Frequently Asked Questions?

•   What is an arc?
    An arc is the flow of current through the air between phase conductors or phase conductors and neutral or ground. An arcing fault can release tremendous amounts of concentrated radiant energy at the point of the arcing in a small fraction of a second resulting in extremely high temperatures up to 35,000 degrees F, a tremendous pressure blast up to 2100 PSF, and shrapnel hurling at high velocity (in excess of 700 miles per hour).

•  Why are the standards for arc flash changing?
    In 2002, the National Electrical Code (NEC) expressed a need for an arc flash warning label to be attached to certain equipment. Again in 2005, the NEC was updated with even more requirements. The NFPA 70E "Electrical Safety in the Workplace " publication made it mandatory for all non-dwelling facilities to follow these regulations. The OSHA 1910 publication further supports these regulations.
    

•  What is one calorie?
    A calorie is the energy required to raise one gram of water one degree Celsius at one atmosphere. The onset of second-degree burns will occur at 1.2 calories per centimeter squared per second. One calorie per centimeter squared per second, can be equal to holding your finger over the tip of the hottest part of the flame of a cigarette lighter for one second.
   

•  Are all arcs equal?
    No. You must conduct a hazardous assessment to determine the level (intensity) of energy from the arc in calories. From that you can determine the proper PPE needed.
   

•  What causes an Electrical Arc?
    An arc occurs when electric current flows between two or more separated energized conducting surfaces. Some arcs are caused by human error. Another common cause of an arc is equipment or conductor insulation failure. Build-up of dust, impurities, and corrosion on insulating surfaces can provide a path for current. Sparks produced during racking in and out of breakers, replacement of fuses, and closing into faulted lines can also produce an arc.
  
   

•  Can I be exposed to an arc flash?
    The exposure to arc flash depends on...                                                                                                   ...how often a worker performs a task involving exposed live equipment.
  ...the complexity of the task performed, action performed, available space, safety margins, reach, etc.    ...the training, skills, mental and physical agility, coordination with helper.                                                    ...the types of tools used.                                                                                                                            ...the condition of equipment.
  
    

•  Exposure to arc flash does what?
    Exposure to an arc flash can result in a variety of serious injuries and in some cases death.  Workers have been injured even though they were a considerable distance away from the arc center.  Worker injuries can include damaged workers' hearing, eyesight, and severe burns requiring years of healing and rehabilitation.
  
    

•  What are steps I can take to reduce my risk to arc flash exposure?
    Preventive maintenance, worker training, and an effective safety program can significantly reduce arc flash exposure. Preventive maintenance should be conducted on a routine basis to ensure safe operation.  As part of a preventive maintenance program, equipment should be thoroughly cleaned and routine inspections should be conducted by qualified personnel who understand how to uncover loose connections, overheated terminals, discoloration of nearby insulation, and pitted contacts. A comprehensive preventive maintenance plan should also include:
  Using corrosion resistant terminals and insulate exposed metal parts, if possible. 
  Sealing all open areas of equipment to ensure rodents and birds cannot enter. 
  Verifying that all relays and breakers operate properly. 
    
   

•  How do you determine what PPE is required?
    In order to select the proper PPE, incident energy must be known at every point where workers may be required to perform work on energized equipment.  These calculations need to be performed by a qualified person such as an electrical engineer.  All parts of the body that may be exposed to the arc flash need to be covered by the appropriate type and quality of PPE.  Proper PPE can include Flame Resistant clothing, helmet or headgear, face shield, safety glasses, gloves, shoes, etc. depending upon the magnitude of the arc energy.
    

•   What standards regulate arc flash hazards?
    There are four main regulations governing arc flash.  They include:
  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.
  The National Fire Protection Association (NFPA) Standard 70 - 2002 “The National Electrical Code” (NEC) contains requirements for warning labels.
  NFPA 70E 2004 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.
  
    

•   Who enforces these new standards?
    OSHA is an enforcer of safety practices in the workplace.
  OSHA 1910.132(d), and 1926.28(a) states that the employer is responsible to assess the hazards in the work place, select, have, and use the correct PPE, and document the assessment. Though OSHA does not, per se, enforce the NFPA 70E standard 2004 Edition, OSHA considers the NFPA standard a recognized industry practice and the administration’s field inspectors carry with them a copy of the NFPA 70E and use it to enforce safety procedures related to arc flash. Citations and fines are usually issued based on the employers failure to meet the general duty clause of OSHA 1910. Fines can be as high as $500,000.00 per incident.
  The employer is required to conduct hazard assessment in accordance with 29CFR1910.132(d)(1).  Employers who conduct the hazard/risk assessment, and select and require their employees to use PPE, as stated in the NFPA 70E standard 2004 Edition, are deemed in compliance with the Hazard Assessment and Equipment Selection OSHA Standard.
  Electrical inspectors across the country are now enforcing the new labeling requirements set forth in the 2008 National Electric Code (NEC).
   

•   How does an effective preventive maintenance program reduce arc flash hazards?
    A preventive maintenance program on protective devices is recommended as part of the arc flash program. All arc flash calculations require the arc clearing time in order to determine incident energy and establish the flash protection boundary.  The clearing time is derived from the engineering coordination study based on what the protective devices are supposed to do. If maintenance and testing is not performed, it could result in extended clearing times, unintentional time delays, open or shunted current transformers, open coils or dirty contacts.  All of these factors could cause the results of flash hazard analysis to be inaccurate—causing the flash protection boundary to potentially be inaccurate.  This could also affect the recommendations for the proper PPE.  It is recommended that facilities adopt NFPA 70B Recommended Practice for Electrical Equipment Maintenance.
   

