I doubt it's Halon. That's some nasty stuff. Yes, you'll live, but it's a known carcinogen, and the oxidized material from after the dump is mildly corrosive.
I work in IT, and Halon was popular for years in datacenters, because it does a very good job of binding to oxygen. We had some flunky who was supposed to test fire-station pulls in our building walk into the data center, march up to the "pull in case of fire" handle (with a huge red sign saying "WARNING: HALON DUMP" over it), and pulled it anyway. 30 seconds later (When your entire datacenter goes off-line, you respond quickly), he was still standing there, hand on handle, looking terrified, standing in a 3 foot cloud bank with strobes going off.
Unless the room is totally air-tight, it's only going to temporarily remove the oxygen, even for the CO2 systems. The last I heard, nitrogen is popular-- it's inert, common, and is usually enough to squash out the oxygen that's feeding the fire-- and doesn't leave a nasty, slightly greasy residue on everything. It's not quite as good, as it has to displace the oxygen, rather than consume it, but it still works.