ARC FLASH ANALYSIS

Safety  -  Integrity  -  Quality

What is an Arc Flash?

An arc flash (or arc blast) is a release of energy that results from a low impedance connection to ground or another voltage phase in an electrical system.  This rapid release of energy creates a fiery explosion that devastates everything in its path, creating deadly shrapnel as it dissipates.  It is a deadly workplace danger that annually causes unnecessary human injury and high costs associated to property damage and downtime.

From the war of the currents between George Westinghouse (AC) and Nikola Tesla and Thomas Edison (DC) in the late 1800’s, the safety and protection of the factory worker, maintenance professional or construction electrician whether in an office, commercial building or an industrial plant has been a concern. Though facilities are safer now, the electrical hazards of the past are still present within the electrical distribution systems of today. We have more reliable distribution systems and lower transformer winding losses; commercial and industrial facilities are accepting higher service entrance voltages and the relationship between the distribution voltage and the end-use device voltage and the use of generator emergency and back-up power; all of which mean that there has never been more potential for hazards to the worker than today.​

Arc flash incident estimates indicate there are 10-15 serious occurrences (requiring treatment in a burn center) daily in the US; out of these, 1-2 incidents result in death. It’s not surprising that these numbers are getting attention from the Occupational Safety and Health Administration, (OSHA). When arc flash incidents occur in the work place, the average cost is over 2 million dollars in direct costs. When one also considers indirect costs, it is estimated that the total cost is 5-7 million dollars per case. If there are permanent disabling injuries, the cost of lifetime medical and long term-disability can cost upwards of 23 million dollars. One incident, no matter how insignificant, will result in significant costs to an employer whether it’s lost work days, a permanent disability or death.

Currently, the 2011 National Electrical Code (NEC) 110.5 requires that equipment be field marked indicating there is a potential “Arc Flash Hazard”. The NEC does not require that a complete study or hazard assessment be completed, or that instant energy level, approach distance or the level of personal protective equipment (PPE) type be marked. This has been left to NFPA 70E-2015 and IEEE 1584 to set the standards and OSHA 29 CFR 1910 to enforce these requirements. Many authorities having jurisdiction (AHJ’s) are reluctant to enforce the actual requirements of NFPA 70E because they appear in the NEC as a fine print note (FPN). Although an AHJ can recommend that the requirements be implemented, ultimately it is the responsibility of the employer and/or the facility owner to ensure that the requirements are met. In a legal situation, this responsibility could potentially be extended to the electrical engineer and installing contractor on the project as well. If a facility utilizes an electrical contractor for any construction or modifications, the responsibility for safety still comes back to the employer or facility owner. Article 110.5 of NFPA 70E requires that host employers inform contractors of known hazards covered by NFPA 70E relating to the work to be done. The contract employer shall ensure that each employee working in their facility is instructed about the potential hazards.

 

Training requirements, audits, retraining and written emergency procedures are also a big part of the NFPA 70E requirements. Each employee, whether a facility employee or a contractor employee, is required to be trained in the appropriate procedures, be made aware of proper PPE equipment selection for the hazard and receive ongoing training. Emergency procedures are also required to be in writing and training on such given to each employee including cardiopulmonary resuscitation (CPR). This training shall be certified annually by the employer.

Besides all of the above, NFPA 70E Article 200 requires maintenance and testing of the electrical equipment. As part of the electrical distribution system, Article 205.3 states “Overcurrent protective devices shall be maintained in accordance with the manufacturer's instructions and industry standards.” A regular maintenance plan and procedure is a critical part of the requirements. This requirement not only insures that the equipment is operating in a safe condition but also lessens the likelihood that an overcurrent device would not operate properly when required. As you can see from the above, these requirements are not simple...they require the expertise of those who understand the standards and real-life practices.

 

Here is a recap of the steps to bring your facility into compliance:

  1. Site Hazard Analysis

  2. Collection of Data

  3. Testing and Maintenance of Electrical Distribution Equipment

  4. Short Circuit and Coordination Study

  5. Arc Flash Study

  6. Installation of Arc Flash Labels

  7. Purchase of appropriate PPE

  8. Training on use of PPE and all test Equipment

  9. Training on Emergency Procedure Requirements including First Aid and CPR

  10. Audit procedures, retrain and maintain

Obviously, the best way to prevent an arc flash hazard is for equipment to be totally de-energized when any type of servicing is done. 

Here are some of the common tasks that are done on energized equipment:

  • Using test equipment such as meters to check for troubleshooting, checking voltage and amperage and phase rotation

  • Removing or opening panel covers doors and dead fronts for inspections, repairs or
    trouble shooting

  • Replacing fuses

  • Operating breakers or fused switches with the cover off or doors open

  • Racking breakers in and out

  • Installing breakers or fused switches in energized equipment

  • Pulling wire into energized equipment

When and if equipment cannot be totally de-energized, a
hazard assessment must be performed, a written method of procedure (MOP) must be developed and all employees must be familiar with the appropriate procedures. We must ensure that workers are trained on the appropriate use of PPE, testing equipment and emergency procedures to follow. This will provide as much protection as possible from the devastating effects of an arc flash occurrence.

 

This information is not intended to be a complete guide, but
to highlight the key points in protecting employees from arc flash hazards.

 

Based on NFPA 70E 2015 - National Fire Protection Agency

Written by Howard Herndon, Copyright - 2009-Present

Typical information required for a Short Circuit, Coordination and Arc-Flash Study

 

To get started on the Short Circuit, Coordination and Arc-Flash Study we will require the following information.

  1. One-Line drawings and specifications of Project

  2. Source supply information:

  3. Serving Utility Company or Service Provider

  4. Serving Transformer Size

  5. Transformer Type (Submittal or Record Drawing)

  6. Transformer Fusing if applicable (Submittal or Record Drawing)

  7. Conduit & Cable information from Transformer to Building Supply including distance, size of conduit and conductors, type of conduit and conductors. 

  8. Complete submittal on all Distribution Equipment including, Switchboards, Panels, Transformers, Motor Control Centers, ATS, Generator and UPS systems.

  9. Conduit & Cable information for each feeder from the switchboard to each Switchboard, Panel, Transformer, Generator, Motor Control Center, ATS, Generator and UPS as applicable. This should generally continue to the panelboard level. This should including distance, size of conduit and conductors, type of conduit a conductors. (ie: 1-4” PVC w/4-500kCMIL Alum & 1-4/0 Grd)

  10. Nameplate information off of any Motor, 20HP or larger.