It took more than 90 firefighters almost nine hours on Wednesday to gain control of a fire that rated among the worst that has hit the city’s historic core in years, devastating four businesses and raising questions about why the blaze was allowed to grow unabated before authorities were even alerted.

Officials said late Wednesday they had arrested a 25-year-old homeless man named Darren Denley for starting the fire in an alcove in order to keep warm.

Ultimately, firefighters won the struggle to prevent a full-blown structural collapse and kept the fire from spreading beyond two neighboring structures. Officials reported only one injury — to a firefighter whose hand was burned.

But New Orleans Fire Department Superintendent Timothy McConnell said the fire, which began inside the building at 1016-1022 Canal St., just down the street from the historic Roosevelt Hotel, had been going for 90 minutes before anyone called for help.

McConnell told reporters that neither the building nor its neighboring structures had alarms or fire-suppression systems. “Having an alarm system that would have reported this in its incipient phase would have made a huge difference for these buildings,” he said.

Those systems are generally required only for large occupied commercial and residential structures, like hotels.

Instead of an electronic alarm, the chief said, “We got a call from somebody who saw it from the street.”

“Unfortunately, it went and burned for over an hour and a half before we got on the scene, before we got the call,” McConnell said. “To me, if you’re a business owner and you’re not putting an alarm in that’s going to report the fire and get it to us early, you’re putting your livelihood at risk. I would encourage everybody to have it.”

Officials said the cleanup and ongoing investigation will likely keep the block closed down during Mardi Gras, meaning altering some parade routes.

The first call came in at 3:22 a.m., and fire crews were there three minutes later, McConnell said. By then, he said, “the fire was well ahead of them.” Firewalls helped isolate the blaze to one building, but the situation inside the structure kept worsening.

A fourth alarm was called around 3:39 a.m. as firefighters realized there was a high likelihood the building could collapse. As the blaze spread to more businesses around 4 a.m., fifth and six alarms were called. The fire was now attacking neighboring 1012 Canal St. as well. Scattered bursts of flames could still be seen shooting above the building’s roof at about 7 a.m.

Finally, just before noon, the NOFD declared the fire under control. McConnell said crews would remain at the scene throughout Wednesday night and Thursday morning.

It took 91 firefighters in all to tame the blaze.

The last six-alarm fire to hit the city was in 2012, when an entire city block in Central City went up in flames, displacing families and damaging a neighborhood church.

Inside the two buildings on Wednesday, McConnell said, four businesses — Sweet Sticky Stuff, Cellphone Masters, Diva’s Beauty Supply and a women’s clothing store — were a total loss. The top three floors of both buildings were fortunately unoccupied, he said.

“We could have had a much, much worse situation,” McConnell said.

Although the facades were largely intact, the blown-out windows allowed onlookers along Canal Street a clear view of scorched interiors and the sky beyond.

Staring across the street as firefighters pumped a steady stream of water onto the buildings, 54-year-old Elton Wilson recalled the time he spent peddling African-American jewelry and incense from a stand across the street. He rattled off the stores, like Odyssey Records, that used to occupy the building.

“I’m just hoping it don’t collapse,” said Wilson. “If it collapses, they’re going to have an empty lot.”

Though several interior walls had collapsed, the building’s exterior remained intact Wednesday evening. McConnell said engineers were still assessing their structural integrity.

“The initial information that we’ve received is that the façade is stable. There is severe damage toward the backs of the buildings,” Jared Munster, director of the city’s Department of Safety and Permits, said.

Fallout from the fire was mostly limited to the upriver side of a single block of Canal Street. A nearby convenience store closed for cleaning, and the employees of an Athlete’s Foot store next door to one of the compromised buildings swept water that had seeped through the ceiling off the floor.

While the fire still burned, wind sent most of the smoke upriver, forcing pedestrians to cover their faces with scarves or coat collars. The smell permeated the lobby of the Roosevelt, which remained open throughout the fire.

One man at the hotel for business fretted about lead paint or other dangerous chemicals the fire might have pushed into the air from the old Canal Street buildings. McConnell said the air was being monitored and that officials had so far seen nothing alarming.