Technical Note 1871 

Workshop on the Research Needs 

Concerning the Exothermic Reaction 

of Halogenated Hydrocarbons 

Gregory Linteris 

Jeffrey Manion 

This publication is available free of charge from: 

http://dx.doi.org/10.6028/NIST.TN.1871 
 

NIST Technical Note 1871 

Workshop on the Research Needs 

Concerning the Exothermic Reaction 

of Halogenated Hydrocarbons 

Gregory Linteris 

Fire Research Division 

Engineering Laboratory 

Jeffrey Manion 

Chemical Sciences Division 

Material Measurement Laboratory 

This publication is available free of charge from: 

http://dx.doi.org/10.6028/NIST.TN.1871 

February 2015 

U.S. Department of Commerce 

Penny Pritzker, Secretary 

National Institute of Standards and Technology 

Willie May, Acting Under Secretary of Commerce for Standards and Technology and Acting Director 

2
 
Certain commercial entities, equipment, or materials may be identified in this 

 document in order to describe an experimental procedure or concept adequately. 

Such identification is not intended to imply recommendation or endorsement by the 

National Institute of Standards and Technology, nor is it intended to imply that the 

entities, materials, or equipment are necessarily the best available for the purpose. 

National Institute of Standards and Technology Technical Note 1871 

Natl. Inst. Stand. Technol. Tech. Note 1871, 195 pages (February 2015) 

CODEN: NTNOEF 

This publication is available free of charge from: 

http://dx.doi.org/10.6028/NIST.TN.1871 

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Workshop on the Research Needs Concerning the Exothermic

Reaction of Halogenated Hydrocarbons

WORKSHOP

PROCEEDINGS

February 9, 2015

National Institute of Standards and

Technology

Gaithersburg, MD

October 27‐28, 2014

Gregory T. Linteris, and Jeffrey A. Manion,

Editors

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TABLE OF CONTENTS

1. ABSTRACT..............................................................................................................................................6
 

2. ACKNOWLEDGEMENTS ......................................................................................................................... 7
 

3. LIST OF ABBREVIATIONS ....................................................................................................................... 8
 

4. INTRODUCTION.....................................................................................................................................9
 

5. WORKSHOP ORGANIZATION AND OBJECTIVES .................................................................................. 10
 

6. PARTICIPANTS LIST.............................................................................................................................. 11
 

7. AGENDA ..............................................................................................................................................15
 

8. WORKSHOP ATTENDEE RECOMMENDATIONS ................................................................................... 18
 

8.1 Aircraft Fire Suppression Research Recommendations (related to the use of halogenated
 

hydrocarbons).........................................................................................................................................18
 

8.2 Refrigerant Flammability Research Recommendations ............................................................. 24
 

9. SUMMARY/CONCLUSIONS / FOLLOW‐UP........................................................................................... 37
 

9.1 Aircraft Fire Suppression Summary.................................................................................................. 37
 

9.2 Marginally Flammable Refrigerants Summary................................................................................. 37
 

10. APPENDIX: PRESENTATIONS CLEARED FOR GENERAL RELEASE ..................................................... 40
 
                                 

                            

                         

                             

                      

                             

                               

1. ABSTRACT

A workshop was held at NIST Gaithersburg on October 27 and 28, 2014 to discuss the exothermic

reaction of halogenated hydrocarbons. The industries that gathered to discuss the topic were the fire

suppression industry with both ground‐based and aircraft applications, and the Heating, Ventilating, Air

Conditioning, and Refrigeration industries. In the former, the compounds of interest are used as fire

suppressants, and in the latter, as working fluids for vapor compression heating/cooling equipment. The

purpose of the workshop was to identify the important parameters controlling the flammability of the

compounds, and identify research needs for overcoming the obstacles to their safe and effective use.

