Mr Ferrari said using a methodology that showed the average indoor pollution levels over a six-hour period downplayed peaks when nitrogen dioxide, carbon monoxide, carbon dioxide and formaldehyde were concentrated in classrooms.

Tests at Blackheath Public School in the Blue Mountains were undertaken 18 months ago.

They showed gas levels in 30 per cent of classrooms exceeded international health guidelines.

Dangers of heaters in schools concealed, Ben Cubby, Sydney Morning Herald, 31 May 2010