do you remember where you were?
I was in college. Someone had spliced the taping of the launch up to the explosion. It ran continuously, over and over with the tape player and TV in the Electrical Engineering main lobby. There was a crowd of us standing shoulder to shoulder watching in stunned silence. I had to have stood there through at least a dozen runs before I moved or spoke.
We rushed over to the Space Systems Division building and watched the NASA live feed, unedited and unnarrated. One co-worker who had worked for Gates rubber in Carlsbad saw the feed once and said "It's the seals". He knew right off and showed us the puff of smoke at the interstage on the next playback.