“Creating An Electrically Safe Work Condition”
“Kill the Circuit.” This phrase is a colorful way of saying, “De-energize the Circuit.” Easy enough — just open a switch or other protective device and the circuit is “dead.” It should then be safe to work on right?
WRONG! Simply opening a switch does not guarantee the circuit is de-energized. Really? What could go wrong?
There are many who still consider this simple “kill the circuit” approach to be standard electrical safety practice. This is a very dangerous method, for example, instead of the circuit being dead, the worker could end up dead!
According to NFPA 70E, there are many additional steps necessary to ensure the circuit is truly safe to work on. This multi-step process is known as creating an “electrically safe work condition,” which requires the following steps:
- Determine all possible sources of electrical supply – check up-to-date drawings, diagrams, etc.
- Interrupt the load and open the disconnecting devices.
- Visually verify that all blades of the disconnecting means are open if possible – drawout devices must be withdrawn to the fully disconnected position.
- Apply lockout/tagout devices in accordance with established policy.
- Use an adequately rated test instrument to verify absence of voltage.
- Apply properly rated ground connecting devices if there is a possibility of induced voltage.
(These steps are paraphrased from NFPA 70E 120.1 Process of Achieving an Electrically Safe Work Condition, which should always be used to define the complete procedure).
Why are there so many steps? Isn’t opening the switch enough?
Each step needs to be thought of as a safety net. Using multiple safety nets, if one fails, the next one should catch you; however, you don’t want to rely on it. If steps are not correctly used or missed, a serious hazard can still exist.
Case One – Tragedy
Having conducted many accident investigations throughout my career, I’ve found the root cause of them to be incorrect use of proper procedures. One such case I investigated was an electrician that sustained third-degree burns throughout his body, lost several fingers, and was extremely debilitated and unable to return to work.
So what was the main cause of this accident?
Failure to use proper safety procedures! The steps for establishing an electrically safe work condition were either performed incorrectly or altogether ignored.
The worker thought he knew what he was doing, after all, he never had an accident before. The first mistake was a failure to review electrical drawings or tags to determine all possible sources of power. Even though drawings were available at the job site, they had been ignored. The electrical system appeared simple enough at first glance, a double-ended substation with two main circuit breakers and a tie circuit breaker. This is a common design and appeared “obvious” that only opening the A side main circuit breaker and the tie was necessary. That isolates the A side bus and kills the circuit; however, the electrical drawing not reviewed indicated a third supply to the A side bus from another tie through a feeder. In fact, there was also a key interlock on the second tie.
Both the A side main and tie circuit breakers were opened and locked out, absence of voltage was verified, and work began. Due to the scope of the project, work carried over into a second week and the site was left vacant over the weekend with locks still in place. At some point during the weekend, an auxiliary load on the A side bus had to be brought online, and the weekend operations crew closed the second feeder tiebreaker, energizing the A side bus. Returning to the jobsite Monday morning, the worker saw his locks were still in place and assumed the A bus was still “dead.” His logic: if the locks are still in place, everything must be SAFE.
The proper electrical safety practice is when a job site has been left unattended and/or multiple crews are involved, the circuit should be retested for absence of voltage. Why is this necessary if the breakers are still locked in the open position? As the accident victim lay in the hospital on life support from the resulting arc flash, he began to realize why.
The investigation determined the primary cause of this accident was the victim did not follow ALL steps for establishing an electrically safe work condition. Many “safety nets” were not properly in place or used at all. It is no secret that taking the time to follow each step for establishing an electrically safe work condition is more complicated than just killing the circuit; yet, each step is designed to ensure it is the circuit that ends up dead and not you!
Case Two – Tragedy Avoided
Another situation involved a training client years ago, they were taught the Process of Achieving an Electrically Safe Work Condition. During follow up training for another group a few months later, the lead person told me this procedure saved two lives just a few weeks earlier.
They were performing routine maintenance on a very old system with old 480 volt open buswork. Two contractors were present and the buswork was going to be cleaned. As in past cleaning operations, they opened the one and only switch to “kill the circuit” and were about to begin. At the last moment, the lead person yelled out “STOP”. “I just attended an electrical safety program and we now are required to check the absence of voltage” I guess they were not doing this before.
The Lead person then stated “Since I’m the lead guy here, humor me for a minute. I need to get my volt meter and test the bus” To his horror, it was energized – and the switch was OPEN! He opened the switch and found that although the switch WAS in the open position, the switch mechanism broke in the closed position. He stated they were probably seconds from killing two contractors.
Even though extra time and effort is necessary to place circuits into an Electrically Safe Work Condition – All of the steps ARE worth it – especially when you get to go home at the end of the day!
Attend an upcoming Arc flash safety training course by Jim Phillips to:
- Avoid Arc Flash accidents
- Establish an Electrically Safe Work Condition
- Learn how to perform an arc flash study
- Perform a Shock Risk Assessment
- Perform an Arc Flash Risk Assessment
- Determine appropriate Limited and Restricted Approach and Arc flash boundaries
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