Locks on Doors

it sure is...

You never heard of safe or panic rooms? Of course, they're legal. You ask the most random questions (given the zero necessary context behind their raison d'etre).

Yes, don't most bathrooms have locks? And if several people are sharing, likely they can install bedroom door locks.

Exactly this.

Region Philbis-

I found the answer:

There is a Fire Department of New York regulation that applies to residential interior doors having “entry” type locks, i.e. lockable with a removable key.

This regulation does not apply to “privacy” (bathroom lock that allows it to be locked from one side and usually has a feature to defeat it from the other). The purpose of this regulation is to avoid a locked, supposedly unescapable space within the confines of a residence blocking a possible escape route in case of emergency.