Trivia: Ron Howard's father, Rance, makes a cameo as one of the Cardinals locked in conclave. (00:32:10)
Trivia: Considering Dan Brown's works anti-Catholic blasphemies, the Catholic church would not allow Tom Hanks and director Ron Howard to shoot film scenes in two historic cathedrals in Italy's capital city: Santa Mariadel Popolo and Santa Maria della Vittoria. They were allowed to film external shots only.
Trivia: Thure Lindhart, who plays Lieutenant Chartrand, was considered for the role of Silas the albino monk in The Da Vinci Code, but was later deemed too young and lost the role to Paul Bettany.
Trivia: Langdon says the Illuminati wanted revenge for La Purga. There was no such thing.
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 ★