The Incident Energy Analysis Method is a sophisticated approach that utilizes intricate calculations to determine the incident energy for each specific piece of equipment. According to NFPA 70E 130.5(G), the incident energy exposure level is determined based on the working distance of an employee’s face and chest areas from a potential arc source related to the specific task at hand. While this method can be manually calculated, precision is significantly enhanced when performed through computerized analysis. This method categorizes Personal Protective Equipment (PPE) into three distinct levels:
- Incident Energy < 1.2 cal/cm2:
- Protective Clothing: Non-melting or untreated natural fibers (e.g., untreated cotton, wool, rayon, silk, or blends) with a fabric weight of at least 4.5 oz/yd2.
- Apparel: Long-sleeved shirt, long pants or coveralls.
- Protective Equipment: Face shield for projectile protection (as needed), safety glasses or goggles (required), hearing protection, heavy-duty leather gloves, or rubber insulating gloves with leather protectors (required), and leather footwear.
- Incident Energy 1.2 – 12 cal/cm2:
- Arc Rated Clothing: Arc rating equal to or greater than the estimated incident energy.
- Apparel: Long-sleeved shirt (required), long pants or coveralls (required), or an Arc Flash Suit (required).
- Protective Equipment: Arc-rated face shield & arc-rated balaclava OR arc flash suit hood (required), arc-rated outerwear (e.g., jacket, parka, rainwear, hard hat liner, etc.) as needed, heavy-duty leather gloves, arc-rated gloves, or rubber insulating gloves with leather protectors (required), hard hat, safety glasses or safety goggles (required), hearing protection, and leather footwear.
- Incident Energy ≥ 12 cal/cm2:
- Arc Rated Clothing: Arc rating equal to or greater than the estimated incident energy.
- Apparel: Long-sleeved shirt (required), long pants or coveralls (required), or an Arc Flash Suit (required).
- Protective Equipment: Arc-rated arc flash suit hood (required), arc-rated outerwear (e.g., jacket, parka, rainwear, hard hat liner, etc.) as needed, arc-rated gloves OR rubber insulating gloves with leather protectors (required), hard hat, safety glasses or safety goggles (required), hearing protection, and leather footwear.
- Note: The incident energy analysis method has no upper cap on incident energy, whereas the PPE categories method ends at 40 cal/cm2.
Additional Considerations:
- Undergarments:
- NFPA permits the wearing of flammable, non-meltable undergarments beneath PPE. Cotton is often the fabric of choice.
- Gloves:
- Leather gloves are mandatory for any level of arc flash protection. Heavy-duty leather gloves with specified characteristics have demonstrated arc thermal performance exceeding 10 cal/cm2.
- Foot Protection:
- Footwear with an arc rating is unavailable. Heavy-duty leather or dielectric footwear offers some arc flash protection and should be used for exposures exceeding 4 cal/cm2.
- Outer Layers:
- Outer layers, such as jackets or rainwear worn over arc-rated clothing, must also be made from arc-rated material to prevent potential flame sources.
- Conductive Articles:
- Conductive articles like jewelry or clothing items should not be worn within the restricted approach boundary or where they pose an electrical contact hazard with exposed energized electrical conductors or circuit parts.
Ensuring adherence to these guidelines enhances workplace safety and mitigates the risks associated with arc flash incidents.
