Seventeen people were taken to hospital on Saturday from the Kontiolahti ice hockey arena when a carbon monoxide leak was detected inside.
Several junior hockey games and ice skating lessons were being held in the arena that day. There were an estimated 200 people inside it during the day.
Some children in the hall are reported to have suffered from headaches and weakness.
Rescue crews at the scene found elevated concentrations of carbon monoxide and emptied the arena.
The ice resurfacing machine was revealed as the source of the leak.
Carbon monoxide is a colourless, odourless and tasteless gas resulting from an incomplete combustion process.
Carbon monoxide binds with red blood cells more efficiently than oxygen and causes a lack of oxygen in the body.
