Dangerous arc fault flash can be cause when a large current travels thru the air between the phase conductors or a phase conductor and the neutral or ground. This, very fast high energy fault is like a bomb exploding in your face. The high temperature pressure blasts and flying pieces of molten metal can seriously injury or kill the workers in the general area this is called the Arc Flash Boundary. Most hospital admissions due to electrical accidents are from arc flash burns, not from electrical shocks passing through the person's body.
Arc fault can be caused due to a variety of factors: lack of employee safety training, simple human error, improper wire connections, overheated connections which cause insulation breakdown. This can also be caused by someone dropping a tool into energized electrical equipment when an electrician thinks the equipment is de-energized when it is not. This happen when the lock out, tag out rules were not followed correctly. Additionally breaks or gaps in insulation, dust, corrosion, moisture or other impurities on the surface of the conductor can cause arc faults along with many other reasons.
Federal Safety Standards
Federal safety standards require electrical workers to have training to recognize the risk hazard categories I, II, III and IV, Arc Flash Boundary, Incident Energy Level and Personal Protective Equipment (PPE) for each hazard category of the employees work area. The four main agencies that regulate arc fault safety standards include:
OSHA Standards 29-CFR, Part 1910.Occupational Safety and Health Standards. 1910 sub part S (electrical) Standard number 1910.333 Standards for Work Practices and references NFPA 70E.
The National Fire Protection Association (NFPA) Standard 70 "The National Electrical Code" (NEC) contains requirements for warning labels.
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.
The Institute of Electronics and Electrical Engineers (IEEE) 1584. Guide to Performing Arc-Flash Hazard Calculations.
When working with all the previous conditions and areas Personal Protective Equipment (PPE) must cover all part of the workers body for the determined Incident Energy Level. Proper PPE for the electrician could include: flame resistant clothing, hardhat, hood, face shield, safety eye glasses, glove, work boots, etc.
Safety protection equipment and protective work clothing must meet requirements of ASTM 1506, OSHA 1910-269 and NFPA 70E.
Upon completion of your respected job you must seek the instructions from the jobs engineer or refer to the flash hazard calculation software for the type of labeling your equipment requires to be applied. Installing proper labeling of with ANSI z535 approved Arc Flash warning label is crucial. Certified training programs, continuing education units (CEU) or classes from accredited instructors may be offered from your local trade school or an online electrical safety training course.