Montgomery County Executive Isiah Leggett ordered a group of Ride On buses out of service Wednesday hours after a bus caught fire, the seventh such vehicle in the fleet to do so in the past three years.

The Ride On bus was out of service on Ramsey Avenue between Bonifant and Wayne avenues, with only its driver aboard, when the fire occurred, county spokeswoman Esther Bowring said. The driver smelled smoke and exited before the bus caught fire, and no one was injured, she said.

Hours later, Leggett (D) issued an order suspending service for Ride On buses manufactured with components from Thor Industries’ Champion Bus and Navistar companies, officials said.

The county had been in the process of replacing these models in its fleet following bus fires that prompted a federal safety investigation and a union grievance by drivers.

“We are very fortunate that no one was injured in today’s fire and there were no passengers on the out-of-service bus,” Leggett said in a written statement. He said the county expected to replace the remaining Navistar Champion buses by the end of August.

Gino Renne, president of the Montgomery County government employees union, applauded Leggett’s move. Until Wednesday, Renne said, union members had been impatient with the county’s progress on removing the buses from the fleet. As soon as he heard that another bus had caught fire, Renne said, he called Leggett and urged the county executive to take more decisive action, and Leggett did.

Wednesday’s fire occurred weeks after a fire destroyed a Ride On bus of a different make on New Hampshire Avenue in Montgomery County on July 3. No passengers were aboard that bus, which was an Orion V, and there were no injuries.

Renne had faulted the previous administration for ignoring union concerns about the buses before the county bought them. Mechanics and other union members warned that the vehicles might not be heavy-duty enough to withstand the long pounding of the county’s commuter shuttle.

“They’re retrofitted trucks,” said Renne, who is head of the Municipal and County Government Employees Organization. “They’re a bus on a truck chassis.”

About 39 Navistar Champion models remained in the fleet, but county officials could not immediately say how many were still running routes, Bowring said.