The fire broke out on the top floor of the building at 229 Keap St. in Williamsburg.
Heavy smoke from the fourth-floor kitchen fire left a man in critical condition.
"The victim felt his life was threatened and jumped as units got on scene," said FDNY Deputy Assistant Chief Joe Duggan.
From above, a gaping charred hole could be seen where the fire started, but down below, the NYPD Bomb Squad arrived on the scene as the investigation expanded further down Keap Street.
Emergency Service Unit pulled in as the bomb squad suited up to see if there were two possible pipe bombs inside.
Fire marshals and counterterrorism officers also arrived on the scene.
"I was in the bomb squad when I was in my early years," said neighbor David Azran. "I know what it is diffusing bombs and seeing those pipes and they are dangerous and we definitely have to make sure that it's not dangerous."
The extra precaution was taken by authorities in the mostly Hasidic Jewish neighborhood in Brooklyn, with a Jewish school just yards away.
"Not good. I hope it's not an antisemitic attack. I hope not. It's been too many attacks," said neighbor Yossi Prero.
The investigation happened just days after a deadly terrorist attack in Australia - a mass shooting that left 15 people dead during Hanukkah.
"They don't do no harm to nobody. They just walk by. They don't do no harm to nobody," said neighbor Yecenia Johnson.
Several hours later, investigators determined the objects in question were clear exercise weights filled with sand that only resembled pipe bombs.
The scene was no longer deemed as suspicious.
"New York is a very diverse place. I pray that it doesn't happen here but you know what, in this world we live in, you never know," said paraprofessional Tatiana Heredia.
The man who jumped from the fourth-floor window was rushed to the burn unit at Bellevue Hospital, where he remains in critical condition.
There's no word yet on what started that fire.
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