Arc flash is a violent flash-over of electric current that leaves its intended path and travels through air from a one conductor to another conductor, or to ground. Arc flash can occur through accidental contact, equipment failure, insulation breaks or gaps, deterioration or corrosion of equipment or parts, dropping a tool, etc., and usually occur in electrical systems where bus voltage is above 120V. These events can cause substantial equipment damage, fire, serious injury, and death.
An arc flash study, also known as arc flash analysis or assessment, is used to determine the amount of potential thermal energy in the event an arc flash incident occurs. The results are used to define a flash protection boundary around the potential source, and to determine the level of arc-rated PPE that must be worn when the boundary is crossed. Equipment must be labeled based on this information notifying personnel of arc fault potential and necessary precautions. A full electrical coordination study and arc flash study are usually spec and commissioning requirements in new facilities.
Protecting Workers from Arc Flash
An arc flash can produce heat as high as 35,000 F, flying molten metal, blast of 2,000 lbs./sq. ft., and deafening 140 dB noise. To prevent catastrophic injury or death, energized equipment of 50V or more must undergo an arc flash study, and an Arc Flash Hazard label listing the required PPE, nominal system voltage, and arc flash boundary must be affixed to the equipment.
The National Fire Protection Association (NFPA) has identified four Hazard Risk Categories (HRC) that determine the arc rating of PPE worn during a given job task. These standards range in severity from HRC 1, which calls for requires one layer of flame-resistant clothing, to HRC 4, which requires a multilayer flash suit with a minimum arc rating of 40. NFPA has also developed four specific approach boundaries – Flash Protection, Limited Approach, Restricted Approach, and Prohibited Approach – that are calculated based on specific system information and require increasing levels of PPE, permits, and documentation.
Omni Instrumentation Services, Inc. is a premier instrumentation and electrical contractor, providing superior total care solutions since 1986. Services include instrument installation, tubing installation, instrument calibration, control loop testing, startup and commissioning, power and lighting, process control wiring, BMS wiring, telecommunications and data wiring, fire alarm wiring, security wiring, process network wiring, and control panel fabrication. Omni Instrumentation Services, Inc., is certified in Foundation Fieldbus, Profibus, DeviceNet and ASI-Bus installation.