release of stored energy. Normal production operations, cords and plugs under exclusive control, and hot tap operations are not covered. This standard applies to energy sources such as electrical, mechanical, hydraulic, chemical, nuclear, and thermal.
Procedures for applying the lock/tag:
1. Before the shutdown, know the unit and power sources
2. Power down the equipment
3. Isolate the power source(s)
4. Apply the lock and/or tag
5. Use proper techniques, personal protective equipment, and test measuring devices to verify that the electrical circuit is de-energized
6. Release residual energy
7. Try to power up
Procedure for removing the lock/tag:
1. Inspect machine and/or equipment
2. Give notification to personnel
3. Remove the lockout/tagout device
National Fire Protection Association Standard NFPA 70E
There are a number of important electrical industry consensus standards that have indirect or direct impact on human safety. NFPA 70E, the "Standard for Electrical Requirements for Employee Workplaces," is one of the most important. This standard focuses on protecting people and identifies requirements that are considered necessary to provide a workplace that is generally free from electrical hazards
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