In the context of workplace safety, 85 dB per NIOSH or 90 dB per OSHA is acceptable over an 8-hour work shift. I have never seen threshold levels as low as 80 dB cited before but perhaps that assumes 24-hr exposure duration.
Real time sound levels
This is a follow up to a previous post concerning hearing damage from excessive sound levels. I have discovered that by adjusting the spl of the music you’re listening to in real time you can keep it under 80 dB or even 75dB. Use your remote volume control. Your ears adjust to the lower level. If you limit the high decibels there is no reflex contraction of the stapedius muscle to dampen the stapedius bone to try to limit damage to the cochlea from excessive sound levels. I use NIOSH to measure spl. I enjoy the music as much and will for a longer time. I found that I was routinely listening to music at levels higher than 80 dB. Some damage has already been done but I’m trying to limit further damage.