Although noise is unrelated to the reproduction of bacteria within a controlled environment, an operating room that would otherwise function normally cannot be used properly if the noise is too loud. Noise sources can propagate through the air or through solid objects such as walls and panels, and can even travel a great distance via duct supports rigidly connected to powered equipment. Noise control design is by no means something that can be made foolproof simply by installing a few silencers. The permissible noise values specified in the Standard take into account China's national conditions and represent the maximum acceptable noise values; compared with permissible values abroad, they are slightly on the high side. If conditions permit, it is advisable to keep noise below the values specified in the Standard. The permissible noise value refers to the average of all measurement points. In Switzerland, the value is 50dB(A) for high-grade aseptic operating rooms and 45dB(A) for aseptic operating rooms, while the German standard is 45dB(A) for both.

Domestic practice has proven that 45dB(A) is achievable; therefore, the Code adopts ≤50dB(A) for most rooms, while taking 52dB(A) for Class I operating rooms. Different project situations should be treated differently.

Indoor noise refers to the average of all measurement points.