15.11.2026 23:42
Fifteen people fell ill after being exposed to excessive chlorine in a hotel swimming pool in Germany, and four people were taken to hospital. An investigation following the incident revealed that the technical fault that caused too much chlorine to be added to the pool could not be reported to management due to an outage in Microsoft Outlook. After what happened, it was decided to make changes to the hotel's security system.
Guests staying at the Ling Bao Hotel, part of the Phantasialand amusement park in Brühl in Germany's North Rhine-Westphalia state, fell ill after entering the swimming pool. After some guests had difficulty breathing, medical teams were called to the hotel. When the cause was investigated, a connection was found between the technical problem in the pool and an outage in Microsoft's email service.
CHLORINE LEVEL IN THE POOL REACHED DANGEROUS LEVELS
According to the German newspaper Bild, the automatic dosing system that maintains the chemical balance of the water in the hotel pool malfunctioned. As a result of the system adding too much chlorine, the amount of chemicals in the pool water rose. Meanwhile, guests using the pool developed complaints such as irritation of the respiratory tract and shortness of breath.
15 PEOPLE BECAME ILL
According to German public broadcaster WDR, it was initially determined that 13 people were affected, and the number later rose to 15. Four people were taken to hospital. It was reported that one of those hospitalized was moderately injured and three were slightly injured. The other 11 people were examined on site.
OUTLOOK OUTAGE PREVENTED WARNINGS
The technical investigation also determined why the malfunction in the chlorine dosing system was not reported to hotel management in time. Under normal conditions, automatic warning emails should have been sent when the chlorine level in the pool rose. However, due to an access problem in the Microsoft Outlook service at the same time, the warnings did not reach the managers. Thus, the notification system that could have enabled the dangerous chlorine level in the pool to be noticed early remained nonfunctional.
MICROSOFT EXPLAINED THE CAUSE OF THE OUTAGE
On November 13, when the incident occurred, access problems were experienced worldwide in Microsoft's Outlook, Teams and other Microsoft 365 services. The company announced that the outage was caused by a technical problem that emerged after an update previously made to increase network capacity. Microsoft also reported that there was no finding that the problem was caused by a cyberattack.
SAFETY MEASURES ARE CHANGING
After the poisonings, the hotel's swimming pool was temporarily closed. The pool water was completely changed and the chlorine level was brought back to safe limits. After the necessary checks were completed, the pool was reopened.
According to a November 15 report by German television RTL, Phantasialand management plans to reorganize the warning system to prevent a similar incident. Under the new measures, the aim is to change the practice based on sending critical safety notifications only by email.