Howell students had ringing in their ears after the Aug. 15 fire drill.

A one-time, sharp “impulse” noise can cause temporary threshold shift (TTS) in the ear, according to the National Institutes of Health. The threshold shift is the way the ear protects itself from more damage by reducing the sensitivity of the ear. Symptoms of TTS include muffled or distorted sound or ringing in the ears. These symptoms are signs that the ear has suffered trauma, but should disappear in 48-72 hours.