Qualifications
To become a bona fide mine inspector, there are two paths you can take that'll get you in the running for the job (source). You can either come up through the ranks as an experienced miner who's learned a thing or two about mine safety, or you can get a master's degree. How's that for two roads diverged?
On one side of the track, you've worked in mines your whole life. You've dug, you've drilled, and you've dynamited with the best of them. You've made a special effort to learn safety and can recognize problems before they happen on a wide variety of machines. Sure, you've been in classrooms, but you've also spent your life staying safe and keeping others that way, too. You still have all ten fingers to prove it.
On the other route, maybe you spent a few summers working with your cousins in a coal mine, then went to college to learn about mechanics and engineering. You have an eye for detail, and your professors think you're responsible enough to think about inspecting full-time. You get a bachelor's degree, then a master's, all the while stopping in at local mines and getting your hands dirty.
Either path you choose will get you down deep into holes across America, but the best chance for the job is to have that mining experience under your belt—even MSHA says so. If you're in a hole, it doesn't really matter what got you there, just so long as you know what you're doing when you're down there.
Also, if you run into any Fraggles, just know they're not dangerous. You also may have found a tunnel to the 1980s, so enjoy the hair bands and good Michael Jackson music while you can.