When PPE is used effectively, the boundary lessens considerably due to its reliance on electrical conductivity. Generally speaking, an employee must wear personal protective equipment when they are inside the arc flash boundary.

This can increase your costs, or result in PPE failure that could also impose danger on your employees when they are within the arc flash boundary. Further, the increased wear and tear on the equipment could result in its prematurely wearing out. In the case of personal protective equipment, wearing it too often can result in worker negligence due to being “overly cautious” and not appreciating the potential dangers they could face. If you miscalculate the arc flash boundary at a substantially great distance than it is, you run the risk of having equipment be misused. Naturally, the opposite possibility is also real. This says nothing about worker morale, which could result in workers being unwilling to operate in potentially unsafe areas. The poor calculation can also expose you, as management, to legal action and could even result in having to close down your establishment until more effective safety precautions can be put into place. On the one hand, an employee who underestimates the arc flash boundary is at an increased risk of sustaining an electric shock that could jeopardize their wellbeing. If you or one of your employees performs a bad arc flash boundary calculation, the danger is substantial. The highest level of risk, the prohibited approach boundary, is to be treated as if the individual were in constant contact with the live electrical equipment. An employee crossing a restricted approach boundary requires PPE every time, as well as specialized training due to a high level of risk. This is differentiated from the prohibited or restricted approach boundaries because of risk level. If electrical equipment has not been deemed safe to approach, it is to be considered live and the arc flash boundary should be no less than four feet until safety is determined or further calculations are done. For higher voltages, up to and including 15kV, the arc flash boundary and calculations can be used for gaps between 3 mm and 153 mm. Wearing PPE also impacts the arc flash boundary.

There are times when the arc flash boundary will be reduced, such as with different materials between the person and the equipment. The “rule of thumb” arc flash boundary for lower voltage, sub-600V systems is four feet. The arc flash boundary is detailed as a safe approach distance from parts or equipment that is currently energized, also known as “live.” According to the NFPA 70E standard, there are complex calculations that one can perform, but the general rule is that exposure at the arc flash boundary is 1.2 cal/cm squared. Without an accurate calculation of this boundary, your employees will be under unnecessary risk or may prematurely wear out their equipment due to wearing it needlessly. The arc flash boundary is a vital metric to figuring out how far away your employees must be before they don their personal protective equipment (PPE).

Arc flash boundary approach distances