Once the room starts to collapse, head back to the entrance of the room and stay to the far right.As soon as you near what looks like the exit, everything starts to explode - the floor starts breaking away, the room begins to fill with radioactive sludge, and the ladder leading out of the slime becomes electrified.

You'll eventually come to a room where all sorts of bad things are about to happen.Shoot him, grab the shotgun next to the dead Marine, and continue. Head underground via the nearby ladder, and continue until you run across a Vortigaunt. Once back at the chopper, listen to the radio, where you're told to make your way to the extraction point.Don't miss the pistol on the floor next to the security guard before heading back. Find the power switch, turn it off, and leave via the now unlocked gate. Use your night vision to find your way through the vent, and be sure not to get zapped by the electricty when you emerge inside the fenced area.The power switch is behind those gates, but you'll have to access it through the vent on the side. Head over to the area where the generators are fenced off, and watch as a security guard falls victim to a now-electrified fence.You'll need to pass the chopper to progress, but first you'll have to turn off the power or you'll get electrocuted. Once through the door, crawl through the hole in the rock and emerge outside where you'll find a downed chopper.You'll have to do some jumping to make your way to the exit door, and be sure to pick up the knife by the dead Vortigaunt. Continue through the hallways and head outside to the cliff face.This will cause a chain reaction that will deactivate the lasers and allow you to continue to the next area. Crouch under the lasers, and then smash the mirror with the purple laser with the wrench. You'll come across a lab room with lasers blocking your path.This will be your primary weapon for a bit, so don't miss it! After going through the doors, pick up the red pipe wrench on the floor.He will only open the doors if you have your vest. After he kills the zombie, talk to him and have him open the security doors. After getting your vest, head down to the area where a security guard is shooting a zombie.There is a scripted sequence where a zombie throws a scientist through a glass window, and then begins to chase you. It is on a table in the area where the scientists are examining alien specimens. After waking up in the laboratory, listen to the scientist and head out to get your PCV vest.During the opening sequence, don't forget to look around - events happen outside that you don't want to miss.

Half life black mesa