Advertisement

Fire Technology

, Volume 44, Issue 3, pp 239–261 | Cite as

Analysis of Hold Time Models for Total Flooding Clean Extinguishing Agents

  • Todd M. HetrickEmail author
Article

Abstract

This study documents the experimental results of a research program designed to evaluate the validity of the widely published hold time prediction models found in NFPA 2001, Annex C and ISO 14520-1, Annex E. The models discussed in these standards obtain a measure of the equivalent leakage area, which, when coupled with ‘worst case’ assumptions, can be used to determine the minimum hold time. Three hold time prediction theories are adopted from these standards for validation; a wide descending interface model as implemented in ISO 14520-1 and two sharp descending interface models from the 2004 and 2008 publications of NFPA 2001. The experimental program is comprised of 15 tests conducted in a 103 m3 test enclosure. Three commercially available clean agents are selected to span a wide range of agent vapor densities including FK-5-1-12, HFC-125, and IG-541. A series of holes were drilled through enclosure boundaries at upper and lower elevations which were opened or closed as a means of regulating the amount of leakage area for any given test. Vertical profiles of agent concentration and ambient pressure are used to evaluate the agent concentration distribution, rates of agent draining, and the effective lower leakage fraction. A non-dimensional hold time is used to compare experimental results involving differing agent types and leakage areas. Results show that empirical values of the hold time are up to 50% longer than the theoretical hold time predictions when evaluated as the time to reduce the agent concentration to half its initial value. When evaluated as a 15% drop in concentration the model validity is significantly reduced. Under this condition, empirical hold time values are up to 50% shorter than the predictions of the sharp descending interface models and up to 100% longer than the wide descending interface model.

Keywords

hold time retention time total flooding clean agent validation study 

Nomenclature

A

Theoretical orifice area (m2)

AF

Enclosure floor area (m2)

Ai

Orifice area for gas flowing into enclosure (m2)

ALL

Summed orifice area of all lower leakages (m2)

Ao

Orifice area for gas flowing out of enclosure (m2)

AT

Total theoretical orifice area in the orifice flow equation (m2)

AUL

Summed orifice area of all upper leakages (m2)

C

Combined coefficient in the orifice flow equation (s2n−1/m2n−3)

Cd

Discharge coefficient in the orifice flow equation (–)

Co

Discharge coefficient for the orifice described by A o (–)

CU

Unit conversion constant in the orifice flow equation (various)

ci

Initial clean agent volume concentration (Vol. %)

cf

Final clean agent volume concentration (Vol. %)

F

Lower leakage fraction, Eqs. 2 & 4 (–)

\( \ifmmode\expandafter\tilde\else\expandafter\sim \fi{F} \)

Dimensionless ratio of outflow and inflow orifice areas (–)

g

Acceleration due to gravity (9.81 m/s2)

Ho

Enclosure maximum height (m)

He

Interface equivalent height (m)

Hi

Interface height (m)

Hnp

Neutral plane height (m)

Hp

Protected height (m)

\( \ifmmode\expandafter\tilde\else\expandafter\sim \fi{H}_{{{\text{SDI}}_{{2004}} }} \)

Dimensionless height for the sharp interface theory of the 2004 NFPA publication (–)

\( \ifmmode\expandafter\tilde\else\expandafter\sim \fi{H}_{{{\text{SDI}}_{{2008}} }} \)

Dimensionless height for the sharp interface theory of the 2008 NFPA publication (–)

\( \ifmmode\expandafter\tilde\else\expandafter\sim \fi{H}_{{{\text{WDI}}}} \)

Dimensionless height for the wide interface theory of published in ISO 14520-1 (–)

n

Orifice flow exponent in the orifice flow equation (–)

ΔPLL

Pressure difference (with reference to ambient) across enclosure boundary at lowest leak elevation (Pa)

ΔPUL

Pressure difference (with reference to ambient) across enclosure boundary at highest leak elevation (Pa)

Pin

Absolute ambient pressure inside the enclosure (Pa)

Pout

Absolute ambient pressure outside the enclosure (Pa)

Q

Flow in the orifice flow equation (m3/s)

\( \ifmmode\expandafter\tilde\else\expandafter\sim \fi{t}_{1} \)

Dimensionless hold time used when orifice flow exponent is variable (–)

\( \ifmmode\expandafter\tilde\else\expandafter\sim \fi{t}_{2} \)

Dimensionless hold time used when orifice flow exponent is equal to 0.5 (–)

\( {\mathop V\limits^. }_{{\text{i}}} \)

Flow into the enclosure (m3/s)

