How loud are orchestras?

In certain sections, musicians are exposed to an average 90 dBA and peak exposures of 130 dBC!

Answer Extra: 

In 2006, the Liz Brueck of the UK Health & Safety Laboratory performed a study on the noise exposures classical musicians experienced during both rehearsals and performances. While many people consider classical music a “quieter” music, to be enjoyed for its subtle nuances, live performances can be particularly stunning – and loud!

In measuring average and peak ambient noise levels, it was determined that the musicians were exposed to over 87 dBA – the EU Exposure Limit Value, or the maximum allowable noise level in the ear with all hearing protection in place! Strings averaged 90 dBA during a performance. The brass section averaged 95 dBA in the center, and 131 dBC in peak exposures. In the percussion section, musicians averaged exposures over 90 dBA, with upwards of 130 dBC.

The study recommended that the orchestra layout be rearranged to protect players from the loudest sounds – and that brass musicians wear hearing protection!

source: 
Brueck, Liz. “Orchestra pilot of the industry / HSE noise guidance.” UK Health & Safety Laboratory. http://www.hse.gov.uk/research/hsl_pdf/2006/hsl0696.pdf