The following provides definitions for a range of useful terms in relation to electrical and oil and gas PPE.

Arc Flash or Electrical Arc

An arc flash or electric arc is the passage of substantial electrical current through ionised air. Typical characteristics include:

• Lasting less than a second
• Having extremely high RADIANT energy
• Being explosive in nature
• The ability to IGNITE and/or MELT conventional work clothing
• Radiant heat through clothing, which can causing burns.

Arc Rating

A value of the energy necessary to pass through any given fabric to cause with 50% probability a second or third degree burn. This value is measured in calories/cm². The necessary Arc Rating for an article of clothing is determined by a Hazard/Risk Assessment and the resulting HRC.

ATPV (Arc Thermal Performance Value)

ATPV is the amount of energy required to produce a second degree burn.

Note: when ATPV ratings are given to fabrics/garments there is still a 50% chance of receiving a burn under this test method.

Calorie

The energy required to raise one gram of water one degree Celsius at one atmosphere pressure. Second-degree burns occur at 1.2 calories per centimeter squared per second (cal/cm²).

A Cigarette lighter placed under your finger for 1 second equals roughly a 1 calorie burn.

An electric arc blast can reach temperatures of up to 35,000 degrees Fahrenheit in the centre, and 11,000 degrees on the perimeter.

Flame Resistant

The characteristic of a fabric to resist ignition and to self extinguish if ignited. Abbreviated as FR.

Flame Retardant

A chemical substance used to impart flame resistance – not part of the basic fibers chemistry. Flame retardant treatments can diminish overtime or with use.

Flash-fire

A sudden, unexpected and intense fire caused by ignition of flammable solids, liquids, gases or dusts.

HRC (Hazard Risk Category)

The classification of the listed task according to the type of hazard present when performing the task. Zero represents minimal risk, four represents the greatest risk.

The four Hazard/Risk categories are specified by the chart listed in NFPA 70E. The HRC is used to determine the necessary arc rating of a garment worn during a given job task.