Understanding What Accessories Should NOT Cross an Arc Flash Boundary

When it comes to electrical safety, understanding and adhering to strict guidelines is paramount to protecting yourself from potential hazards. When working near energized electrical components, it’s crucial to know what is and isn’t permissible within the protection boundaries set forth by standards such as NFPA 70E, Standard for Electrical Safety in the Workplace, and in Canada, CSA Z462, Workplace Electrical Safety. This blog post delves into the significance of these protection boundaries and why certain accessories should never cross the line.

In the video below, Scott Margolin, Tyndale’s Vice President of Technical, highlights examples of everyday accessories that may seem harmless but could pose a severe risk if worn within the arc flash or restricted approach boundary.

 

As Scott explains, every accessory from head to toe – other than arc-rated clothing, hard hats, face shields, rubber gloves, and leather keepers – must be carefully considered to ensure it meets the safety standards required for electrical work or to be within the arc flash boundary. For instance:

  • Headwear such as baseball caps, hard hat liners, doo rags, or bandanas must be arc-rated to prevent flammability or melting.
  • Metal accessories like eyeglasses, watches, jewelry, or wedding rings are unsafe to wear within the restricted approach boundary, as they can conduct heat and electricity, increasing the risk of injury. Choose silicone wedding rings and non-metallic eyewear as safer alternatives.
  • Pens or other loose metal objects – outside of properly rated and inspected insulated tools – should never be brought across the restricted approach boundary.
  • Even seemingly innocuous items like metal belt buckles can pose a threat if they cross the restricted approach boundary, potentially causing an arc or drawing one toward the wearer. Leather belts without metal buckles are generally safe since an arc flash does not typically generate enough energy over time to cause the leather to ignite.
  • The small eyelets in shoes and boots don’t present a significant risk, but in general, it’s best to avoid metal components in footwear.

While the list above highlights some common examples and is not exhaustive, workers must be aware of these guidelines and adhere to them diligently to minimize the risk of injury from electric arc flash incidents.

What is the Arc Flash Boundary?

During an arc flash event, an enormous amount of thermal energy is released. The amount of thermal energy at a given distance from an arc source is referred to as the “incident energy.” Where an arc flash hazard exists, NFPA 70E and CSA Z462 define the arc flash boundary as the approach limit distance from an arc source where the incident energy equals 1.2 calories per square centimeter (1.2 cal/cm2). When measured in joules, this incident energy equals five joules per square centimeter (5 J/cm2). This incident energy rating is significant, according to the Stoll skin burn injury model, as it is when the onset of a second-degree burn is likely to occur on unprotected skin when exposed for one second. A second-degree burn is painful and blistering but is typically curable and has no lasting damage.

Electric Shock Protection Boundaries

In addition to the arc flash boundary, NFPA 70E and CSA Z462 define two types of electric shock protection boundaries that are applicable where personnel are approaching exposed energized electrical conductors or circuit parts. These two boundaries are:

  • The Limited Approach Boundary (LAB) is the closest distance an unqualified person can approach an energized electrical component without appropriate protection. The LAB is not to be crossed by unqualified persons unless advised of the possible hazards and continuously escorted by a qualified person.
  • The Restricted Approach Boundary (RAB) allows only qualified personnel to enter, and they must be equipped with the necessary PPE and training.

To learn more about arc flash boundaries, shock protection boundaries, and other crucial aspects of electrical safety as outlined in NFPA 70E, stay tuned for upcoming installments of Tyndale’s NFPA 70E Made Easy video series. This series aims to provide comprehensive insights into the standards and best practices for electrical safety.

In summary, strict adherence to safety guidelines and ensuring certain accessories are not worn or carried within the arc flash or restricted approach boundary are paramount to the well-being of workers in environments with arc flash hazards. By understanding and respecting the protection boundaries set forth by industry standards, we can create safer work environments for all.

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