At 2:47 AM, the operator paged "Code Blue, Room 312, Third Floor." What the night-shift nurses on the second floor heard was "Code... oooo... Room... eeee... Thirrrr... ooor." Two nurses heard "Code Blue" and ran upstairs. One nurse heard "Code Green" (combative patient) and approached Room 312 with a completely different mental preparation. A fourth nurse heard "Code" and nothing else, and had to call the switchboard to ask which code it was.

Hospital overhead paging is a life-safety system operating in one of the worst acoustic environments imaginable: long corridors with hard floors, acoustic tile ceilings at varying heights, multiple T-intersections creating sound shadows, and a background noise floor from HVAC and medical equipment averaging 55 dBA. The PA speakers were 8-inch ceiling tiles installed at 10-meter intervals — too far apart for the corridor width.

STI measurement revealed 0.32 at the nurse's station and dropped to 0.24 at the far end of the corridor. Color-coded emergency announcements rely on distinguishing between "blue," "green," "red," and "orange" — words that share vowel sounds and differ only in consonants that require STI above 0.50 to be distinguishable.

Hospitals need the highest PA intelligibility of any building type because the consequence of mishearing is potentially fatal.

The Moral: Hospital PA is life safety. Measure STI at every nurse's station and corridor endpoint with SonaVyx STI — if it's below 0.50, people will hear codes wrong.