Noise Levels of Emergency Generators

I need help on information required to permit a building containing an Emergency Genertor. I need to submit the noise level at some distance say 100 feet from a steel building that has a 60kW 480VAC diesel generator with a silencer type muffler inside the building exhausting to outside the building.

Anybody point me to some specifications or literature from suppliers. I am just looking for typicals to submit with the building permit.