Arc Flash Safety: Create a Plan for Compliance

According to the National Fire Protection Agency (NFPA) 70E: Standard for Electrical Safety in the Workplace, arc flash is a “dangerous condition associated with the release of energy caused by an electrical arc.” In laymen’s terms, that translates into a sudden and dangerous blast of extreme heat, intense light, and pressure waves that happens when a high-voltage gap exists between a phase bus bar and another phase bus bar, neutral or a ground.

Injuries are often devastating, as arc flash temperatures can reach 35,000° F, which is three times hotter than the surface of the sun. An arc flash also can produce noise reaching 140 decibels—about as loud as a gunshot—and molten metal shrapnel.

Arc flash incidents can often be traced to human error or poorly maintained systems. Factors such as worn cable insulation, dirty or corroded contacts or electrical parts, a dropped tool, and occasionally an ill-fated rodent or bird, can all cause a catastrophic accident.

This is an example of the Emerson Appleton Plexpower Fiber panel board. Photos courtesy of Emerson, St. Louis, Missouri

Some plant managers may justify their decision to not provide workers with arc rated, flame resistant (AR/FR) clothing or safety training by suggesting that arc flash incidents are so rare that it’s not worth the expense. However, a 2013 report published in the May 31, 2013, edition of Industrial Safety & Hygiene News disputes that claim. It estimates that, on average, there are 30,000 arc flash incidents every year in the United States or about 5-10 per day. The report went on to say that those incidents resulted in annual totals of 7,000 burn injuries, 2,000 hospitalizations, and 400 fatalities. Costs incurred by arc flash damage can reach millions of dollars in employee claims, insurance costs, equipment replacement and lost productivity.

Given the risk, frequency and severity of arc flash events, it is imperative that plants employ a host of mitigation processes to pave a safer path for workers who maintain electrical distribution, power control and protection systems.

Dress for Duress

Example of arc flash suit

In April 2014, OSHA issued a final rule on electric power generation, transmission and distribution, and electrical protective equipment. Under the rule, employers must protect their workers from hazards posed by flames and electric arc in the following ways:

• Identify employees who will be working around these hazards.
• Estimate the incident heat energy of any electric-arc hazard to which a worker would be exposed at various points along the power chain. Accuracy is essential with such measurements, so plant managers who lack direct and extensive experience with arc flash incident energy assessment should always seek assistance from a qualified power systems engineer.
• Ensure workers exposed to such hazards wear protective clothing and other protective equipment with an arc rating equal to or greater than the estimated heat energy.

Wearing flame-resistant clothing can drastically improve the chance of walking away from an arc flash. Some of the different types of PPE that should be worn includes an arc flash suit, hardhat, leather footwear, rubber gloves, arc-rated face shield and more. Workers should always avoid wearing jewelry, including metal watches, metal fasteners on clothing, or any other conductive material.

In addition, only use tools, meters, and other equipment that are suitable for the voltage and current levels present when performing electrical work. Look for tools that meet IEC standards with an independent lab testing verifying it. The lab’s symbol on the tool means an independent testing agency has checked the safety claims and CAT ratings.

Six Ways to Prevent Arc Flash Accidents

As crucial as PPE is, it should be considered the last line of defense against arc flash. With the safety procedures outlined below, it’s possible to minimize the risk of arc flash.

De-energize equipment

The only way to completely eliminate hazards is to de-energize equipment. Be sure to test for the absence of voltage while wearing the appropriate PPE. Until the absence of voltage testing proves the circuits are dead, they must be considered energized. Note that OSHA doesn’t require that energy never be present; instead, it requires that the employer eliminate hazardous energy as the first option. If eliminating the hazard is not possible, only then can the employer consider reducing the risk to a tolerable level. Examples of when energized work is permitted include troubleshooting that requires voltage and when shutting down creates a greater hazard. OSHA does not permit energized work simply because it may be inconvenient or production-inhibiting to de-energize.

Maintain equipment

NFPA 70E Article 205.3, General Maintenance Requirements, states: “Electrical equipment shall be maintained in accordance with the manufacturer’s instructions or industry consensus standards to reduce the risk of failure and the subsequent exposure of employees to electrical hazards.” This especially applies to breakers. If the breaker hasn’t been maintained and tested as required, there is no assurance that it will respond in accordance with its published time-current curve. Many manufacturers recommend that breakers be removed from service and inspected at least once per year. Additionally, damaged insulation on high-voltage wiring and dust or other impurities accumulated on equipment can create a pathway for the flow of electricity and may possibly lead to an arc flash when high-voltage components are involved.

Don’t overstep your boundaries

The arc flash boundary is the minimum “safe” distance from exposed energized conductors or circuit parts that has the potential for an arc flash. NFPA 70E recommends defining three boundaries to minimize risk of electrical injuries. The outermost Flash Protection Boundary is set at a distance where, if a worker were exposed to an arc flash, they would sustain a curable second-degree burn. The Limited Approach Boundary is set at a distance where a worker would experience a shock hazard. The Restricted Approach Boundary is set at a distance where a shock hazard is increased. The innermost Prohibited Approach Boundary is set at a distance so close to the energized equipment that it is considered the same as making contact with the live part. Depending on the piece of equipment being worked on, these boundaries will fluctuate in distance.

Four standards, one goal

Four separate industry standards concern the prevention of arc flash incidents: OSHA 29 Code of Federal Regulations (CFR) Part 1910 Subpart S; NFPA 70-2002 National Electric Code; NFPA 70E-2000 Standard for Electrical Safety Requirements for Employee Workplaces; and IEEE Standard 1584-2002 Guide for Performing Arc Flash Hazard Calculations. Knowledge equals safety.

Label Machinery

Another way a plant manager can improve arc flash safety is through labeling. Arc flash labels indicate two key pieces of information: the expected incident energy (measured in calories per cm2)—at a working distance of 18 inches or 24 inches—which drives the PPE required for protection; and the distance a worker without PPE must work to avoid a non-curable burn (typically measured in feet). By using correct labeling on critical equipment, facilities can get ahead of potential safety issues to ensure personnel are protected. Note that the NFPA 70E standard explicitly requires employers to post signage notifying employees of potential arc flash dangers. Organizations that ignore this requirement dramatically increase their chances of paying substantial fines and exposing themselves to significant liability.

Train Personnel

Finally, training is one of the surest ways to keep workers safe from an arc flash. Most courses are structured to help companies fulfill requirements set forth in OSHA 29 CFR Part 1910, Subpart S Electrical and NFPA 70E, which mandates this type of instructor-led training for anyone working with electrically energized equipment.