The logical explanation would be that he compared the known intensity of sound with energy needed and calculated the known displacement of the submarine in the equations.
Speed of the final event made me think that instant death was the result in milliseconds however I can’t stop thinking of the sounds which is produced by the hull as it goes over the construction limits. I studied quite some portion of books about submarines and final moments make me sleepless at times. The percentage of losses of the U-boot crews was horrifying and the number of all-hands fatalities in most of the cases popped up in my memory when I heard about this recent tragedy. If they lost control they knew what was coming. That thought is painful and even more for the families. Godspeed.