As several commentors have mentioned, in ear monitor (IEM) type headphones have pretty good sound isolation properties. It's important to note that active noise cancelling (ANC) headphones increase the total sound pressure on your ear drums, while IEMs decrease it, overall. With ANC headphones, you have the environmental sound pressure added to the cancellation signal (which cancels according to perception, not accor…
Do you have a reference for ANC headphones being more likely to cause hearing loss compared to regular headphones? I find it hard to believe (but would love to stand corrected).
So, upon further reading, I was less informed on that than I had thought. The best explanation I could find is here[1]. Basically, ANC does reduce sound pressure level when it lines up correctly. If you're listening to the sort of ambient noise that it does well with, it gets the phase offset close enough to right to significantly reduce the mechanical force applied to your ear drums. If, on the other hand, you're in an environment where it does a mediocre job, it will still be producing a cancellation waveform, but it won't actually cancel anything, and that will increase the mechanical force applied to your ear drums. So, in an office environment, you'd expect a reduction from the ambient noise of the HVAC system, but an increase from the random nature of your coworkers' conversations. It's hard to say whether you'd have a net reduction or not, but it's not certain, whereas passive noise isolation is certain.
[1] http://www.reddit.com/r/askscience/comments/1ios4u/does_prod...