If your job requires FR clothing, your safety officer probably handed you a spec sheet and said "buy this." The spec sheet was likely written for someone with a year of arc-flash training. You weren't given the year of training. So here's the version that actually helps.
FR stands for flame resistant. Not fireproof. Nothing is fireproof. FR fabric is engineered so that when an ignition source goes away, the fabric stops burning instead of continuing to burn on you. That's the whole game.
There are two ways a fabric becomes FR. One: the fibers themselves are inherently flame resistant — Nomex, Modacrylic, PBI. Two: the fabric is treated chemically to make it FR — most FR cotton works this way. Inherent fabrics keep their FR rating forever. Treated fabrics can lose effectiveness if you wash them with bleach, with fabric softener, or with the wrong detergent. Read the care tag. Actually read it.
NFPA 70E is the National Fire Protection Association standard for electrical safety in the workplace. It's not a clothing standard — it's a workplace standard that, among other things, dictates what FR clothing electrical workers should wear at different incident-energy levels. When someone says "NFPA 70E compliant," they mean the clothing meets the requirements that 70E references.
ASTM F1506 is the actual fabric standard. F1506 is the test that says: this fabric, when exposed to flame for a defined duration, won't melt, won't drip, will self-extinguish when the source is removed, and won't break open. Every legitimate FR garment has an F1506 label sewn in. If it doesn't have that label, it's not FR for arc-flash purposes — even if the marketing copy says "flame resistant."
ATPV is the number that matters most. Arc Thermal Performance Value, expressed in cal/cm². It's the energy level at which the fabric will provide protection from a second-degree burn. Higher number = more protection. An 8 cal/cm² shirt will protect you in an arc-flash incident up to that energy level. Above it, you'll get burned.
HRC — Hazard Risk Category — used to be how 70E categorized PPE. The current version of 70E has moved to PPE Categories 1 through 4, but a lot of safety officers still say HRC out of habit. Category 1 is around 4 cal. Category 2 is around 8 cal. Category 3 is 25 cal. Category 4 is 40 cal. Your job hazard analysis tells you which category you need.
Layering matters. A non-FR cotton t-shirt under an FR shirt is fine. A polyester t-shirt under an FR shirt is dangerous — polyester melts, and FR clothing only protects against flame, not melted plastic stuck to your skin. If your employer requires FR, the base layer should also be FR or natural fiber. Period.
We carry FR shirts, pants, and hoodies from Carhartt's FR line and a few others. If you're not sure what your job requires, bring the spec sheet your safety officer gave you. We'll match it. If you're buying FR for yourself because your employer doesn't supply it, tell us what trade you're in and we'll get you to the right ATPV without overpaying for protection you don't need.