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2. ACKNOWLEDGEMENTS

The workshop was highly successful, which was a direct result of the eagerness of attendees to attend

and actively participate. In particular, the clear, high‐quality, and appropriate talks by the presenters

provided excellent background both to understand the challenges, and formulate the discussion as to

what next is required. Of course, the willingness of the companies represented to permit their

researchers and engineers to share their results was the essential first step in this process, from which

the open discourse and clear understanding then flowed naturally. Finally, the list of participants was

developed using input from individuals in the HVAC/R, aircraft fire safety, and fire suppression

industries, as well as Chairs of the ASHRAE committee members, and the authors gratefully

acknowledge that input, which was very helpful.

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3. LIST OF ABBREVIATIONS

2‐BTP – C3H2F3Br, CH2CBrCF3

AHRI – Air‐Conditioning, Heating, and Refrigeration Institute

ASHRAE – American Society of Heating, Refrigeration, and Air‐Conditioning Engineers

FAA – Federal Aviation Administration

FAA‐ACT – Federal Aviation Administration Aerosol Can Test

FLACS – Flame Acceleration Simulator

GWP – global warming potential

Halon 1301 – CF3Br

HFC – hydrofluorocarbon

HFO – hydrofluoroolefin

HVAC/R – Heating, Ventilating, Air‐Conditioning and Refrigeration

NIST – National Institute of Standards and Technology

NFPA – National Fire Protection Association

Novec 1230 – C6F12O, FK‐5‐1‐12, CF3CF2C(=O)CF(CF3)2

ODP – ozone depletion potential

R1234yf – 2,3,3,3‐Tetrafluoropropene, C3H2F4, CH2CFCF3

R1234ze(E) – 1,3,3,3‐Tetrafluoropropene, C3H2F4, CFHCHCF3

R125 – CHF2CF3, HFC‐125

R32 – CH2F2, HFC‐32

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4. INTRODUCTION

This document presents the results for a workshop held at NIST in Gaithersburg, MD, on Oct. 27 to Oct.

28, 2014, dealing with the high‐temperature, exothermic reaction of halogenated hydrocarbons in

hydrocarbon‐air combustion environments.

The high‐temperature reaction of halogenated hydrocarbons is important in several areas, many of

which are of high recent interest, including: civilian aircraft Halon (CF3Br) replacement, clean agent fire

suppression, suppression of electrically energized fires, and refrigerant flammability. These disparate

industries are related in that the chemical compounds are often similar or the same. Interest in industry

and among researchers has piqued lately for reasons described below.

In civilian aviation, some fire suppressants, considered as replacements for CF3Br in aircraft cargo bays,

unexpectedly failed an FAA‐mandated test (exacerbating the explosion rather than suppressing it).

Moreover, recent analysis by NIST has estimated that at the conditions of the enhanced combustion, the

expected burning velocities of the mixtures were in the range of only a few cm/s (significantly below the

usual rule‐of thumb flammability limit value of around 5 cm/s). For example, in the FAA test, mixtures

with a very low overall reaction rate (characterized by the burning velocity) can react and have an

overpressure up to 5 bar higher than with no agent. For the civilian airline industry, the problem is

pressing because the European Union deadline for halon replacement is now approaching.

In the HVAC/R industry, the high‐ODP (ozone‐depletion potential) refrigerant working fluids (typically

also high‐GWP, global‐warming potential) have been largely phased‐out (as a result of the Montreal

Protocol); however, the replacements typically still have relatively high‐GWP. The refrigerant working

fluids have been estimated to be a major contributor to the expected increase in global warming caused

by human activities.1 Low‐GWP replacements have been (and are being) developed; however, they tend

to be mildly flammable. While use of the low‐GWP, mildly‐flammable refrigerants would have great

environmental benefits, their adoption has been hindered because there do not exist codes and

standards for their safe use.

Finally, given that these suppressants can react exothermically and add heat to the fire/explosion, it

would be helpful for the system designer if rules for safe and effective applications can be developed.

In order to overcome the challenges in these fields, a workshop was held at NIST in Gaithersburg, MD on

Oct. 27‐28, 2014 to bring together a small number of select researchers from industry, government, and

academia who have relevant expertise. This manuscript describes the results of the workshop and its

recommendations.

1 A recent Science article estimated that of the total increase (between 2012 and 2050) in the atmosphere’s

radiative forcing from all sources, about 20 ± 5% will be due to refrigerant working fluids.
     

