The definition of an arc flash is "an undesired electric discharge that travels through the air between conductors or from a conductor to a ground." The arc flash is a part of an arc fault, which is an example of an electrical explosion caused by a low-impedance connection that goes through the air to the ground.
When an arc flash occurs it creates a very bright light and intense heat. In addition, it has the potential to create an arc blast, which can cause a traumatic force that can severely injure anyone in the area or damage anything nearby.
What Happens During an Arc Flash
An arc flash begins when the electricity exits its intended path and begins traveling through the air toward a grounded area. Once this happens, it ionizes the air, which further reduces the overall resistance along the path that the arc is taking. This helps draw in additional electrical energy.
The arc will travel toward a ground of some type, which will typically be whatever object is closest to its source. The exact distance that an arc flash can travel is known as the arc flash boundary. This is determined by the potential energy present and a variety of other factors such as air temperature and humidity.
When working to improve arc flash safety, a facility will often mark off the arc flash boundary using floor marking tape. Anyone who is working within that area will be required to wear personal protective equipment (PPE).
Potential Temperature of an Arc Flash
One of the biggest dangers associated with an arc flash is the extremely high temperature it can create. Depending on the situation, they can reach temperatures as high as 35,000 degrees Fahrenheit. This is one of the hottest temperatures found anywhere on earth and is actually about 4 times hotter than temperatures found on the surface of the sun.
Even if the actual electricity doesn't touch a person, they can be severely burned if they are anywhere near it. In addition to direct burns, these temperatures can quickly start fires in the area.
What an Arc Flash Looks Like
The following video shows just how quick and explosive an arc flash can be. This video has a controlled arc flash with a "test dummy" so people can see what a real arc flash looks like:
How Long an Arc Flash Lasts
An arc flash can last anywhere from a fraction of a second to several seconds, depending on a number of factors. Most arc flashes don't last very long because the source of the electricity is cut off quickly by circuit breakers or other safety equipment.
The most advanced systems today use devices known as arc eliminators, which detect and extinguish the arc within just a few milliseconds.
If a system does not have any type of safety protection, however, the arc flash will continue until the flow of electricity is physically stopped. This may occur when an employee physically cuts the power to the area or when the damage caused by the arc flash becomes severe enough to somehow stop the flow of electricity.
See a real life example of an arc flash that goes on for an extended period of time in the following video. Luckily the individuals in the video were wearing their personal protective equipment and escaped without injury. The powerful explosion, loud noise, bright light, and intense heat are all extremely dangerous and could have been much worse.
Damage Potential of an Arc Flash
Due to the high temperatures, intense blasts, and other results of an arc flash, arc flashes can cause a lot of damage very quickly. Understanding the different types of damage that can occur can help facilities plan their safety efforts.
The two main types of damage include damage to the facility and damage (injury) to people in the area.
Potential Property Damage:
- Heat - The heat from an arc flash can easily melt metal, which can damage expensive machines and other equipment.
- Fire - The heat from these flashes can quickly cause a fire, which can spread through a facility if not stopped.
- Blasts - The arc blast that can result from an arc flash can break windows, splinter wood in the area, bend metal, and much more. Anything stored within the arc blast radius can be damaged or destroyed in just seconds.
Potential Human Injury:
- Burns - Second and third degree burns can occur in a fraction of a second when someone is near the arc flash.
- Electrocution - If the arc flash travels through a person, he or she will be electrocuted. Depending on the amount of electricity, where it enters the body, and where it leaves, this can be fatal.
- Auditory Damage - Arc flashes can cause extremely loud noises, which can cause permanent hearing damage to those in the area.
- Eyesight Damage - Arc flashes can be very bright, which can cause temporary or even long-term damage to the eyes.
- Arc Blast Damage - An arc blast can create a force that is thousands of pounds per inch. This can knock a person through the area several feet. It can also cause broken bones, collapsed lungs, concussions, and more.
Wearing personal protective equipment can provide a significant amount of protection, but it cannot eliminate all risk. Employees who are present when an arc flash occurs are always at risk, no matter the PPE they are wearing. This is why it is important to de-energize a machine before it is worked on whenever possible.
Potential Causes of an Arc Flash
Arc flashes can occur for a wide range of reasons. In most cases, the root cause will be a damaged piece of equipment such as a wire. It could also be a result of someone working on equipment, which makes it possible for the electricity to escape from the path it is normally confined to.
Even when there is a potential path outside the wiring, the electricity is going to follow the path of least resistance. This is why an arc flash will not necessarily happen as soon as something is damaged or an alternate path is made available. Instead, the electricity will continue down the intended path until another option that has less resistance becomes available.
