How torpedoes, gunfire, and fire combined to sink Blucher

Did the Admiral Hipper-class torpedo defense leave the boiler rooms unprotected, and why?

It protected part of the boiler-room area; the answer attributes the hit to a gap and explains how existing gunfire damage, broken steam lines, and spreading fire compounded the torpedo damage.

The follow-up corrects the suggestion that the Admiral Hipper-class torpedo-defense system left the boiler rooms wholly unprotected. Protection covered part of the machinery area, but the account attributes the damaging hit to a gap in that geometry. Gunfire had already damaged one boiler room and started fires before a torpedo struck another. Damaged steam pipes then prevented the remaining boilers from restoring useful turbine power. Fire reached 105 mm ammunition between turbine rooms, and its explosion ruptured the machinery spaces. The explanation emphasizes the spreading fire created by the combined damage. Blucher commissioned on 20 September 1939, but German commissioning preceded final trials, leaving less fully operational service before April 1940 than the dates alone suggest; British practice is described as commissioning after yard trials.