If Darcy DaCosta had had a normal work morning, or if her husband Chris hadn’t stopped in unexpectedly, things might have been much worse.

But a combination of good luck and a fast response by Warren firefighters and police saved the DaCostas’ 10 Long Lane home from what could have been a catastrophic fire Wednesday morning.

The DaCostas just moved into their new home a few weeks ago and on Wednesday morning Ms. DaCosta, who usually leaves for work at 8 a.m., was packing for a work trip to New York City. Just before 9 a.m. she started to smell smoke but couldn’t see where it was coming from. As she looked around her husband Chris, a member of Warren Fire Department’s Engine 5, stopped home for a minute and immediately noticed the smoke too. They kept looking as the smoke thickened, and called 911.

“It was pretty scary,” Darcy said. “We couldn’t figure out where it was coming from.”

Police arrived first and ran in with fire extinguishers. Within a minute, fire crews arrived too and started running lines.

Crews were able to pinpoint the fire to a crawl space under the family room. They cut holes in the floor and a wall to access it, and were able to get the fire under control in short order.

Though they don’t know for sure how it happened, Ms. DaCosta suspects that loose mortar in the fireplace chimney wall allowed a stray ember to find its way to the enclosed crawl space under the family room’s floor. With very little air down there, the fire likely smoldered for days before it got enough air to fully ignite.

“The last time we had a fire was Sunday, so it must have been smoldering for days,” she said.

The family room subfloor shows evidence of a long, slow burn, Ms. DaCosta said, and that entire area of the home will need to be rebuilt. As for Warren’s emergency responders, Ms. DaCosta said she is beyond impressed.

“They couldn’t have been more professional,” she said. “To actually see them in action, I was very impressed with how professional and methodical they were.”

She was especially heartened by volunteer firefighter Jason Sousa, who was given the task of crawling under the crawl space to make sure the fire was actually out.

For now the DaCostas — Darcy, Chris, their two children and two dogs — are staying at the Residence Inn in Taunton. They have pre-existing plans to vacation in Florida next week, so they’ll be out of the house for at least two weeks, which she said should be enough time for the fire, smoke and water damage to be repaired.

“We’re very lucky,” she said. “Had we not been home, the fire would have taken a while to show itself outside. It could have been a lot worse.”