Firefighters worked Monday to control a 925-acre wildfire that destroyed at least two homes in the northern Colorado foothills as authorities said the blaze and another one that burned at least 166 homes were sparked by household fires.

Crews were hopeful they could stop the newest fire near Loveland from damaging more houses. They attacked it quickly with aircraft and hundreds of firefighters brought in to fight the week-old wildfire near Boulder.

Containment lines have been built around 20 to 25 percent of the second fire, which broke out Sunday near Loveland.

"We're making progress. It's slow progress," said Merlin Green, division chief for Loveland Fire and Rescue.

The larger fire — which scorched at least 10 square miles and has cost $8.3 million to fight — was fully contained Monday night, according to a post on the website of the Boulder Office of Emergency Management. It was most likely sparked Sept. 6 by a fire started days earlier in a pit on a lifelong area resident's property, Sheriff's Cmdr. Rich Brough said Monday.

The resident doused the fire with water and stirred the ashes to put it out but gusty winds brought the embers to life and blew them out of the pit, Brough said. The Denver Post reported earlier that authorities were looking at that possibility.

Denver's KUSA-TV reported Monday that the Four Mile Fire Department chief said the resident is a longtime volunteer firefighter with the department. Brett Haberstick, a spokesman for area fire departments, confirmed that the man investigators have been talking to is a volunteer firefighter but declined to give his name.

Brough wouldn't comment on the report, saying the department has not yet released the person's name.

Officials hope most people displaced by the blaze will be able to return to their homes by Wednesday, he said.

Meanwhile, Green said a resident burning a brush pile started the fire near Loveland. It quickly spread in the tinder dry conditions even though winds were much calmer than a week ago.

Larimer County sheriff's Maj. Justin Smith said the person who acknowledged starting the fire is cooperating with authorities.

Investigators looking at what caused each fire say they don't know if criminal charges will be filed.

On Monday, the federal team managing operations at the fire near Boulder took over operations at the fire near Loveland, which was less active than the day before but still grew. No more structures burned during the day.

Crews used four air tankers and three helicopters to battle the blaze.

A firefighter who fainted was being treated and was awake and alert, Green said.

Authorities declined to predict when the fire would be fully contained but said they didn't expect any more evacuations.

"We're hopeful of getting some people back in their homes tomorrow (Tuesday)," Smith said.

Residents within a four-mile radius of the Loveland fire — an area with an estimated 200 structures — were told to evacuate Sunday. City spokesman Andy Hiller said evacuation notification calls went to more than 1,700 phone numbers.

It was unclear how many people were out of their homes. Officials said 74 people had registered with the Red Cross at shelter in Loveland.

Helicopters assigned to the Boulder fire were brought in to drop bucket loads of water Sunday. Air tankers also dropped fire retardant to slow the spread of the blaze, allowing fire crews to get in and build containment line.

The fire was burning in steep, rugged hills covered with scrub brush and some cottonwood and pine trees.

Ron and Carol Christensen confirmed that the fire destroyed their home on Turkey Walk Trail, according to the Loveland Reporter-Herald. The Larimer Humane Society was able to rescue the couple's sheltie.

Numerous cars and vehicles also were destroyed, and an unknown number of horses, sheep and other livestock had to be left behind.

Claudine Busleta and her daughter, Julia Garcia, live in an area on standby for evacuations, but they didn't wait for things to get worse. They evacuated Sunday with four children and grandchildren as soon as they smelled smoke and saw the haze.

"There's only one way down the hill. When we see smoke, we don't wait for a 911 call," Busleta said Monday.

About 300 firefighters — including elite hot shot crews — were expected to be working on the fire by the end of the day.