To explore the effect of the five acid mists(hydrofluric acid,chromic acid and hydrochloric acid,sulfuric acid,nitric
acid(three acids)on nosal mucosa below maximun allowable concentration(MAC)in the workplace and the dose effect relationship,a case control study was conducted in 18 factories of Shanghai.Total 766
workers were enrolled as exposed group,while 174 healthy office staffs as control.All the subjects were given physical and lung
function examination with the same standards.The result showed that 30 16%(231 in 766)of exposed workers had nosal damage such as mucosal erosion(225),ulcer(3)and septal perforation(3);29 51%(185 in 627)workers developed respiratory damages such as decreased lung functions(18)and small airway obstruction(167),both damage incidences were significantly higher than that of control group(P<0 05～0 01).The mixed exposure to chromic acid and “three acids” showde synergistic action on nosal mucosal damage(P<0 001)which was positively correlated with the working periods(r s=0 892).About 1/5 and 1/3 workers developed small airway obstruction under the exposure level at 1/6 MAC of chromium trioxide and less than MAC of hydrochoric acid respectively.The conclusion seems that the damages on nosal mucosa and lung function may be a objective clinical manifestation to low concentrations of acid mists,and the current MAC seems not so safe.