Safe listening time is the recommended time you can be exposed to sound at certain levels without causing permanent and irreversible damage to your hearing. Generally noise is considered excessive when you must use a raised voice or shout in order to be able to speak to someone at an arm's length. No matter your past listening habits or the condition of you current hearing it is important to note that a hearing impairment does not make you less susceptible to further damage caused by high noise; it is critical to protect the hearing you have. Listening at high levels will only make your hearing worse. 

Please note* As with all headphones the sensitivity rating 82+/- 3db relates to specification output, real-world output may differ slightly dependant on factors such as player power & music sample bit-rates but should remain at a safe level for players less than 30mw for up to 8 hours per day.