Switch 5 shuts off the second pair of burners and it is timed. So from the moment you pull this switch until you clear all 4 burners to reach the exit, you will need to hurry. Here's the sequence:

Save the game. Then if you mess up, you can reload without having to replay any more than is necessary. Flip the switch.

This turns off the second set of burners. Press Look to skip the cut scene.

Roll and race back to the other door (B): First, take a running jump into the doorway.

Hop down into the wet area and turn right. Jump over the pipe and continue straight on through the hallway with the portholes on the left (following the path marked with the DARK GREEN broken line on the map).

Take running jumps along the straightaway to go faster. Turn right at the corner.

Leap over another pipe.

Run straight on past the corridor with the burners, leap over the next pipe and turn right.

Follow the hallway to the end, taking running jumps to cover the ground faster.

As you turn right at the end of the corridor, take a running jump into the doorway (B).

Inside pull switch (3) again to turn off the first pair of burners.

All the burners should be off now, but they won't stay off for long. So quickly press Look and Roll.

Take a running jump into the doorway, hop down on the other side.

Turn left. . .

. . . and run like mad to the burners.

Be sure to jump over that last pipe just before turning into the burner hallway (YELLOW path on the map).

As soon as you've cleared all 4 burners, you can stop and breathe. Lara is safe here.

Pull the last switch (6) to open the exit. Whew!

[Part 2 | Return to the 40 Fathoms Walkthrough]