Reducing Laboratory Fume Hood Minimum Exhaust Rates: A Case Study of How University of California, Irvine Developed Criteria to Safely Reduce Exhaust Flow Rates in its Laboratory Fume Hoods
David Kang, LEED AP®, University of California, Irvine
Dale Hitchings, P.E., CIH, SAFELAB Corporation
Thomas C. Smith, Exposure Control Technologies, Inc.
The 2012 American National Standards Institute (ANSI)/American Industrial Hygiene Association (AIHA) Z9.5 "Laboratory Ventilation" standard, currently under draft review, recommends new minimum fume hood flow guidelines that are based on the internal volume of the fume hood and internal air changes per hour (ACH). Instead of specifying that a minimum flow of 25 cubic feet per minute per square foot (cfm/ft2) be maintained, the draft version of ANSI/AIHA Z9.5 now states that "laboratory fume hoods shall maintain a minimum exhaust volume to ensure that contaminants are properly diluted and exhausted from a hood," where a range of 375 ACH to 150 ACH is recommended. An internal air change rate of 375 ACH is roughly equivalent to 25 cfm/ft2 and 150 ACH corresponds to roughly 10 cfm/ft2. The ANSI Z9.5 standard requires users to consider the following when selecting an appropriate minimum air change rate and minimum fume hood flow:
- Control of ignition sources within hood
- Design of hood (materials, etc.)
- Maximum chemical generation rates in hood
- Potential for increased hood corrosion due to decreased flow
- Effect of reduction on exhaust stack discharge velocity
- Fume hood density
- Need to affect directional air flow
- Operating range of fume hood
Reducing the minimum flow from 375 ACH to 150 ACH could reduce annualized flow by approximately 45 percent in the closed sash position. For a six-foot VAV fume hood, the annualized flow reduction would result in a cost reduction of approximately $570 per fume hood, with the sash closed at least 75 percent of the time and a cost of ventilation of $5 per cfm/year. Therefore, reducing the minimum flow through fume hoods where appropriate can yield significant reductions in energy and operating costs for a laboratory.
As part of its strategic energy and Smart Labs programs, University of California (UC), Irvine investigated the feasibility of reducing the minimum fume hood flow below 25 cfm/ft2. This discussion will present a case study of UC Irvine's attempt at determining a safe minimum exhaust flow through its VAV fume hoods based on the hazard of the materials used.
Biography:
Dale Hitchings is president of SAFELAB Corporation of Indianapolis, Indiana, a consulting firm specializing in laboratory planning, safety and design consulting, laboratory fume hood testing and commissioning, industrial ventilation, and indoor air quality consulting. He received his Bachelor of Science in mechanical engineering from Northwestern University. He is a licensed Professional Engineer and a Certified Industrial Hygienist. He served as the first chairman of ASHRAE TC 9.10 Laboratory Systems Technical Committee, was the principal author of the Laboratory Ventilation section of "Prudent Practices in the Laboratory—Handling and Disposal of Chemicals" published by the National Research Council, and is presently a member of the ANSI/AIHA Z9.5 Laboratory Ventilation Standard committee and the ASHRAE-110 Standard Committee. He has published many technical journal and newsletter articles and is a frequent seminar and conference speaker on the subject of laboratory commissioning, planning, safety, and design.
Thomas C. Smith is the president of Exposure Control Technologies, Inc. Mr. Smith is a leader in safety and energy management for research facilities. 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 (industrial hygiene) from the University of North Carolina. Mr. Smith is active in developing national and international standards for laboratory ventilation and serves as chair of the ANSI/AIHA Z9 Standards for Ventilation and Health, vice chair of ANSI/ASHRAE 110 Fume Hood Testing and past Chair of ASHRAE TC9.10 Laboratory Systems. Since 1985, Mr. Smith has participated in hundreds of laboratory ventilation projects and evaluated thousands of laboratory hood systems. His work has improved the safety of laboratory environments, reduced energy consumption, and saved millions of dollars in operating costs for facilities throughout North America.