Revealing mistake: Following the drowning cardinal scene, Richter is shown loading a pistol with a magazine and chambering a round. You can immediately hear the hammer striking the firing pin on the pistol, revealing the gun was empty. As well as Commander Richter's pitiful trigger discipline. (01:40:30)
Revealing mistake: When Langdon and Victoria walk towards the Pantheon, the first two angles show them walking alone with some stunt-women behind. But in the third angle, a couple of seconds later, a huge line of people appears, lining perfectly in the back, watching the camera. Obviously a group of real tourists standing behind a security line watching the shooting.
Revealing mistake: When Langdon first has an audience with the Camerlengo, you can quite easily see foundation on the Camerlengo's collar. This skin coloured compact is the base of any film makeup and often rubs off onto white collars if not checked.
Revealing mistake: When the reporters say that the second black smoke is showing, an aerial panning shot of the Vatican is shown, yet the smoke remains fix as if it were a painting.
Chosen answer: In reality, they would have perished from CO2 poisoning long before the room ran out of breathable oxygen causing them to simply suffocate. Without knowing the exact dimensions of the room it is impossible to give any time more specific than "several hours" for this to happen in a room as big as that one appeared to be.
Phixius ★
I just re-watched the movie, and as Langdon and Vittoria enter the room, it's mentioned to them that the oxygen levels are always kept at a bare minimum to protect the ancient tomes and documents stored there. That helps to answer my own question about why Langdon and the cop were so quickly affected when the power was shut off.
raywest ★