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.