Beryllium is one of the largest of the Obsidian levels, a feature characterised by the mines in the Icicle Cluster. It is also one of the most dangerous. While the deadly Class IV Heavy Driller has yet to show up at this point, the IDR, Sniper-RF and Hornet robots more than make up for it. You had better watch your step here, but also remember to keep a sharp eye out for secret areas, as this is the first level in which you can find the Omega Cannon.
You simply have to blast your way through all of the triggers and pick up all three keys. Leave the hostages until just before you destroy the reactor - you don't want to lose them.
Remember to take caution when entering heavily occupied areas.