Through the doorway next to the dead scientist is a shotgun and box of shells and two pistol magazines. Smash the wooden crate that was next to the blue one for a pistol magazine. Push the crate toward the turret, taking shelter behind it, until you're under a platform where you'll see a switch.

Jump down and quickly crouch behind the blue crate. Wait for the turret to kill the headcrab, then find the large blue crate below you. After the scientist is killed, a headcrab will come. Wait until a scientist comes and gets mowed down by a turret. Stand in this position at the intersection with your grenades, and throw one to the first left passage, then the second, and then take out your shotgun to kill the Vortigaunt on the right passage. Destroy the grate, but don't drop down yet. Jump off to the left and go up to the grate. Use these boxes to climb up to the ladder and climb up into the ceiling.

Find the smaller crate and push it next to the big one. Find the large blue crate and push it so it is sitting under the gray ladder hanging down from where the headcrabs fell. You'll have to make the guard wait as you go around and unlock it. At the end of this hall is yet another locked door. Back at the double red doors, several headcrabs will fall through the ceiling as you walk down this hallway, but they're no problem for the security guard. Open both doors, then go find the security guard and ask him to follow you again. You will fall into the hallway that was behind the locked double red doors. Keep following the vent shaft until you get to another grate. Make sure you hold the crouch button to stay crouched because as soon you stand up, a fan will take a little too much off the top. Shoot all three of the headcrabs that are hiding in the vent, then crouch jump into the shaft. Smash the grate with your crowbar and switch to your pistol. Walk up to the vent shaft nearby and turn on your flashlight ( F is the default). Hide behind this blue crate and keep pushing it forward until you reach the turret's switch. We won't worry about the other rooms for now. Go to the very end of hallway, past the storage closet. Crouch jump through the window, and take a left. Now that the power is off, walk past the hanging wire and to the end of the hall where you'll have to destroy the window with your crowbar. Go back the way you came, exiting out into the hallway. Shoot the two headcrabs from behind the cage with your pistol, and take the ammo near the dead guard. Keep following the path and it will lead to a fan, where a dead security guard with two pistol magazines lie. Before we go to the next area, go back into the vent shaft and take the left passage. Go through the double red doors and back into the hallway. Before you leave this room, murder both of the scientists with either your crowbar or pistol (a single shot to the head is sufficient) to spare them the grisly end they would inevitably face later. This disables power within the local area, including the dangerous light. Go through the doorway labeled 'DANGER: HIGH VOLTAGE' and flip the switch inside. Kill all three headcrabs from behind this cage and then collect the ammo. Barnacles will then begin to come through the ceiling, so watch your step. If your conscience allows, you can let him get killed by the barnacle, or you can save him. Drop down into the room below to find two scientists, one of which gets dragged up by barnacle after he gets scared. This will bring you to another grate, which you must destroy. Crouch down and take a right from the vent shaft entrance.

The electricity from the fallen light will destroy the vent shaft, opening a passage. If you go past it, you will meet the same fate as those poor creatures. Watch as the electricity kills the headcrabs, then walk up to the vent shaft. Second is the small vent near the live wire. If you even attempt to walk past the wire, you will get fried. You need to turn off the power before you head this way. The first is the broken ceiling tile and the live electric wire that is hanging down. There are several things to take notice of here. Take the battery and the medkit that are nearby. When the elevator reaches the ground floor, the doors will open. Go into the room with the danger sign and press the switch inside to disable the power.

Half life source walk through