Re: My manager used halon...
"I'm puzzled, why would Halon, an inert gas, need to be sealed off from the rest of the building?"
The 'Halon' (nowadays it's never Halon in a new installation, it's something like FM200, which works under similar principles, so everyone just calls it Halon) needs to be delivered to the problem quickly enough and in high enough concentrations to be effective. If the server room is not relatively sealed off or if someone partitions the room and changes the airflow patterns after the suppression system is designed, you risk not getting high enough concentrations to suppress the fire.
You are very correct about the dangers of the burning byproducts. For what it's worth, according to the fire suppression contractor who did our FM-200 installation at $job[-4], the FM-200 also produces byproducts that aren't particularly healthy for you, but "they're a lot less toxic than the shit that would be burning otherwise". He told us that if we were in the room and the FM-200 dumped, we would survive just fine, but if stuff was on fire, getting away from the fire is a good idea.
Our system had an ultra-sensitive smoke detector, plus a conventional fire alarm wired to the building's system. The ultra-sensitive would warn of a smoke byproduct well before it would dump the agent (there was a network of sniffer tubes in the ceiling, multiple zones had to trigger at a high level to dump). The sniffer warned us of a failed power supply in a server it was so good (something in one supply let out the magic smoke). If the FM-200 failed to suppress the fire, we had conventional sprinklers as a backup (they may have been converted to pre-action, sprinklers, I don't recall).
"If there is something burning in a building, _everybody_ should get the fsck out of the building immediatly,"
^This. Call the fire department on your way out or from the parking lot. Fire grows exponentially, every second you delay in calling the fire department makes their job much harder and more dangerous. Also, if everyone is out of the building and *confirmed* to be out, that means the firefighters need to spend less time looking for victims in the fire building.