The fire that broke out at a Punggol construction site on Tuesday appeared to have been caused by burning rubber.
The rubber was meant to line water retention tanks that were to be installed in the Global Indian International School site, the school said yesterday.
How the rubber caught fire is still under investigation.
Two workers were taken to the hospital for smoke inhalation after they were trapped in a gondola during the blaze, which was extinguished at about 5.30pm.
They have been discharged with two days of medical leave, the school said.
It added that the fire was confined to a 30m by 50m area on level one of a building that is under construction.