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Estimation of Fireball Dimensions from NFPA 68

Fire Protection Research Foundation report: “Estimation of Fireball Dimensions from NFPA 68”
Authors: Gregorio M. Mesa and Scott R. Rockwell. Ph.D.
Date of issue: April 2018


The current equation (from NFPA 68:2018 eq. 8.9.2) to estimate fireball dimension is only valid for KSt ≤ 300 bar m/s (KSt ≤ 200 bar m/s for (NFPA 68:2013)), Pmax ≤ 9 bar and Pstat ≤ 0.1 bar. There are many common dusts with properties outside of these ranges and extension of the fireball equation beyond these ranges in needed to allow end users to properly define safe zones around explosion vents. Further, it needs to be noted that EN 14491:2012 - Dust explosion venting protective systems provides a slightly different method for estimating fireball dimensions and has different limits.

This project is comprised of the following tasks:

  • Literature review to identify previous research and data available related to fireball dimension estimation.
  • Review the basis for the existing limits to understand reasoning for the current limits.
  • Identify methods (e.g. models) that can possibly extend the existing equations to a broader range of conditions (KSt, Pmax and Pstat).
  • Provide recommendations for extending current limits using models identified and create a future research plan in order to generate a guidance/criteria for further extending these limits.
  • Submit a final report based on findings from all the above tasks.

The Fire Protection Research Foundation expresses gratitude to the report author Gregorio M. Mesa under the guidance of Scott R. Rockwell, Ph. D., who are with UNC Charlotte located in 9201 University City Blvd, Charlotte, NC 28223, USA. The Research Foundation appreciates the guidance provided by the Project Technical Panelists, and all others that contributed to this research effort. Thanks are also expressed to the National Fire Protection Association (NFPA) for providing the project funding through the NFPA Annual Research Fund.

The content, opinions and conclusions contained in this report are solely those of the authors and do not necessarily represent the views of the Fire Protection Research Foundation, NFPA, Technical Panel or Sponsors. The Foundation makes no guaranty or warranty as to the accuracy or completeness of any information published herein.