Reduction of ambient pressure, as in a diver's ascent from depth, causes intrapulmonary gas to expand inaccordance with Boyle's law. This expansion presents the possibility of alveolar rupture of the lungs which cancause subsequent interstitial and mediastinal emphysema, pneumopericardium, and subcutaneous emphysema on theneck, or pneumothorax through the pleural rupture. Continued normal breathing during ascent usually permits theexpanding gas to escape unnoticed, but emergency ascents under holding of breath many result this kind ofaccidents. This type of illness differs from decompression sickness (bends, caisson disease) that results theformation of gas bubbles in the blood or tissues leading into intravascular air embolism and infarction. Thisoccurs only when the divers are decompressing with excessively dissolved insert gas under the pressureenvironment, and not becomes in shallow diving. The author had experienced one case of hyperinflation accident in26 years old male diver recently, and accordin to this case, discussed the diving accidents including definitionclassification, mechanism and treatment.