Every arc-rated garment we make carries a number — 9.6, 12.7, 5.6 — and that number is the whole point. ATPV, Arc Thermal Performance Value, is the amount of heat energy in calories per square centimetre a fabric can absorb before there’s a 50% chance it lets a second-degree burn through to the skin underneath. Higher number, more protection.
What does ATPV actually measure?
ATPV comes from a lab test — an electric arc generated under controlled conditions, aimed at a fabric sample, with sensors behind it reading how much heat gets through. The result is expressed in cal/cm². It’s not a guess and it’s not a marketing number; it’s tied to test methods like ASTM F1959 (the standard our Nomex® IIIA and FR cotton garments are rated under) or F1930 for flash-fire testing.
A garment with no ATPV listed hasn’t been tested for arc exposure — full stop, whatever else it claims on the tag.
How do I know what ATPV I actually need?
That number doesn’t come from a catalogue. It comes from your site’s arc flash risk assessment — the study that calculates incident energy at each piece of equipment you work on, done by a qualified person under CSA Z462. Once you have that number in cal/cm², you choose a garment rated equal to or higher than it.
An article can explain the system; it can’t tell you what your switchgear will do to you, so treat this as the map, not the territory. If your employer hasn’t handed you that number, that’s the first phone call to make — not a coverall order.
Does layering change the ATPV?
Yes — and this is where people get caught out. Layered FR garments generally test higher combined than either piece alone, but you can’t just assume it.
Our Nomex® IIIA Insulated Parka is rated ATPV 5.6, HRC-1 — lower than the HRC-2 coveralls it’s usually worn over. Worn alone in cold weather, that parka doesn’t cover an HRC-2 task. Worn over a 6oz Nomex® IIIA coverall rated 12.7, the system does.
Never assume outerwear inherits the rating of what’s underneath — check both pieces, every time.
Does the same fabric always carry the same ATPV?
No — and this is worth checking every time, not assuming. Our Nomex® IIIA Wildland Coverall uses the exact same fibre blend and weight as our standard 6oz Nomex® IIIA Coverall — 93% meta-aramid, 5% para-aramid, 2% carbon, 6oz — but it’s rated ATPV 5.6, HRC-1, tested to ASTM F1506, against the standard coverall’s 12.7, HRC-2, tested to F1959.
Same fibre, different garment, different number. Construction, weight distribution, and intended use all factor into the tested result, not just the raw fabric. The fabric name on a spec sheet tells you the fibre family; it doesn’t tell you the number. Only the garment’s own label does.
What ATPV do Northland’s garments carry?
Our everyday coveralls and vests run HRC-2: the 7oz G2® FR Coverall at 9.6 cal/cm², and the 6oz Nomex® IIIA Coverall, 9oz FR Cotton Coverall, FR Cotton Hi-Vis Surveyor Vest, and FR Cotton Supervisor Vest all at 12.7 cal/cm².
For winter, the FR Cotton Insulated Parka and FR Cotton Insulated Bib Overall match that 12.7 rating. The lighter Nomex® parka and the Wildland Coverall both sit at HRC-1, ATPV 5.6.
Nine garments, all UL certified to NFPA 2112, all built here in Edmonton.
Not sure which combination clears your task’s incident energy?
Call (780) 465-2699 — we’ve fit enough crews to talk it through in plain terms. Or request a quote and tell us the rating you need to hit.