Unfortunately, there was an accident at your workplace a few days ago, and several team members were injured. You heard the safety office declare that the accident was an Arc Flash. After viewing the remnants of this accident, you wanted to learn more about an Arc Flash. Let’s research the anatomy of an Arc Flash.
An Arc Flash is an energy discharge of light and heat that forms when a fault occurs in an electrical circuit. The arcing results in a tremendous amount of energy being released as current flows through ionized air. An Arc Blast, separate from an Arc Flash, is a supersonic shockwave produced when the uncontrolled arc vaporizes the metal conductors. The terms are used interchangeably. However, they really are different entities.
What Are Arc Flash and Arc Blast?
An arc flash is the sudden release of thermal energy, intense light, and radiant heat caused by an electrical current traveling through ionized air. It can occur when an unintended conductive path forms between energized conductors or between a conductor and ground.
An arc blast is the pressure wave produced by the rapid expansion of air and the vaporization of conductive materials during an arc fault. Although arc flash and arc blast are closely related and may occur during the same event, they describe different hazards. Arc flash refers primarily to the thermal energy and intense light, while arc blast refers to the pressure, sound, and flying debris.
The Anatomy of An Arc Flash
As an arc develops and gets hotter, the electrical resistance decreases and draws more and more current until some part of the system melts, trips or evaporates. When an uncontrolled arc develops and forms at high voltages, the Arc Flash can produce deafening noise, superheated shrapnel, supersonic concussive forces, intense high-energy radiation, and temperatures that far exceed the temperature of the Sun.
An Arc Flash also produces a cloud of plasma and ionized particles, and if inhaled, the ionized gas causes severe burns to the airways and lungs. The charged particles may also be attracted to metallic objects nearby, such as jewelry, belt buckles, keys, and eyeglass frames, resulting in severe burns.
What Is an Arc Blast?
An arc blast is the explosive release of pressure that can accompany an arc flash. As the electrical arc heats the surrounding air and metal, those materials expand rapidly. This expansion creates a pressure wave capable of knocking workers down, throwing them against nearby structures, damaging hearing, and propelling molten metal or equipment fragments through the work area.
The severity of an arc blast depends on factors such as available fault current, arc duration, equipment configuration, enclosure size, and the worker’s distance from the source. Enclosed electrical equipment can direct pressure and hot gases toward anyone standing in front of an open door or panel.
How Arc Flash and Arc Blast Occur
An arc flash begins when electrical current leaves its intended path and crosses an air gap. Once the air becomes ionized, it can conduct electricity and form a plasma channel. Current may continue flowing through this channel until a protective device interrupts the circuit or equipment is damaged enough to stop the fault.
Common triggers include:
- Accidental contact with energized components
- Dropped tools, loose hardware, or conductive objects
- Damaged or deteriorated insulation
- Loose or corroded electrical connections
- Dust, moisture, condensation, or contamination
- Equipment failure or incorrect installation
- Improper switching or racking operations
- Pest or animal contact
- Inadequate electrical maintenance
- Working on equipment that has not been properly de-energized
System voltage alone does not determine the severity of the event. Available fault current, protective-device clearing time, working distance, and equipment configuration all affect the incident energy to which a worker may be exposed.
Arc Blast and Arc Flash Hazards
- Shrapnel – Arc Flash/Blasts spray droplets of molten metal at speeds that exceed 700 MPH that can easily penetrate standard Personal Protective Equipment (PPE).
- Extreme Temperatures – Arcs produce some of the highest temperatures recorded on Earth, up to 35,000° F, which is three times the temperature of the Sun.
- Sudden Air Expansion – All known materials are vaporized at this temperature. The rate of expansion is comparable to a pea-sized piece of copper expanding to the size of a boxcar. Blast pressure waves have thrown workers across the room.
- Fatal Burns – Fatal burns can occur even when the worker is several feet away from the arc. Clothing can ignite from 10 feet away unless proper PPE is used.
- Hearing Loss – An Arc Blast can have a sound magnitude of 140 dB two feet from the arc and can cause permanent hearing loss.
What Are the Main Injuries and Risks from Arc Flash and Arc Blast?
Arc flash and arc blast events can expose workers to several hazards at once. The main risks include:
- Thermal burns: Radiant heat can cause severe skin burns and ignite clothing. Molten metal may also cause direct contact burns.
- Blast pressure: The pressure wave can knock workers off balance, cause internal injuries, or throw them against nearby equipment and structures.
- Flying debris: Vaporized metal, equipment fragments, and molten material can cause penetrating injuries.
- Hearing damage: The sound pressure produced by an arc blast can cause temporary or permanent hearing loss.
- Eye injuries: Intense light, ultraviolet radiation, smoke, and debris can damage the eyes.
- Respiratory injuries: Hot gases, smoke, and vaporized materials may burn or damage the respiratory system.
- Electric shock: Workers may also contact energized conductors before, during, or after the arc event.
- Secondary injuries: Falls, impacts, fires, and panic responses can cause additional harm.
An arc event can also destroy switchgear, damage adjacent assets, start fires, interrupt critical operations, and expose other workers in the area.
Safety Precautions
The National Fire Protection Association (NFPA) published the 2018 Edition NFPA 70E, putting forth new and revised regulations to protect workers from hazards that can cause injury or death. See a past article on these new regulations that describe a “Hierarchy of Controls” for establishing safe working procedures.
