The generally accepted standard to minimize hearing risk is based on an exposure to 85 dBA (noise level)for a maximum limit of eight hours per day, followed by at least ten hours of recovery time at 70 dBA or lower (at which the risk of harm to healthy ears is negligible). Then a "3-dB exchange rate" formula is applied, which means that for every 3 dB above 85 dBA, the maximum exposure time is cut in half.