Establishing Minimum Flow Rates for Laboratory Fume Hoods
Thomas Smith, Exposure Control Technologies, Inc.
A laboratory fume hood system protects people working in laboratories through containment, capture, and exhaust of potentially hazardous airborne contaminants generated within the enclosure. The exhaust flow required to provide capture and containment depends on the sash opening area and the resulting face velocity. A fume hood operating with the sash 100 percent open might require a higher average face velocity and more flow than a fume hood operating with a reduced sash opening area. A fume hood operating with the sash closed requires the lowest flow to maintain containment. A VAV system can reduce energy use by modulating flow in proportion to the sash opening area. The minimum energy use corresponds to the minimum flow when the sash is closed; however, the minimum flow required for a fume hood with the sash closed depends on the inflow velocities required to maintain containment and the volume required to minimize accumulation of unsafe concentrations within the hood. According to the 2004 NFPA 45 Standard on Fire Protection for Laboratories Using Chemicals, the required minimum flow for fume hoods is 25 cfm/square feet of work surface. Many people believe that this volume is unnecessarily high and leads to wasted energy. This presentation will explore the issues and provide recommendations to establish minimum flow rates that ensure safety while minimizing energy costs.
Biography:
Thomas C. Smith is the president of Exposure Control Technologies, Inc. Mr. Smith is a leader in laboratory safety and energy management. He specializes in helping laboratories provide safe, dependable, and energy-efficient operation of laboratory hoods and ventilation systems. He holds a Bachelor of Science degree in mechanical engineering from North Carolina State University and a Master of Science degree in environmental engineering from the University of North Carolina. Mr. Smith is active in developing national and international standards for laboratory ventilation and has served as chairman of ASHRAE TC9.10 Laboratory Systems and vice chairman of ANSI/ASHRAE 110 Fume Hood Testing. He is currently the vice chairman of ANSI/AIHA Z9 Standards for Ventilation and Health. Since 1985, Mr. Smith has participated in hundreds of laboratory ventilation projects and evaluated thousands of laboratory hood systems. His work has helped improve the safety of laboratory environments, reduced energy consumption, and saved millions of dollars in operating costs.