I've got a 1/4" of lexan between me and the jar(and safetys as well). I've got some plans for a larger pulse jet that can be made out of black iron pipe. If that goes succesful I'll invest in making one out of some stainless (full sized it is like 5 feet long ish and the pipe diamter is 4" and 6" for the combustion chamber)

If the jar did fail it would not explode really. It would crack first and the pressure difference would immediatly stop combustion and the jar would crumble.. But thats if you introduce it to thermal shock or get it waaay to hot.