My only experience was second hand, from an amateur mechanic who races farm tractors at contests. An engine he had been working on suddenly started to rev uncontrollably for no reason, fortunately it was parked & not in gear. He had just enough time to warn everyone, and he ran behind the tractor on the end opposite the engine before the engine exploded. I don't know how long the whole process took, but he described the explosion as a bomb going off with pieces of shrapnel flying & ricocheting in all directions.
I would only try the remedy of blocking the air intake on a runaway diesel if I was already under the hood & the air cleaner was already off the machine. It takes too long to open the hood, remove the obstructing parts, and block the air intake with something. The basic cause of this problem is the diesel feeding on its own oil supply through an internal leak, which could be a bad seal, a crack in the block, or whatever. The only limit to the engine's speed would then be how fast the engine oil was getting sucked into the cylinders (something a witness can't determine until later, and maybe never), the amount of oil in the engine, and whether or not a key part seizes up due to overheating or oil starvation. That's why I said it would take a braver man than I to try to strangle a runaway diesel engine.