What is an arc flash study, and why do you need one now?

Arc flash study insights

• Arc flash, a catastrophic release of energy caused by an electric fault that occurs in equipment, can result in serious injuries or even death.
• Conducting an arc flash study can help organizations protect their workers.
• The National Fire Protection Association recommends conducting an arc flash study every five years.

An arc flash study could mean the difference between life and death. But what exactly is an arc flash study, and why does your organization need one?

Let’s start with what an arc flash is.

An arc flash is a dangerous release of energy caused by an electrical fault that occurs in equipment such as circuit breakers, switchgear and other electrical components.

An analysis of your arc flash risk could be all that’s standing between your workers and serious injury or even death. It’s important to recognize that an arc flash explosion can cause shrapnel to propel across a facility and can cause electrocution and potential burns. These injuries, which are life-threatening, should not be taken lightly.

When is an arc flash study required?

Knowing that lives are on the line, the necessity of a study goes without saying. But just how often should your organization conduct one?

The National Fire Protection Association’s NFPA 70E standard recommends conducting an arc flash study:

• Every five years
• Whenever significant changes are made to a facility’s electrical system
• When upgrading or purchasing personal protective equipment for workers to identify potential electrical hazards

What exactly does this type of study entail? The study, which can take between six and eight weeks to conduct, depending upon the size of the facility, looks at:

• A facility’s power distribution data
  • Nameplate specifications
  • Fuses
  • Breakers
  • Transformers’ kilovolt-amperes (kVA)
  • Cables
• A short-circuit analysis
• Incident energy levels/flash protection boundaries
• Calculations of equipment based on boundaries developed by the Institute of Electrical and Electronics Engineers (IEEE)
• A protective device coordination study
• Analysis report
  • These calculations are compiled into a comprehensive report, which will be used to develop appropriate warning labels, identifying incident energy and working distance, an official arc flash boundary and system voltage, as well as recommended PPE

Is an arc flash study required by OSHA?

Although this study is a good practice and a smart move to keep your workers safe, the Occupational Safety and Health Administration (OSHA) has no specific requirement about marking equipment with a flash hazard warning. Even so, OSHA offers the following requirement:

Paragraph (e) of §1910.303 requires employers to mark electrical equipment with descriptive markings, including the equipment’s voltage, current, wattage, or other ratings as necessary. OSHA believes that this information, along with the training requirements for qualified persons, will provide employees the necessary information to protect themselves from arc-flash hazards.

Additionally, in §1910.335(b), OSHA requires employers to use alerting techniques (safety signs and tags, barricades, and attendants) . . . to warn and protect employees from hazards which could cause injury due to electric shock, burns or failure of electric equipment parts. Although these Subpart S electrical provisions do not specifically require that electric equipment be marked to warn qualified persons of arc-flash hazards, §1910.335(b)(1) requires the use of safety signs, safety symbols, or accident prevention tags to warn employees about electrical hazards (e.g., electric-arc-flash hazards) which may endanger them as required by §1910.145.

Courtesy: WTWH Media

Basic equations for calculating arc flash boundary distance

Let’s talk about the basic equations for calculating arc flash boundary distance from the NFPA.

The short-circuit symmetrical ampacity, I_sc, assuming a bolted 3-phase fault at the transformer terminal is:

I_sc = {[MVA base x 10⁶] / [1.732 x V]} x {100 / %Z}

In this equation, I_sc is in amperes, V is in volts and %Z is based on the transformer megavolt-amperes (MVA).

A typical value for maximum power, P, in. 3-phase arc can be calculated using:

P = [maximum bolted fault in MVA_bf] X 0.707²

You can calculate the arc flash boundary distance using this formula:

D_c = [2.65 x MVA_bf x t]^1/2

D_c = [53 x MVA x t]^1/2

In these equations:

• D_c = distance in feet of a person from an arc source to incur a curable burn, defined as a skin temperature of below 80ºC

• MVA_bf = bolted fault at the point involved

• MVA = MVA transformer rating. For transformers with MVA ratings below 0.75 MVA, multiply the transformer MVA rating by 1.25

• t = time of arc exposure in seconds

Who can perform an arc flash study?

A licensed professional engineer who has experience with power systems and arc flash hazard studies must conduct the study.

This could be an in-house engineer, a specialist hired on to conduct the study or a private firm brought on for the purpose of the arc flash study.

Understanding the importance of arc flash study

Now that you know how arc flash studies are conducted and the importance of them, you can decide when and how to set up a study, post appropriate warning labels and keep your workers safe.

Whether it’s been five years since your last arc flash study, you’ve recently made significant electric system upgrades at your facility or it’s time to select PPE for your workers, an arc flash study is a smart move – not just for your bottom line but for your workers’ lives.

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