Lieutenant Richard A. Nappi, 47, of Engine Company 237 in Brooklyn, lived in Suffolk County and is survived by a wife and two children.
The fire broke out at about 1 p.m. in a two-story warehouse leased by American Medical Response, a private ambulance service, at 930 Flushing Avenue.
Nappi arrived with several additional companies and within minutes a hose line was established in the mezzanine area on the first floor. Shortly after, Nappi became overheated and collapsed.
He went unconscious in the ambulance and suffered cardiac arrest on the way to Woodhull Hospital, where he died, according to the fire commissioner's office.
The Flushing Avenue warehouse is used as a storage unit by the city's Office of Emergency Management, a Fire Department spokesman said. Officials said compressed cardboard boxes in the warehouse fed the fire until more than 100 firefighters got it under control at 4 p.m.
However, witnesses said no smoke or flames could be seen protruding from the deadly flames, which left more than six firemen in need of medical attention.
“I saw the helicopters, I'm like, where's the fire?” said Ray Torres, 47, who lives in Bushwick.
In response to the fatal fire, Brooklyn Borough President Marty Markowitz released a statement, saying Nappi joined the list of firemen who bravely gave their lives in the line of duty.
“It's a sobering reminder of the dangers our brave men and women face each day when they put on the uniform,” Markowitz said. “I join all New Yorkers in mourning this devastating loss and in sending our deepest condolences to Lt. Nappi's wife, two children, friends and colleagues.
“We also pray for a speedy recovery for his fellow firefighters injured in the fire,” he added.
Nappi's death was the first Fire Department fatality since 2009, when Paul Warhola suffered a stroke while helping to fight a fire in Williamsburg.