In the USA, at what minimum dB threshold is hearing protection required? Maybe I should also ask at what min dB level might hearing protection be recommended? Last, how do you know if ear plugs vs. a headset is required? (obviously, by the reduction in dB desired, but…) Is there some max dB protection from earplugs and this is where a headset would start to give protection?
Thanks to all for their input,
The US noise regs are not all that clear, and the OSHA website is not all that good either.
In general, it is reckoned that around 85dBm can damage your hearing, however it isn’t quite that simple, as the type of noise, and the amount of exposure also play a part.
Take a look at this link,
http://www.cdc.gov/niosh/topics/noise/abouthlp/noisemeter_flash/soundMeter_flash.html
This CCOHS: Hearing Protectors
Gives you some idea of the sources of noise and how much each produces, there is a small bar chart that shows how much noise you can handle within a set period of time, 85dB for 8 hours, through to 112dB for one minute.
The type of noise makes a differance, a hard percussive noise, such as a gunshot lasts only a fraction of a second, however being exposed to just a few incidences of this level of sound like at a firing range will cause temporary hearing loss very quickly, any more would lead to some permanent damage.
Noise happens at certain frequencies, jet noise is not the same as diesel engine noise, and you need to select hearing protection suited to the type of exposure, you can damage one part of your hearing spectrum and not the rest, which leads to the classic ‘machine plant’ hearing damage, where the subject finds that they can’t hear converstaion well but are ok with higher frequency sounds. Not all salesmen promoting hearing protection products realise this and when you look around the net, you will not find vast amounts of information - you just get figures of overall noise reduction instead of figures of frequency ranges.
This is a much better website for advice, its couched in less technical terms and is far clearer in the levels of exposure.
In the UK employers must take certain actions at certain noise levels and lenghts of exposure, so at 80dB we have to do a risk assessment and find ways to reduce noise, 85dB is around 3 to 4 times louder, and here the provision of hearing protection is mandatory.
You will need to identify exactly what is your noise source, before you can select the right equipment, as not all hearing protection is designed for all situations.
In general you are looking to select noise reduction capacity on the basis of the NRR figures, but user preferance is important or it simply will not be worn if it is uncomfortable to them.
A rule of thumb we learned was if you have to shout to be understood by someone 1 meter away, you should be wearing hearing protection.
Thanks all for the “sound” advice! 
And, I’ll be looking into the links provided above…