07/12/2012 09:11 EDT | Updated 09/11/2012 05:12 EDT

Niagara Chlorine Leak Sends 12 To Hospital At St. Catharines Pool

ST. CATHARINES, Ont. - Twelve people between the ages of 7 and 50 were taken to hospital following a chlorine leak at a St. Catharines pool.

The worker delivering the chlorine, five teen lifeguards and six bathers suffered symptoms including shortness of breath, chest tightness, scratchy throat and wheezing.

By Thursday night, all but two patients had been released from hospital.

St. Catharines Fire imposed a "shelter in place" order covering some 60 homes in the area around the Lion Dunc Schooley pool.

People living in those spots were told to lock up after a toxic gas wafted out from a utility building next to the community pool.

The residents were told they could open their windows and doors and restart their air conditioners around 8 p.m.