Water sprinklers and electronics are a poor combination, so data halls often use other methods. Very early smoke detection systems sample the air continuously and raise an alarm long before flames. Clean-agent gas systems flood the room with a gas that interrupts combustion without damaging equipment. Some use water mist at high pressure, which wets far less than a sprinkler.
Fire risk also shapes building design: fire-rated walls separate halls, battery rooms get their own treatment, and cables use low-smoke materials. The 2021 Strasbourg fire is a reminder that even well-run sites can be hit, and that separate-site backups are the final defence.
Detecting it early
An ordinary office smoke detector waits for smoke to drift to it. In a data hall, where air is being pushed around at speed and smoke is diluted, that can mean noticing a problem late. Aspirating detectors work the other way: a network of thin pipes with small holes draws air from the room, ceiling void and under-floor space back to a central unit that analyses it with a very sensitive sensor. They can pick up the faint trace of an overheating component or a cable insulation starting to cook, minutes or hours before there is any visible smoke.
These systems usually have several alarm levels. The first is an alert to staff, who can walk to the rack and look. A higher level might shut down air handling to stop smoke spreading, and the highest level, confirmed by two independent detectors, releases the extinguishing agent. Requiring two signals before discharge is a deliberate design choice, since an unnecessary discharge is itself a very expensive event.
Putting it out
| Method | How it works | Trade-off |
|---|---|---|
| Clean-agent gas | Fills the room to a concentration that stops the fire from sustaining itself | Needs a sealed room; cylinders must be refilled; the discharge is loud and sudden |
| Inert gas | Lowers the oxygen level enough to stop combustion, while remaining breathable for a short time | Needs many large cylinders and pressure-relief venting |
| High-pressure water mist | Very fine droplets cool the fire and displace oxygen | Some wetting, though far less than a sprinkler |
| Pre-action sprinklers | Pipes are normally dry and fill only after detection, then each head opens individually | Water can still reach equipment, but only after two events |
Older halls used halon, which worked well but damages the ozone layer and was phased out under international agreements. Current systems use alternatives, and the details of which agent is used vary by site and by regulation. Rooms with gas systems also need warning signs, delay timers and a way to abort, because people can be inside.
Where the fires actually start
In practice most data centre fires begin in the supporting equipment rather than the servers: batteries, power distribution, transformers, cable runs. Lithium-ion cells are more energy-dense than the older lead-acid blocks, and a cell in thermal runaway generates its own heat and can reignite after the flames are out, so a gas discharge alone may not settle it. That is why battery rooms are walled off, given their own detection, and increasingly monitored cell by cell. Fire-rated walls separate halls so that a problem in one stays there, and cables use low-smoke, halogen-free sheathing so that a small fire does not fill the building with corrosive fumes.
What it means for a customer
Fire design is a mixture of regulations and insurance requirements, so most professional facilities have a sound system in place. The things a customer cannot see are how well it is maintained and tested. What a customer can do is plan for the case where it all fails. A fire that is contained but triggers a discharge will still shut a hall down for a while, because the equipment has to be inspected and the room declared safe. A fire that is not contained, like the Strasbourg one, destroys machines and, with them, whatever was only stored on them.
Verifying it
Look for the facility's published fire safety statement or certifications, the type of suppression system, and a description of how halls are separated. Ask in a support ticket where your backups are held and whether it is in a separate building. For your own data, run a quick check that a backup exists away from the server and can be read:
ls -lh /backups/offsite/
tar -tzf /backups/offsite/site-latest.tar.gz | headIf the file listing stops at last year, the plan has already failed. The troubleshooting guide has more on checking what is actually stored where.
Common questions
Will the gas harm my servers?
The agent is chosen not to. The pressure wave and noise from a discharge can affect spinning disks, which is one reason sites have moved to solid state.
Are sprinklers banned from data centres?
No. Many sites use pre-action sprinklers, either because regulation requires water or as a backup to a gas system.