Arc Flashes occur in a distribution system when a low resistance path between conductive elements allows current to pass through air. When these incidents occur, they can release energy in the form of heat and pressure (causing injuries and equipment damage), emit radiation that can damage eyes and burn skin, and can cause audible damage due to sound (over 160 dB) and pressure waves generated by the incident. Based on statistical data, there are approximately 30,000 Arc Flash workplace incidents per year with varying safety effects.
Arc Flash potential originates with the available short circuit current at the utility service entrance, varies throughout the electrical distribution system based on impedance, and changes unpredictably due to the utility grid infrastructure upgrades and modifications. A distribution system is normally designed and sized to handle the maximum short circuit duty at the time of installation. However, if a short circuit coordination study and arc flash analysis was not done, it does not provide the required arc flash protection for maintenance/service personnel to work on the equipment. Furthermore, it does not provide the selective overcurrent protection that prevents the distribution from tripping on multiple levels during an incident. The result can be unnecessary loss of service, extended outages, or equipment losses that require extended outages to repair or procure replacements.
When an Arc Flash or Short Circuit Coordination Study is performed there is extensive investigation which takes place and is usually a joint effort between the Engineer and the Resident Electrician. The electrician collects the field data (based on engineering directive and prescribed methodology) which should include data such as cable length/impedances, switchboard/panel ratings, generators, transformer ratings, UPS equipment, disconnect switches, starters, variable frequency drives, and transfer switches. The Engineer then uses this data to develop a system model of the distribution, utilizes the utility short circuit information as a starting point, and calculates the available short circuit current at each equipment (or bus) location.
The model is then used to calculate the “incident energy”, which is based on the available short circuit current (and service clearances from equipment) available at the specific bus that is being analyzed. The incident energy is calculated in Cal/Cm2 and is used to properly determine the type of Personal Protection Equipment (PPE) that is required to work on the equipment. PPE is classified as Level 1-4 and requires varying degree of equipment with each level, with Level 4 providing the highest level of protection. The study also determines the boundary zones, which when personnel are within these zones, the PPE must be worn for servicing of the equipment. In the analysis of the Arc Flash hazards, equipment is provided with the proper labeling and identification for required Personal Protection Equipment (PPE) to work on energized equipment.
After completion of an Arc Flash study the Owner is presented with a report summarizing the findings of the calculations, which may reveal equipment that is over-dutied for the available short circuit current. This should trigger equipment upgrades, which is an effective preventative maintenance procedure, so that the equipment can be discovered before an incident causes a failure.
Equally important to an Owner conducting an Arc Flash study is the enforcement of the guidelines developed. The Owner will need to purchase PPE for their maintenance staff to use as well as they will need to enforce the PPE requirements with outside vendors. Most electricians are familiar with the requirements of the program, however, there are general contractors, plumbers, HVAC contractors, etc. that will need to be educated on the requirements to establish a successful program that will mitigate the risks and dangers associated with Arc Flash.
By performing the proper studies for facilities, Owner’s can mitigate personnel injuries, optimize system reliability, comply with the required safety codes and avoid violations, as well as develop a preventative maintenance approach instead of having to address a large-scale facility upgrade at one point.
In addition to being a National Electrical Code requirement to have Arc Flash labels and documentation (based on NEC 2017), many of the insurance carriers may offer premium reductions for establishing an Arc Flash program (such as FM Global).
Engineering Humor
Playing golf with his buddies, my grandfather had to make a slick 25-foot putt. As he lined it up, he announced, “I have a dollar bill that says I can make this putt. Does anyone want to bet?”
His three friends eagerly agreed to the wager. My grandfather missed the putt by ten feet, and his friends gathered around to collect their money. Granddad pulled out a dollar bill on which he had written, “I can make this putt.”
His pals are still trying to collect on the bet and grandpa is too.
When a job application asks who is to be notified in case of an emergency…
I always write, “A very good doctor!”
There was a job opening in the country’s most prestigious law firm and it finally came down to Robert and Paul. Both graduated magma cum laud from law school, are intelligent, and well spoken. It’s up to the senior partner to choose one, so he takes each aside and asks, “Why did you become a lawyer?”
In seconds, the senior partner chooses Paul. Baffled, Robert takes Paul aside.
“I don’t understand why I was rejected. When Mr. Armstrong asked me why I became a lawyer, I said that I had the greatest respect for the law, that I’d lay down my life for the Constitution and that all I wanted was to do right by my clients. What in the world did you tell him?”
“I said I became a lawyer because of my hands,” Robert replies.
“Your hands? What do you mean?”
“Well, I took a look one day and there wasn’t any money in either of them!”
“The marketing department is pleased to announce that during the 2020 softball season we came in 2nd place, having lost just one game all year! The sales staff, however, had a rather dismal season, as they won only one game.”
The sales staff whipped the marketing department soundly 10 to 1. But the marketing department showed how they earn their keep by posting this memo on the bulletin board after the game:
An interoffice softball game was held every year between the company’s marketing and sales staff.
A young and foolish pilot wanted to sound cool on the aviation frequencies. This was his first time approaching a field during the nighttime.
Instead of making any official requests to the tower he said, “Guess who?”
The controller switched the field lights off and replied, “Guess where?”