I'm trying to prevent hearing loss having a mild hearing loss. At what decibel below is the safe level? And at what decibel above do we need to use earplugs? Also do we develop hyperacusis from overuse?
I am not a doctor; I am not qualified to answer medical questions.
What I can do is share my own opinions as they apply to myself (i.e. the guidelines that I live by). What others choose to do with that information is then up to themselves.
Personally, I use ear plugs whenever I leave my house (even for a short 5-minute walk). You never know when a loud noise might hit you - and the problem is that, without ear plug protection, by the time you register the noise, it might be too late (e.g. a fire-cracker). Personally, I have had that happen twice over the past six months - once with a military grade fire-cracker going off about 10 meters from me (I could feel the pressure wave in the air - that's how bad it was...). The other problem is that daily noise is relatively loud and not really good for our ears (i.e. our ears were never really designed for a modern noisy lifestyle).
The links you provided also reflect a similar line-of-thought:
Many otologists feel that the OSHA guidelines do not provide enough protection.
I tend to agree with that assessment. I also tend to think that ears which have already suffered auditory damage may be more susceptible to further damage (and hence it could possibly be argued that the standard guidelines do not apply to people with hearing loss and that this group people should take further precautions).
About hyperacusis and ear plugs, I tend to think that the risk is overestimated and possibly not even accurate. To me, the advice of refraining from wearing ear plugs because it could lead to hyperacusis is like the laissez-faire advice we used to be told in relation to the common cold: wear warm clothing otherwise you could catch a cold! Turns out, of course, that catching a cold has nothing to do with cold weather exposure, as such, it has to do with catching a virus - which - for the most part is best avoided by regular hand washing. Where there are human beings, there also are logical fallacies, and that would unfortunately include the medical community (from time-to-time). Would I wear ear plugs at home? No, there is no need (at least not for myself). But as soon as I leave my home, I put in my ear plugs, and I do not take them out before I return.