I’m often asked what arc flash PPE layering means. This article will answer that question and explain how layering impacts the overall protection level of the PPE.
First, let’s define layering. Layering for Arc Flash Protection is the method of combining two or more arc-rated garments into a layered system for the purpose of achieving a higher level of arc flash protection. The concept is simple—just wear an arc-rated garment over another arc-rated garment to increase the protection level. However, determining the level of added protection is not a simple calculation. Adding an 8-calorie coverall over a 4-calorie shirt and pants does not necessarily result in a 12-calorie level of protection.
Actually, layering can increase the total arc rating to levels greater than the sum of the individual arc ratings. The reason is because air is a good thermal insulator. When a worker wears layers of arc-rated PPE, the air gap between the layers adds to the overall rating of the system. As a result, an 8-calorie coverall over a 4-calorie shirt and pants can increase the level of protection up to a level 24 calories/cm2. NFPA 70E states in Annex M that the arc rating of a two-layered arc-rated clothing system would typically provide more than 3 times the level of protection of the individual layers.
This is good news because the total layered system is much lighter than wearing a thick, hot, and cumbersome arc flash suit. It is also advantageous in situations in which an arc flash suit is not available.
The ultimate question, therefore, is how to determine the overall arc thermal protection value of a layered system. In order to do this, all layers of the system must be tested together for an accurate arc rating to be determined. The best time to do this is upon purchase from the manufacturer. If a determination was not made at the time of purchase, reach out to the manufacturer to see if they can provide an answer. Either way, you will want to get proof of verification. If you are audited by OSHA or another AHJ, you will probably need this proof.
• Increased level of protection can be more than the sum of its parts
• Reduced PPE weight and more comfort for the worker
• Reduced heat exposure to the worker
• Increased protection beyond the rating of any PPE that may be in the maintenance shop
• Testing is necessary to determine the overall system rating
• Possibility of decreased protection. NFPA 70E states in Annex M, “In a few cases it has been observed that the total system arc rating actually decreased when another arc-rated layer of a specific type was added to the system as the outermost layer.”
Thank you for your time.
Mitchell & Lindsey offers Arc Flash Risk Assessments and Electrical Safety Training. If we can be of service to you in these areas or if you have any questions about this article, please reach out to me at the email or phone number below.
Bobby Lindsey – CESCP
Mitchell & Lindsey – President
M: (502) 836-4217