Duncan Fraser collapsed after coming into contact with the gas from a corroded refrigerator at Dundee's Craigie High School.
The 61-year-old was rushed to the city's Ninewells Hospital where he spent the night.
The gas is described as very toxic.
Mr Fraser says he has had long-term breathing problems and post traumatic stress due to the incident on September 28 2012. He said: "I can't walk so far and it's quite hard to get a breath."
Lawyers Digby Brown have raised an action at the Court of Session in Edinburgh.
A spokesman for Dundee City Council said: "It would not be appropriate for the council to comment on an ongoing legal matter."