A loud sound emitted by a fire suppression system has destroyed the hard drives of a Swedish data center, downing Nasdaq operations across Northern Europe.

The incident took place in the early hours of Wednesday, April 18, and was caused by a gas-based fire suppression system that is typically deployed in data centers because of their ability to put out fires without destroying non-burnt equipment.

These systems work by releasing inert gas at high speeds, a mechanism usually accompanied by a loud whistle-like sound. With non-calibrated systems, this sound can get very loud, a big no-no in data centers, where loud sounds are known to affect performance, shut down, or even destroy hard drives.

Gas-based fire suppression system caused the incident

The latter scenario is what happened on Wednesday night, as the sound produced by the errant release of the inert gas destroyed hard drives for around a third of the Nasdaq servers located at the Digiplex data center.

There was no fire at the data center, and the gas' release seems to be caused by accident.

Because of the incident, Nasdaq Nordic could not start trading operations at 09:00, local time, when stock markets across Northern Europe were set to open. Affected markets included the ones in Sweden, Finland, Denmark, Iceland, and the three Baltic states.

Nasdaq Nordic fixed the issue by 14:00, local time, when it brought online a backup system to facilitate stock and securities trading in the area. Nasdaq officials told Finnish media the backup system will remain in use until Monday when they'll be able to replace affected equipment.

Not enough servers in Sweden to replace the damage

A Digiplex spokesperson told Bleeping Computer that Nasdaq only rents space in the data center, and uses its own equipment. Nasdaq said there weren't enough servers in the whole of Sweden to replace the destroyed ones, and had to import new machines.

"Airplanes are just coming down," Lauri Rosendahl, President of Nasdaq Nordiq, told Finnish newspaper Helsingin Sanomat.

Digiplex is one of the largest data centers in the area, with hundreds of servers housed in a 20,000 sqm (215,000 sqft) building in Väsby, near Stockholm, Sweden.

This is not the first time a loud noise caused by a fire alarm suppression system has shut down a data center. In September 2016, a similar incident shut down the data center of ING Bank Romania for ten hours.

Article updated to point out that Nasdaq rented data center space with Digiplex, but used its own equipment.