A total of 23 people taken to hospital in St. Catharines following a hazardous workplace incident on Tuesday have been discharged.

According to Niagara Health, the incident occurred around 10:30 a.m. at the THK Rhythm Automotive Plant in the Louth Street and Ridley Road area.

St. Catharines Fire Chief Dave Upper told CTV News Toronto a contractor was working and accidentally hit a valve, which released five litres of hydrochloric acid.

Upper said the acid turned to vapour and three people were nearby. They managed to close the valve, but they were exposed to the fumes, he said.

Officials on the scene said about 20 other people were exposed, and decontamination showers were used. Most of them were taken to the hospital by bus.

Upper said the exposure to the acid was more minor, and the other 20 people were taken to the hospital as a precaution.

"The chemical typically provides burns to respiratory and skin if you are exposed heavily," he said. "We don't believe they had that heavy saturation."

EMS Operations Sgt. Bryce Brunarski confirmed paramedics brought nine people to the hospital with minor exposure, while another 10 asymptomatic individuals with limited exposure to the leak went to the hospital by bus.

At 1:30 p.m. on Tuesday, Niagara Health confirmed its St. Catharines Site’s Emergency Department has been brought back to its normal operations, and has started to wind down from the response to the hazardous materials incident.

The health agency confirmed all patients were assessed, and are all expected to be discharged at some point today.

 - With files from The Canadian Press