According to industrial safety and hygiene news, there are an estimated 30,000 instances of arc flash each year in the United States. On average, these incidents result in 7,000 burns, 2,000 hospitalizations and 400 deaths. Many, if not all, arc flash accidents are completely preventable. Therefore, it is important to understand and identify potentially hazardous scenarios and how to maintain a safe work environment.
What is arc flash? According to the Occupational Safety and Health Administration, “Simply put, an arc flash is a phenomenon where a flashover of electric current leaves its intended path and travels through the air from one conductor to another, or to ground. The results are often violent and when a human is in close proximity to the arc flash, serious injury and even death can occur.”
What happens during an arc flash?
Dust, dropping tools, accidental contact, condensation, material failure, corrosion or faulty installation can all result in arc flash. However, three of the major factors that determine the severity of an injury are proximity to the hazard, temperature and duration of the arc flash. The severity of an arc flash is based on the incident energy. The main factors that define the incident energy are arcing short circuit current, duration and working distance. Obviously, the results increase in severity the closer a person is to the arc, the higher the temperature and the greater the duration.
Arc flash can cause burns, fires, flying objects, extreme pressure and extraordinarily loud noises. For people who experience an arc flash injury, their quality of life may never be the same. Arc flash may ignite or melt clothing and often destroys skin tissue. Unfortunately, victims sometimes require skin grafts or amputations as a result. Arc flash fatality rates increase with burn severity and extent on the body. Extended medical care for these injuries can cost in excess of $1 million.
Explosions or blasts may also occur with arc flash. It can throw victims great distances. When this occurs, broken bones, concussions and internal injuries are common. The sound pressure created by arc flash—which has been recorded at over 140 decibels at 2 feet from the source—can also cause hearing damage or loss.
Arc flash can create heat intense enough to melt metal electrical components and blast molten droplets considerable distances. These droplets can harden rapidly and become lodged in a victim’s skin or be inhaled, causing lung damage.
As a result, the National Fire Protection Association developed the arc flash boundary, designed to protect individuals working on or near energized equipment. It also established boundaries to protect against shock hazard. These boundaries, described below, must be observed to ensure safety.
- Limited approach is the distance from an exposed energized electrical conductor or circuit part within which a shock hazard exists. No unqualified workers are allowed inside this boundary.
- Restricted approach is the distance within which there is an increased risk of shock, due to electrical arc-over combined with any inadvertent movement while working close to an energized electrical conductor or circuit part. Even qualified workers may not work in the restricted boundary unless they are guarded or insulated from energized electrical circuit parts and conductors.
- Arc flash boundary is the distance from a prospective arc flash source where the incident energy is 1.2 cal/cm2. It is used to define where arc rated protection is required to be worn. The 1.2 cal/cm2 is based on the Stoll skin burn injury model, which suggests second-degree burns on unprotected skin begin at that level. Appropriate PPE with an arc rating for the potential incident energy level is required within this boundary.
When determining the appropriate boundary for a given arc flash, the severity of the hazard must be assessed.
Additionally, according to the OSHA Workplace Safety Awareness Council handout on arc flash, “Each piece of equipment operating at 50 volts or more and not put into a deenergized state must be evaluated for arc flash and shock protection. This evaluation will determine the actual boundaries (i.e., limited, restricted, etc.) and will inform the employee of what PPE must be worn. Once the evaluation is complete, an Arc Flash Hazard warning label must be affixed to the equipment and readily accessible to employees who may work on the energized equipment.”
Finally, the National Institutes of Health indicates that employers have the responsibility to prevent arc flash injuries by providing a safety analysis of the workplace and developing engineering controls to eliminate hazards. Employers also must provide the appropriate tools, PPE, regular equipment maintenance and training. A commitment to training is a commitment to safety.