I recommend this study to you:http://www.hearingconservation.org/d...FligorIves.pdf
The authors measured the average listening volume of a variety of earphones and found that in louder environments, people listened to the ER6i at substantially lower volumes than they did with other types of earphones. For example, with 80dB of background noise, the test subjects listened to the ER6i at an average volume of 78dB, while they listened to Apple earbuds at 89dB.
Significantly, the listening levels were measured "in the subjects’ ear canal using a thin tube attached to a microphone, which fed the information out of the booth to a computer for recording." Thus, the results of this study confirms that IEMs produce less
pressure on the ears than certain other forms of earphones, because the listener tends to use them at lower volume.
(Note that the volume measure in the study is in "dBA." Though the study doesn't specifically say, "dBA" usually refers to A-weight dB SPL, where SPL means "sound pressure level." Thus, this study measured the actually sound pressure level produced by IEMs in the ear canal