[Relation of the temporary threshold shift to the permanent threshold shift due to impulse noise, especially in the...

Observations on long serving soldiers who are frequently exposed to impulse noise trauma show that, in spite of ear protection, continued strain may gradually lead from a TTS to a PTS. On the other hand it is obvious that, despite increasing TTS and increasing duration of recovery, recovery is still possible even after several months. The experience that hearing damage caused by a single acoustic trauma tends to improve during the ensuing period or to remain constant, obviously applies also to hearing damage developing gradually due to multiple insults caused by impulse noises (blast noises). Due to today's compulsory wearing of ear protectors, the percentage of endangered persons has fallen to about 5%. But even these subjects have a chance to recover after several months, if the subject's exposure ceases. This is of importance with regard to a survey particularly in the evaluation of occupational disability.