Abstract: Nitrogen oxides are common irritative gases including NO₂, NO, and N₂O, etc. NO₂ is the main component of gases generated by metal pickling. The patient had worked in pool without any protection for about 3 hours. The NO₂ concentration was beyond the national allowable concentration 41 hours after the accident occurred. The exposure to NO₂ was confirmed. The patient presented pulmonary edema and was diagnosed as acute severe nitrogen oxides poisoning according to the Diagnostic Criteria of Occupational Acute Nitrogen Oxides Poisoning (GBZ 15-2002).