All too frequently, and especially in new construction, we are running into rooms or laboratories that present problems with normal conversations. Typically, this results from ventilation systems.

Excess noise is not a good thing. It can make conversation difficult, affect concentration, distract workers, and increase fatigue not to mention the potential adverse affects on the research animals. How can you tell 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 Institute of Health Office of Research Facilities recommends a maximum noise level of NC-45 in operating rooms, research laboratories, and research animal housing areas for reasonable speech communication. 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. It is important to keep in mind that the NIH recommendation is for worker conversation.

NIH goes on to say that when evaluating noise in research animal housing areas you should consider both the people and the animals in these spaces. The National Research Council states that assessment of potential effects of noise on animals consider intensity, frequency, rapidity of onset, duration, vibration, hearing range, noise exposure history, and sound-effect susceptibility of the species, stock, or strain.

How do we evaluate room noise and what criteria should we be aiming below when designing facilities or making corrections? The American National Standards Institute (ANSI) has published a standard titled “Criteria for Evaluating Room Noise,” S12.2-1995 (R1999). This consensus standard provides excellent guidance for assessing noise in many different types of spaces. Basically, there are two sets of criteria. Room criterion (RC) curves are defined for the octave bands 16 Hz through 8000 Hz by a set of curves with a constant slope of –5 dB/octave. The second set, which has gained wider acceptance, are the balanced noise criterion (NC) curves defined by a set of sound pressure levels taken at octave band mid-band frequencies also for bands 16 Hz through 8000 Hz.

When evaluating noise using this standard you will need a sound level meter with an octave band filter in order to measure sound levels in decibels at each octave band frequency. These are then matched to the levels for the NC curve you are trying to meet. The standard also defines the speech interference level, rumble and hiss, and details how to evaluate for compliance with these based on the different criteria used. Until more research studies are available, aiming for the NC-45 criterion curve should be your goal.

From What Did You Say? by the Safety Guys