Honestly hate to be that guy but a tube sheet weld letting go on a 300 PSI boiler is a lot more than just blowing a weld. At that pressure the water flashes to steam the second it hits open air and the whole boiler room turns into a sauna in about two seconds. The tube sheet is where all the tubes tie into the drum, so if that seam goes you got hot water and steam dumping from every tube at once. Crawling out fast was the right call, that room would've been impossible to see or breathe in.