How to Escape the Gas Chamber in "Final Fantasy 7"by Dan Ketchum ; Updated September 22, 2017
In many ways, 1997's Final Fantasy VII (FFVII) was ahead of its time; in addition to its plentiful cinematics and sweeping orchestral score, FFVII featured diverse mini-games and Hollywood-inspired moments that broke free of the game's turn-based foundations, making Square's iconic RPG a truly memorable experience. Tifa's confinement in the gas chamber is among these moments, deftly switching the character perspective and changing the gameplay style to keep you on your toes. To escape, you'll have to execute a series of precise and specific button presses.
For PlayStation Gamers
Read the prompts that appear as gas seeps into the chamber. Tifa is bound to a chair with a key just out of reach, and the directions instruct you to move your feet, arms and head to escape. Using a PlayStation controller, the “Triangle” button moves Tifa's head, the “Square” button moves her right arm, the “O” button moves her left arm, and the “X” button moves her legs.
Press “X” twice to use Tifa's feet to grab the key and drag it closer to her. Press “Triangle” sit to back up in the chair, then press “X” and “Triangle” simultaneously to get the key into Tifa's mouth, allowing her to use it to unlock her arms.
Press “O” and “Triangle” at the same time to unlock Tifa's right arm. Press “O” one final time to free her left arm and escape the chair. Rush over to the gas panel and inspect it to turn off the gas, then try to open the door to activate a cutscene. After the cutscene, Tifa is free from the gas chamber and ready to move on.
For PC Gamers
Read through the text prompts that appear, instructing you to use the “Menu” or “+” button on the keyboard to move Tifa's head, “Switch” or “.” to move her right arm, “OK” or “Enter” to move her left arm, and “Cancel” or “0” to move her legs. Take note of the key on the floor, just out of reach of the chair that Tifa is trapped in.
Press “0" to use Tifa's legs to grab the key, then "0" again to drag the key back toward the chair. Press "+" to sit back up in the chair, then “0" and "+” at the same time to transfer the key to Tifa's mouth, where she can manipulate it to unlock her bounds.
Unlock Tifa's right arm by pressing “Enter" and "+” simultaneously, then press “Enter” to free her left arm. Run from the chair to the gas panel and inspect it to shut off the gas. Try to to open the door. This triggers a cutscene -- after the scene, Tifa is free from the chamber and you can continue your adventure.
After Tifa has the key in her mouth, you can press “Square” and “Triangle” at the same time to unlock her left instead of right arm. If you make this choice, press the “Square” button afterward to free her right arm. For the PC, these controls would be "." and "+" simultaneously, then "." again. 
Despite the gas, you don't have to worry about a ticking clock during this sequence: you have as much time as you need to free Tifa.
Think of the buttons on your controller or keyboard as corresponding to the different parts of Tifa's body -- the head, arms and legs match the button locations. Rather than pressing buttons in rapid succession, take your time. You won't have to start over if you make a mistake; you can correct your mistake simply by pressing the button or combo corresponding to the correct body part.