We have been Using Fox 40 products for 8 years at Footsteps of Discovery, this is the loudest of the three types of whistle that our instructors use at 120 decibels plus. When we need to get the attention of people this normally ourt go to piece of equipment.
The Fox 40 Sharx are a 2 chamber design with 4 resonators, they are pealess and they are very loud, it would be advisable not to use in a confined space. The Sharx are also S.O.L.A.S. (safety of life at sea) approved.