24 October 1960. A Soviet R-16 ICBM prototype exploded on the launch pad at the Baikonur Cosmodrome facility after premature ignition of the second stage. Over 100 died, including Chief Artillery Marshal Mitrofan Ivanovich Nedelin, head of the R-16 development program.

You could see people running away on fire!

I looked him up because I had read of a Soviet Rocket Officer who had reportedly setup a chair near the pad to personally observe a launch. I thought it might be this person and may be. Because the report of casualties seem to match in this incident,close to what I read earlier.

The flow on effect was the Cuban Missile Crisis. The R16 became horribly delayed as a result and by mid 62 very few were deployed (~10?) and not in silos. The R7 was also not viable, very big and slow to prepare. So kruschev tried to smuggle IRBMs into cuba to close the gap

Instantly establishing Explosive Safety Distances in the USSR