\( {\mathop V\limits^. }_{{\text{o}}} \)

Flow out of the enclosure (m3/s)

Greek Symbols

β1

Dimensionless coefficient used when orifice flow exponent is variable (–)

β2

Dimensionless coefficient used when orifice flow exponent is equal to 0.5 (–)

ρ

Fluid density in orifice flow equation (kg/m3)

\( \ifmmode\expandafter\tilde\else\expandafter\sim \fi{\rho } \)

Dimensionless density parameter (–)

ρag

Clean extinguishing agent vapor density at 21°C (kg/m3)

ρair

Density of air; 1.202 in NFPA & 1.205 in ISO standards (kg/m3)

ρmix

Agent and air mixture density (kg/m3)

Abbreviations

FK

Fluoroketone

HFC

Hydrofluorocarbon

IG

Inert gas

ISO

International Standards Organization

NFPA

National Fire Protection Association

Notes

Acknowledgements

This research effort was begun under the auspices of the NFPA 2001 Technical Committee on Gaseous Fire Extinguishing Systems. 3M Company, Ansul Incorporated and Fike Corporation provided FK-5-1-12, IG-541 and HFC-125 clean agents, respectively, for discharge testing. Additionally, Fike Corporation provided a modern test facility and multiple technicians aiding in making this effort possible. 3M Company and Sevo Systems provided all halocarbon gas sampling instrumentation. Ansul Incorporated and Fike Corporation provided all oxygen concentration gas analyzers. Equipment for and execution of all door fan integrity testing was provided by Retrotec Incorporated. I would like to acknowledge the industry specialists who were able to find the time and means to travel to Fike Corporation and support in the test process. Contributing members of the research team include Dale Edlebeck of Ansul Inc., Colin Genge of Retrotec Inc., Richard Niemann of Sevo Systems, Bob Whiteley of Tyco Fire and Integrated Solutions, and Brad Stilwell, Mark McLelland and John Schaefer of Fike Corporation. Discussions with faculty and fellow students at Worcester Polytechnic Institute are graciously acknowledged.

References

  1. 1.
    Dewsbury J, Whiteley RA (2000) Review of fan integrity testing and hold time standards. Fire Technol 36(4), 249–265CrossRefGoogle Scholar
  2. 2.
    DiNenno PJ, Forssell EW (1989). Evaluation of the door fan pressurization leakage test method applied to Halon 1301 total flooding systems. J Fire Protect Eng, 1(4), 131–140CrossRefGoogle Scholar
  3. 3.
    Mowrer F (2006) Analysis of vapor density effects on hold times for total flooding clean extinguishing agents. In: Halon options technical working conference, 16th proceedings, Albuquerque, New Mexico, May 2006, pp 1–12Google Scholar
  4. 4.
    O’Rourke ST (2005) Analysis of hold times for gaseous fire suppression agents in total flooding applications. Master thesis, University of Maryland, College Park MDGoogle Scholar
  5. 5.
    Dewsbury J, Whiteley RA (2000) Extensions to standard hold time calculations. Fire Technol 36(4), 267–278CrossRefGoogle Scholar
  6. 6.
    Emmons HW (2002) Vent flows, chapter 2–3. In: The SFPE handbook of fire protection engineering, 3rd edn. NFPA, Quincy, MAGoogle Scholar
  7. 7.
    Saum D, Saum A, Messing M, Hupman J (1988) Pressurization air leakage testing for Halon 1301 enclosures. In: Substitutes and alternatives to chlorofluorocarbons and Halons. Washington, DCGoogle Scholar
  8. 8.
    ISO 14520-1 (2006) Gaseous fire extinguishing systems – physical properties and system design – part 1: general requirements. International Standards Organization, Geneva, Switzerland, Annex EGoogle Scholar
  9. 9.
    NFPA 2001 (2008) Standard on clean agent fire extinguishing systems. National Fire Protection Association, Quincy, MA, Annex CGoogle Scholar
  10. 10.
    NFPA 2001 (2004) Standard on clean agent fire extinguishing systems. National Fire Protection Association, Quincy, MA, Annex CGoogle Scholar
  11. 11.
    Genge C (2005) Preventing excessive enclosure pressures during clean agent discharges. In: Halon options technical working conference, 15th proceedings, Albuquerque, New Mexico, May, 2005, pp 1–16Google Scholar

Copyright information

© Springer Science+Business Media, LLC 2008

Authors and Affiliations

  1. 1.Department of Fire Protection EngineeringWorcester Polytechnic InstituteWorcesterUSA

Personalised recommendations