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Arc Flash Explosion Video |
An Arc Flash is an electrical explosion due to a fault condition or short circuit when either a phase to ground or phase to phase conductor is connected and current flows through the air.
Arc flaSHEs cause electrical equipment to explode, resulting in an arc-plasma fireball. Temperatures may exceed 35,000° F (the surface of the sun is 9000° F). These high temperatures cause rapid heating of surrounding air and extreme pressures, resulting in an arc blast. The arc flash / blast will likely vaporize all solid copper conductors which will expand up to 67,000 times its original volume when it is vaporized. The arc flash / blast produces fire, intense light, pressure waves and produces flying shrapnel.
When an arc flash happens, it does so without warning and is lightning quick. The result of this violent event is usually destruction of the equipment involved, fire, and severe injury or death to any nearby people. Proper safety and protection measures must be taken to limit the damage from an arc flash which include conducting an arc flash study, short circuit study, and NFPA 70E electrical safety training.
There are a variety of reasons why an Arc Flash can occur, but most of them are human error and preventable. Many arc flashes occur when maintenance workers are manipulating live equipment for testing or repair and accidentally cause a fault or short circuit. Improper tools, improper electrical equipment, corrosion of equipment, improper work techniques and lack of electrical safety training are just some of the events that can lead to a devastating arc flash or arc blast.
Summary: OSHA mandates that employers identify electrical hazards, warn employees about the hazards and provide them proper protection and training regarding the hazards. Compliance with OSHA is mandatory for all US companies. While OSHA tells you "what to do" for arc flash, they don't tell you how to do it. The role of NFPA 70E, IEEE 1584 and NEC is to provide guidance on "how" to properly implement the OSHA regulations.
The regulations that govern arc flash analysis and labeling are:
1. OSHA Standards 29-CFR, Part 1910. Occupational Safety and Health Standards. 1910 sub part S (electrical) Standard number 1910.333 specifically addresses Standards for Work Practices and references NFPA 70E. OSHA 29CFR 1910.335 (a) (1)(i) requires the use of protective equipment when working where a potential electrical hazard exists and 29CFR 1910.132(d)(1) which requires the employer assess the workplace for hazards and the need for personal protective equipment.
2. NFPA 70E provides guidance on implementing appropriate work practices that are required to safeguard workers from injury while working on or near exposed electrical conductors or circuit parts that could become energized. Part II 2-1.3.3 regarding Arc Flash Study / Analysis states that an " Arc Flash Hazard Analysis shall be done before a person approaches any exposed electrical conductor or circuit part that has not been placed in an electrical safe work condition". This Arc Flash Hazard Analysis / Study must be done to determine the level of PPE safety equipment that a worker must use, and the Arc Flash Boundary in inches along with the incident energy found at each location. Each panel must be marked with an ANSI z535 approved Arc Flash Hazard Warning Label according to NFPA 70E.
3. The National Fire Protection Association ( NFPA ) Standard 70 - “The National Electrical Code” (NEC) contains requirements for warning labels, including ANSI compliance.
4. The Institute of Electronics and Electrical Engineers (IEEE) 1584 – Provides the Guide to Performing Arc Flash Hazard Study and Analysis Calculations.
An Arc Flash Study / Analysis is a calculation performed by Professional Engineer to determine the incident energy found at each location which determines the various arc flash boundaries and what personal protective equipment (PPE) must be used in approaching each boundary. As part of the study, the engineer should also provide recommendations to reduce the incident engery / arc flash hazard category. An Arc Flash Analysis / Study should only be performed by experienced and qualified electrical engineers familiar with power quality, short circuit studies, NFPA 70E and IEEE 1584.
The NEC® and NFPA 70E require labeling of equipment to warn of potential arc flash hazards. Each panel must be marked with an ANSI approved Arc Flash Hazard Warning Label to warn and instruct workers of the arc flash hazard, voltage, arc flash boundary and required PPE (Personal Protective Equipment) for safety. Subject to the requirements of the facility and arc flash analysis, labels are attached for each analyzed point of concern. Information on the labels is based on the results of the arc flash analysis / study.
