Factory workers were reportedly given gas masks and ordered to stay in work when their building filled with car exhaust fumes.
Many of them had complained of watery eyes, coughing fits and headaches for three days before the Chinese company issued the free masks.
The trouble began when builders installed an air conditioning system which sucked supposedly fresh air in from an underground car park below – but it turned out to be car exhaust fumes instead.
Instead of closing the Nanchong factory in Sichuan province, southwest China, down, managers ignored the complaints before finally giving each employee a gas mask and ordering them to carry on working, according to reports.
The builders have reportedly refused to change anything, saying the company had told them to reinstall the system through the wall of the elevator shaft.
And they are insisting it was not their fault that the underground car park was on the other side of the wall.
Health experts said most of the pollution was from methanol and told staff as long as they keep wearing the masks, there is no need to close the factory while the problem is fixed.