Part 4

Leave the break room and follow the green wall stripe to the employee locker room.

Enter the HEV suit room in the back left corner and use the control panel to put on the HEV suit.

Find the locker labeled "Freeman" near the bathroom entrance, open it, and pick up an armor battery.

Use the first aid station around the corner for practice (it makes a "hee-yee-hee-yee" sound unless your health is 100%).

Go back and down the corridor with the blue wall stripe to the security post. The guard will open the security door for you.

Proceed through the next door to load section c1a0a.

Use a button panel to open doors, then take the lift down to a lower level.

Go through doors and down a corridor until section c1a0b loads.

Enter the control room and wait for scientists to talk.

After a retinal scanner unlocks a door, go through it.

Across from two scientists, use a button panel to summon a lift and go up a level.

Exit the lift and go down the corridor to the test chamber door, loading section c1a0e.

Enter the outer room and wait for scientists to open the main test chamber doors.

Go across the chamber, up a small ramp, and climb a ladder to an upper walkway.

Use the computer panel on the walkway to activate the big scanning machine.

Climb back down and stand next to the cage near the ramp's bottom.

When the "specimen" arrives, quicksave, then push the gadget it's mounted on into the scanning beam.

Move back and wait to be teleported to the "Unforeseen Consequences" chapter.

Check for a rare vortigaunt in the test chamber ruins; if present, restore quicksave and try again. Avoid pulling the specimen's gadget out of the scanning beam after insertion.

Leave the test chamber through the jammed-open doors.

Use the retinal scan device next to the exit door.

Go through the opened door and past a scientist trying to revive a guard. (The guard is not helpful due to rubble).

Go around the corner, past a falling computer bank and debris, to a lift.

Take the lift, go through doors, and get Dr. Vance to follow you to the control room's retinal scanner.

After he opens the door, move in to trigger an electrical surge. Wait for the surge to blow open the far door.

Carefully time your run across the room to avoid being zapped. Section c1a1 will load in the next hallway.

Run through the next room and out the other door quickly, as a headcrab will teleport in.

Crouch-walk under the first red laser beam.

Run around the second laser beam after it breaks free.

Pick up the crowbar next to the nearby doors.

Go back to the room where the headcrab teleported in. Quicksave.

If the headcrab is levitating, dodge its leap by right-strafing at the last instant.

Quickly turn, run up to it, crouch, and crowbar-whack it before it can leap again.