Eleven people were treated for minor injuries after an acid fog was released into the air in the city’s west end.

It happened at Nitta Gelatin, a small industrial building on Paton Road, near Bloor Street and Lansdowne Avenue, around 10:10 a.m. on Thursday.

Hydrochloric acid was mixed with sulphuric acid inside the building, causing an irritating fog. The building was evacuated and the fog was felt on Wade Avenue.

Toronto Fire acting platoon chief Rob Pennington said a supply company was offloading some acid into a vessel, when a worker accidentally attached a hose to the wrong pipe. As a result, a small amount of hydrochloric acid was mixed with a large amount of sulphuric acid.

The reaction was contained inside the vessel and plant. A vapour cloud formed. By the time firefighters arrived, the reaction was over.

Pennington said 11 people were treated by paramedics for irritated eyes and throat, but that no one had direct exposure to the acid.

Paramedics said nine people were de-contaminated at the scene. They are being transported to hospital to be evaluated.

Residents in the area were being asked to remain indoors and close their doors and windows. However, just before noon, Toronto Fire tweeted it was “safe to go outside and resume normal activities.”

Wade Ave update 3 – it is safe to go outside & resume normal activities – acid reaction is over. pic.twitter.com/BYFbmp76Z1 — Toronto Fire Service (@Toronto_Fire) November 3, 2016

Police say the incident was first reported when a resident walked outside, witnessed a cloud of smoke and began coughing.

Update: Our Sergeant OS with the @Toronto_Fire chief have advised that the situation is contained to the building. ^adc 1/2 — Toronto Police OPS (@TPSOperations) November 3, 2016

No safety concerns/risk for the public. Road closures will remain in effect for now to allow team to work on the issue. ^adc 2/2 — Toronto Police OPS (@TPSOperations) November 3, 2016

With files from The Canadian Press