Sound Transit says it had no choice but to order passengers off its trains in South Seattle for about nine hours Wednesday, because technicians needed hours to restart and test emergency ventilation fans inside the Beacon Hill tunnel.

Full service resumed at 6 a.m. Thursday. Though a rare kind of problem, the blockage follows months of frequent train stalls and other disruptions for repairs and construction.

“Folks worked all through the night and by this morning we were able to have the entire line open as usual, and we’re going to continue troubleshooting,” CEO Dow Constantine told a transit board committee Thursday morning.

The fans may have been disrupted by a Seattle City Light power outage, though details are still being investigated. Once workers found the problem in routine over

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