I used to have a low temperature salt setup that was roughly 10 inches deep, and use some stump killer grade potassium nitrate on and off in a different setup. Id leave a smooth steel rod in it for cooling, a little torch heat on the rod would let it wiggle out of the solid block, leaving a vent hole for reheating.
I just wear full leather welding gear and a full face shield around the stuff when its warmed up, no big deal. It doesnt do unpredictable things. I made a little three hole rack that I could adjust a stop depth on, best control and simplicity for me to anneal rifle brass.