Here are some things that can create a path with lower resistance and therefore cause an arc flash:
- Dust - In dusty areas the electricity may begin passing outside the wiring or other equipment through the dust.
- Dropped Tools - If a tool is dropped onto a wire, for example, it can damage it and allow the electricity to pass into the tool. From there, it must find another path to continue on.
- Accidental Touching - If a person touches the damaged area, the electricity may travel through his or her body or at least out of the normal path, creating an arc flash.
- Condensation - When condensation forms, the electricity may escape the wiring through the water, and then the arc flash will occur as the electricity seeks its destination.
- Material Failure - If a wire is damaged to the point where the electricity has trouble passing through, the path may be more resistant than going outside of the wire.
- Corrosion - Corrosion can create a path outside the wire, at which point the arc flash occurs.
- Faulty Installation - When equipment is installed improperly it can make it difficult or impossible for electricity to follow the intended path, which can cause an arc flash.
Arc Flash Safety Requirements
Companies with electrical equipment need to take arc flash safety very seriously. There are many things that can be done to reduce the chances an arc flash will occur and keep people as safe as possible if one does happen.
Preventing Arc Flashes
The first step in arc flash safety is minimizing the risk of one occurring. This can be done by completing an electrical risk assessment, which can help identify where the biggest dangers are in a facility. IEEE 1584 is a good option for most facilities and will help identify common problems.
Routine inspections of all high voltage equipment and all wiring are another essential step. If there is any sign of corrosion, damage to wires, or other issues, they should be fixed as soon as possible. This will help keep the electrical currents safely contained within the machines and wires where they belong.
Some specific areas that should be inspected include any electrical switchboards, panelboards, control panels, socket enclosures, and motor control centers.
Proper Labeling Efforts
Anywhere in a facility where high electrical currents can exist should be properly labeled with arc flash warning labels. These can be purchased pre-made or printed with any industrial label printer as they are needed. The National Electrical Code article 110.16 clearly states that this type of equipment needs to be marked to warn people of the risks.
De-Energizing Equpment when Performing Maintenance
Whenever a machine needs to be worked on in any way, it should be completely de-energized. De-energizing a machine is more than just turning it off. All machines should be shut down and physically disconnected from any power source. Once disconnected, a voltage check should also be done to ensure there is no latent energy that was stored up.
Ideally a lockout tagout policy should be in place, which will put a physical lock on the electrical supply so that it cannot be accidently plugged back in while someone is working on it.
Arc Flash Personal Protection Equipment
It should be very rare, but there are some cases when machines must be worked on while they are still energized. When this is the case, all employees working in the area should be required to wear proper personal protective equipment.
The specific PPE that is worn should correspond to the maximum potential risk based on the amount of electricity going through the machine. Having head to toe personal protective equipment can help to prevent serious injury or even fatalities should an arc flash occur while the machine is being worked on.
Whenever possible, circuit breakers should be put in place on all machines. These breakers will quickly detect when there is a sudden surge in electricity being drawn and stop the flow immediately. Even with circuit breakers, an arc flash can occur, but it will only last a fraction of the time since the electrical current will be cut off.
Even a very brief arc flash can be deadly, however, so circuit breakers should not be seen as a sufficient arc flash safety program.
Arc Flash Safety Standards
All facilities must consider the various arc flash safety standards that have been put in place by government and private institutions. Determining which standards must be followed can help ensure a facility is in compliance with area rules and regulations, in addition to helping keep the facility safe.
The following are the most common standards that cover arc flash safety:
- OSHA - OSHA has several standards including 29 CFR parts 1910 and 1926. These standards cover requirements for electrical power generation, transmission, and distribution.
- National Fire Protection Association (NFPA) - NFPA standard 70-2014, the National Electrical Code (NEC) pertains to safe electrical installation and practices. Standard NFPA 70E, the Standard for Electrical Safety in the Workplace, details a variety of requirements for warning labels, including warning labels concerning arc flashes and arc blasts. It also offers recommendations on implementing workplace best practices to help keep employees who work around high voltage equipment safe.
- Canadian Standards Association Z462 - This is very similar to the NFPA 70E standards, but is applicable for Canadian companies.
- Underwriters Laboratories of Canada - This set of standards is for any situation where electricity is generated, transmitted, or distributed, and covers safety requirements. Similar to the OSHA standards but for Canada.
- IEEE 1584 - This is a set of guidelines for accurately calculating arc-flash hazards.