I don't think an explosion is in your near futuer. I also have a few Jackson auto dark hoods. The only problem that I have encountered realted to heat is the loss of the lense ability to tint. I welded for around 4 hours straight on an alu. injection mold shoe. The shoe was 6"x10"x24" in rought terms. I was filling 1 1/2" holes and other major wear areas. The block was held at '275F and welding was done with a 3/16 tungsten at 300-350 amp. After about 2 hours of welding the left side of the lense stopped changing shades, it just stayed dark. I took a temp gun reading of the outside cover lense and it was over '200F. I changed back to a standard class lense and completed the job.
Long story short...the lense took a beating, nut never exploded.
MDG