A better understanding of NFPA 70E - What injury are you comfortable with?

Blog Post created by ccoache Employee on May 18, 2017

Have you ever had a sunburn? Is a bad sunburn really that bad? The answer to that question will depend on who you ask. If you ask a person not likely to be exposed to the possibility of the burn, they probably will say no. If you ask a person who has been burned, they will probably say yes. The following assumes that you have read each of my posts about the authority having jurisdiction, consensus standards, risks to workers, and workers having some say regarding their safety.

The minimum standard is that should an arc flash occur while you are performing a task on justified energized electrical equipment that you be able to survive without permanent physical damage. Think about this. For anything other than an electrically safe work condition (which your employer has determined not appropriate for the task assigned to you), the standard does not prevent injury to you. While compliant and properly rated PPE increases the possibility that you emerge from an incident unscathed, you are not guaranteed to be uninjured. The severity of the burn injury permitted by the standard is limited by the 1.2 cal/cm2 incident energy. Why is 1.2 cal/cm2 used? Testing determined that this is the level where exposed skin can suffer a second-degree burn.

The Merriam-Webster dictionary defines a second-degree burn as: a burn marked by pain, blistering, and superficial destruction of dermis with edema and hyperemia of the tissues beneath the burn. This type of burn results in red, white, or splotchy skin, swelling, and blisters. A second-degree burn penetrates the second layer of skin. When the first layer is destroyed, it separates from the second layer. The raw nerves in the second skin layer make this burn painful. If a second-degree burn is larger than 3 inches in diameter or is on the hands, feet, face, groin, buttocks, or a major joint, the Mayo Clinic suggests treating it as a major burn and getting immediate medical help.

Those of you who think that arc-flash PPE will prevent an injury are wrong. Testing determines the incident energy level at which the PPE has a 50% probability of successfully preventing an injury. Half of the time there is a possibility of a second-degree burn if the rating is based on the arc thermal performance value (ATPV) and the incident energy exposure does not exceed that rating. Remember back to my post on consensus standards. It discussed how you determined the incident energy level and whether PPE rated for that exact level was a best practice. The arc-rated PPE that you are wearing has an increased probability of success if subjected to an incident energy lower than its rating. This also ties into my last blog on compliant PPE because if your employer has provided you with substandard equipment, the severity of your injury will most likely be greatly increased.

Another side point to this discussion is that the working distance for equipment is generally stated as 18 or 36 inches. If the incident energy is calculated to be below 1.2 cal/cm2 at this distance, how much closer to the origin of an arc-flash are your hands, arms or head when you perform the energized task? Those body parts could suffer worse than a second-degree burn if not protected.

Compliant and properly rated PPE should limit your injury to a second-degree burn when a higher incident energy is present during an incident. The minimum requirements of the consensus standard use 1.2 cal/cm2 because there is a probability that you will not suffer a permanent physical injury. The standard has no requirement to provide you with arc-flash protection below 1.2 cal/cm2. Only you and your employer can decide if a second-degree burn is acceptable.

For more information on 70E, read my entire 70E blog series on Xchange.


Next Time: Working below 1.2 cal/cm2