Fahy was killed on Tuesday morning when a marijuana grow house exploded in a Kingsbridge home at 304 W. 234th St., according to officials and sources.
Firefighters had been on the scene checking on a reported gas leak when they discovered what looked like a hydroponic marijuana growing lab, sources said.
Firefighters, Con Ed workers and police officers evacuated the building and shut off its main gas line, sources said.
Fahy was in the street supervising the operation when the building exploded roughly one hour later, causing large parts of the roof to slam him in the head and body.
A bunting ceremony was held for Fahy on Wednesday morning at the 19th Battalion, where about 150 firefighters joined together for a moment of silence and a salute to Fahy, according to the New York Post.
Officials have taken Julio Salcedo, 34, into custody as a suspect, as he is believed to be the tenant who rented the apartment that was turned into a marijuana lab, sources said.
Fahy had been part of the FDNY for 17 years, and his father was a battalion chief as well.
FDNY Commissioner Daniel Nigro remembered him as a rising star in the department and said they had "lost a hero."
UFA President James Slevin expressed his "deepest condolences" to Fahy's family in a statement.
"He was widely respected by all who knew him and a friend who will be greatly missed," Slevin said. "This tragedy is yet another sad reminder of the enormous risks firefighters of all ranks face each and every day as they protect the citizens of New York."