Part 16

Return to the firing chamber. Go along the walkway to a room where you must hit a red switch to change which door is open, which will take you back to section c1a4b.

In section c1a4b, turn right after exiting the door-switch room and move towards the area with a bullsquid. Shoot the explosive crate next to the bullsquid with your pistol, then finish it off if the explosion did not kill it.

Turn and shoot the explosives on the nearby path until they detonate.

Crouch-walk across the blue pipe that survived the explosion.

On the other side, break open the two non-explosive crates to find health packs.

Move down the corridor until section c1a4d loads.

In section c1a4d, move along until you reach an area with an unopenable fuel room door on the left and a ladder on a metal platform on the right. Do not climb down the ladder; instead, jump over the railing next to it.

As soon as you hit the floor, run for the large floor grating ahead. Bash it open and descend the long ladder beneath it.

At the bottom, get onto the large brown pipe and move carefully along it until it divides.

Go down the left pipe until you reach a short ladder leading up to a large bashable grating.

Before bashing through, shoot the zombie visible through the grating with your pistol.

After climbing up, locate a small room with grenades to resupply.

Move down the corridor to get section c1a4e to load.

In section c1a4e, find the opening control for the closed door on the wall to its right.

Warning: Two zombies are just past the door. Toss a grenade at their feet as the door opens and back up to avoid the explosion. Finish them off with shotgun blasts to the head if necessary, or try to run past them on their right side.

Past the door is a huge shaft with a giant fan. Move around the upper walkway until you find a ladder to the lower walkway.

Climb down a ladder from the lower walkway to reach a short, narrow platform leading to the fan's button panel.

Warning: Quicksave before using the button panel to turn the fan on. Immediately start running backwards to climb the ladder without being affected by the fan.

Jump into the space over the fan to be blown to the top of the shaft.

Use your crowbar to bash through some boards.

Once floating above the boards, move to a large vent covering on a wall and bash it out.

Warning: A headcrab is just past the vent covering. Toss a grenade in there and back away.

After the explosion, drop into the vent shaft and move along it.

When you reach a large metal vent covering, turn on your flashlight and shoot a headcrab through the covering before bashing it away.

Past that, you will encounter a board barricade. Shoot the headcrab through the barricade, then bash through it to return to section c1a4d.

In section c1a4d (again), bash through some metal vent coverings around the corner past the barricade and drop down to find yourself next to the fuel room.

Warning: There are three zombies and a headcrab in the fuel room. Use your pistol to headshot (a shot that lands on the enemy's head, usually an instant kill) the first two zombies you see.

Go through the doorway and blast the third zombie with your shotgun.

Shoot the headcrab from a distance with your pistol; it is on top of a green machine next to two red lights.

Go to the control panel left of the headcrab's machine and press the "OXY ON" and "FUEL ON" buttons.

After the lights next to the buttons illuminate, find the ladder in the alcove to the right of the headcrab's machine and climb it.

Use the control on the wall to the right of the door to open it, then head down the corridor on the right to return to section c1a4b.

In section c1a4b (yet again), return to the blown-up walkway and cross it by crouch-walking along the blue pipe.

In the door-switch room, hit the switch to be returned to section c1a4i.

In section c1a4i (again), go past the doorway into the rocket firing chamber to a red railing. Jump onto the railing and crouch-drop to the floor below, losing approximately 20 health. Alternatively, try getting onto the left end of the railing and hugging the wall while going down, using the "Jump" key or direction keys.

As you go along the walkway, you will come across a wide gap.

Warning: Quicksave before attempting to cross the gap. Take a running jump across the left side of the gap.

Get out your shotgun, run forward without stopping until you reach an area with a zombie.

Quickly double-barrel the zombie in the head to kill it. This tactic also allows you to cross a new walkway breach.

Enter the door-switch room past the zombie and hit the switch to return to section c1a4b.

In section c1a4b (fourth time), exit the door-switch room to find yourself in the area with the bullsquid you killed previously.