ANSI Z9.5: Reduced Air Change Versus Process Hazards Considerations

Jonathan Eisenberg, Arup
Brooks Stout, Research Facilities Design

A major revision to the 2012 edition of ANSI Z9.5 included commentary that suggested that saving energy could be achieved by the reduction in the air change rate for fume hoods from the traditional 25 cfm per square foot of work surface to 150 hood air changes per hour. Although an obvious energy savings, this reduced minimum exhaust airflow can result in unintended consequences with respect to process hazards mitigation.

Our discussion, focusing on bench top hoods, will examine several hazards considerations and the need to perform a quantitative consequence analysis as the air change rate is reduced to current ANSI Z9.5-2012 acceptable levels. Even at bench scale quantities, certain NFPA Class 3 and 4 hazardous materials present challenges. Considerations for our discussion, in the context of the new air change reductions include:

  • Flammable liquid processing vs. 25% of the LEL and standard 25 cfm/sq.ft.
  • Polar vs. non-polar flammable solvents and static charge dissipation
  • Flammable gas use and consequence of a leak
  • Corrosive materials vs. life of the hood and materials of construction
  • Highly toxic liquids and gases vs. lab personnel exposure
  • How to perform a quantitative process hazards evaluation for specific chemicals vs. hood air change rates
  • Mitigation options will be presented, with a goal of getting as close as possible to the intent of the ANSI Z9.5-2012 changes. Real-world examples will be used to provide context for the issues and mitigations discussed.

    Learning Objectives

    • Understand the context of the ANSI Z9.5 fume hood air change rate revisions.
    • Learn why different chemistries and process conditions impact decisions on fume hood air change rates.
    • Hear about specific process hazards involving flammable liquids & gases, corrosive materials and highly toxic materials.
    • Find out about methodology used to perform quantitative analysis of fume hood process hazards


    Jonathan Eisenberg is an Associate Principal at Arup, where he leads the process hazards, risk & compliance offering. Jon has nearly 30 years of fire and chemical engineering experience, combined with a chemical processing background. He is a nationally known expert in industrial, chemical, and laboratory fire protection and hazard analysis. Jon holds a BS in Chemical Engineering from Lafayette College and a MS in Fire Protection Engineering from Worcester Polytechnic Institute.

    Brooks Stout has over 12 years of operational experience with project procurement, project design, and project management. At RFD he is responsible for the management and implementation of laboratory related engineering efforts, including design of specialized cleanroom facilities and associated HVAC systems, process gas piping systems, process exhaust systems, laboratory piping systems, laboratory equipment heat load calculations, and HVAC design for laboratory ventilation systems.


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