Know Your Arc Flash Sticker: Arc Flash Boundary and Limited Approach
In our last article, we went over the first few components that make up an arc flash sticker. Hopefully you’ve seen these around your facility or have more recently been keeping an eye out for them. If you haven’t, this would be a good time to start as we begin touching more on working distances and what can occur within them. Take note of the room layout, where doorways are in relation to the panels, and if foot traffic would be an issue during maintenance.
Let’s continue from where we left off in our dissection of the warning label. We have already familiarized ourselves with, or refreshed our knowledge of, calorie ratings, incident energy, and PPE. In this article, we’ll be digging into the Arc Flash Boundary and the Limited Approach along with what can happen within those boundaries.
First, there’s a value I want you to become familiar with: 1.2 cal/cm2. This is the incident energy needed to cause a second-degree burn. If you are unfamiliar with the severity and types of burns, a second-degree burn is known as a partial thickness burn because it involves more than just the first layer of your skin. These burns will result in a deep red discoloration, blister, swell, and be very painful. The common example often used to illustrate this is holding your finger over the tip of the flame from a lighter for one second. However, an arc can be much larger than a simple flame, and in the event of an arc flash, it is more likely that a much larger area of your body will be affected, and it will happen in less than a second.
It is also important to remember that 1.2 cal/cm2 will cause a second-degree burn to persons not wearing appropriate PPE within the Arc Flash Boundary noted on the sticker. In our example sticker above, that boundary is three feet. An additional note about PPE, specifically garments not rated for arc flash environments, is that some materials will melt onto your skin rather than burn away as you would imagine in the event of a flash. Some shirts, pants, and underlayers are woven with various materials to award them properties such as “stretch” or “moisture-wicking” and will not burn the same as 100% natural fibers such as cotton. As a result, this clothing will melt and adhere to your skin if they were to ignite. The more common types of synthetic materials to watch out for are nylon, polyester, and spandex. And obviously metal. Don’t let me catch you wearing those hip new jeans with all the extra zippers down the legs.
The takeaway from this is found in NFPA 70E 103.7(C)(6) where it is made clear that any individual within an area where potential arc flash exposure exists above the incident energy of 1.2 cal/cm2 shall wear arc-rated clothing. This “arc-rated clothing” is more commonly known as FR gear, which refers to PPE made of self-extinguishing materials. There are many high-quality brands available today that offer comfortable work garments that are treated to properly protect you in these environments, so be sure to pay attention to the labels when selecting PPE.
Hopefully your brain has been working in the background this whole time remembering where you’ve seen some arc flash stickers and where the corresponding gear is in relation to the rest of the room. If not, you’ll realize why this is critical to your job preparation as we address the Arc Flash Boundary.
The Arc Flash Boundary is the distance at which the incident energy is 1.2 cal/cm2. And with the aforementioned information of second degree burns and PPE, we can understand these two things about the Arc Flash Boundary:
Any person who is at the edge of the Arc Flash Boundary without arc-rated clothing is at risk of a second-degree burn in the event of an arc flash.
Any person who is closer to the source than the Arc Flash Boundary shall wear appropriate arc-rated clothing.
Now at this point you may have noticed that I have not included whether these “persons” are “qualified” or “unqualified” to be within those boundaries. This may seem like an unnecessary point if you are more familiar with some of the other boundaries, but it is still important to remember: electricity doesn’t care who you are. No matter your level of training or experience, distance will always benefit you in these scenarios. Proper PPE will always benefit you. Risk Assessments, Boundaries, barriers, and clear communication (from personnel and labeling) will always benefit you.
With these things in mind, picture an area in your facility that may seem cramped or an area with a higher frequency of foot traffic. In circumstances like these, working on energized equipment could be hazardous to those who aren’t aware of the boundaries you are working within. It is the responsibility of qualified personnel to either inform those working near him who are unqualified of the potential hazards and what the boundaries are. And in most cases, it is easiest to tape off your boundaries or use existing physical obstacles such as a work cart to create visible barriers. Communication in these instances is key, as there are very few reasons for an unqualified person to cross the Arc Flash Boundary, which is why we have the Limited Approach Boundary.
The Limited Approach Boundary is simply the boundary which no unqualified person is permitted to cross. Naturally you would not want to place unqualified people at risk of serious burns unnecessarily. So, when you are considering placing physical barriers or communicating the hazards to those around you, feel free to inflate these boundaries or remove people with no immediate need to be there.
However, the standards do provide guidance for the rare case that an unqualified person may be needed to cross the Limited Approach Boundary. NFPA 70E 130.4(E)(3) outlines that it is the responsibility of the qualified person to not only make known to the unqualified person the potential hazards inside the Limited Approach Boundary, but to continuously monitor their actions while they are within the boundary.
The Arc Flash Sticker is provided for your safety and required by the standards. As you continue to learn what each section means you will come to understand that it is not only to provide you with adequate information to perform your task safely, but to keep those who are not as experienced as yourself free from harm.
As always, feel free to contact us for more information on Arc Flash Training or Risk Assessments.