CoIin

Best answer as chosen by Asker / Ratings
Literally it's destroyed in the same way as the first generator, you lean against it, and your suit does the rest. If your real question is how do you get out of the room once you've done that, because you're now surrounded by Flood, here's two ways:

I too found it very hard to survive all that Flood, but then I figured out that I could jump into one of the holes that they come out of, and at my leisure pick them off. The jump into the hole is tricky, partly because the game's frame rate drops a lot while the generator is blowing up.

The other way, which may be the official solution, is to get grenades and the rocket launcher, and as soon as you've blown up the generator head towards the door, and rocket launch at the many Flood coming in at the time. Once you've killed enough of them you can jump past the remainder to get outside, without worrying too much about any behind you.

One other thought about the room, you may be having a hard time when you first get into the room. Instead of trying to kill the Flood right away, let them fight it out with the Sentinels, and make sure to kill anyone left, so that you get a save checkpoint before you blow up the generator.