How to Reduce Arc Flash and Arc Blast Risk
Risk reduction should follow the hierarchy of controls, beginning with eliminating exposure wherever possible. De-energizing equipment and establishing an electrically safe work condition provide stronger protection than relying on PPE alone.
Effective controls may include:
- De-energizing equipment before work begins
- Applying complete lockout/tagout procedures
- Verifying the absence of voltage with an appropriately rated test instrument
- Performing arc flash risk assessments
- Maintaining accurate electrical system studies and equipment labels
- Using current-limiting protective devices and faster fault-clearing settings
- Installing arc-resistant equipment, remote switching, and remote racking systems
- Maintaining electrical equipment according to an established program
- Restricting energized work to qualified personnel
- Establishing approach boundaries and safe work procedures
- Providing task-specific electrical safety training
- Using insulated tools, barriers, and protective shields
- Selecting arc-rated clothing and PPE for the assessed exposure
Infrared inspection windows can also support safer thermographic inspections by allowing technicians to collect thermal data without opening or removing energized enclosure panels. This helps reduce exposure, but the window does not eliminate every electrical hazard or make energized work automatically safe. The inspection must still be planned and performed according to the facility’s electrical safety program.
Arc Flash and Arc Blast Standards and Workplace Safety
OSHA addresses arc flash through its electrical safety-related work-practice, personal-protection, and equipment requirements. OSHA generally requires exposed live parts to be de-energized before employees work on or near them unless de-energization creates additional hazards or is infeasible because of equipment design or operational limitations. Equipment that has been switched off but has not been properly locked and tagged must still be treated as energized. OSHA also requires appropriate safeguards and protective equipment where workers may be exposed to electric arcs, flashes, or electrical explosions.
NFPA 70E provides a widely used framework for electrical safety in the workplace. It addresses electrically safe work conditions, energized work, arc flash risk assessment, boundaries, job planning, training, and PPE selection. The standard requires employers to apply the hierarchy of risk controls, with elimination placed ahead of administrative controls and PPE. NFPA 70E guidance emphasizes that PPE is part of an overall risk-reduction strategy rather than the first or only control.
Employers should determine which OSHA regulations, NFPA standards, electrical codes, and local requirements apply to their facilities and work activities. Electrical tasks presenting shock or arc flash hazards should only be performed by qualified personnel following an established electrical safety program.
Conclusion
An Arc Flash or Arc Flash Blast is an extremely dangerous event that can cause injury or death to workers and damage to electrical assets, structures, and equipment failure. Understanding the anatomy of an Arc Flash or Arc Blast can raise the awareness of workers in hazardous environments. Recognizing the hazards associated with an Arc Flash or Arc Blast helps workers understand why the use of PPE and maintaining electrical safety as part of Arc Flash protection is critical when working with energized electrical equipment. Regulations, like the 2018 Edition NFPA 70 E, are created to protect workers.
Frequently Asked Questions
Is arc flash the same as arc blast?
No. Arc flash describes the intense heat, light, and radiant energy released during an electrical arc fault. Arc blast describes the associated pressure wave, sound, and flying material. Both can occur as part of the same electrical event.
What triggers an arc flash?
An arc flash can be triggered by accidental contact, dropped tools, loose connections, damaged insulation, contamination, corrosion, equipment failure, improper work practices, or switching operations. The initial fault creates a conductive path through the air, allowing electrical current to form and sustain an arc.
What are the three dangers of arc flash?
The three primary dangers are extreme thermal energy, explosive pressure, and flying molten metal or equipment debris. Workers may also be exposed to electric shock, intense light, hazardous sound levels, smoke, and hot gases.
At what voltage can an arc flash occur?
There is no voltage level that should automatically be treated as free from arc flash risk. OSHA states that even 120/208-volt systems can produce enough energy to burn exposed skin, ignite clothing, and cause catastrophic or fatal injuries. Incident energy is affected by available current, fault-clearing time, equipment configuration, and working distance, not voltage alone. OSHA specifically warns that low voltage does not mean low risk.
How long does an arc flash explosion last?
An arc flash may last only a fraction of a second, but that can still be long enough to cause severe injury. The duration depends primarily on how quickly a fuse, circuit breaker, relay, or other protective device interrupts the fault. If protection does not operate as intended, the arc may continue longer and release substantially more energy.
Can you survive an arc flash?
Yes, people can survive arc flash events, but the outcome depends on the incident energy, distance from the arc, exposure time, equipment configuration, and protective measures in place. Properly selected arc-rated PPE can reduce injury severity, but it cannot prevent every injury or protect against every blast effect. Eliminating exposure remains the preferred control.
What does OSHA say about arc flash?
OSHA requires employers to protect workers from recognized electrical hazards, including arc flash and arc blast. Applicable requirements may include de-energization, lockout/tagout, safe work practices, hazard assessment, training, barriers, insulated equipment, and PPE. OSHA also recommends using consensus standards such as NFPA 70E to identify appropriate arc flash safety practices.
How can I protect myself from arc flash?
Do not work on or near exposed energized components unless you are qualified, authorized, and following an approved electrical safety procedure. Whenever possible, de-energize the equipment, apply lockout/tagout, and verify the absence of voltage. If energized work is justified, follow the arc flash risk assessment, observe established boundaries, use properly rated tools and equipment, and wear PPE selected for the assessed exposure.
