Protecting Against Arc Flash Accidents
They happen in an instant, but the effects can last indefinitely.
An arc flash is an amazing, violent phenomenon you never want to witness. These flashes happen in an instant and can cause burns, electric shock and worse. A worker who survives exposure to one may require long-term medical care.
An arc flash occurs when an electric current leaves the intended path and travels through air, releasing thermal and mechanical energy. The initial arc ionizes the air. Concentrated radiant thermal energy can reach 20,000 degrees F — hotter than the surface of the sun. Rapidly heated metals expand and generate blast pressure that reaches more than 2,000 pounds per square foot. Tools become missiles, toxic fumes discharge and decibels of 140 or higher stun the ears. Second and third-degree burns happen within three seconds.
Here’s how to help protect against these accidents.
Keep non-qualified workers away
Only qualified workers should install, examine, troubleshoot or repair switchboards, panel boards, motor control centers, transformers, fused disconnects and any equipment that presents an arc flash hazard. Qualification occurs through training, which the company must document.
Workers must be able to recognize the potential for an arc flash and how to prevent one. The level of training determines the tasks the worker is qualified to perform.
Wear arc-rated PPE
Arc flash safety programs emphasize wearing the right PPE. Arc Rated Flame Resistant (FR) pants, shirts, coveralls, jackets and full flash suits resist ignition and protect workers from extreme heat. Insulating gloves, eye and face protection, flame-resistant boots and respiratory protection round out the PPE needed for working in potential arc flash areas.
A garment’s arc rating indicates the insulating capability of the material. The higher the rating, the more protection the material offers. The rating references either the Arc Thermal Performance Value (ATVP), which indicates the ability of the fabric to protect against burns, or the Energy Breakdown Threshold (Ebt), which indicates its ability to resist breaking open when exposed to high thermal energy.
The Hazard Risk Category (HRC), also on the label, is used to determine the arc rating needed for a given task. The categories of risk range from 0 (little to none) to 4 (extreme) and are based on the amount of energy the equipment could deliver to a point at a specified distance from an arc flash.
Use insulated tools
Workers who are repairing equipment near an arc flash hazard should use insulated tools. The tools must meet arc insulation standards for specific voltage levels. Workers should inspect the tools for damage to the insulation and remove damaged tools from service.
Establish flash protection boundaries
Flash protection boundaries define the distance from the potential arc flash and dictate PPE choices. You can determine approach boundaries by using equipment voltage information and charts provided by OSHA.
- The prohibited approach boundary brings workers to the closest proximity of the exposed live part and requires bulkier, HRC Category 4 PPE.
- The restricted approach boundary establishes a longer distance from the potential arc flash but still exposes workers to increased risk.
- The limited approach boundary keeps unqualified workers wearing HRC Category 1 PPE away from ark flash hazard.
Install barriers, blankets, warning signs and labels
Put up barriers to prevent unauthorized workers from entering the arc flash boundary area. Some barriers actually slow the progress of an arc through equipment and prevent arcs from moving beyond the area. Arc suppression blankets absorb the arc blast force and must remain between workers and the potential fault area.
Use prominently placed permanent signs to warn qualified workers about the potential of an arc flash before they begin equipment troubleshooting or maintenance.
Arc flash labels attach to equipment and show the system’s nominal voltage and the applicable arc flash boundary. Labels may also show the available incident energy and working distance, the minimum arc rating of clothing, required level of PPE and the highest HRC.
Shut the circuit down and use LOTO procedures
The most effective method for avoiding arc flash is shutting down the equipment and confirming that all parts have powered down. Install grounding devices to eliminate the risk of induced or stored voltages. Use established lockout/tagout procedures to prevent other workers from energizing the equipment while work is being done.
Remember, it’s your responsibility
An arc flash accident can permanently disable workers, not to mention damage equipment and facilities, increase legal liability, boost insurance costs and result in fines. Your company owns the responsibility for using methods to avoid this hazard.
John Ross has written about industrial, automotive and consumer technologies for 17 years.