PROSPECT, Maine — A mechanical problem with one of the doors on the elevator at the Penobscot Narrows Observation Tower shut down the elevator Monday afternoon, leaving two visitors stranded in the car at the top of the 420-foot tower.

The two people were stuck in the elevator for an hour and 20 minutes before a technician arrived to open the doors. Tower attendants and personnel from Fort Knox were able to talk with the people the whole time. Both passengers and six other people who were stranded at the top of the observation tower walked down the auxiliary stairway to the emergency exit at the bridge level.

The incident occurred at about 2:30 p.m. Monday, according to Maine Department of Transportation spokesman Mark Latti.

“They were right at the top,” Latti said Tuesday. “The two people got in to go down. When the doors closed, the elevator wouldn’t run and the doors wouldn’t reopen.”

When the representative from Stanley arrived, they were able to open the doors and get the people out.

The Department of Transportation and the Department of Conservation, which collaborate on the tower operations, have an emergency plan and a crew from the Prospect Fire Department arrived to help the tower visitors from the exit onto the bridge deck. A van took all the tower visitors back to the park.

The firefighters set up cones to keep traffic moving on the bridge while the people were removed from the tower.

This was the second time in eight days that the elevator had stranded visitors. A crew from Stanley Elevator Co. kept the elevator shut down for almost 24 hours while they repaired the door mechanism and ensured that the elevator was safe. The elevator was back in service by 1 p.m. Tuesday and the observation tower was reopened to visitors.

“The elevator is designed to stop when one of the safety systems senses something not quite right,” said Latti. “The systems are redundant. No one was in any danger.”

On Sept. 21, the elevator also stopped with people in it. Although the elevator was at the ground level at the time, several people were stranded at the top of the tower and had to be guided down the stairs to the bridge deck.

When the observation tower opened in May 2007, there were a number of instances when service was disrupted when the computers shut down the elevator. At the time, technicians indicated that the new elevator cables were stretching as they were being used, which set off the sensors. They stressed then that it was not a mechanical problem with any of the elevator’s operational equipment.

The elevator has operated for the last half of 2007 and most of 2008 without problems, Latti said.

“When you think of the thousands of trips it makes, to have it stop only twice is a pretty phenomenal record,” he said.

He noted that at 420 feet, the elevator ride was a very long one with just two stops, one at the top and one at the bottom. A technician from Stanley visits the site once a month to check the system and calibrate the equipment.

“It only calibrates at those two stops,” he said. “Different things have triggered the safety mechanism. It’s only happened twice this year, and we’ve been able to fine tune it so it doesn’t happen so often.”