Arc Flash

Monday, 26 March 2012 21:26



ARC FLASH COMPLIANCE
There are four main regulations that govern electrical safety and arc flash:

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. OSHA compliance is required by any plant building or facility.

2.  The National Fire Protection Association (NFPA) Standard 70 - 2002 “The National Electrical Code” (NEC) contains requirements for warning labels.

3.  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 Analysis states that a "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 must be done to determine the level of Personal Protection Equipment PPE 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 Warning Label.

4.  The Institute of Electronics and Electrical Engineers (IEEE) 1584 – 2002 Guide to Performing Arc-Flash Hazard Calculations

ARC FLASH ANALYSIS
An Arc Flash Analysis is a calculation performed by Professional Engineer to determine the incident energy found at each location that determines the various arc flash boundaries as well as determining what personal protective equipment (PPE) must be used in approaching each boundary.  An Arc Flash Analysis should only be performed by experienced and qualified electricians and engineers.

ARC FLASH LABELING
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 Warning Label to warn and instruct workers of the arc flash hazard, voltage, arc flash boundary and required PPE (Personal Protective Equipment). Subject to the requirements of the facility and arc flash analysis, labels are provided and attached for each analyzed point of concern

ARC FLASH FAQS

WHY CAN'T I JUST USE THE DEFAULT TABLES INSTEAD OF DOING A CALCULATED ARC FLASH ANALYSIS?

By performing a proper arc flash analysis, you can ensure that your workers have the proper protective safety equipment while avoiding the expenses and lost productivity that may result from over or under specification of PPE that can happen when using default tables of NFPA 70E.  An arc flash analysis may also help you to eliminate some arc flash hazards all together.

WHY ALL THE FOCUS ON ARC FLASH?
Historically, the shock hazard has gotten the most attention in electrical safety since it was so common and well understood.  It wasn’t until the early 1980's that a paper "The Other Electrical Hazard: Electric Arc Blast Burns" by Ralph Lee was published in the IEEE Transactions on Industrial Applications.  Dubbed as the second major hazard of electricity, we began to realize the need to educate and protect workers from the dangers of arc flash.

WHAT ARE THE INDUSTRY STANDARDS THAT COVER ARC FLASH?
There are four main regulations that govern electrical safety and arc flash:

  1. 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 NFPAOSHA 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. OSHA compliance is required by any plant building or facility.
  2. 2.The National Fire Protection Association (NFPA) Standard 70 - 2002 “The National Electrical Code” (NEC) contains requirements for warning labels.
  3. 3.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 Analysis states that a "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 must be done to determine the level of Personal Protection Equipment PPE 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 Warning Label.
  4. 4.The Institute of Electronics and Electrical Engineers (IEEE) 1584 – 2002 Guide to Performing Arc-Flash Hazard Calculations

WHAT COMPLIANCE DOES OSHA HAVE FOR ARC FLASH?
Compliance with OSHA involves adherence to a six-point plan:

  • A facility must provide, and be able to demonstrate, a safety program with defined responsibilities.
  • Calculations for the degree of arc flash hazard.
  • Correct personal protective equipment (PPE) for workers.
  • Training for workers on the hazards of arc flash.
  • Appropriate tools for safe working.
  • Warning labels on equipment. Note that the labels are provided by the equipment owners, not the manufacturers. It is expected that the next revision of the National Electric Code will require that the labels contain the equipment's flash protection boundary, its incident energy level, and the required personal protective equipment (PPE).

Companies will be cited and fined for not complying with these standards.

WHAT IS NFPA 70E?
The National Fire Protection Association (NFPA) 70E is a comprehensive standard that establishes best electrical safety practices standards on how to protect electricians from electric arc flash and arc blast exposure and resulting potential injury and death. OSHA has referenced this electrical safety standard in numerous cases. In fact, many organizations have now designed an NFPA 70E Compliance Guide to help protect their electrical personnel from the hazards associated with arc flash.

OSHA adopted regulations on safe electrical work practices in 1990 based on NFPA 70E, and is proposing a revised standard that conforms to the most recent editions of NFPA 70E. Given that the NEC (National Electrical Code) and OSHA have both started referring to it in their documents, citations are now being written based on NFPA 70E.

NFPA 70e applies to employees who work on or near exposed energized electrical conductors or circuit parts. This includes electrical maintenance personnel, operators, troubleshooters, electricians, linemen, engineers, supervisors, site safety personnel or anyone exposed to energized equipment of 50 volts or more.

The goal of the standard is to keep electrical workers free from the hazards of shock, electrocution, arc flash and arc blast

WHAT IS A SHORT-CIRCUIT ANALYSIS AND MUST THIS BE PERFORMED?
The short-circuit analysis is based on a review of one-line drawings by a professional engineer.  Maximum available fault current is calculated at each significant point in system. Each interrupting protective device is then analyzed to determine whether it is appropriately designed and sized to interrupt the circuit in the event of a bolted type of short circuit. Next, the associated equipment must be reviewed to insure that the bus bar is adequately braced to handle the available fault current. Finally, the bolted fault currents are converted into arc fault currents for additional analysis.

A short circuit analysis is not required, however, doing this analysis one can determine if minor revisions in breaker settings or fuse changes can lead to major reductions of arc flash hazards.  No arc flash analysis should be completed without first doing a short circuit analysis in order to save money and to remove potential hazards.

WHAT IS A COORINATION ANALYSIS?
A coordination analysis is the examination of the electrical system and available documentation with the goal of ensuring that over-current protection devices are properly designed and coordinated. Over-current protective devices are rated, selected and adjusted so only the fault current carrying device nearest the fault opens to isolate a faulted circuit from the system. This permits the rest of the system to remain in operation, providing maximum service continuity. The study consists of time-current coordination curves that illustrate coordination among the devices shown on the one-line diagram. Note that protective devices are set or adjusted so that pickup currents and operating times are short but sufficient to override system transient overloads such as inrush currents experienced when energizing transformers or starting motors.

WHAT TYPES OF INJURIES CAN OCCUR FROM AN ARC FLASH?
The degree of injury is directly related to the power of the arc flash, the distance the person is at the time of the arc flash and the protective equipment worn by an individual during an arc flash.  Due to the force from the explosion of energy and the intense heat, burns, concussions, collapsed lungs, hearing loss, shrapnel injuries, broken bones are the common injuries.  Death can and does occur from these injuries.

WHAT IS AN ARC FLASH BOUNDRY?
NFPA 70e defines a “flash protection boundary within which a person could receive a second-degree burn if an electrical arc flash were to occur". It also defines incident energy as “the amount of energy impressed on a surface, a certain distance from the source, generated during an electrical arc event.”  NFPA 70e requires the calculation and creation of a “flash protection boundary”. This imaginary boundary, which surrounds the potential arc point, specifies what level of personal protective clothing and equipment must be used by qualified workers who enter within that boundary