I don’t believe that there are any normal circumstances that would cause the cars to break away from each other. The couplings must have been released. I’m thinking teenagers pulling a tragic prank.
Thank you. The little I know about them seemed to require some intention action, rather than a loss of power, pressure, etc.
There could have been some attempt during the first fire (when the engine was shut down) to separate the cars, but that is only my speculation; I haven’t read anything like that.