AN INVESTIGATION has been launched after children and staff from a Helston school became ill following swimming lessons at the town's sports centre.
It has emerged that drain cleaner, said to contain dangerously corrosive sulphuric acid, was being used at the time.
St Michael's School head teacher Shaun Perfect said it was "disappointed" such material was used while children were attending the pool on Friday.
Children complained of nausea while staff, including one teacher who is seven months pregnant, were sent to hospital.
Now health and safety officers from Cornwall Council and personnel from the Health Protection Agency (HPA) are looking into the incident. All the children and staff were back at school on Monday.
Mr Perfect said that 30 pupils aged 6 and 7 accompanied by staff and parent helpers attended their weekly swimming lessons.
"My understanding is that contractors carrying out maintenance of the drains used some strong drain cleaner which contained sulphuric acid."
He said some of the boys may have had brief exposure to some gas when the drains were being cleaned in the changing rooms.
"Some of them complained of nausea and they all came back to school." At least one was taken to his doctor, complaining of a tight chest and sore throat. He added: "In the afternoon we then sent a number of staff to Helston Community Hospital who were feeling unwell."
A midwife was also contacted and the pregnant teacher went to Royal Cornwall Hospital at Truro as a precaution.
Mr Perfect said: "The school will be contributing to a full investigation into this matter to ensure it is not repeated.
"The school is relieved that the children and staff affected have recovered over the weekend."
Sarah Harrison, consultant for the HPA, told parents in writing it was unlikely any harm had been done to their children. She also said the drain cleaner contained sulphuric acid.
The sports centre is run by Carrick Leisure Ltd, which said in a statement: "A small amount of chemical was used by the sub-contractor that resulted in the release of fumes within the male changing rooms for the swimming pool.
"The fumes affected the workmen who had to leave the building. Although no other people were in the actual changing room a school class were assembling in the adjoining corridor and some students reported being aware of the fumes.
"In response the centre staff vacated the areas and made arrangements for the school class to change in another area. Action was also taken to ventilate the changing rooms.
"Although the school group reported no other immediate effects of the fumes it is understood that some students and staff have sought medical attention after returning to school."