A dozen students needed hospital treatment following the incident on Tuesday morning which occurred during a Year Nine exam being held at Minster College on the Isle of Sheppey.
The Health and Safety Executive have spent today examining the scene
A HSE spokesman said: 'HSE is investigating the incident
'We currently have inspectors on site including a specialist construction engineering inspector.
'We are working with Minster College and Kent County Council to ascertain the cause of the incident and see if there are any lessons to be learnt
'We can confirm that there was no asbestos present in the heating duct or the hall.'
The college's head teacher Alan Klee has insisted the sports hall was regularly checked and he was not aware of any problems regarding the ducting system.