Enforcing use of hearing protection
So, you've provided a selection of lovely hearing protection, given them all a fascinating and insightful training session on noise and it's dangers and put nice signs up around the place warning everyone to use hearing protection. Is that enough?
And the answer you will be unsurprised to hear is nope, that's not enough, sorry. The employer has to do all the above but also has to have suitable supervision to make sure the hearing protection is being worn and is being worn correctly.
Employees 'opting out' of using hearing protection?
One issue which comes up every so often is an employee or group of employees saying 'OK, we don't like wearing hearing protection, so how about we sign something saying we accept the risk of any hearing loss and our employer isn't liable for it'?.
Unfortunately these have no legal standing at all and an employer cannot allow this. There are a few reasons why but the main one is that the employer has a general duty of care and this means they cannot knowingly allow anyone to be at risk when it is possible to do something about it. Employers cannot opt out of that responsibility and it can't be over-ridden by an employee saying they will accept the risk.
If an employer does allow an employee to sign something like that and then they do have noise induced hearing loss, the employer will lose any claim against them. And their insurer will be less than pleased with them.
(This is the same for all PPE by the way so also applies to safety glasses, foot protection, and so on.)