Experimental: Safety Arm

Non-firefighter control subjects will receive MTH-treatment and normothermia-sham through the device alternated over 8 sessions. Subjective assessments and audiologic testing pre- and post-treatments will be compared between MTH-treatment and sham in each subject. n=24.

Experimental: Efficacy Arm 1 - Treatment

Firefighters will receive hypothermia treatment delivered with ReBound devices, applied post-work shift. Baseline hearing function will be measured prior to initiation of the treatment. Treatments and functional assessments will be repeated quarterly over one year. Temporary and permanent threshold changes in this chronically noise exposed group of firefighters receiving MTH-treatment will be compared with firefighters receiving sham-treatment and with controls receiving MTH-treatment. Subjects in this group will also be sent home with a device to use after noise exposure during the study period. They will complete weekly, remote surveys collecting data on their noise exposure and device use. n=24.

No_intervention: Efficacy Arm 2 - Non-Therapeutic

Firefighters will receive non-therapeutic treatment delivered with normothermic ReBound devices, applied post-work shift. Baseline hearing function will be measured prior to initiation of the treatment. Treatments and functional assessments will be repeated quarterly over one year. n=24.

Active_comparator: Efficacy Arm 3 - Control

Age- and sex-matched non-firefighter control group will receive MTH-treatment quarterly over the same duration. Baseline hearing function will be measured prior to initiation of the treatment. Treatments and functional assessments will be repeated quarterly over one year. Subjects in this group will also be sent home with a device to use after noise exposure during the study period. They will complete weekly, remote surveys collecting data on their noise exposure and device use. n=24.