Human lung injury caused by the inhalation of nitrogen dioxide($NO_2$) has been reported in occupational situations other than agriculture, including arc welding, production of nitric acid or explosives, and blasting operations. Nitrogen dioxide reacts with the water in the respiratory tract to form nitric acid. The nitrates and nitrites formed from dissociation of nitric acid cause extensive local and systemic tissue damage. We present two cases of acute lung injury due to accidental inhalation of $NO_2$ gas in occupational situtions with a review of the literature.