A broken standpipe blamed for hindering the battle against a fire that killed two firefighters in the former Deutsche Bank building was declared operational yesterday, fire officials said.

The declaration came more than three weeks after the fire; both the city’s fire department and buildings department signed off on the repairs. Fire officials said a full hydrostatic test of the pipe was conducted — meaning water was run through the pipe at pressures sufficient to reach the upper floors of the 26-story building.

During the seven-alarm blaze at the building on August 18, fire marshals found that the standpipe had been dismantled. They later discovered that hydrostatic testing of the pipe, required every five years, had not been conducted in a decade.

Contractors working in the building, along with its owner, the Lower Manhattan Development Corporation, are currently being investigated in a criminal probe into the fire.

The building is being dismantled after it was damaged and contaminated by toxic debris when the twin towers collapsed in the attacks of September 11, 2001.

Pieces of the pipe have been sent to an FBI laboratory to determine if it was purposely dismantled or blew apart under pressure when water pressure was turned on while a valve was shut. The results of that analysis have yet to be released.

After the fire last month, the fire department required the LMDC to make other changes to improve fire safety inside the structure. During the fire, which started on the 17th floor and spread downward, firefighters encountered a maze of debris and blocked stairwells. The firefighters who died, Robert Beddia and Joseph Graffagnino, could not escape.

Fire officials said yesterday that all flammable debris had been removed. The owners have also cleared the stairwells and enclosed them, a fire official said, so that if a fire breaks out on the stairs, it will not move between floors.