The idea of the PPE categories was developed by Dr. Tom Neal at DuPont. He sent me his table and a list of the PPE he had tested which met the four categories. Since I tested for many companies and he had only DuPont data, I validated his findings. We did tweak the categories based on my data, but the idea was Tom’s.
HRC 0 was added before publication because it was the primary industry standard and common in underwear. Strong consensus that non-melting was better, though the data from the 1980’s proved that wasn’t as much of a panacea as expected. HRC 0 was removed in 2015.
The idea was that every single layer system on the market in 1998-1999 (or so because this entered NFPA 70E in 2000) would meet HRC/ARC/CAT 1.
Every two layer system would meet HRC/ARC/CAT 2. In 1999 HRC2 was ALL two layered systems and a few Single layers which no one would wear.
Every Three layer system would meet HRC/ARC/CAT 3
And a two layer with a flash suit would meet HRC/ARC/CAT 4. HRC 4 was a system WITH a flash suit since NO flash suit had been developed in 1999 which was 40 cal and hoods had no standard and most hoods didn’t have testing much less a rating until after the hood standard appeared in 2002.
There was very quickly a move to 100 cal suits, but these are still HRC 4, though one suit manufacturer lobbied and even taught about HRC 5. It was never included in the standard, but there was a proposal in at least two cycles.
There is no magic in the PPE categories, but at the time most garments and almost NO systems were rated, so we developed this idea with the NFPA 70E Table committee to offer protection and ease of selecting PPE.
Now with systems and garments rated, we know many single layer systems can meet HRC/ARC/CAT 2 and many two or three layer systems can meet HRC/ARC/CAT 4. Over time we eliminated the layering concept, but this was the original idea. Match to the hazard was the concept, but we didn’t have enough data to require that at the time. Now it is easier. If you have calculations, you don’t even need the categories.
This is just a little history lesson on the PPE Categories in NFPA 70E. The concepts are taught in our NFPA 70E Low Voltage Qualified Class at e-Hazard.com