Readers may remember Submarine Matters’ article Russian Submarine Fire - Orel Perhaps a Write-Off? Of April 8, 2015. This was about a fire aboard the Orel (Oscar II class SSGN submarine, on April 8, 2015, which began during welding and cutting works. The fire started in the rubber insulation between the outer and the pressure hulls.
The main problem appears to be systemic - pockets of flammable gas from rubber, oil and grease build up between the hulls – then the gas ignites on contact with a welder’s flame or sparks from hull cutters.
There was another similar but potentially catastrophic fire on a Delta IV SSBN, Ekaterinburg K-84 in dry dock in December 2011, as recounted below.
On December 29, 2011 a Russian Delta IV SSBN (Ekaterinburg K-84 underwent unscheduled maintenance. The large hole was cut in Ekaterinburg's bow (apparently) before the fire. It is odd such a large hole was cut (perhaps over 3 meters across) - perhaps to replace torpedo tube gear, or the large bow sonar or to fix a distortion in hull steel? Cutting and/or welding this hole apparently started the fire. (This and other photos are in the Barents Observer, April 16, 2012).
On December 29, 2011 Ekaterinburg K-84 on fire - which increased in intensity. Four torpedoes were in their tubes near the fire. More crucially 10 to 16 nuclear armed missiles (each with rocket fuel and 4 nuclear warheads) were also onboard behind the sail (Photo courtesy Barents Observer, January 3, 2012)---
The 7 Feet Beneath the Keel website reported, January 1, 2012:
"....[on December 29, 2011] a fire broke out aboard Ekaterinburg [K-84], the second hull of the Delta IV class of SSBNs ...the submarine was undergoing dock repairs in a floating drydock...in the port of Roslyakovo (near Murmansk).
Sparks from ongoing hull-cutting operations apparently ignited either oily residue or trash lubricants floating in the free-flood space between the outer and inner (pressure) hulls. This space, which contains the submarine's cylindrical sonar array, is flooded when the submarine is afloat, but it is supposed to be drained when placed in drydock.
In this instance, openings located under the sonar dome were welded shut, thus preventing the space from being fully drained. The presence of water in the space should have been obvious to shipyard workers, especially given that the submarine was placed in the drydock three weeks earlier on December 8, 2011...
About thirty minutes after the fire ignited, the rubber material within the free-flood space began to burn. The flames then spread outside the space and onto the outer hull. Subsequently the submarine’s anechoic tiles, which are made of rubber and used to reduce the amount of noise emanating from inside the submarine, began to burn, as did the adjacent wooden scaffolding...
Adding to the seriousness of the accident is the fact that at least ten SS-N-23 Skiff ballistic missiles and four combat torpedoes were loaded aboard the submarine. As this repair period was “unscheduled,” naval officials decided not to fully offload the submarine’s weapons. For “scheduled” repairs, all weapons are offloaded before repair work begins.
The immediate danger of the fire was to the four torpedoes, which were amazingly still loaded into torpedo tubes that are located in a separate, confined space above the free-flood space containing the cylindrical sonar array. Crew members were able to pull three torpedoes from their tubes, but the fourth torpedo was wedged inside the torpedo tube. [Russian fire crews would have been mindful of the explosion of torpedo fuel in the Kursk nuclear submarine submarine disaster in 2000] News video from December 30 clearly shows water being sprayed directly into at least one of the starboard torpedo tubes.
By 3PM local on December 30, shipyard workers had flooded the drydock in order to lower the submarine into the water. This allowed seawater to flood the free-flood space between the outer and inner hulls, thereby dousing all flames and rapidly lowering the temperature within the space. Shortly afterwards, the fire was reported to be completely extinguished...
Now that most of Russia is enjoying a week-long New Year’s holiday break, investigators and military officials will be able to better craft a story for the public while simultaneously trying to figure out who’s to blame. The more things change, the more they stay the same."
The main risk with Ekaterinburg K-84 was probably less a nuclear fission explosion but more the risk of torpedo fuel and torpedo warheads exploding. If that happened then further back rocket fuel exploding, blowing warheads out of the tubes and rupturing the submarine's two nuclear reactors would be catastrophic. The city of Murmansk, population around 300,000, and probably a much wider area would then have a major radiation problem.
The two events (Orel and Ekaterinburg) have much in common and point to a whole range of Russian submarine safety problems.