WASHINGTON — The image is unnerving: a school bus fully engulfed in smoke from a fire.

On Oct. 2, the Twitter feed of Montgomery County’s fire and rescue department featured a photo of the bus near the intersection of Georgia Avenue and Shorefield Road. There weren’t any passengers on board and no one was hurt.

On Wednesday morning, a bus on its way to Westland Middle School in Bethesda was disabled after a seal broke on the bus’ turbocharger. Some oil got into a hot exhaust stream and produced a lot of smoking oil,  said Todd Watkins, the system’s transportation director.

Students were taken from the bus. There weren’t any injuries.

School bus fires aren’t common, accounting for just 1 percent of all vehicle fires between 2006 and 2010, according to the National Fire Protection Association. Some 2,130 bus fires are reported each year without fatalities, the association said.

Under Maryland regulations, local school districts are required to practice school bus fire drills twice a year. The local districts have four inspections per bus each year. In Montgomery County Public Schools, buses are inspected every 30 days, Watkins said.

Designs have evolved to increase school bus safety. Fire retardant seats minimize the dangers of fire; they burn slower to allow more evacuation time, Watkins said.

In Prince George’s County, schools spokeswoman Sherrie Johnson said there’s been one incident involving a school bus this year. What a bus driver thought was a fire turned out to be an issue with the braking mechanism. There was heavy smoke, but no fire.

In Fairfax County, schools spokesman John Torre said all students take part in bus evacuation drills. The exercises are required during the first 30 instructional days of each semester, and during the first 10 days of summer school.

WTOP’s Kate Ryan contributed to this report.