(CNN) -- Investigators in Colorado are trying to figure out why some people did not receive automated warning calls ahead of a wildfire that has claimed two lives.
The Jefferson County Sheriff's Office said that 12% of people in the danger area did not get calls from a reverse-911 system to warn them about the blaze.
"If they never got (the call), it's a software glitch. It's a problem with the system," sheriff's spokesman Mark Techmeyer said.
The fire Friday morning remained 45% contained, though firefighters hoped helpful weather conditions would result in big advances.
Strong winds that were expected Friday will not come until Saturday, giving firefighters a day of relative calm to work in.
"That could really work in our favor," Techmeyer said. "It also puts on the heat today to really make some progress and see if we can button this thing up before that wind event happens tomorrow."
Five helicopters and more than 600 firefighters were working on containing the wildfire, he said.
The efforts come as an urban search-and-rescue team continues to look for Ann Appel, a woman missing since the blaze swept through her home this week, authorities said.
The team of 32 people and six dogs has covered more than 200 acres during the search, according to the sheriff's office, but has not found any evidence of her whereabouts.
Authorities plan to search another 80 acres Friday.
Firefighters held their ground Thursday, keeping the flames of the Lower North Fork fire at 4,140 acres.
While the situation has improved enough that some families are returning to their homes southwest of Denver, 180 residences remain evacuated, authorities said.
For one family, this week's evacuation was like a scene straight out of hell. With their car shrouded by billowing smoke, the Gulicks hurtled toward safety as a cell phone captured their flight.
"Daddy?" says a small, tearful voice, tinged with panic.
"We're going to make it," Doug Gulick tells his child. "We're going to be fine."
"Where's Mom?" the child says, then, urgently, "Why is she stopping?"
Kaleb Gulick, 13, shot the video in the car with his father as his family, in two cars, fled a deadly Colorado wildfire that crept too close to their home this week.
Doug Gulick told CNN on Thursday that as the family loaded the cars, "the last thing I saw was this large flame shot up, and we realized we had to go right then."
"We turned that corner and went from daylight into pure darkness," he said.
Gulick's wife, Kim Olson, was in the vehicle in front of her husband. She explained Thursday that she put the brakes on -- prompting her child's panic -- because she was fumbling for the headlights in the darkness, and because she hesitated, wondering if the family was going to make it out or whether she and Gulick should turn around.
But then, she said, their neighbor went "flying" past them, and she decided to keep going.
"There it is, right there," Doug Gulick tells the children on the video as they pass flames.
"Oh, my gosh!" a child exclaims, and Gulick soothes them as the sky brightens, "We're out. We're out."
Kaleb Gulick said his father handed him the phone, and "I just did my best to capture the whole experience."
Jefferson County Coroner John Graham identified the two victims as a married couple, Samuel Lucas, 77, and Linda Lucas, 76. "They were found very close together," said Jacki Kelley, a public information officer with the Jefferson County Sheriff's Office. "One was found outside; one was found inside."
Officials were trying to determine why the couple did not leave the fire zone by Monday night.
The Colorado Forest Service has apologized for the wildfire after it was revealed that it was caused by a "controlled" burn that got out of control.
The revelation pushed Gov. John Hickenlooper to suspend such burns. A team is being formed to investigate how the March 22 controlled burn re-erupted Monday as a wildfire.
He suspended the use of prescribed burns by state agencies on state lands. The suspension will be effective until the review of protocols and procedures of prescribed burning is complete.
CNN's Rich Porter and Ashley Hayes contributed to this report.