Excess noise is not a good thing. Background noise from HVAC systems or other laboratory activities can become insidious. It can make conversation difficult, affect concentration, distract workers, and increase fatigue not to mention the potential adverse effects on other support personnel that enter the area. How do we know if the noise is excessive? One rule of thumb is if normal conversation or talking on the telephone is difficult or impossible. A better way is to have the area assessed by someone knowledgeable about sound, its measurement techniques, and data interpretation, such as an industrial hygienist or acoustical engineer. The National Institutes of Health Office of Research Facilities recommends a maximum noise level of NC-45 in research laboratories, operating rooms, and similar areas for reasonable speech communication.¹ NC- 45 refers to a balanced noise criterion curve, which is a set of octave band sound pressure levels used to characterize the noise in a space. (More on NC curves in a minute.) It is important to keep in mind that the NIH recommendation is for “adequate speech intelligibility with normal voice effort,” i.e. normal worker conversation. The NC-45 equates to 53dB (A) and is chosen to account for the frequency distribution based on normal speech. It is considered the maximum design goal for occupied research areas.

From: Can You Hear Me Now? by Vince McLeod, CIH in The Safety Guys