Firefighters are working to douse a brush fire that broke out Monday afternoon at Marine Corps Air Station Miramar, San Diego Fire-Rescue officials said. The fire has spread to about 10 acres by mid-afternoon, but officials said the progress had slowed and one of the two helicopters assigned to the scene had been release. No structures are threatened. The blaze was first reported around 2:20 p.m. in brush near Kearny Villa Road and Miramar Way, Fire-Rescue officials said. The fire was spreading slowly in medium fuel. The agency said as of 2:45 p.m., it appeared that fire crews had favorable wind, and no structures were threatened. Aside from the helicopters, several ground crews were working at the scene to contain the blaze, officials said. Within about a half-hour of the first report of the fire, the San Diego fire officials said the spread had been slowed. They also said one of the engines from a Miramar crew was out of service at the scene, but all its crew members were safe. According to the National Weather Service, the relative humidity in the area is 13 percent, and winds are blowing from the west about 16 mph. The weather service says a red flag fire-weather warning will be in effect from 4 p.m. Monday to 6 p.m. Wednesday in the eastern half of the county. Forecasters said early Monday that the most intense winds could occur on Wednesday, a day later than expected. Staff writer Gary Robbins contributed to this report.