The escape of chlorine gas in a swimming pool in Bergheim near Cologne injured 21 children and three adults on Tuesday. All children would be taken to nearby children’s hospitals with minor to moderate injuries, the fire department said.

The three adults, all teachers, would also be treated in the hospital. The injuries are respiratory irritation, severe coughing and watery eyes, said a fire department spokesman.

During maintenance work, a small amount of chlorine gas escaped for reasons unknown. The teachers and the lifeguards noticed a pungent odor and immediately evacuated the children from the affected area and alerted the rescue workers. The fire brigade then drove to the scene with several units.