FR stands for flame-resistant. FR clothing is made to catch fire slowly, put itself out once the flame is gone, and not melt onto skin. It is not fireproof. No shirt will let a worker stand in a fire. What FR buys is seconds: time to get away from a flash fire or an arc blast without the clothes themselves adding to the burn.
That last part matters more than most people think. In burn injuries at work, a big share of the damage comes from regular clothes catching fire and staying lit, or from synthetic fabric melting. A plain polyester shirt can melt at high heat. FR fabric chars instead. That is the whole point of the ratings below: they prove a garment behaves the right way when things go wrong.
FR ratings confuse people because there are two different dangers, and each one has its own rulebook.
The first danger is a flash fire: a quick burst of flame, like a gas ignition in a refinery, a chemical plant, or a grain or dust explosion. The rulebook for that is NFPA 2112. It is a pass-or-fail test for the whole garment. Test garments go on a heated manikin, get hit with a short flash fire, and sensors measure how much of the body would be burned. To pass, the garment must keep that predicted burn at or below a set limit, must not melt or drip, and must self-extinguish. If a shirt is certified to NFPA 2112, the label inside will say so. No label, no proof.
The second danger is an electric arc flash: the explosion of heat and light when electricity jumps through air, common in electrical panel work and utilities. The rulebook here is NFPA 70E, and the garment testing standard behind it is ASTM F1506. Arc-rated clothing is scored with a number, not just a pass. That number is where ATPV comes in.
ATPV stands for Arc Thermal Performance Value. It is measured in calories per square centimeter (cal/cm2). In plain terms, it is the amount of arc energy a fabric can take before there is a strong chance of a second-degree burn through it. Higher number, more protection. If a job's hazard study says the possible arc energy is 9 cal/cm2, the clothing worn on that job needs an arc rating of at least 9. A shirt rated 8 does not round up.
EBT stands for Energy Breakopen Threshold. Some fabrics break open, splitting or forming holes, before they let enough heat through to burn. For those, the rating is based on the breakopen point instead, and the label will show an EBT number. Either number works the same way when you buy: the rating on the garment has to meet or beat the rating the job needs. You may see labels that say 'arc rating' with one of these two values. That is the number that counts.
One more rule people miss: ratings do not stack the way people hope, but layering arc-rated clothing does add protection. Two rated layers trap air and rate higher together than either alone, but you cannot just add the two numbers and call it exact. And a non-rated layer on top, like a regular hi-vis vest or a plain jacket, can undo the whole system if it melts or burns. Every layer worn over FR should be rated too.
NFPA 70E groups arc-rated clothing into categories, called CAT 1 through CAT 4. They are shortcuts for minimum arc ratings. CAT 1 needs at least 4 cal/cm2. CAT 2 needs at least 8. CAT 3 needs at least 25. CAT 4 needs at least 40. Your employer's hazard assessment, done by a qualified person, sets which category a task falls into. The clothing tag should show both the CAT level and the actual arc rating number. Buy to the number, not just the category, because two CAT 2 garments can have different real ratings.
Also check for the small print. Arc-rated garments should carry a label showing the standard (ASTM F1506 or NFPA 70E), the arc rating, and the maker. Street clothes sold as 'FR' with no standard on the label show up in cheap listings all the time. If the seller cannot name the standard the garment was tested to, treat it as not rated.
Most modern FR fabric keeps its protection for the life of the garment, because the resistance is built into the fiber, not sprayed on. But care still matters. Skip fabric softener and bleach unless the maker's care label allows them: softeners can coat fibers with a flammable film, and bleach can break fibers down. Wash FR separate from shop rags and anything soaked in oil or solvents. Oil-soaked FR is not FR anymore until it is truly clean, and heavily soiled garments should be taken out of service.
Repairs must use FR thread and FR fabric patches. A torn sleeve sewn up with regular thread has a seam that will burn. Do not wear insect repellent with DEET under or over FR without checking the garment maker's guidance, since DEET is flammable and can damage some fabrics. And retire garments with holes, thin spots, or broken closures. A rating only protects the skin the garment actually covers.
Match the hazard first (flash fire or arc), then the rulebook (2112 or 70E), then the number (arc rating at or above the job's level). Read the label, not the ad. Plan the whole outfit: base layer, FR shirt and pants, and any vest or jacket over them all need to be rated. In the Inland Empire, electrical contractors, utilities, water districts, and oil and gas service crews are the main buyers of arc-rated gear, while refinery and chemical work calls for 2112. The suppliers in our uniforms and FR workwear listings can help fit a crew and set up replacement cycles, which matters: a program that replaces worn FR on schedule is worth more than the cheapest first order.
Shop the listings: browse uniforms and FR workwear suppliers serving the Inland Empire.