Detailed information about Noise and Ultrasound can be found on the Health, Safety and Wellbeing website.
Essentially the manufacturer of any powered handtool or item of machinery must provide information on the typical noise (and vibration) levels that you may encounter when using the equipment. This information, together with the duration of time you are likely to be using the equipment, should indicate whether the risks are sufficient to require you to be wearing hearing protection.
As a general rule of thumb, if you have to raise your voice to have a normal conversation when about 2 m apart for some of the day, or you are using noisy powered tools or machinery for over half an hour a day, of if you have muffled hearing at the end of the day, even if it is better by morning, then you should be wearing hearing protection. For help in selecting the most appropriate hearing protection for the type of equipment that you are using, please contact the Health and Safety Helpdesk.
To understand more about how hearing and hearing protection, please take a look at the video which was produced by WorksafeBC as found on the HSE website: