Lots of good information on the UK H&SE website which will explain action levels and ear protection.

Google: OSHA 1910.95 OCCUPATIONAL NOISE EXPOSURE for the U.S. noise regulations.

Google: OSH ANSWERS: NOISE - OCCUPATIONAL EXPOSURE LIMIT IN CANADA for an overview of the various Canadian noise regulations and regulatory sources.

RPM7:

Occupational noise exposure varies around the world. Google: NOISE EXPOSURE STANDARDS AROUND THE WORLD. This will give you a 10 page synopsis of noise exposure levels for various countries, provinces, etc.

If you are interested only for Ireland, contact your local Health and Safety Authority, Ireland for a copy of European Communities (Protection of Workers) (Exposure to Noise) Regulations, 1990.

The exposure levels within the cab are the same as exposures outside of the cab for operators as well as other noise exposed employees. Ireland has an 85 db maximum exposure over an eight hour time weighted average with a maximum peak exposure to continuous, varying, intermittent, or impulsive noise not to exceed 140 dBA These exposure levels are the most common around the world.

Using the above exposure levels, employees would be required to wear hearing protection when engaged in work that exposes them to noise that equals or exceeds 85 dBA as an 8-hr time weighted average or when the noise exposure equals or exceeds the designated 140 db peak level.

This is a quick answer to a complex subject. For additional information on noise exposure you can Google: NIOSH PUBLICATION NO. 98-126: CRITERIA FOR A RECOMMENDED STANDARD OCCUPATIONAL NOISE EXPOSURE. This is an occupational noise overview from the U.S. Center for Disease Control (CDC).

Your local HSE office should also have educational information available on occupational noise exposure.