The accident happened in Dive4Life, an indoor dive center located in Siegburg, Germany. Initially an explosion was reported, but the suspicion is now that impurities or incorrect grease have caused the oxygen to ignite.
Dive4Life did an excellent job in handling the emergency. When the fire rescue services arrived, all guest were already evacuated from the building. The fire rescue services cleared all smoke from the building and tonight the dive center is open again.
German source