Hi, forum lurker here...anyways I'm surprised no one answered this yet since this is a very simple question, Hopefully someone posts before I do , English isn't my primary language so I apologize if I make a few typos. (I'll edit any I find after I post this.) .
If you want to prevent the excavator from decompressing any of the tunnels or the biodome, I believe only the player with the hacker can stop it. The player with the hacker must run all the way back to the QR machine and look and see if one of the machines are beeping green lights. When you find the right one glowing, hack it . You earn 1000 points as a result of hacking it and stopping the excavator. There are three ecxatavators, one for each oxygen level. Excavator Epsilon (You will know when it's announced, because she will specifically call it Excavator Epsilon.) is the one can take out the biodome's oxygen, so make that your top priority. The other two name of the excavators, excavator Pi attacks tunnel 6, and excavator Omnicron attacks Tunnel 11. If it's tunnel 6 it's going to attack the MPL/M16 rooms, if it's tunnel 11 it will attack the PM63/STAMINNUP/SEMTEX rooms. Bear in mind if you want to attempt the easter egg you have to LET tunnel 6 get excavated, but you to be in the QR room before it gets excavated. This is so you can deactivate the excavator and be able to run around the tunnel again (although it'll have no oxygen obviously .) Oh, and it's best if you make some crawlers to hack the excavators. Also if you do unfortunately lose an oxygen level you can always get another astronaut helmet from the doors, it'll be either on the right or left.
I hope this helped, but don't expect anymore posts from me anytime soon . I will probably get ninja'd by another member because this took me long to type .*steps back in the shadows to continue lurking...*