Updated at 2:31 p.m.

Firefighters briefly responded to smoke coming from Metro tracks just north of the Twinbrook station on Friday afternoon.

When they arrived, shortly after 1:30 p.m., Metro workers already had the situation under control, Montgomery County Fire Department spokesman Pete Piringer said. There was no fire, just smoke, Piringer said.

An “arcing insulator,” which caused large amounts of smoke but no fire, caused a major problem on Monday at the L’Enfant Plaza station, where more than 80 people became ill from breathing in smoke while trapped on a Yellow Line train and one passenger died.

Metro spokeswoman Morgan Dye said that the smoke at Twinbrook, an above-ground station, was not caused by arcing. Instead, she said it was caused by leaves hitting a heating element near the switches on the track.

Piringer said that firefighters left the scene in less than 10 minutes.

Trains were single-tracking from Grosvenor to Shady Grove, causing delays in both directions on the Red Line, for about an hour.

Earlier on Friday, Metro had also reported an arcing insulator causing smoke at the Ballston station on the Orange and Silver Line. But on Friday afternoon, Metro said there was no arcing at Ballston. Instead, the smoke was caused by debris coming in contact with the third rail.