When you do, the elevator will immediately start to descend.but so do a bunch of headcrabs. I would definitely save before you pull the lever. Follow the passageway to get to a large elevator (a loadzone will trigger).Д«efore you pull the lever, grab the two clips of pistol ammo near the dead security guard. Swim up to the opening where the zombie came from to get to the next area. Start turning the valve handle (press the use key) and water will start to rise. Now drop down into the opening and follow the right passageway until you see a valve handle. However, in the Source version, the headcrab is not there, so you don't have to worry about it. In the original Half-Life, a headcrab is directly under the opening (you can kill it easily by just throwing a grenade down). Either throw a grenade in the room or start shooting the zombie to kill it. Go near the small opening and a zombie will emerge from behind the gate. Turn the valve handle to make the water rise.

There's also a health station behind the dumpster (not to mention a scientist inside of the dumpster) if you need it. Pick up the two clips of ammo that are in this room, and then kill the headcrab that's hiding behind the barrels. The door will start to be ripped apart by a Vortigaunt, and as soon as it's destroyed, throw a grenade in there to kill it. Take your grenades out and start walking backward from the small brown door. Now jump down from the walkway (try crouching before you jump down to avoid being damaged) and go down the passageway labeled '19.' Inside is three clips of pistol ammo, fifteen grenades, and a health station. Kill the zombie and then have the scientist open the door for you. Have him follow you to the narrow walkway (which leads to a storage room) on the left, where a zombie is having it's dinner. To the right of the ladder is a passage that leads to a scientist. This will kill the zombie and the two headcrabs that are nearby. Climb up the ladder so you can see the large explosive tanks, and then shoot them quickly. Take your pistol out before you go up the ladder. Kill it immediately, and then follow the narrow passage. Open the door and a headcrab will jump out of nowhere. Now go up to the door with the yellow hazard sign. Throw a grenade in here to kill the Vortigaunt.

Now take out your crowbar and crouch under the left glass pane to proceed to the next area. Grab his Glock pistol nearby (you may already have one if you killed the first security guard). Now go through the passageway to see a dying security guard (there's no way to save him). scientist scene, and the room across from here has a rather frightning display. Crouch under the vent and go down into the next area.ДЄvoid the fallen vent in the corner, as a headcrab will jump out of it once you get close.

Jump on the first fallen machine that's blocking the doorway, and then jump on the one in front of it to get to the vent. There's another vent in the top right corner which we need to get to. Use the nearby health station if you have to. Now crouch under the small vent to go into the next room. The security guard that you left behind serves no purpose now, so you can either kill him for extra ammo or just leave him there. Jump on the machine near the doorway and then jump to the next one to get to the vent.

Half life 1 secrets