This video is really good. It shows what was known at the time. It shows that the commanding officers really got up to speed really fast on what was needed to be done, and the risks involved.
They sent in troops, AND hired civilians to perform a 45 second task of taking 1 shovel full of rad debris, and then running to edge of roof and throw it off. They had to use humans because the robots were getting killed too quickly on the roof. After that the human would be "retired" they took their maximum lifetime dose or more. However, I also heard that some of these bio-bots as the liquidators were sometimes nicknamed, went back for 10 of these 45 second visits.
This video is both entertaining and enlightening.