                           

                       

                   

                             

                       

                       

                           

                           

                          

                                     

                         

                                  

                         

                               

                              

                         

                                     

                    

                             

                          

                                   

                            

                                  

                                 

                      

                                                            

                                    

                             

       

5. WORKSHOP ORGANIZATION AND OBJECTIVES

The workshop participants (listed in the next section) consisted of researchers, engineers, and managers

from industry, academia, government, and codes and standards organizations. There were

approximately fifty registered attendees (and several more informal participants), representing world

experts in their respective areas. Two major industries were represented at the workshop: aircraft

manufactures (and their associated fire suppression suppliers), and residential and commercial Heating,

Ventilating, and Air Conditioning/Refrigeration (HVAC/R) industries (and their suppliers). While these

industries are somewhat disparate, they share an interest in the flammability of the relevant

compounds—which are often the same compounds, or similar ones, but used for different purposes

(i.e., as fire suppressants, or vapor‐compression system working fluids). Nonetheless, the research of

the two industries in this area has been separate, and it seemed of value to combine the communities at

the workshop to facilitate the sharing their results, approaches, and background work.

There were several objectives of the workshop. The major objective was to formulate a list of research

priorities for understanding the exothermic reaction of halogenated hydrocarbons, as it relates to air

craft fire suppression, and refrigerant flammability, so as to allow the safe use of the relevant

compounds in their desired application. The second was to bring together interested parties to open

the flow of information between the individuals and industries so that mechanisms of collaboration

could be explored. In an overall sense, the goal was to share information to aid each community in

solving its problems related to the flammability of the halogenated hydrocarbons.

The meeting was facilitated by NIST personnel from the Fire Research Division and the Chemical

Sciences Division. Fifteen presentations were given, and their titles are listed in the Agenda Section

below. For some talks, the presenters were able to make the materials available to anyone, and those

talks are presented in the Appendix2

. After the presentations, two break‐out groups were formed,

representing the two industries. A list of research priorities was prepared by each group, and these are

listed in Section 5 below. The conference ended with more informal discussion and laboratory tours of

NIST facilities of relevance to the workshop.

2 The policy of NIST is to provide statements of uncertainty for all original measurements. In this document

however, data from organizations outside NIST are shown, which may include measurements in non‐metric units

or measurements without uncertainty statements.

