Microsoft has apologized to users of its Azure cloud in Europe who could not access some services for seven hours late last month.

The reason for the snafu? An errant fire alarm. Or, as the Microsoft Azure status report put it: “During a routine periodic fire suppression system maintenance, an unexpected release of inert fire suppression agent occurred.”

At that point, the data center’s air handling units shut down automatically, as they are supposed to, while the conditions were assessed. Some Microsoft Azure cloud services were difficult or impossible to access between 1:27 p.m. and 8:15 p.m. local time on September 29, 2017, according to the status report which tech news site The Register picked up.

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While this glitch may spook would-be cloud customers, all data centers—whether they are dedicated to a single company or shared by several—are subject to such mixups. Public cloud leaders Microsoft msft , Amazon, and Google googl would say that they are better able to keep data centers running smoothly than most companies that focus on their core business.

And, as more businesses weigh whether to move data and/or application software to shared public cloud data centers, their IT staffs need as much detail as possible about what goes on inside those facilities. Reports like this one are even more important for existing cloud customers, as Geekwire pointed out.

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Ironically, Microsoft msft two weeks ago unveiled plans to add availability zones, or backup cloud data centers, to its Azure regional facilities. Availability zones, as Amazon amzn Web Services has long noted, boast their own cooling, power, and presumably fire suppression systems so customer workloads can “fail over” fast to the second facility in the case of fire or flooding at the first.

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The Microsoft post noted that customers in Northern Europe customers were affected. The Microsoft Azure data center location page lists Northern Europe as being served from Ireland.

In Europe, the company also operates Azure regions from data centers in London, Cardiff (Wales), Frankfurt, Magdeburg (Germany), with two more to come in Paris and Marseille. Fortune contacted Microsoft to confirm which data center was affected in this case and will update this story as needed.