Suspicious Russian Submarine Fire, Vladivostok, Diesel Vapour? Battery Hydrogen?

KQN has drawn Submarine Matter's attention to a January 21, 2018 Russian claim that the Russian Navy intentionally set a Russian conventional, diesel-electric, Kilo class submarine on fire, on January 21, as part of a “damage control exercise”. This fire was/is at Vladivostok Main Naval Base, Russian Pacific Fleet.

The Kilo is most likely part of the Russian Pacific Fleet's, Vladivostok, 19th Submarine Brigade and may well be an unimproved Project 877 Kilo (likely Pennant Number "B-260", "B-445", "B-394", "B-464", "B-494", "B-187", "B-190" or "B-345"). Intentionally starting a fire is highly unlikely given the cost of a Kilo and close proximity of several other Kilo subs near the fire (see photo below).

Russian Kilo submarine on fire, January 21, 2018, at Vladivostok. (Photo courtesy Anonymous Russian via a scoop by Tyler Rogoway, The Drive January 21, 2018, website).

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REASONS FOR FIRE?

It will be interesting if the Russians admit the real reason, eg:

-  residual diesel fuel vapour catching alight 

-  angle grinder or welding equipment started a fire of insulation or diesel fuel vapour between the 

   outer hull and pressure hull,

-  in what supports diesel burning KQN suggested January 22, 2018 "From the photo [above] it
   appears smoke is coming out from the rear escape hatch? Diesel generator fire? The diesel engines
   and motor is in the back. There seems to be diesel fire on water as well? [also noticed by
   Anonymous 23/1/18 11:51 AM]. There appears to be light ice on sea surface, I am sure it is cold
   there so do they need to run the generators or main engine to maintain the inside at a controlled
   temperature for the sake of electronics?"

-  Pete suggests another theory - that extreme cold surface temperature or water temperature
   caused diesel fuel tank/fuel in the diesel engines/or pipes to freeze-expand-and-split the
   tanks/engines/pipes with some diesel leaking into the water. A short term rise in temperature
   (Sun during the day) and ignition (bored sentry/crew smoking?) all caused the fire. 

I doubt that one would put up a real fire as an exercise on a $300M submarine. Strange things have happened with the Russian armed forces like the time some soldier cooked inside an IFV and then the IFV ended up being barbecued...

-  battery maintenance causing release of flammable Hydrogen gas from the batteries, leading to fire. 

OR

-  fire of highly volatile torpedo propellant, then subsequent "cooking-off" of torpedo warheads

Precents include:

-   the welding caused fire between outer and pressure hulls on the Russian Oscar class SSGN "Orel" 
    on April 8, 2015

-  the fire and explosion of Indian Kilo submarine INS Sindhurakshak, on August 14,  2013.

Pete