Concord firefighters envisioned the call before it became reality, imagining what it would be like to have to put out a fire at the massive 1850 farmhouse – converted into apartments – at 4 Garvins Falls Road.

“I think somebody told me last night,” fire Chief Dan Andrus said, “this is the building you drive by and you go, ‘I hope I’m not on duty the night that comes in.’ ”

The chief added: “This building is 167 years old. It’s a lot of very old and dry timber.”

Just before midnight Sunday, the imagined call happened. Residents of the Farmhouse Apartments smelled smoke, and within five minutes, 19 Concord firefighters were on the scene.

Then, almost immediately, they rang a second alarm, beckoning crews from seven towns and bringing the total to 40 firefighters.

Investigators determined Monday that the fire was “caused by the improper disposal of smoking materials, which fell through cracks into the building’s basement where it ignited dry leaves and other combustibles.”

That meant that the flames crept through the gaps in the walls, “which gives fire a good avenue to move through a building, sometimes undetected,” Andrus said.

In the dark of night, when temperatures plunged as low as 10 degrees, firefighters tore into the walls to ensure the flames would have no escape. This environment – coupled with the hazard of the old building – necessitated backup from surrounding towns to relieve the responders who were exhausted from heavy physical labor, the chief said.

“It’s difficult to sustain hard work in temperature extremes,” Andrus said.

But relative to the size of the building, which stretches roughly 200 feet end to end, according to city assessing records, the fire was contained to a small portion.

Deputy Fire Chief Sean Toomey credited the aggressive response and the building’s sprinkler system with averting “a potentially catastrophic fire.”

“Sprinklers don’t cover all of the spaces in a building,” Toomey said. “In this case, it took a considerable amount of effort to stop the fire from spreading through the voids and save the building.”

No one was injured, the chief said, but the fire caused “heavy damage to two units” of the complex, which has white clapboards and a green roof and is located behind the Dunkin’ Donuts on Manchester Street.

The Red Cross said it was assisting 23 adults and four children as a result of the fire. It was the second house fire in a week in the city that prompted assistance from the Red Cross.

“They met at the Red Cross Regional Headquarters in Concord, N.H., to stay warm while they were assisted,” the nonprofit wrote in a statement. “Local firefighters were on site to assist as well.”

The building – assessed at $775,000 – has been owned by Farmhouse Apartments LLC since 2008, according to city assessing records.

A man who answered a phone associated with the company’s owner, Matthew LoGuidice, said he wouldn’t be available to speak about the incident.

“I’ve got nothing to tell you at this time,” said the man, who also said he was not LoGuidice.

The Red Cross didn’t immediately return a phone call seeking more information on the displaced residents.