What volume level is considered safe for listening with the Beats Studio headphones?

Comfortable hearing levels are under 60 dB, and hearing damage begins at 85 dB with 8 hours of exposure. You should turn down the volume on your music player before connecting the headphones, then gradually increase it to a comfortable level. The manual notes that a typical person can safely listen to an iPod for 4.6 hours per day at 70% volume. (Page 2)