What is the safe volume level I should use to protect my hearing?

Comfortable hearing levels are under 60 dB according to the manual (Page 3). Exposure to noise at or above 85 dB can cause gradual hearing loss, and a typical person can safely listen to an iPod for 4.6 hours per day at 70% volume. The louder the volume, the less time you can be exposed to it without risking hearing damage.