Arc flash

What is arc flash?

There are several workplaces where you need to be protected against arc flash. For example, some work with electrical installations, other occupations perform maintenance of equipment in systems that are not secured against arc flash, and someone can work with high-voltage equipment. And for all of these occupations – protection against arc flash is essential for everyone. Arc flash can occur in high and low voltage electrical systems, and the energy in an arc flash can be powerful even in low voltage systems on account of a high short circuit level and/or a long disconnect time.

Calculation of arc flash energy

The potential scope of damage from arc flash short-circuits is described using the concept of “incident energy”. Incident energy is stated in calories per square centimeter (cal/cm2) and it shows how much energy is released while the arc lasts, and the distance from the arc flash.

The calculations of arc flash are based on voltage level, short circuit current, protection settings, and the active users’ connections. The incident energy is usually calculated at a defined distance, often an “arm’s length” (90 cm) from the busbar to where the arc flash occurs. The time the arc flash continues to burn is crucial to the level of the incident energy. In principle, you should attempt to reduce incident energy by disconnecting equipment and adjusting protection measures to keep the cut-out time as short as possible.

Incident energy, arc flash:

  • PPE 0 ≤ 1.2 cal/cm² (no requirement for arc flash-safe clothing)
  • PPE 1 ≤ 4 cal/cm²
  • PPE 2 ≤ 8 cal/cm²
  • PPE 3 ≤ 25 cal/cm²
  • PPE 4 ≤ 40 cal/cm²
  • PPE x > 40 cal/cm² (extreme danger)

Clothing in relation to ATPV rating

Working with arc flash it is important to wear clothing that protects you. The clothing must have an ATPV (Arc Thermal Performance Value) rating equal to, or higher than, the applicable value for the arc flash energy that is at the workplace.

Wearing layered clothing that is arc flash tested will produce a minimum ATPV rating. Thanks to the combination of the layered clothing, it can produce a higher ATPV rating than the sum of the ratings of each unique layer.

Stay protected from head to toe

When protecting yourself against arc flash, it is important to make sure that the other safety equipment you are using (gloves, shoes, helmet, face protector, ear protectors) – is certified to the same level. Wearing protection that is certified to the same level is necessary and required to ensure the best possible protection for your entire body.

Required clothing for working with arc flash

The following combination of clothing must be worn while working on electrical panels with calculated arc flash energy:

  • Helmet with arc flash-tested face protector
  • Ear protectors/ear plugs (not containing unprotected metal parts)
  • Arc flash-tested clothing
  • Gloves (electrically insulated gloves where necessary)
  • Undergarments should be made of wool/cotton. Avoid synthetic fabrics

Electrical current can cause three types of injury:

  • Surface burn
  • Deep burn
  • Alteration of cardiac rhythm – possible cardiac arrest