Part 14

Crouch-walk back into the shaft after passing under the unbreakable grating.

Approach the next opening on the right slowly with your pistol and flashlight to sneak-shoot a headcrab.

Descend the headcrab's shaft. You can likely ignore the two marines below and gather ammo from the room ahead, or eliminate them. For the marines: use a double-barrel shotgun blast through the nearest floor grate for the red-beret marine, then use the assault rifle on the other marine through the same grate when he's visible.

Return to the main vent shaft, turn right, and find a left branch leading to a room with a first aid station, two armor batteries, and assault rifle clips.

Climb onto the green crates under the unbreakable vent grating and use it to return to the shaft.

Go back to the fan room, move along the narrow ledge to drop to another ledge, and enter an adjoining vent shaft that leads back to section c1a4d briefly.

At the end of this shaft, drop to a ledge with shotgun ammo. Climb back into the shaft and return to the fan room.

Drop to the floor and enter the shaft opening below.

At the end of the long shaft, climb a ladder and get off on the lower of two small platforms.

Use its vent shaft to reach the silo door control room. Press the big red button to open the silo door. Pick up shotgun ammo and exit the control room.

Use nearby first aid and HEV stations if needed, then go through the silo door to where the "Blast Pit" chapter begins.

Go to the far left end of the big barricade and shoot the bullsquid in the distance with your pistol.

Use the crowbar to break down the barricade.

Shoot the two headcrabs among the boxes past the barricade.

Move through the big doorway, watching for another headcrab to your right.

Go up the ramp to the small control booth. Slowly approach the metal door. When you hear a zombie hitting the door, back away.

Run to the lever on the panel, then immediately back up.

Toss a grenade through the doorway to detonate explosives and kill the zombie.

Check the room for grenades and a health pack.

Use the lever on the control booth's panel to raise a big lift to the lower-floor area.

Use the ladder to climb down to the lift. Get on the lift and use its button panel to start it moving. Turn around to face the opposite direction.

When the lift stops, move onto the walkway with health packs, turn right, and drop to the tracks next to the rail car.

Whack the houndeyes with your crowbar or shoot them with the shotgun.

Jump onto the rail car and press the "Use item" key near its control panel to bring up the speed display. Press the "Move forward" key multiple times to reach top speed.

Crouch near the control panel to avoid bullsquid spit.

When the speed display disappears, stand up and look ahead. If the car stops, quickly back off to avoid being thrown.

As soon as you hit the ground, run toward the car. Jump-crouch back onto it, then get on the two side beams on its right and jump-crouch onto the ledge.

Crouch-walk along the narrow part of the ledge to a wider section.

Before crossing, find a spot to shoot the bullsquid on the other side, using a large pipe for cover.

Reach the end of the ledge and drop to the bullsquid's floor.

Crouch-walk under a large pipe and climb the ladder on its other side.

Get on top of the pipe and carefully make your way to a smaller side pipe with an open hatch.

Drop into the pipe and move along until section c1a4k loads.