Over 85dbA average for an 8 hour day is the trigger point industry standard for workplace audio metric testing. A weighted scale reduces the time exposure allowed if higher levels are present. I you are, for example, exposed to jet air craft noise levels of 120dbA for 10 minutes you would be in trouble.
We have lecture rooms at work where the background noise level is 70dbA because of loud air conditioners, they are fitted with sound systems to allow lecturers to be heard. It's recognised that the spoken voice needs to be 15dbA above background level for the hearer to be able to process information, so the sound systems are set at just over 80dbA at 3m.
Euro4 standard is for equipment to produce less than 65dbA at approx 3 metres. You can talk to the person next to you and be heard without raising your voice at this level. 70dbA is still relatively quiet, but flaming annoying at 10pm at night!
