Wrong. It was on a several day "weapons exercise".
I suggest that you read "Cry from the deep", by Ramsey Flynn. The Kursk was a disaster waiting to happen.
The book gives some insight into the "short shrift" that the Russian submarine fleet was given in Russian military spending.
For instance, very few of the cranes used to load torpedos into the subs were functional. They had been built by the Ukrainians and Russia was reluctant to give the Ukrainians money to keep them maintained. In fact, while loading the Kursk, one of the torpedos was dropped onto the dock.
The HTP torpedos were a disaster. They leaked and were subsequently subject to "cooking off". The warehouses which kept the torpedos typically released the worst ones, to get them the hell out of the building.
It was one such HTP torpedo that eventually "cooked off" while in the tube, awaiting firing. The resulting fire set off another four or so non-HTP torpedos.
"The HTP torpedos were a disaster. They leaked and were subsequently subject to "cooking off". "
Nothing new at all. The Soviets lost a Yankee class SSBN off the course of North Carolina due to a chain failure. What started the chain? The missiles in that Yankee boat were fueled at the time by liquid propellant, dimethyl hydrazine and nitrogen tetroxide. Nasty stuff to handle. The birds were in the launch tubes fueled, the Red Navy tried storing the fuel separately in the past (I would assume on their Hotel, Golf, and Zulu IV boats) and ran into too many problems fueling the bird at sea before launch. In this particular Yankee boat, seawater got into one of the launch tubes via a leak, mixed with the nitrogen tetroxide from another leak, flooding the boat with nitric acid fumes and other stuff. How the leaks? Remember the old saying in the Soviet Union, "They pretend to pay us, and we pretend to work", in addition to many shipyard welders fueled by vodka.