ELECTRICAL HAZARD EXAMPLES

Transcription

1 ELECTRICAL HAZARD EXAMPLES UNFORTUNATELY, THE EVENTS LISTED BELOW ARE MORE COMMON THAN YOU WOULD EXPECT Circuit breaker does not open the circuit when operated manually or remotely. The contacts within single and three phase breakers may not open. One or more poles can and do occasionally stick in the closed (energized) position. Test before you touch any conductive material and test the load side of the circuit breaker after you place it in the open (de-energized) position. Disconnect switch does not open the circuit when operated manually or remotely. On three phase, gang operated disconnect switches one or more poles can and do stick in the closed position. Visually inspect and confirm ALL blades of the disconnect switch moved as expected. Test before you touch any conductive material and test the load side of the disconnect switch after you place it in the open position. Power Plant generator destroyed due to reverse power. Worker inadvertently closed the generator circuit breaker while the generator was at standstill. Power from the electrical grid flowed through the closed generator disconnect switch, then through the generator circuit breaker, reverse powering the generator and causing catastrophic failure. Plant personnel previously deactivated reverse power relay protection. Worker burned when multi-meter leads created arc/blast. Worker used test leads that did not have insulation on the end connected to the meter. While performing the test, one of leads unplugged from the meter and contacted the conductive compartment metal. The other end of the lead came into contact with 480 volts during the test. Use test leads that have insulation on both ends. Two workers killed when crane contacted high voltage overhead conductor. Crane operator caused serious burning/arcing between crane, conductor, and ground. Another worker tried to rescue crane operator and was immediately electrocuted. Plan to avoid contact when working near any nearby conductors. Teach safe rescue techniques and warn workers of hazards. Do not touch energized persons or equipment. Page 1 of 5

2 Worker electrocuted when rolling-up 120-volt extension cord. Worker did not un-plug the extension cord from the feed receptacle. The extension cord had a defect that exposed energized conductors. Un-plug cord before winding or un-winding. Inspect cords for defects. Worker seriously shocked and burned when digging postholes. Worker was using a powered auger to dig holes and made contact with an energized underground 4kv cable. The auger welded itself to the cable and tripped the power supply. The worker was taken to a hospital burn center for treatment. Worker did call the appropriate number to have underground utilities identified. The underground utility locating company representative did not identify the 13kv cable. Operating toggle on the molded case circuit breaker is broken. This prevents proper operation of the circuit breaker from the operating handle on the front of the circuit breaker compartment door. Even though the handle on the front of the compartment door moves to the desired position, it does not position the circuit breaker in the desired position. The linkage from the handle on the front of the compartment door to the circuit breaker toggle could also be defective or misaligned. Always open the circuit breaker compartment door and test the load side of the circuit breaker after you place it in the open position. Opening or Closing a high energy disconnect switch under load. Most disconnect switches are not designed as load break disconnects. Always use the associated circuit breaker or other safe methods to make or break load. Worker electrocuted trying to save person in contact with energized conductor. Never touch a person or equipment while it is energized. Take appropriate steps to de-energize the conductor before touching the person or equipment. Use specially designed rescue hooks or other appropriate insulating material to remove a person from contact with energized equipment. Racking-out or Racking-in a high-energy circuit breaker in the closed position. Most circuit breaker manufacturers incorporate systems that are designed to prevent racking-out (withdrawing) or racking-in (inserting) a high-energy circuit breaker into its compartment, in the closed position. On rare occasions, these systems may fail, or personnel may intentionally defeat these systems. Never rack-in or rack-out a high-energy circuit breaker while it is in the closed position. Use remote racking mechanisms.

