A carbon dioxide leak at Bokjeong Station on Seoul’s subway Line Eight affected five nearby workers on Friday morning.

According to city-run subway operator Seoul Metro, the accidental release from a discharge unit occurred at around 9:30 a.m., prompting authorities to order subway trains from both directions to pass without stopping at the station. Operations were normalized at 10:28 a.m.

The five workers, who were inspecting a nearby elevator, were sent to a hospital with two reportedly experiencing impaired consciousness.

A Seoul Metro official said there was no fire and an investigation into the cause of the leak is under way.