An arc flash is the sudden release of energy associated with a short circuit. Current leaves its intended path and travels through the air to another bus bar, conductor, or to ground. Energy is released in the form of heat, light, sound and pressure. Arc fault explosions vary greatly in intensity, from a small puff of smoke all the way to an explosion that vaporizes metals, produces temperatures in the 1000’s of degrees, and includes a pressure wave capable of crushing a person’s chest.
This explosion can cause significant damage to your electrical equipment and facility, as well as severe injuries or death to employees.
Arc flash can be caused by many things, including dust, dropping/slipping of tools, accident contact, condensation, material failure, corrosion, and faulty installation.
The severity of the arc flash injury to a worker is determined by proximity of the worker to the hazard, use of proper protective equipment, the available fault current, and the length of time that passes before a protective device (breaker or fuse) opens the circuit.
“We now have the ability to quantify the explosion that takes place during a short circuit. The arc flash study collects and analyzes the information that is required for this quantification. Based on the severity of the explosion that is possible, we can select protective equipment clothing that affords the worker reasonable protection. The information on the arc flash label guides the worker in the selection of this protective equipment.”
Dana Lund, P.E.
D.P. Lund Company Founder
The most important reason to become Arc Flash Compliant is for the safety of your employees and facility. According to the National Fire Protection Association (NFPA):
The safety of your employees should be the #1 reason you have a fully compliant Electrical Safety Program. Keep in mind though; whether or not you have a safety program in place, if someone at your facility gets hurt in an arc flash blast, the standard for determining negligence will be OSHA 29 CFR 1910, NFPA 70 and NFPA 70E.
The Occupational Safety & Health Administration (OSHA) is the agency enforcing arc flash safety in the workplace. They have cited many companies for not following regulations and the guidelines provided in the National Fire Protection Association's (NFPA) two standards, the NFPA 70: National Electrical Code, and the NFPA 70E: Standard for Electrical Safety in the Workplace®.
Along with citing specific OSHA regulations, OSHA requires employer compliance with the General Duty Clause. The General Duty Clause Section 5(a)(1) states:
"Each employer shall furnish to each of his employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees."
The requirement for arc flash labeling is relatively new. Until all electrical equipment is labeled, NFPA 70E provides for a prescriptive approach to personal protective equipment (PPE) selection in the form of a table. The problem is that it’s difficult, and oftentimes impossible, for a worker in the field to determine if the table applies to their situation. Even when the table can be utilized its results are conservative; oftentimes requiring more robust personal protective clothing than what would be necessary if the calculations were done and the equipment was labeled. Working in higher rated PPE is more difficult, slower, and therefore more costly.
It’s not unusual for an arc flash study to determine that equipment can be safely worked without arc rated PPE; in other words, the standard protective equipment that should be worn every day by an electrician. This is a real money saver when you consider the alternative of using the prescriptive tables.
Let’s look at one example; panelboards or other equipment rated 240-volt and below. Here are the parameters that must apply before you can use the table.
“Maximum of 25 kA short circuit current available; maximum of .03 second fault clearing time; minimum of 18 inch working distance.”
A few installations have the short circuit current available to them. I know of none that have any idea how quickly the protective device will clear the arc fault. It’s just not something that is intuitive or available in the field.
The bottom line is that it’s unrealistic to assume that a worker can effectively use the tables to select PPE.
All of the information required for an arc flash study is also used for a short circuit and coordination study. In fact, you must complete a short circuit study to complete an arc flash study! The arc flash analysis is based on the available fault current. Equipment that is inadequately rated for the available short circuit current cannot be given an arc flash label; the equipment does not meet code and will explode if subjected to a fault.
This study analyzes the short circuit current from the utility and from internal sources like generators and running motors to determine if the electrical system is properly rated for the fault current that is present at panels, equipment disconnects, and other similar locations. When subjected to fault currents above their ratings, electrical equipment can fail catastrophically, including explosion. The results of the short circuit study are reported as well as used in the coordination study and arc flash study.
By analyzing the electrical system using time-current curve graphs, D.P. Lund Company makes recommendations for the settings associated with adjustable trip breakers and fuse values. The goals of a coordination study are twofold. First, to increase the equipment protection from overload and short circuits. Second, to increase the reliability of your overall electrical system by having downstream breakers trip to clear faults without involving upstream breakers, thus minimizing the resulting outage. Coordination of breakers and fuses is code required in some cases (hospitals, fire pumps, emergency systems, etc.) and highly desirable in others.
The selection of arc rated personal protective equipment (PPE) is determined from the incident energy value that is shown on the arc flash label. Arc rated PPE is rated in calories per centimeter squared. The worker’s PPE must be rated equal to or greater than the incident energy level that is shown on the arc flash label. The arc flash study calculates the incident energy at each piece of equipment that received a label.
Once the analysis is complete, you will have a better understanding of what PPE your facility needs. You can find quality PPE from a number of manufacturers, including:
Yes they do! Here's a portion of a recent OSHA ruling:
OSHA Regional News Release, U.S. Department of Labor Office of Public Affairs
"The U.S. Department of Labor's Occupational Safety and Health Administration has cited Interstate Electrical Services, a North Billerica electrical contractor, for alleged willful and serious violations following a November 2011 arc flash blast at an Andover jobsite. Two workers installing electrical service were seriously burned when a piece of equipment made contact with an energized part of an electrical panel, resulting in the arc flash.
OSHA's Andover Area Office determined that the energized electrical panel was not effectively guarded to prevent workers from coming in contact. As a result of this condition, OSHA issued a willful citation, with a $70,000 fine. A willful violation is one committed with intentional knowing or voluntary disregard for the law's requirements, or with plain indifference to worker safety and health.
OSHA also issued the contractor two serious citations, with $11,000 in fines, for additional electrical hazards posed by a damaged power cord and an energized electrical wire that was not protected against damage. A serious violation occurs when there is substantial probability that death or serious physical harm could result from a hazard about which the employer knew or should have known."
©2013-2019, D.P. Lund Company, All Rights Reserved