3 Power Plant generator circuit breaker exploded. While troubleshooting the generator circuit breaker, the worker initiated a slow closing of the circuit breaker. The generator was near synchronous speed but the slow closure of the circuit breaker caused an out-of-sync condition stressing the generator and causing the circuit breaker to explode catastrophically. Two workers were severely burned when the oil in the circuit breaker ignited. This incident could have been avoided by simply opening the associated generator disconnect switch during the troubleshooting effort. Worker seriously injured using improper voltage tester. Worker used a voltage tester rated at 600 volts to test a 13kv conductor. Tester exploded and worker was burned. Arc/Blast severely injures several workers in and near circuit breaker compartment. While troubleshooting cause of a 4kv circuit breaker tripping, workers caused a tremendous arc/blast inside of the circuit breaker compartment. Using an insulation tester, the worker inadvertently inserted the probes into the bus (energized) ports and caused the air to ionize and create a phase-to-phase fault. Should have used insulating barriers and lockout/tagout to prevent this incident. Working on the wrong (energized) equipment. Worker did not confirm equipment was properly de-energized. Incorrect circuit breaker was locked-out/tagged-out. Worker did not test before touch. High Voltage detector did not indicate presence of voltage. One type of proximity voltage detector did not indicate when positioned at certain angles between conductors. Manufacturer claims there is a field cancelling effect that causes this problem. Read manufacturers warnings and use personal protective equipment. Working on the wrong (energized) equipment. Compartment doors were interchanged during previous station outage. Circuit breaker identification was not accurate. Serious attention to detail issue. More reason to TEST BEFORE TOUCH! Circuit breaker exploded when racked-in the compartment. 13kv circuit breaker exploded due to excessive dirt and moisture on the circuit breaker. Circuit breaker was not properly stored when outside of compartment.

4 Worker seriously burned when closing a disconnect switch. Worker did not know that someone failed to remove temporary protective grounding cables. Closing the disconnect switch initiated a ground fault and serious arc/blast. Workers killed working in and near circuit breaker compartment. Worker entered circuit breaker cubicle and caused an electrical arc/blast that burned him and two other workers near the compartment. All three died from serious burn injuries. Cause was not determined since all three workers died. De-energize entire bus when working in high-energy circuit breaker compartments. Use personal protective equipment to avoid or minimize injury. Worker lost arm when he came in contact with energized 13kv bushing on transformer. Someone moved a ladder that was used for several days to access top of a 13kv transformer. Worker assumed he was on the correct isolated/de-energized transformer. Lock ladders in-place. Rope-in safe work area. Attention to detail. Circuit breaker will not trip when trip mechanism is activated. Do not try to remove/rack-out a breaker that will not trip/open. De-energize the bus and follow approved procedures to remove defective circuit breakers. Use lockout/tagout and use personal protective equipment. Use remote racking mechanisms. Worker shocked after contact with energized 480-volt conductor. Worker used a high voltage detector with a threshold voltage of 1200 volts (this type of detector does not indicate voltage below 1200 volts), to test a 480-volt system. Proper selection, testing, and use of voltage testers/detectors are essential for safe performance. 13kv Generator destroyed when worker closed the generator disconnects. Worker was removing lockout/tagout components as prescribed on an approved form. Generator was off and worker did not realize that maintenance personnel left the generator circuit breaker in the closed position after they performed maintenance on the circuit breaker. The closed disconnect switch allowed energy to flow from the electrical grid through the disconnect switch, through the circuit breaker causing serious damage to the generator (reverse power), and disconnect switch. Worker avoided serious injury.

5 Worker swallowed wire connector (wire nut) while working on lamp ballast. Worker tried to replace lamp ballast while still energized. He had a wire nut in his mouth when he received an electrical shock that caused him to swallow the wire nut. He also suffered serious burn injuries to both hands. Lockout/tagout. Worker seriously burned while removing electrical meter from meter socket. Several cases involving meter socket arc/blasts have occurred in recent years. Remove the load before installing or removing the meter. Wear FR clothing and equipment to avoid burn injuries. Worker electrocuted while disconnecting 480-volt cord and plug connected equipment. Cord and plug connected equipment could cause serious arcs, and/or shock when operated under load. De-energize the equipment before connecting or disconnecting equipment that is cord and plug designed. Special connectors are available to make or break electrical connections under load. Many manufacturers offer equipment with interlocks that ensure the power or load is off before cord and plug equipment is connected or disconnected. MOST OF THE FATALITIES AND INJURIES SHOWN IN THESE EXAMPLES COULD HAVE BEEN AVOIDED/PREVENTED WITH THE APPROPRIATE PERSONAL PROTECTIVE EQUIPMENT (PPE). EVEN IF YOU MAKE A MISTAKE, PROPER FR CLOTHING AND EQUIPMENT MIGHT PROTECT YOU WHEN EXPOSED TO THE INTENSE HEAT OF AN ARC. LOCKOUT/TAGOUT AND OTHER PROCEDURES ARE ESSENTIAL FOR PREVENTING MOST OF THE INCIDENTS SHOWN IN THESE EXAMPLES. Page 5 of 5