Know Your Arc Flash Sticker: Incident Energy
One aspect of my job that I really enjoy is having the opportunity to hold training classes that involve a hands-on portion of arc flash safety and awareness. During these on-site trainings is where I typically see a lot of growth in one’s understanding of the concepts presented by the standards and how they are applied in the field. A comprehensive working knowledge of your systems and an appropriate balance of confident and safe work practices can only be achieved through years of field work where this information is correctly applied. So, while practice makes perfect, understanding also comes through clarification.
“Everyone hears only what he understands.”
“Whatever you cannot understand, you cannot possess.”
“Knowing is not enough; we must apply. Willing is not enough; we must do.”
- Johann Wolfgang von Goethe
I like quotes simply for the reason that they sound different than my internal voice and easily sound like an outside opinion. However, quotes can often be seen as superfluous or pretentious and the effectiveness of a quote in a speech depends on a lot of things: the quote itself, who it is attributed to, and context. Quotes are a snapshot of a moment in time, and many of them have been dissected for centuries and attributed to several great moments in history. You can learn a lot from a few simple words. But, just because you may see or hear a quote frequently, should you stop considering its meaning?
With that in mind, consider a label or warning sign. You see them all around your facility and they display helpful snapshots of information. These values often have greater meanings and require you to prepare in various ways for work in those areas. But do you fully understand the consequence of ignoring that label? Should you learn through trial and error? Is there a difference in an electrician who has experienced an electric shock and one who hasn’t? Why do we have arc flash stickers? How many arc flash incidents still occur every year even with proper signage?
The effectiveness of an arc flash sticker is limited only by your understanding of its various components. So, in an attempt to further simplify the arc flash sticker and help you all easily understand the critical information it presents, I’m going to spend the next few weeks breaking down a sample sticker.
Let’s begin by discussing the calorie rating. The rating you see here is the amount of thermal energy that you would be exposed to if an arc flash were to occur, also referred to as the incident energy. Arc Flash heat is measured in either calories or joules per cm2 (1 calorie is the amount of energy needed to raise one gram of water by one degree Celsius at one atmosphere ~ about 4.184 Joules). So, while you may see that the arc flash sticker expresses an arc flash hazard of 3.9 calories/cm2 exists in the gear you may be servicing, what you need to be thinking is, “My face will be near this.”
Now I don’t mean to make light of this subject, as it is a serious matter and needs to be understood by all qualified personnel working in an arc flash environment, but let’s stop for a moment and think about the other unit of measurement that appears in that first line of the sticker. 18 inches.
This distance is considered to be the average working distance between the source and your torso. It is likely that your arms and hands will be closer but looking at this sticker we know that at 18 inches, the incident energy will be 3.9 calories/cm2 if an arc flash were to occur. If you happen to be closer than 18 inches, the incident energy would be greater. More distance, less heat. Less distance, more heat. It is important to remember that when it comes to an arc flash, distance is your friend.
If you were curious and took a moment to measure your arm from chest to fingertips, you might have found that you have unusually long arms and are closer to 22 inches or so. Now, when was the last time you worked on something with your arms held completely straight, with good posture, and your head held up? Consider how you hold your phone when you text, because this is often our natural inclination when we work on small parts or wiring. Now remember, arc flash environments are live, and we don’t want to break that air gap, so you will more than likely not have your face as close to these parts as you do to your phone.
With all of this in mind, let’s move on to your PPE. The main thing to understand here is that your PPE needs to be higher than the available incident energy you may encounter. However, it is also important to understand that the Arc Thermal Performance Value (ATPV) of your FR gear does not mean that it negates the heat produced by an electric arc up to that value. Arcing is often unpredictable, and these values were obtained through controlled testing environments, so making sure that your PPE is more than you would need is key in these situations.
All of this information is found in NFPA 70E Article 130 but must be practiced and applied consistently to really be of any use. Remember, you are responsible for being alert and protected when you are in an arc flash environment, especially if you are within one of the boundaries.
As a qualified person who has electrical training and experience working in potential arc flash environments, your continued understanding of equipment labeling is vital to your safety and the safety of those around you. Your knowledge of arc flash stickers will enable you to select the proper PPE for your task based on the values represented in the labeling. If you’re placing yourself within a typical working distance where your hands, arms, and face are near enough to be in the flash hazard zone, your PPE needs to exceed the calorie rating resulting from the incident energy.
For more information on training or to find out if your equipment has the proper and up-to-date arc flash labeling, give us a call.
