Unbelievable, the crap you read on this Kursk-thang...
As the man from Mammoet company said, the explosion came from inside-out, not from outside.
What happened was one of the accidents captains fear most: a mishandling of a torpedo, or a torpedo performing a "hot run" inside the boat.
Don't forget, Oscar II boats have a double hull, and even if one torpedo's fuel tank had exploded - without the warhead, which we assume wasn't activated - then, in theory, only the inner hull would most likely have ruptured. Because as the bulkheads were obviously not closed, approximately 30% of the blast would have gone straight through the sub.
As you can see on this photo,
the quite tough metal of the outer hull is blown outwards, not inwards.
On the "myth" of another sub colliding with the Kursk...
Simply do the math.
In order for a submarine collision to do enough damage to set off an explosion, that submare must have made at least 80 knots for its hull to penetrate that of the Kursk, and even then the colliding submarine would never have made it back home - it would have sunk together with the Kursk.
Then look at the location where the Kursk sank - not far from Poliyarni.
Any Russian submariner will tell you that sub drivers like to order drills not long after leaving port - especially torpedo drills.
For many submariners on the Kursk, that fateful tour of duty was their first. Any average Russian submarine captain would have ordered (torpedo) drills as a habit; almost every captain knows that even today, Russian training standards at academies and for non-commissioned sailors are well below Western standards, and so are security levels.
Something went wrong, something inside the Kursk torpedo room, and it caught everyone by surprise. If bulkheads were left open during a drill, which some specialists have said was the case, then that is one hell of a mistake to make, especially because most Russian experienced submarines knew (and know) quite well that their torpedoes are highly unstable.