The fluid started pooling on the subway tracks overnight on Monday, causing the subway service to be shut down south of Bloor for the entirety of Tuesday morning. Byford said the TTC believed the fluid to be combustible or otherwise dangerous.
After testing, Toronto fire said it believes it to be ground water with higher components of hydrocarbon. The groundwater likely came from a thaw as the weather is warming up, he said. It flooded the tracks just north of College station.
However, what the fluid actually was is still a mystery.
The transit ordeal began when an "odd smell" was reported early in the evening on Monday.
But the smell seemed to come and go, so there was not much cause for concern, said Byford. But around 11 p.m. on Monday, a train operator noticed the fluid, and reported it smelled like gasoline, kerosene or other fuel.
By 6 a.m., Byford said the TTC had to halt the service for safety. He said any other transit service would've done the same.
The leak exposed the TTC's main artery — Line 1, which brings passengers downtown under Yonge Street — as precarious.
"That is a vulnerability of ours," said Byford.
The closure highlighted a need for a downtown relief line, which Byford admitted during his interview on CBC's Metro Morning he wants to see planned and completed.
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