•  What data is required to be on the new arc flash warning labels?
   The NEC 110.16 requires the label states the existence of an arc flash hazard and the corrective action to take. The label must meet ANSI Z525 sign standard.
  The label should include more information on the specific parameters of the hazard including:
  The risk hazard category
  Flash Protection Boundary
  Incident energy at 18” expressed in cal/cm2
  PPE required
  Voltage shock hazard
  Limited shock approach boundary
  Restricted shock approach boundary
  Prohibited shock approach boundary
    

•   How do I determine the flash protection boundary?
    The flash protection boundary is based on voltage, available short-circuit current and predicted fault duration. The NFPA 70E provides acceptable methods that should be implemented by a qualified Electrical Engineer.
  
    

•   What is the difference between NFPA 70E and IEEE 1584 calculations?
    NFPA 70E method estimates incident energy based on a theoretical maximum value of power dissipated by arcing faults. This is believed to be generally conservative. In contrast, IEEE 1584 estimates incident energy with empirical equations developed from statistical analysis of measurements taken from numerous laboratory tests. Both examples are designed to provide adequate information to determine the correct level of PPE that a worker should be wearing.
    
   

•   What data is required for an Arc Flash Study?
    Depending on the method of calculation, you will need to determine the type of enclosure, gap between exposed conductors, grounding type, phases/connection, and working distance.
    

•   What is the hazard/risk category?
    The hazard/risk category is specified as a number representing the level of danger, which depends upon the incident energy.  The category ratings range from 0 to 5 where category 0 represents little or no risk, and category 5 is the most dangerous.
    

•   When is it okay to work on “energized” or “live” equipment?
    It is always preferable to work on de-energized equipment.  However, OSHA regulations state in 1910.333 (a) that workers should not work on live equipment (greater than 50 volts) except for one of two reasons:
  1) De-energizing introduces additional or increased hazards such as cutting ventilation to a hazardous location, or
  2) Infeasible due to equipment design or operational limitations such as when voltage testing is required for diagnostics. When it is necessary to work on energized equipment you should follow safe work practices including assessing the risks, wearing proper PPE, and using the proper tools.
    

•  How can equipment design impact arc flash hazards?
   The incident energy exposure caused by an arc flash can be affected by the system configuration, system fault levels, and exposure time. System fault levels can be reduced by changing the system configuration to reduce available fault current, and by using current limiting devices such as fuses, breakers, and reactors. Using faster acting relays and trip devices can reduce arcing time or exposure time. A protective device coordination study should also be conducted to ensure proper device settings. Instantaneous relays could also improve clearing times limiting the arc exposure time.  Fuse sizes should also be evaluated to determine if a smaller fuse could be used since smaller fuses reduce the exposure time. 
    

•   What is “incident energy”?
    Incident energy is defined in NFPA 70E as, “the amount of energy impressed on a surface, a certain distance from the source, generated during an electrical arc event.”
    

•   What is an “electrically safe work condition”?
    An electrically safe work condition is defined as a state in which the conductor or circuit part to be worked on or near has been disconnected from energized parts, locked/tagged in accordance with established standards, tested to ensure the absence of voltage, and grounded if determined necessary.
    

•   What is an arc flash hazard?
    An arc flash hazard is defined in NFPA 70E as a dangerous condition associated with the release of energy caused by an electric arc.
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•   Why should I have a short circuit and protective device coordination study performed prior to the arc flash hazard analysis?
    The Petroleum and Chemical Industry Committee (PCIC) recommends that Arc Flash Calculations be completed in conjunction with Short Circuit Calculations and Protective Device Coordinations to help ensure that the most accurate Arc Flash Hazard results were achieved. Arc Flash Hazard Boundaries are based on voltage, available short-circuit current and predicted fault duration.
    

•   What is the flash protection boundary?
    The flash protection boundary is the distance from the arc source at which the potential incident heat energy from an arcing fault falling on the surface of the skin is 1.2 calories/cm2.
    

•   What is “Limited Approach Boundary”?
    The limited approach boundary defines a boundary around exposed live parts that may not be crossed by “unqualified” persons unless accompanied by “qualified” persons.
    

•   What is “Restricted Approach Boundary”?
    The restricted approach boundary is the area near the exposed live parts that may be crossed only by “qualified” persons using appropriate shock prevention techniques and equipment.
    

•   What is “Prohibited Approach Boundary”?
    The prohibited approach boundary is the area near exposed live parts that may be crossed only by “qualified” persons using same protection as if direct contact with live parts is planned. This is defined by the nominal voltage.
    

•   What is the definition of a “qualified” person?
    A qualified person is one who has received documented training in the hazards of working on energized equipment in general, and has been trained in the hazards of the particular equipment to be serviced. Training must include the use and proper application of PPE.
    

•   What data is required for a Short Circuit Analysis?   
    Typical data that is required for a short circuit analysis includes the equipment type, voltage, MVA/KVA, impedance, S/R ratio, and phases/connection.
    

•   What data is required for Protective Device Coordination Study?
    For relays you will need to determine the relay type, CT ratio, pickup (tap) setting, delay type (curve) and setting time dial.  For fuses you’ll need the fuse type, amp rating, voltage, and peak let-through current.  For circuit breakers you will need the circuit breaker type, fault clearing time, pickup setting, delay curve, and delay setting.
    

•   What is an Arc Flash Study/Analysis?
    An Arc Flash Study/Analysis is an engineering study that determines the amount of current that could flow at any point in an electrical system, and the timing required for the nearest circuit protective device to operate to clear a fault.