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Comment by NorwegianDude | Hacker News Reader

I can't see anything about a fire suppression system mentioned? Doesn't OVH have one, except for colocation datacenters?

A fire detection system using eg. lasers and Inergen(or Argonite) for putting the fire out is commonly used in datacenters. The gas fills the room and reduces the amount of oxygen in the room so most fires are put out within a minute.

The cool thing is that the gas is designed to be used in rooms with people, so that is can be triggered any time. It is however quite loud, and some setups have been known to be too loud, even destroying harddrives.

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At a datacentre I used to visit years ago, part of the site induction was learning that if the fire suppression alarm went off, you had a certain amount of time to get out of the room before the argon would deploy, so you should always have a path to the nearest exit in mind. The implication was that it wasn't safe to be in the room once it deployed, but I don't know for sure.

Inergen is used to lower oxygen to ~12.5 %, from normal 21 %. Most fires need more than 16 % oxygen.

Inergen consists of 52 % nitrogen, 40 % argon and 8 % carbon dioxide.

Carbon dioxide might sound strange, but it causes the heart to beat faster to compensate for the lowered amounts of oxygen.

The whole point of Inergen is to quickly put out fires where water/foam/powder isn't usable and the room might contain people.

It's cool stuff, and I was under the impression that basically all datacenters used it.

Presumably you would have trouble breathing as it displaced the oxygen in the room?

Yeah, that was always my understanding. GP saying "the gas is designed to be used in rooms with people, so that [it] can be triggered any time" made me second-guess that though.

Maybe there is a concentration of oxygen that is high enough for humans to survive, yet too low to sustain combustion?

The "gas" is more like a fog of capsules. FM-200 is a common one. Basically it has a Fire suppression agent inside crystals which are blasted into the room by compressed air. These crystals melt when they get over a certain temperature and therefore won't kill you; however, breathing that in isn't really pleasant.

Source: I've been in an FM-200 discharge

Does everyone carry an N95 or equivalent? I guess many of us have gotten good at donning them by now...

> Maybe there is a concentration of oxygen that is high enough for humans to survive, yet too low to sustain combustion?

Yes, supposedly (12% ish?). Can't say I'd be thrilled at the idea of testing it.

I heard that the pressure difference might rupture your ear drums.

A few years ago the company I work for installed suppressors on the Inergen system. It did trigger from time to time, which was tracked to the humidifiers. And yes -- it did destroy harddrives because of the pressure/sound waves before we installed the supressors. Haven't had any incidents after we fixed the humidifiers.

But Inergen (and other gas) is more or less useless if you allow it to escape too quickly. So the cooling system should be a fairly closed circut.

Edit: I'm also a Norwegian dude. :)

So how is it safe with people if there is no oxygen left to breathe? Reminds me of my first trip to a datacenter, where the guy who accompanied us said: "In the event of a fire this room is filled with nitrogen in 20 seconds. But don't worry: nitrogen is not toxic!" Well, I was a little worried :)

Newer systems like the ones mentioned above are designed to reduce the amount of oxygen in the room to around 12% (down from around 21%). That's low enough to extinguish fires, but allows people to safely evacuate and prevent people from suffocating if they're incapacitated.

> even destroying harddrives

So loud that it destroys hard drives... That's scary, are people's eardrums much more resistant?

A lot of DCs are loud enough that it’s quite pleasant to wear ear protection. Even better with headphones that play what you want to listen to.

Are fires common in data centres? Specialized fire suppression tech seems to indicate that they are.

They aren't super common, but halon and other gas systems are just the right tool for the job. It can get inside the server chassis and doesn't damage equipment like a chemical application would. We won't know what went wrong at OVH until a proper post mortem comes out. These systems work by suppressing the flame reaction, but if the actual source was not addressed, it could reignite after awhile.

Yes, mostly due to two reasons:

* overall high energy density (lots of current flowing everywhere)

* the batteries for backup power are dangerous, and can easily(ish) overheat when activated.

The decision to design and implement specialised tech comes from a combination of how likely the risk is and the magnitude of the potential loss. Fires are not that common in DCs, but the potential loss can be enormous (as OVH is currently finding out).

What's the point of a fire suppression system that destroys what it should protect?

When it destroys one room but prevents fire spreading to whole building.

In a data center the fire suppression is mostly there to protect the servers.

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