Arc Flash/shock hazard warning labels are specifically designed to help protect qualified workers who have to examine, adjust, service, or maintain electrical equipment while energized. It is important to understand the information given on the label to protect yourself and others.
1. Incident energy
Incident energy, as indicated on the arc flash label, is the level of thermal energy that one would feel at the working distance in the event of an arc flash. This energy is measured in calories per centimeter squared. Commonly noted as cal/cm2. Workers must wear protective equipment that has a rating greater than the level of the incident energy printed on the arc flash warning label.
2. Arc Flash Boundary
The Arc flash boundary is the distance from a possible arc source to where the incident energy drops to 1.2 calories per square centimeter. If a person were standing at this distance from the arc source, they could receive a second-degree burn. Workers who are not protected with PPE must remain outside of the arc flash boundary to ensure their safety. Workers inside of the arc flash boundary must have all parts of their body protected from arc flash.
3. Available fault current
The amount of current supplied by the electrical equipment’s upstream device. Typically this information is used for service entrance equipment and generic warning labels.
4. Recommended PPE
A recommended list of shock and arc flash hazard PPE that shall be worn when working on equipment that is not placed in an electrically safe condition. This section could include company specific PPE requirements.
5. Working Distance
The working distance is the distance at which the incident energy is calculated. IEEE 1584 a guide commonly used for performing arc flash incident energy and boundary calculations, defines the working distance as “the dimension between the possible arc point and the head and body of the worker positioned in place to perform the assigned task.” The typical working distance for low voltage MCC’s and panels (less than 600-volts) is 18 inches as depicted above. Reducing this distance increases the incident energy because the worker is closer to the possible arc point. Increasing the working distance decreases the incident energy.
6. Nominal Voltage
Nominal voltage is a value assigned for conveniently designating a voltage class, such as 120/208V, 277/480V. Many electrical workers have been injured because they used test equipment rated for 1,000 volts on circuits energized at 4,160 volts or higher. Because the label makes workers aware of the nominal voltage they can use this information to select the proper test instrument, shock hazard PPE, and other safe work practices to ensure their safety.
7. Glove Class
Workers must be protected from shock by wearing rubber insulating gloves if their hands enter the restricted approach boundary. Workers must select gloves that have a rating for the level of voltage to which the gloves will be exposed. The glove class section of warning label indicates the minimum rating of the gloves to be worn.
8. Limited Approach Boundary
The limited approach boundary is designed to keep unqualified workers safe from shock hazards. Unqualified worker can only cross this boundary if he or she is continuously escorted by a qualified worker, or the electrical hazard has been eliminated by placing the equipment in an electrically safe condition.
9. Restricted Approach Boundary
Only qualified persons may cross into the restricted approach boundary. Inside this boundary, accidental movement can put a part of the body or conductive tools in contact with live parts. To cross the restricted approach boundary, the qualified person shall be insulated by wearing rubber gloves rated for the voltage to which they will be exposed. If tools are used, they shall be insulated. Under no circumstance shall unqualified workers enter the restricted approach boundary.