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6. PARTICIPANTS LIST

Dr. Valeri Babushok

NIST

100 Bureau Drive

Gaithersburg, MD 20899

United States

valeri.babushok@nist.gov

Phone: 301‐975‐8975

Mr. Pat Baker

Boeing

P.O. Box 3707

Seattle, WA 98124

United States

patrick.t.baker@boeing.com

Phone: (425) 266‐3380

Dr. Steven Baughcum

Boeing Company

Technical Fellow

P. O. Box 3707

MC OR‐96

Seattle, WA 98124

United States

Steven.L.Baughcum@boeing.com

Phone: (425) 266‐9119

Mr. Rainer Beuermann

Airbus

Airbus Allee 1

Bremen

28199 Germany

rainer.beuermann@airbus.com

Phone: +49 (0)4215383986

Mr. Antonio Bouza

U.S. DOE

1000 Independence Ave. SW

Washington, DC 20585

United States

antonio.bouza@ee.doe.gov

Phone: (202) 586‐4563

Dr. Ian Campbell

Meggitt

Director of Advanced Technologies

1785 Voyager Avenue

Simi Valley, CA 93063

United States

ian.campbell@meggitt.com

Phone: (626) 316‐2824

Mr. Barry Chase

NFPA

15 Hunter St

New Bedford, MA 02740

United States

bchase@nfpa.org

Phone: (617) 984‐7259

Mr. Adam Chattaway

SIS‐Kidde Graviner

Engineering & Technology Manager

Mathisen Way

Poyle road

Colnbrook SL3 0HB

United Kingdom

adam.chattaway@utas.utc.com

Phone: 01753 766190

Mr. Warren Clough

Carrier Corp

Carrier Parkway

East Syracuse, NY 13057

United States

warren.clough@carrier.utc.com

Phone: (315) 432‐7506

Dr. Meredith Colket

UTRC Consultant, Senior Fellow Emeritus

36 Gatewood

Avon, CT 06001

United States

med@colket.org

Phone: (860) 470‐3175

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Dr. Scott Davis
 

GexCon US
 

President ‐ Principal Engineer
 

4833 Rugby Ave. Ste 100
 

Bethesda, MD 20814
 

United States
 

sgdavis@gexcon.com
 

Phone: (617)‐407‐3300
 

Dr. Piotr Domanski
 

NIST
 

100 Bureau Drive
 

Gaithersburg, MD 20899
 

United States
 

piotr.domanski@nist.gov
 

Phone: 301‐975‐5877
 

Mr. Brent Ehmke
 

Ehmke Associates
 

516 Pendleton Lake Rd
 

Raleigh, NC 27614
 

United States
 

brent.ehmke@gmail.com
 

Phone: (919) 500‐8658
 

Mr. Doug Ferguson

Boeing Commercial Airplanes

3855 Lakewood Boulevard

P.O. Box 200
 

MC D800‐0059
 

Long Beach, CA 90808‐1700
 

United States
 

douglas.e.ferguson@boeing.com
 

Phone: (562) 593‐2950
 

Dr. Richard Gann
 

NIST
 

100 Bureau Drive
 

Gaithersburg, MD 20899
 

United States
 

richard.gann@nist.gov
 

Phone: 301‐975‐6866
 

Dr. Anthony Hamins
 

NIST
 

100 Bureau Drive
 

Gaithersburg, MD 20899
 

United States
 

anthony.hamins@nist.gov
 

Phone: 301‐975‐6598
 

Sham Hariram
 

Boeing
 

Propulsion Engineer
 

PO Box 3707
 

Seattle, WA 98124
 

United States
 

sham.s.hariram@boeing.com
 

Phone: (425) 237‐1770
 

Mr. Phillip Johnson
 

Daikin Applied
 

Engineering Director
 

PO Box 2510
 

Staunton, VA 24402‐2510
 

United States
 

phillip.johnson@daikinapplied.com
 

Phone: (540) 248‐9483
 

Ms. Debra Kennoy
 

Arkema Inc.
 

900 1st Avenue
 

King of Prussia, PA 19406
 

United States
 

debra.kennoy@arkema.com
 

Phone: (610) 878‐6621
 

Mr. Stephen Kujak
 

Ingersoll Rand
 

3600 Pammel Creek Road
 

La Crosse, WI 54601
 

United States
 

skujak@trane.com
 

Phone: (608) 787‐3766
 

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Mr. Edward Lampert Mr. John Pagliaro

Lampert & Associates NIST

3781 23rd Street 100 Bureau Drive

San Francisco, CA 94114 Gaithersburg, MD 20899

United States United States

lampert@lampert‐japan.com john.pagliaro@nist.gov

Phone: (917) 365‐4440 Phone: 301‐975‐6675

Dr. Thomas Leck Dr. Paul Papas

DuPont Fluorochemicals UTRC

Principal Investigator Multiphase Combustion Discipline Leader

PO Box 2915 411 Silver Lane

Wilmington, DE 19805 East Hartford, CT 06118

United States United States

thomas.j.leck@dupont.com papasp@utrc.utc.com

Phone: (302) 999‐2155 Phone: (860) 610‐7284

Dr. Gregory Linteris Mr. Robert Richard

NIST Honeywell Int. Inc.

100 Bureau Drive Principal Scientist

Gaithersburg, MD 20899 20 Peabody St.

