The Decree of August 1990 the 30th used for the application of Article R. 235-11 of the Labor Code and relating to the reverberation limitation of working premises is applicable to the construction or layout of working premises, where envisaged machinery and equipment may expose workers to a daily sound exposure level greater than 85 dB (A).

This document establishes the minimum characteristics that these rooms must have in order to reduce the reverberation of the noise on the walls when this must significantly increase the level of noise exposure of workers (the increase in exposure is appreciated in relation to what would be the exposure of each of the workers in the same premises ideally treated, that is to say without any reverberation).
The technical requirements of this decree are applicable where it is established that reverberation, as assessed by a predictive acoustic method, would result in an increase of the daily sound exposure level of a worker equal to or greater than 3 dB (A ).

The walls of such spaces shall be so acoustically treated that the decay of the sound level by doubling the distance to the source measured in the empty space without any production machine or installation reaches at least the value given by a rule related to the workroom floor area.
When the decrease in the noise level by doubling the distance at the source is measured in the room after installation of the production machinery and apparatus, the DL value which must be at least reached is given by another rule related to the workroom floor area.

DL is expressed in dB (A).