Dear Mike,
Yes, I saw that letter to the editor you wrote. It was very good. There was one matter you neglected, however. It's not just that the coals are poor conductors of heat but that with firewalking the layer of coals is always very thin, so it is also a question of heat capacity. The coals not only conduct heat poorly but also don't store a lot of heat. To use the oven analogy again, if the oven is at 400 F, if you touch the pan with your bare hands, you'll be burned, but if you touch the air in the oven (which is at the same temperature), your hands will feel warm but won't burn. The reason is that the air has very little heat capacity. It should also be noted that coal walking is often done in sequence, so the first person going across cools the coals with his/her feet, and it's not as hot for the next person. If you tried firewalking with a thick layer of hot coals, your feet would be burned. (Don't try this at home, folks). Anyway, contratulations!
--Kevin