At least eight pupils and a teacher are receiving medical treatment after being affected by fumes coming from a drain that had to be unblocked at Muizenberg High School on Thursday morning, the Western Cape education department said."A company was called into the school to unblock some drains in one of the toilet facilities," said provincial education spokesperson Bronagh Hammond."The chemical they used to unblock the drains reportedly created a reaction, with learners reporting difficulty breathing as a result of the fumes."She said the school evacuated the pupils and they were escorted to the school field."The school immediately called for medical assistance and the fire department are at the scene."Cape Town Fire and Rescue Services spokesperson Jermaine Carelse said a vapour cloud formed when liquid chlorine was thrown into a blocked drain, and it spread through the corridors of the school."Approximately 23 persons (students and teachers) were affected and treated for respiratory distress."Carelse said the information he had was that 10 people had been taken to hospital for further treatment. Hammond said some parents had collected their children and the school was arranging to contact parents while the remaining children were supervised."We await more information as to the cause and the condition of the learners affected," she said.