What is an Arc Flash?
An Arc Flash is an electrical explosion resulting from a low impedance connection to ground or another voltage phase in an electrical system. High temperatures cause rapid heating of surrounding air and extreme pressures, resulting in an arc blast. The arc blast (what results from the arc flash) will likely vaporize all solid copper conductors, which will expand up to 67,000 times its original volume when it is vaporized.
The arc blast releases fire, intense light, and pressure waves in an explosion of flying shrapnel. An arc flash happens without warning. This typically results in the complete destruction of equipment involved and severe injury or death to people inside the arc flash boundary at the time of the incident.
The energy released by an arc flash is a function of system voltage, available fault current at the location, and duration of the arc.
Should you be concerned about Arc Flash Hazards on Low Voltage Equipment?
The theory that Arc flash hazards are greater at higher voltages is a common misconception. It is far more common for low voltages, such as 480v, to have much more significant arc flash hazard levels because the fault currents are much higher.
It is not uncommon to have an arc flash hazard Category 3 or Category 4 on low voltage systems due to the long clearing time of the protective devices and high fault currents.
What causes an Arc Flash?
When significant fault currents are flowing through several conductors that are in close proximity of each other, the differences in potential, among other factors, will ionize the air, allowing a low resistance path between the conductors.
Improper tools, improper electrical equipment, corrosion of electrical equipment, improper work techniques, lack of electrical safety training, and a lack of preventative maintenance are just some of the events that make an arc flash more likely.
What sort of injuries can happen from an Arc Flash?
It is estimated that 5 to 10 arc flash and blast explosions occur in electrical equipment every day in the United States with 2,000 people each year being admitted to burn centers for severe burns (CapSchell Inc.)
The degree of injury is directly related to the power of the arc flash, the distance the person is at the time of the arc flash and the protective equipment (PPE) worn by an individual during an arc flash.
Due to the force from the explosion of energy (the blast) and the intense heat, burns, concussions, collapsed lungs, hearing loss, shrapnel injuries, and broken bones are the common injuries.
What are the costs associated with an Arc Flash accident?
Total costs of arc flash accidents have been estimated to be between $12 and $15 million, and can include medical expenses, down time, equipment replacement, lawsuits, and insurance and litigation fees.
It is widely recommended to outsource arc flash analysis to trained experts, with the knowledge and experience needed to determine all hazards.
Does Proper PPE Protect me from Injury?
Protective equipment is designed to limit burns to second-degree burns. Those who experience an arc flash and are wearing the proper equipment can still be seriously injured or even killed from the force of the arc blast.
An arc blast can knock people off of elevated platforms or blow doors or shrapnel across the room, to which the proper arc flash PPE provides little to no protection!
In an ideal situation, the operator would utilize safety equipment, such a Remote Racking device, that would allow them to stand outside of the arc flash boundary.
How is the correct level of PPE determined?
In order to select the proper PPE (personal protective equipment), incident energy must be known at every point where workers may be required to perform work on electrically energized equipment. These calculations are determined in an arc flash study and need to be performed by a qualified person such as an electrical engineer.
NFPA 70E offers a guide to proper protection.
All parts of the body that may be exposed to the arc flash need to be covered by the appropriate type and quality of PPE. Proper PPE can include Arc Resistant clothing, hardhat, hood, face shield, safety glasses, gloves, shoes, etc. depending upon the magnitude of the incident energy present.
Can an Arc Flash incident be prevented?
There is no way to completely prevent an arc flash from happening in electrical distribution systems. The best one can do is to mitigate or reduce the risk. Below is a prioritized list, based off of The Risk Control Hierarchy by NIOSH, which describes ways to systematically reduce risk to its lowest practicable level by mitigating a given risk.
Higher priority and weight are given to methods that seek to control risk by proactive means as close as possible to the root cause. Meanwhile lower priority is placed on reactive methods of controlling damage after an incident has occurred.
1. Elimination // Remove the hazard
- Only work on energized electrical equipment, when absolutely necessary.
De-energizing equipment removes the arc flash hazard, although there is some risk of arc flash and blast when testing to make sure that the equipment is de-energized, as well as when re-energizing.
- Removing the personnel from the arc flash boundary eliminates the risk of human injury.
Equipment such as Remote Racking devices allow users to stand outside of the arc flash boundary, while operating breakers.
2. Substitution // Replace higher risks with lower risks
This can be done with two methods:
- Arc Flash Study with short circuit study and protective device coordination study can identify how to reduce an arc flash hazard category for some equipment.
- Technologies can be implemented to reduce risks. This includes equipment such as arc limiting fuses and remote racking technologies.
3. Engineering Controls // Reinvent ways to limit and (or) prevent the risk
This can be done by replacing it with equipment that will lower the incident energy, including but not limited to: adjusting breaker settings and redesigning electrical distribution systems.
4. Awareness // Raise knowledge of risks and consequences thereof
- Train all workers on the hazards of arc flash. Although this is #4 on the Risk Control Hierarchy, it should be the first thing done and is mandated by OSHA regulations. It is only through training that workers will understand how to eliminate, substitute or otherwise lower the risk.
- Conduct an arc flash study to properly identify the hazards, boundaries and required PPE.
5. Administrative Controls // Create regulations, work processes, etc.
- Make sure that you have a written electrical safety program AND that it is understood by everyone AND that it is enforced.
- Allow only Qualified Persons wearing the proper PPE and using the correct tools to work on or around electrically energized equipment.
- Implement a preventive maintenance plan for electrical systems based on NFPA 70B. A proper preventive maintenance program will help identify or fix electrical hazards before they become big problems.
Does Preventive Maintenance reduce the potential for an Arc Flash?
Preventive maintenance should be conducted on a routine basis to ensure safe operation. A preventive maintenance program not only ensures that the equipment is functioning properly, but it also identifies potential hazards before they cause an accident.
NETA states, “The ideal maintenance program is reliability-based, unique to each plant and to each piece of equipment.” NETA offers a frequency of maintenance tests matrix and table available here and is recognized as a guide only.
How can system design impact Arc Flash hazards?
System configuration plays a key role in arc flash calculations. Lowering available fault currents leads to either transformer replacement or reactor installations, which generally is a high long-term expense. Trip times can be improved more cost efficiently. The system configuration, system fault levels, and exposure time can affect the incident energy exposure caused by an arc flash.
System fault levels can be reduced by changing the system configuration to reduce available fault current and limit trip time.
Fuse ratings and characteristics can also be evaluated to determine if a smaller and/or faster fuse could be used to help reduce the exposure time. All of these factors must be considered along with the reliability needs of the facility and a protective device coordination.
Reference // Arc flash frequently asked questions by inoLECT