Crazy what some of those guys were put through in the aftermath. From the wiki article about the disaster:
There was a bubbler pool beneath the reactor. It served as a large water reservoir from the emergency cooling pumps and as a pressure suppression system capable of condensing steam from a (small) broken steam pipe. The pool and the basement were flooded due to ruptured cooling water pipes and accumulated fire water. It now constituted a serious steam explosion risk. The smouldering fuel and other material above were starting to burn their way through the reactor floor, mixing with molten concrete that had lined the reactor, and creating a radioactive semi-liquid material comparable to lava. If this mixture had melted through the floor into the pool of water, it would create a massive steam explosion which would eject more radioactive material from the reactor. It became an immediate priority to drain the pool.[34]
The bubbler pool could be drained by opening its sluice gates. Volunteers in diving suits entered the radioactive water and managed to open the gates. These were engineers Alexei Ananenko (who knew where the valves were) and Valeri Bezpalov, accompanied by a third man, Boris Baranov, who provided them with light from a lamp, though this lamp failed, leaving them to find the valves by feeling their way along a pipe. None of the three ever returned to the surface and it is thought one of them died before reaching the gates.
