Several employees at a bank in Bien Hoa City showed signs of fatigue, headache, dizziness and difficulty breathing on Wednesday, and they had been taken to the Hoan My ITO Dong Nai hospital by their coworkers.
Three patients showed signs of partial sensitivity loss, and received oxygen support, fluid transfusion, and had their health monitored.
They have since regained consciousness and their vital signs are stable.
The patients said the bank had a blackout in the morning, so they went to the basement to turn on the power generator. By noon, several employees showed signs of breathing difficulties, headache and fatigue.
Doctors said they might have been suffering from CO poisoning.
CO is a colorless, odorless gas, so it is hard to detect. Those with CO poisoning may experience symptoms like headache, nausea and vomiting, even death.