Arc Flash Facts

What do we know about Electrical Arc Flashes??

Predicting an Arc Flash is not easy.?If it occurs it can dramatically change lives in a matter of seconds. Aside from severe burns in loss of hearing or sight, Arc Flash injuries can cause severe physical harm, concussions from flying shrapnel, and other medical complications.?

What Happens During an Arc Flash??

?Arc Flash is an arcing short circuit and can happen from lack of maintenance and/or material builds up, allowing electricity to travel or carbon tracking. An Arc Flash occurs when an electrical discharge or explosion develops from a low impedance connection between two voltage phases or phase to ground in an electrical system. It ionizes the air, which further reduces the overall resistance along the path that the arc is taking This ionized air is very conductive.?

The arc travels a distance based on the energy of the system.?The systems energy is the complex equation for determining the boundaries for protecting workers.

How Long Does an Arc Flash Last?

An Arc Flash can last anywhere from a few cycles of the 60hz wave form to a few seconds, contingent on maintenance and system design of over current devices. The arc flash is supposed to be cut off within cycles of our 60hz waveform, however due to lack of maintenance or defective equipment it could be longer. ?Engineers today can install optical sensing relays to help clear these events within 3 cycles which reduces the arc time and the arc size.?

What Causes an Arc Flash?

Generally speaking, an Arc Flash could be initiated with something as little as a wire strand. It could be a consequence of somebody causing vibration on the equipment, which allows the power to be bridged phase to phase or phase to ground, because it is no longer being restricted isolated.?85% of the arc flashes are from human error.

Electricity follows the path of least resistance. All things considered, the power will go off and people will be upset with the consequences.

Here are some examples of what can cause an Arc Flash:

Dust - In a dusty facility, the electricity can carbon track and eventual fail into a short circuit event.?The higher the system voltage, the more likely and the shorter time between preventive maintenance that this shall occur.

Dropped non-insulated Tools - If a tool falls onto a bus or open termination, for instance, it can harm it and permit the power to short circuit.?This however should never happen with an adequate electrical safety program where only insulated tools are being used.

Unplanned Touching - If an individual touches a bare bus or wire, the power will likely go through their body destroying their internal organs.

Insulation Failure - If a wires insulation is damaged to where the electricity experiences can leak to ground or another phase, then this would initiate an arc.?

Arc Flash Safety Requirements:?

Companies which own electrical equipment shall implement an electrical safety program to mitigate from an Arc Flash event. Various prescribed methods and measures will decrease the possibility of this event occurring.

The most widely recognized standards for Arc Flash Safety in the United States:

• OSHA CFR 29, 1910, covers the requirements for electrical power generation, transmission, and distribution.
• The NFPA 70E has a variety of requirements for warning labels regarding arc flashes and arc blasts. It also recommends implementing workplace best practices to keep employees and equipment safe.
• IEEE 1584 has a set of guidelines for accurately calculating arc-flash hazards.

Preventing an Arc Flash?

The most important way to prevent an arc flash is to decrease the risk of it occurring. This can be done by completing a Risk Assessment, which can help recognize facility hazards.?

Completing routine inspections of all electrical gear > 50Vac, like electrical switchboards, panelboards, control panels, etc. During the inspection, if there is any indication of failure of wires, or different issues, they need to be repaired quickly based on safety risk. ?This will help ensure a reliable and safe system.?

Proper Label Effort?

NFPA 70E does a pretty good job defining what needs to be labeled, communicating the shock and arc risk, along with the boundaries.?It is anything electrical requiring, adjustment, inspection, maintenance and servicing while energized; NFPA 70e 130.5 (H)???These can be bought pre-made or printed with any modern printer as they are required. The National Electrical Code article 110.16 plainly expresses that this equipment should be set apart to warn individuals of the risks.

De-Energizing Equipment?

OSHA LAW, requires all electrical work performed de-energized!?You can use Lockout Tagout measures to close the power source correctly. To guarantee that the power is actually de-energized, and the energy is stored away. This prevents someone else from unintentionally turning the power source back on.?If you must work energized in the USA, you shall justify it in writing, during your job planning for reasons of infeasibility or life safety or less than 50V

Arc Flash personal protective equipment (PPE)

Everything electrical requires PPE. It is crucial to be wearing the correct PPE to keep yourself safe and adhering to the minimum regulation. There are specific scenarios when you are justified to work on a piece of equipment that is energized, and you need to be certain that employees are wearing the proper attire.?The key is culture, continuously improving and implementing.

The type of PPE that should be worn depends on the amount of potential risk and the amount of shock risk (voltage) and arc flash risk (incident energy in cal/cm2) Having to wear PPE from head to toe is not fun work, but the measures are there to keep someone safe.?If the task is going to take longer than an hour in heavy arc rated PPE, you should seriously consider shutting power off and implementing Lock Out Tag Out.?

Conclusion

Clearing a fault in less than 6 cycles is key to reducing the effects of an arc flash explosion.?When justified energized work is your only alternative then a qualified worker, PPE and process shall be implemented, and job planned with all stake holders to verify that the risk of injury is acceptable.?Working on the electrical system dead is by far the best way and the 1st step in the hierarchy of risk controls.?And PPE is the last resort in working safe in the hierarchy of risk controls.?Solving the electrical safety puzzle is not easy, but with the right person the right PPE and the right process we can work anywhere on the electrical system safe!