Soyuz T-10-1

Soyuz 7K-ST No.16L, sometimes known as Soyuz T-10a or Soyuz T-10-1, was an unsuccessful Soyuz mission intended to visit the Salyut 7 space station. The crew was sitting on the pad awaiting fueling of the Soyuz-U booster to complete prior to liftoff. Approximately 90 seconds before the intended launch, a bad valve caused nitrogen pressurisation gas to enter the RP-1 turbopump of the Blok B strap-on. The pump began spinning up, but with no propellant in it, the speed of rotation quickly exceeded its design limits which caused it to rupture and allow RP-1 to leak out and start a fire which quickly engulfed the base of the launch vehicle.