Copperhead ARE pit vipers.
You corrected my comment correctly. I had been erroneously taught in the past that only snakes with long fangs are pit vipers, but it is, in fact, the heat sensing ability (along with being venomous), that makes them pit vipers.
But copperheads do not have long fangs and are not as likely to penetrate as much as, for example, the sometimes seven-foot-plus diamondbacks that I grew up with in Texas (including school playgrounds). Thick, tall boots and heavier pants are a good extra safety measure around copperheads, although not nearly as important as watching for them.