The Wikipedia article you refer to identifies an explosion caused by fuel used by a dummy torpedo as the reason for the sinking of the Kursk: "At 11:29 local time (07:29:50 UTC), high test peroxide (HTP), a form of highly concentrated hydrogen peroxide used as propellant for the torpedo, seeped through rust in the torpedo casing. The HTP reacted with copper and brass in the tube from which the torpedo was to be fired, causing a chain reaction leading to a chemical explosion."
Other sources indicate that the torpedo involved was an obsolete old model. This supports my larger point, that the disorganized and faltering Russian defense industry had produced a torpedo with deadly defects and that it had been maintained in service too long. Western navies regard HTP as too dangerous for use as torpedo propellant.