Hearing damage risk halves allowed exposure time for every roughly 10 dB increase

Evidence

Another high level border, very important in everyday life, is given in Fig. 2.1 as a thin dotted line - the limit of damage risk. This limit reaches quite high sound pressure levels at very low frequencies, but decreases towards levels near 90 dB in the range between 1 and 5 kHz. … This limit is valid for sounds lasting eight hours per working day and five working days per week. For shorter exposure, the sound intensity can be increased in the same way that the duration is decreased. This means that our ear may be exposed in its most sensitive frequency range to sounds with 100 dB only for about 50 minutes and to 110 dB for only about 5 minutes per day! Such exposure can easily be produced, for example by loud music played through earphones, therefore, using earphones to listen to music which produces high levels must be undertaken with care. Overexposure of our hearing system to sound initially produces temporary threshold shifts. After too many exposures this temporary threshold shift leads to a permanent shift, i.e. to a hearing loss. In this case, threshold in quiet is no longer normal but is shifted towards higher sound pressure levels and will never recover. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 160

Categorization

• ADDENDUM: Connects to the sacrifice/the listener-protection themes only loosely; stronger link to any future piece on everyday environmental risk thresholds. Actually the loud-music-via-earphones point is a strong everyday-life hook for a health piece.
• CANDY: The 110 dB for only 5 minutes per day from earphones is a striking shareable number.