He said the school has only implemented the measure on an "experimental basis" after hearing of its use elsewhere. The school official said he had heard of the technique being used in Mumbai.
He also insisted it had been done with the students' consent - in fact they had brought in their own boxes.
"There was no compulsion of any kind. You can see in the photograph that some students were not wearing it," he said. "Some who wore it removed it after 15 minutes, some after 20 minutes and we ourselves asked them to remove it after one hour."