I'm curious about the fire alarm cable that's being installed in a new building next to my office.
In the fairly distant past, I learned that fire alarm cable was "pryo" cable. Under the red jacket it was a copper tube containing two conductors, all mutually insulated by a white mineral powder. Apparently it would stay working unless a fire melted the copper, because there was nothing inside that could burn or decompose.
What they are using today appears to have layers of polymers. Under the red outer layer is a stiff white jacket. Inside is a bare (earth?) wire and two wires insulated with blue and brown polymer.
What are these polymer materials, and what happens to them in a fire? Was the "pyro" cable deemed overkill and used only for lack of alternatives to PVC in past decades?