Fire managers are confident a fire burning in the foothills west of Boulder isn't going to spread any farther.

The fire is burning on a 10-square-mile area and about half of the perimeter now has fire lines built around it.

National incident team spokesman Terry Krasko said Saturday that the fire isn't spreading and that crews are focusing on putting out fires burning inside the perimeter.

The fire has burned at least 169 homes within that perimeter.

Nearly 1,000 firefighters from 20 states have been working on the fire but Krasko says eight engine crews will start leaving Saturday.

Sen. Mark Udall came to Boulder and visited with fire crews on Friday. He said in a news conference in the morning that he's impressed with how well the different management teams have been working together on the difficult fire. Gov. Bill Ritter also met with emergency crews and praised the work the firefighters have done.

So far there has not been an official announcement about the cause of the fire although initially some reports came in that the blaze was sparked by a car that hit a propane tank.

The blaze has cost $4 million to fight so far. Three firefighters suffered minor injuries such as a broken finger, but no one has been seriously hurt.

Insurers had no immediate estimate on damages. Carole Walker, executive director of the Rocky Mountain Insurance Information Association, said the blaze affected mostly primary residences, not vacation cabins, so the homes burned are more likely to be insured.