United States Buffalo, NY 14210

linteris@nist.gov United States

Phone: 301‐975‐2283 robertg.richard@honeywell.com

Phone: (716) 827‐6306

Mr. Richard Lord

Carrier Dr. Mark Robin

Fellow DuPont

2003 Irby Lane CRP 711

Murfreesboro, TN 37127 Wilmington, DE 19709

United States United States

richard.lord@carrier.utc.com mark.l.robin@dupont.com

Phone: (615) 225‐8152 Phone: (302) 256‐1423

Dr. Jeffrey A. Manion Mr. Paul Rohrbach

NIST Airbus

100 Bureau Drive Airbus Allee 1

Gaithersburg, MD 20899 Bremen

United States 28199 Germany

jeffrey.manion@nist.gov paul.rohrbach@airbus.com

Phone: 301‐975‐3188 00491752260585

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Mr. Dirk Roosendans
 

TOTAL
 

Head of Department Process Safety
 

Beekstraat 101
 

Deinze
 

9800 Belgium
 

dirk.roosendans@total.com
 

+32 475 841 943
 

Dr. Joseph Senecal
 

Kidde‐Fenwal / UTC
 

Senior Fellow
 

400 Main St
 

Ashland, MA 01721
 

United States
 

joseph.senecal@kidde‐fenwal.com
 

Phone: (508) 231‐2772
 

Prof. Peter Sunderland
 

Univ. of Maryland
 

3104 J.M. Patterson Bg.
 

College Park, MD 20742
 

United States
 

pbs@umd.edu
 

Phone: (301) 405‐3095
 

Dr. Kenji Takizawa
 

National Institute of Advanced Industrial
 

Science and Technology (AIST)
 

AIST Central 5
 

1‐1‐1 Higashi, Tsukuba
 

Ibaraki 305‐8565, JAPAN
 

k.takizawa@aist.go.jp
 

Phone: +81‐29‐861‐9441
 

Dr. J. Kelly Thomas
 

BakerRisk
 

Vice President
 

3330 Oakwell Court
 

San Antonio, TX 78218
 

United States
 

KThomas@BakerRisk.com
 

Phone: (210) 824‐5960
 

Dr. Parmesh Verma
 

UTRC
 

Project Leader
 

411 Silver Lane
 

East Hartford, CT 06108
 

United States
 

vermap@utrc.utc.com
 

Phone: (860) 610‐2177
 

Dr. Xudong Wang
 

Air‐Conditioning Heating and Refrigeration
 

Institute
 

2111 Wilson blvd. Suite 500
 

Arlington, VA 22201
 

United States
 

xwang@ahrinet.org
 

Phone: (703) 600‐0305
 

Dr. Gerd Wedler
 

Apparatebau Gauting GmbH
 

Ammerseestr. 45‐49
 

Gauting
 

82131 Germany
 

gerd.wedler@aoa‐dresden.de
 

+49 351 88597154
 

Mr. Samuel Yana Motta
 

Honeywell
 

20 Peabody St.
 

Buffalo, NY 14210
 

United States
 

Samuel.YanaMotta@Honeywell.com
 

Phone: (716) 688‐0286
 

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7. AGENDA
 

NIST Workshop on the Exothermic Reaction of Halogenated Hydrocarbons
 

National Institute of Standards and Technology
 

Gaithersburg, MD
 

Monday, October 27, 2014; Bldg 101, Heritage Room

7:50	 Check‐in at NIST Main Gate (from 7:50 to 8:10), and proceed to Bldg. 101: Heritage Room

8:30	 Welcome Remarks; Joannie Chin, Deputy Director, Engineering Laboratory, NIST

Workshop Agenda, Purpose of Meeting; Greg Linteris, Flammability Reduction Group, NIST

Introductions:

8:45	 Short Introductory Remarks from Participants

Attendees

Overviews:

9:25	 A Perspective on Lower GWP Refrigerant Performance Tradeoff’s versus Open Flammability

Knowledge Gaps for HVACR Products

Stephen Kujak / Bill Hansen, Ingersoll Rand

9:55	 Fluorocarbons as Gaseous Fire Extinguishing Agents: Features, Benefits, and Challenges

Joe Senecal, UTC Kidde

10:15	 Coffee Break

Problem Definition

10:30	 Barriers to Accepting Flammable Refrigerants

Robert Richard, Honeywell

11:00	 Clean Agents in Explosion Inerting

Adam Chattaway, UTC/Kidde

11:30	 Flammability Testing in HVAC Configurations using Low GWP, Alternative Refrigerants

