NASA Clean Room Fan Noise, White Sands Test Facility, Las Cruces, NM
- Client: AlliedSignal Aerospace, Las Cruces, New Mexico
- Project Owner: NASA
Several portable clean rooms had been installed in labs within a high-bay building at NASA’s White Sands Test Facility to assist scientists with their research, but the ventilation fans required to maintain the clean room environment were causing the noise level in the labs to become uncomfortable. The client hired Wieland Acoustics to perform a preliminary investigation towards resolution of this problem.
Wieland Acoustics conducted 1/3-octave band noise measurements to isolate the various noise sources in the labs (HVAC system, computer fans and flow benches, etc.) and determine the contribution of each source to the overall noise level in the labs. Reverberation measurements were also conducted to quantify the effect of the room characteristics on the noise levels. The results of our analysis showed that the clean room ventilation fans had significantly increased the overall noise level in each lab; the bare block walls and corrugated metal ceiling created highly reverberant conditions, which further contributed to the overall noise level.
In order to develop a noise control program, a reasonable design noise goal was required. Three alternatives were considered: (1) OSHA criteria for noise dose, (2) the balanced noise criterion curve (NCB) rating, and (3) pre-clean room conditions (this third criterion was a result of conversations with laboratory staff who indicated that the overall noise level was acceptable prior to clean room installation). Wieland Acoustics’ analysis of the measured data indicated that the noise levels defined by the pre-clean room conditions were more stringent than either the OSHA or NCB guidelines. Therefore, they were used as the design goal for this project.
Wieland Acoustics’ recommendations in this preliminary investigation were limited to an assessment of alternative noise control measures; this was complicated by a number of significant constraints imposed by the nature of the lab facilities. Noise control measures would have to allow access to the fans for regular maintenance without destroying the clean-room environment.
After extensive analysis, it was concluded that the only way to achieve the design goal would be to rework the ventilation fan system to include duct silencers. This was determined to be impractical and cost prohibitive. Therefore, as an interim measure it was recommended that large quantities of sound- absorptive material, specially selected for use in a clean-room environment, be added to the lab rooms. While this would not achieve the design goals, it provided a cost-effective way of providing a noticeable noise reduction for the lab staff.