Fire resistant (FR) vs arc flash rated clothing - what does it mean?

When you’re buying protective clothing for electrical work, two terms come up often: flame/fire resistant (FR) and arc rated (AR). They are not the same, and confusing them can lead to choosing the wrong level of protection.

When ready to browse actual options for your needs, check out Legion’s fire resistant clothing, arc flash rated clothing, and arc flash kits.

Fire resistant clothing is designed to:

• Not ignite easily
• Self-extinguish when the flame source is removed
• Reduce burn injuries from fire exposure

FR clothing is for environments where there is a risk of a sustained fire or a flash fire (for flash fire there is an additional testing standard). However, if a garment is fire resistant, that does not tell you how much energy the fabric can withstand during an arc flash event.

Arc Rated (AR) clothing basics

Arc-rated clothing goes a step further. An arc flash is different from a regular fire - it is normally a short burst of extreme heat - shorter exposure but much hotter than just a flame. Arc flash clothing is specifically tested to:

• Protect against the thermal energy released during an arc flash
• Provide a measurable level of protection, expressed in cal/cm²

Every arc-rated garment has a numeric rating that tells you how much incident energy it can handle before there is a significant risk of a serious burn injury.

AR vs FR differences in the hazard resistance

Depending on the hazard type you have, or the “question” you are trying to answer when looking for safety gear, pick the right type:

• FR - Will it burn?
• AR - How much energy can it protect against?

For electrical work, you should always be looking at arc-rated PPE, not just claims of flame resistance.

What Does “cal/cm²” Mean?

Arc ratings are measured in calories per square centimeter (cal/cm²). This represents the amount of thermal energy the fabric can block. Higher numbers mean higher protection, but also typically more weight, less mobility, higher cost.

So the goal is to match the rating to the hazard, not simply choose the highest number available.

ATPV vs. EBT: What’s the Difference?

Arc ratings are determined through testing, and the result is usually expressed as either ATPV or EBT. These are two different ways of measuring fabric performance under arc exposure.

• ATPV means Arc Thermal Performance Value
  • ATPV is the incident energy (cal/cm^2) that presents a 50% probability of second-degree burn
• EBT means Energy Breakopen Threshold
  • EBT is the incident energy (cal/cm^2) at which the fabric breaks open (creating a hole that exposes the skin)

In practical terms:

• Higher ATPV = better insulation from arc energy. Most arc-rated clothing you see will list an ATPV value.
• Higher EBT = more of a material strength factor under stress, rather than heat transfer.

Whichever event occurs first in testing, first degree burn energy passes the garment or the fabric breaks open - the relevant arc rating should be based on that.

For most buyers, the arc rating number is the key decision point

A Simple Way to Think About It:

1. Flame resistant (FR): Protects against fire
2. Arc rated (AR): Protects against arc flash energy
3. ATPV: Measures heat passing through the fabric
4. EBT: Measures when the fabric breaks open

When selecting PPE for electrical work, focus on arc-rated gear with an appropriate cal/cm² rating. That ensures you are buying protection designed for the actual hazard your technicians face and maximizes their comfort and agility.