I don't understand what it means, but check nfpa 99:
5.1.9.1 General. All master, area, and local alarm systems used for medical gas and vacuum systems shall include the following:
(11)
Where used for communications, wiring from switches or sensors that is supervised or protected as required by 517.30(C)(3) of NFPA 70, National Electrical Code, for life safety and critical branches circuits in which protection is any of the following types: (a) Conduit
(b) Free air
(c) Wire
(d) Cable tray
(e) Raceways