Common undesirable phenomena at insulated schools
Vitiated air contains unhealthy carbon dioxide and also creates an environment where many infectious agents are spread easily
Formaldehyde and other toxic substances vaporise from the painted desks and furniture. In many places there are occurrences of the radioactive gas radon.
Those substances together with dust, odours, humidity, moulds and fungi does not get ventilated due to airtight insulation.