During the chapter ‘Depths’ you’ll find the rebreather, you need to take it with you.
You will need to pass the SECOND stay calm QTE when Olson comes after you with the sledgehammer.
You can fail the first QTE and still keep the rebreather with you, but you won't get to explore the room where Danny is stabbed by Olson.
After the second stay calm QTE (must pass) you can either choose to run (much easier in my opinion) or stay. If you choose to stay you must pass a third stay calm QTE or you will run away without the rebreather!
If you choose to run, you need to complete a one button QTE (Y button) before entering the room with Junior or you will drop the rebreather.
In the room with Junior, select the dialogue options:
Finally when Junior puts the gun to his head, choose ‘Grab Pistol’
You will use the rebreather to calm Junior down and save him from shooting himself.