3/8/2024 0 Comments Arc flash boundary distanceRemember those arc flash labels? The incident energy values on the label are based on how close you can get to the equipment before you receive the onset of a second-degree burn, which is the working distance. The distance between a person’s face and chest area and a prospective arc source. So what is “working distance?” According to the 70E, it is: Remember, if people are working near the limited approach boundary, you must apply alerting techniques! For guidance on alerting techniques, see NFPA 70E 130.7(E).īe sure you know the difference in the boundaries - it’s important! Working Distance Basically, one pertains to non-qualified personnel (limited approach) and one pertains to qualified personnel (restricted approach). The limited approach and restricted approach boundaries are both shock-protection boundaries. You may have heard this term before because we just talked about it. Note: Refer to NFPA 70E Table 130.4(E)(a) for the complete list. The message here: Be careful! While you need to verify before each and every task, here are a few dimensions of an exposed fixed circuit part, in the game of inches, that you should memorize and make part of your everyday knowledge:ħ50-volts Three feet, six inches and below: (42 inches) Now you are in the danger zone! This is the area where there is an increased likelihood of electric shock, most often because of the possibility of arc-over combined with inadvertent movement. For example, an overhead line would be considered an exposed movable conductor. *Note: An exposed movable conductor is a condition where the distance between a conductor and a person is not under the control of the person. If it’s an exposed movable conductor* and the voltage is 72.5 kV or less, stay at least ten feet away (120 inches). Here are a few key excerpts from NFPA 70E Table 130.4(E)(a): Unqualified? Stay Back Ten Feet! Remember, this is the boundary that an unqualified person must stay out of! It’s also the trigger point where you, as a qualified electrical worker, must take extra care and steps to protect yourself and those around you. The limited approach boundary is the distance from an energized part at which a shock hazard exists. So when you see an arc flash label on a piece of equipment and it gives you a distance number – that’s the distance at which unprotected skin will be affected. The magic number? According to the Stoll skin burn model, the formula is 1.2 cal/cm 2 of exposure for one second of time. It’s the distance at which you could receive the onset of a second-degree burn. Simply put, this is how close you can get to a piece of energized equipment or circuit part before receiving a significant burn injury should it be involved in an electrical fault. When working on or near energized conductors or circuits, there are many dimensions and boundaries you should know and, more important, understand why you should know about them. So take time to remind yourself, and those around you, of key dimensional criteria. It can be the difference between having a safe day on the job…or suffering an injury. If you are not familiar with key dimensions in your life as an electrical worker, it can have a significant impact on you. Safe work distances while working on or near electrical equipment are measured in inches. How safe are you on the job? At home? In everyday life? Often, the difference between something good or something detrimental is determined by the smallest of margins. They are in every break of the game, every minute, every second. The inches we need are everywhere around us. One half-second too slow or too fast, and you don’t quite catch it. I mean one half-step too late or too early, you don’t quite make it. Because in either game, life or football, the margin for error is so small. You find out that life is just a game of inches. In the middle of the speech, he says this: In the locker room at halftime, Pacino addresses the team - he needs to get them fired up for the balance of the game. His team is in the biggest game of their lives, and things aren’t going well. The speech scene is a little over four minutes long. If you haven’t seen it, just Google “Al Pacino best speech - Any Given Sunday.” You’ll find it’s a great motivational speech…even beyond football. As we go through football season this year, you will undoubtedly hear many times that it’s “ a game of inches.”įootball being a game of inches was highlighted in a memorable way by actor Al Pacino in the 1999 movie Any Given Sunday. As we enter into the fall season, temperatures are starting to come down, the leaves are turning, and the game of football is cranking up.
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