High carbon monoxide levels in the apartment visited by the late Georgian Prime Minister Zurab Zhvania were caused because of the absence of a ventilation system, said Tbilgaz city gas company emergency service chief Nugzar Mkheidze. \"Technicians have checked the heating system in the apartment where Zurab Zhvania and Raul Yusupov died. They said the gas system and the stove were alright, but the apartment did not have a ventilation system. The stove was burning oxygen and emitting carbon monoxide,\" Mkheidze said. (Interfax)