Performance evaluation of mobile downflow booths for reducing airborne particles in the workplace

ABSTRACT

Compared to other common control measures, the downflow booth is a costly engineering control used to contain airborne dust or particles. The downflow booth provides unidirectional filtered airflow from the ceiling, entraining released particles away from the workers' breathing zone, and delivers contained airflow to a lower level exhaust for removing particulates by filtering media. In this study, we designed and built a mobile downflow booth that is capable of quick assembly and easy size change to provide greater flexibility and particle control for various manufacturing processes or tasks. An experimental study was conducted to thoroughly evaluate the control performance of downflow booths used for removing airborne particles generated by the transfer of powdered lactose between two containers. Statistical analysis compared particle reduction ratios obtained from various test conditions including booth size (short, regular, or extended), supply air velocity (0.41 and 0.51 m/s or 80 and 100 feet per minute, fpm), powder transfer location (near or far from the booth exhaust), and inclusion or exclusion of curtains at the booth entrance. Our study results show that only short-depth downflow booths failed to protect the worker performing powder transfer far from the booth exhausts. Statistical analysis shows that better control performance can be obtained with supply air velocity of 0.51 m/s (100 fpm) than with 0.41 m/s (80 fpm) and that use of curtains for downflow booths did not improve their control performance.

KEYWORDS:

• Downflow booth
• engineering controls
• exposure prevention
• particle reduction

Acknowledgments

The authors wish to thank William Heitbrink for his assistance with designing the mobile downflow booth; Eric Ferguson and Tim Macierowski for constructing and modifying the test downflow booth; and Kevin H. Dunn, Alberto Garcia, Duane Hammond, Chaolong Qi, Jerry Kratzer, and Dan Farwick for helping test the booth. The authors are also grateful to Arthur Miller and Pramod Kulkarni for their insightful comments and suggestions on the early version of the manuscript.

Disclaimer

The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health (NIOSH). Mention of any company or product does not constitute endorsement by NIOSH.

Funding

This research was funded by the National Institute for Occupational Safety and Health under Small NORA program project 939ZXEJ.