How to Read an Arc Flash Label

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Here's a quick cheat sheet for reading an arc flash label

1)  Danger or Warning Header:  A red “Danger” header is commonly used when the nominal system voltage is over 600 or when the incident energy is over 40 calories per square centimeter (cal/cm2). If less than either of these thresholds, an orange "Warning" header is typically used.

2)  Arc Flash Boundary: When an arc flash hazard exists, the shortest distance at which the worker—if not properly protected by flame-resistant clothing—may be permanently injured (the onset of a second degree burn or worse). The onset of a second degree burn on unprotected skin is likely to occur at an exposure of 1.2 cal/cm2for one second.

3) PPE Hazard Category: Represents minimum criteria PPE must meet to avoid onset of permanent injury if inside the arc flash boundary. Represented as category 1-4.4)

4) Arc Rating of Clothing:  Measured in calories/cm2, this rating measures the thermal energy at a working distance from the arc fault.

5) Incident Energy:  The amount of thermal energy impressed on a surface, a certain distance from the source, generated during an electrical arc event and typically expressed in cal/cm2. Incident energy increases as the distance from the arc source decreases.

6) Working Distance:  The distance between a person’s face and chest area and a prospective arc source.

7) Nominal System Voltage: A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class.

8) Limited Approach Boundary:  An approach limit at a distance from an exposed energized electrical conductor or circuit part within which a shock hazard exists.

9) Restricted Approach Boundary: An approach limit at a distance from an exposed energized electrical conductor or circuit part within which there is an increased likelihood of electric shock due to electrical arc-over combined with inadvertent movement.

10) Arc-rated/Additional PPE: Flash apparel, flame-resistant clothing, and other PPE that protect workers from hazards presented by an arc flash and/or shock.

11) Equipment ID:  Identifies the piece of equipment that the warning label is associated with.

Arc Flash Label


The information contained in this article is intended for general information purposes only and is based on information available as of the initial date of publication. No representation is made that the information or references are complete or remain current. This article is not a substitute for review of current applicable government regulations, industry standards, or other standards specific to your business and/or activities and should not be construed as legal advice or opinion. Readers with specific questions should refer to the applicable standards or consult with an attorney.


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