Well, the problem ist simply the track and the speed. We call such railroads "field trains", which means, that those narrow gauge lines were usually build on the agricultural areas, so run betwen the fields. They transport milk bulks, agricultural guts and delievered stuff to agricultural stores or agricultural facilities, like mills, traders and other... tracks were often uneven, because were derived from poineer railroads of the military railroads.
Thus the locomotives had a very low weight and are good balanced, thus uneven tracks were not the problem.
Also, those locomotives seldom flip over.. if they derai, they simple bounce of the track and with the wheels right into the dirt... So with some bars your evenly get all hands and get the locomotive or car back on the rail and go on again.
The speed here is critical, but it seems the did this with experience and for sure: derails happen often, and I am sure, the experience on get the train back on track is high - thus no need to slow down.
There is no problem of boiler problems. If a locomotive flips over, the boiler won't explode. Usually the boiler might rip and huge amounts of steam will blow off, but: the stability of the main material is still given, and thus widstand further tear and ripping... In most cases the locomotive simply falls on one side, and personal will blow off the steam manually and extinguish the fire - before the boiler is drained ...
So calm down a little. Buy a backyard close to the line and hope, that someday a locomotive drops into your backyard - then claim it yours
Allways keep two-thrid level in gauge and a well set fire, that's how the engineer likes a fireman
