Part 49

When the lift stops, exit and use the Hornet Gun to open the doors. Fire hornets at a spot beneath the large lambda symbol on the orange sign to hit an unseen Vortigaunt.

Move to the back of the lift and watch the passage to the right of the "02 COOLANT SYSTEM" sign with the Assault Rifle. If the Vortigaunt appears, shoot it.

If the Vortigaunt goes towards an explosive crate near a hallway entrance to the left, move close to the lift doorway and fire hornets to the left. This should cause it to move into the hallway.

Peek out and blow up the explosive crate with altfire hornets to kill the Vortigaunt. (Alternatively, crouch-walk to the railing and sneak-shoot it with the pistol.)

Engage the two remaining Vortigaunts in the hallway. Approach slowly, use a double-barrel shotgun blast, and strafe for cover. Use the explosive crate in the hallway to help kill them. (Alternatively, use an AR grenade.)

At the T-intersection at the back of the hallway, prepare for three sets of teleport-in aliens.

The first set may have already teleported in. Go along the left edge of the hallway until you can see a Vortigaunt on a walkway to the right.

Let it see you, hit it with hornets, back up, and shoot it in the head with the Assault Rifle as it comes into view.

Move along the left side of the hall until you can see the blue "01 COOLANT REACTOR" sign. Fire hornets towards the sign to hit an Alien Grunt over there.

Return to the hallway intersection and turn right. Pass a security guard, go down stairs, and find a room with rechargers and ammo. Refill and return to the hallway split.

Go down the other hallway, but do not open the door. Run to its end and return to the T-intersection. This should trigger the second pair of teleport-in aliens.

Repeat the process of killing the Vortigaunt and then the Alien Grunt.

If the third pair doesn't appear, go to where the Vortigaunts appear, then down the ramp to a hallway with red machinery. Run back and forth to trigger them. Sneak-shoot them near the bottom of the ramps. Repeat hallway-running if necessary until all three pairs appear. (Note: Source text mentions only one pair.)

Get the security guard to follow you. Follow the "01 COOLANT SYSTEM" signs to a spot with two dead scientists.

Move past the scientists, facing them, as a Vortigaunt will teleport in. Position yourself so the security guard is between you and the Vortigaunt.

After the guard is zapped, shoot the Vortigaunt with altfire hornets. Your guard may help. If the guard survives, whack him for ammo. (Alternatively, use a C4 satchel bomb.)

Move to the door at the end of the hall to open it. Fire hornets into the left side of the room beyond to kill three Alien Grunts, one on a higher walkway, before entering. (Be careful not to be seen when opening the door.)

Climb the ladder to the upper walkway, go along it to a door, then up stairs to the pump room.

Use hornets to kill the nearby headcrab. Move forward to kill another headcrab on the lower floor to the right of the blue pump machine.

Move to where the walkway splits, then retreat to the corner by the stairs. Wait for two Vortigaunts to teleport in.

Use hornets to sneak-shoot the Vortigaunt on the upper walkway. (Alternatively, wait at the walkway split with the shotgun.)

Crouch-walk along the walkway to a spot where you can use the Crossbow to sneak-shoot the Vortigaunt on the other side of the pump machine.

Examine the pump machine with the flashlight until you see its red lever. Quicksave, drop off the walkway near the lever, use it, and run for the ladder back to the walkway.

Two more Vortigaunts will teleport in. If fast enough, you can leave the area without being zapped.

Make your way back to the hall.