https://www.dna.fr/faits-divers-justice/2021/03/10/strasbour...
Edit:
Video at https://www.youtube.com/watch?v=a9jL_THG58U
Satellite view of the site on Google Maps https://goo.gl/maps/L2T6YNFCtiyDdiNv7
...then I read in some other comments here that they used wood in the interior construction.
It takes a good while to start burning, and even when significantly charred it still retains most of its strength.
The issue is you'll have lots of plastic (cabling) in a DC, and plastic will burn
it was an interesting proof of concept, but finding the right people to maintain the infra with both IT and Scuba skills was a narrow niche to nail down ;)
I used to work for a provider whose 2 main datacenters of 8k+ sq ft could pull all oxygen out of the building in 60 seconds.
In the case of a fire, it would dump a lot of argonite gas in and consume a large amount of the oxygen in the room, depriving the fire of fuel. It's also safe and leaves minimal clean-up work afterwards, doesn't harm electronics etc. unlike sprinklers and the like.
The amount of oxygen left is sufficient for human life, but not for fires, though my understanding is that it can be quite unpleasant when it happens. You won't want to hang around.
Flames are extinguished by this cooling effect (identical to water in that regard), but humans rely on catalytic processes that aren't affected by the cooling effect.
If you could keep the existing oxygen inside, while adding Novec 1230, humans could continue to breathe while the flames would still be extinguished, but this would require the building/room to be a pressure chamber that holds about half an atmosphere of extra pressure. I'm pretty sure just blowing in some extra oxygen with the Novec 1230 would be far cheaper to do safely and reliably.
I mean, in principle, if you gave re-breathers to the workers and have some airlocks, you could afford to keep that atmosphere permanently, but it'd have to be a bit warm (~30 C I'd guess). Don't worry, the air would be breathable, but long-term it'd probably be unhealthy to breathe in such high concentrations and humans breathing would slightly pollute the atmosphere (CO2 can't stay if it's supposed to remain breathable).
Just to be clear: in an effective argonite extinguishing system you'd have about a minute or two until you pass out and need to be dragged out, ideally get oxygen, get ventilated (no brain, no breathing) and potentially also be resuscitated (the heart stops shortly after your brain from a lack of oxygen, so if you're ventilated fast enough, it never stops and you wake up a few externally-forced breaths later). Having an oxygen bottle to supplement your breaths would fix that problem for as long as it's not empty.
At this point I feel like it would be cheaper just to not have workers go there. Fill the place completely full of nitrogen with an onsite nitrogen generator (and only 1atm pressure). Have 100% of regular maintenance and as much irregular maintenance as possible be done by robots. If something happens that requires strength/dexterity beyond the robots (e.g. a heavy object falling over), either have humans go in in some form of scuba gear, or if you can work around it just don't fix it.
For exit, basically just the reverse, with the pump pumping the air around the person to wherever the person came from.
The general issue with unbreathable atmospheres is that a failure in their SCBA gear easily kills them.
And re-breathers that are only there so you don't have to scrub the atmosphere in the room as often shouldn't be particularly expensive. You may even get away with just putting a CO2 scrubber on the exhaust path, and giving them slightly oxygen-enriched bottled air so you can keep e.g. a 50:50 oxygen:nitrogen ratio inside (so e.g. 20% O2, 20% N2, 60% Novec 1230). And it doesn't even need to be particularly effective, as you can breathe in quite a bit of the ambient air without being harmed, and the environment can tolerate some of your CO2. Like, as long as it scrubs half of your exhausted CO2 it won't even feel stuffy in there (you could handle the ambient air you'd have without re-breathers being used, as it'd be just 1.6% CO2, but you'd almost immediately get a headache).
They'd have an exhaust vent for pressure equalization, which would chill the air to condense and re-cycle the Novec 1230. For pressure equalization in the other direction, they'd probably just boil off some of that recycled Novec 1230.
So yeah, re-breather not needed, if you just get a mouth+nose mask to breathe bottled 50:50 oxygen:nitrogen mix. That 50% oxygen limit (actually 500 mBar) is due to long-term toxicity, btw. Prolonged exposure to higher levels causes lung scarring and myopia/retina detachment, so not really fun.