Table of NPC hazard levels in relation to the NPC difficulty level of their "birth area": each area in the game can be, at MS's discretion, set to generate and host only NPCs of a certain level. These levels, calculated using a benchmarking script that "virtually" generated 100 NPCs for each tested level, are as follows:

The "Main" area, the one you begin in, is of course level zero. The Average HL is what you can reasonably expect from a NPC generated at that level, the Low peak was the minimum HL found in the 100 runs of the test, and the High peak was the maximum HL found in the same 100 runs. The above table may change as the game scripts evolve in time, especially if I begin to think about further "typical NPC items" for the game to equip NPCs with, but I'll care for keeping it up to date.