Paul Papas, UTRC

12:15	 Lunch NIST Cafeteria

13:15	 Testing of Aqueous Solutions of Inhibitors for Mitigation of Vapour Cloud Explosions

Dirk Roosendans, TOTAL Refining and Chemicals

Metrics

13:45	 Burning Velocity and Flame Quenching Issues for Mildly Flammable Compounds

Kenji Takizawa, AIST

14:15	 Coffee Break

14:30	 Ignition of R‐32 and R‐410A Refrigerant Mixtures with Lubricating Oil

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Peter Sunderland, Univ. of Maryland

15:00	 Laminar Flame Speed Measurements and Calculations

Med Colket, Consultant/UTRC

15:30	 Experimental and Numerical Approaches for Understanding Explosive Behavior of Mildly

Flammable Combustible Gases

Scott Davis, Gexcon

16:00	 Discussion

18:00	 Dinner

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AGENDA (continued)

Tuesday, Oct. 28, 2014  ‐ Building 101; Heritage Room

(Please go to the NIST Main Gate at around 8am; you can use the same badge and ID as on Monday, and

don’t have to stop in the Visitors’ Center)

Tools and Approaches for Solutions

8:30	 Review of Standard and Code Changes to Reduce GWP Gas Emissions and to Support the Use of

new 2L Semi‐Flammable Refrigerants

Dick Lord, Carrier

9:00	 The Use of Thermodynamic and Chemical Kinetic Models to Understand Explosive Behavior of

Mildly Flammable Combustible Gases

Greg Linteris, NIST

9:30	 Reduced‐Scale Experiments for Screening, Model Validation and Understanding Full‐Scale

Results of Marginally‐Flammable Mixtures

John Pagliaro, Univ. of Maryland

10:00	 Coffee Break

10:15	 Measurements & Data for Fundamental Kinetic Modeling of Halocarbon Flammability

Jeff Manion, NIST

10:40	 Assorted Properties of Mildly Flammable Systems

Greg Linteris, NIST

Workshop Participants’ Recommendations

11:00	 Break‐out Groups:

Research Needs (in Support of Codes and Standards) in Fire Suppression by Halogenated

Compounds. (Facilitator: Greg Linteris, NIST)

Research Needs (in Support of Codes and Standards) for the Safe Use of Mildly Flammable

Refrigerants. (Facilitator: Jeff Manion, NIST)

11:45	 Presentation of Break‐out Group Recommendations.

12:00	 Lunch NIST Cafeteria

13:00	 Discussion

14:00	 Tour of Fire Research Division Labs

Gas‐phase Flame Inhibition, Greg Linteris, NIST

Tour of Chemical Sciences Division
 

Gas‐Phase Chemical Kinetics Laboratory, Jeff Manion, NIST
 

15:30	 Adjourn

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8. WORKSHOP ATTENDEE RECOMMENDATIONS

Two break‐out sessions were conducted (in parallel) at the end of the second day. The first included

participants whose primary interest was in aircraft fire suppression, and the second, refrigerant

flammability. The sessions were moderated by Greg Linteris (NIST), and Jeff Manion (NIST), respectively.

Using hand‐written notes from, and audio recordings of the sessions, the following research

recommendations have been assembled based on the suggestions of the participants.

8.1 Aircraft Fire Suppression Research Recommendations (related to the use of halogenated

hydrocarbons)

1. Issue

Effects of temperature, pressure, and humidity need to be understood for various active flame‐

inhibiting moieties and hydrocarbon components of the agents.

Need

Improve the understanding of the parameters (e.g., humidity, temperature, pressure, active chemical

moiety) affecting agent chemical inhibition and enhancement, to provide guidance on the necessary

properties of new compounds or blends for effective suppression of the FAA‐ACT.

Background

Aircraft operate over a range of temperature, pressure, and humidity. For a given agent, there is

competition between the fuel effect and the inhibition effect. There appears to be an overall

reaction rate (or alternatively, flame speed) for mixtures below which the FAA‐ACT explosion will not

occur. Temperature and humidity will likely have a large influence on this limiting overall reaction

rate for a given agent, determining whether suppression or enhancement occurs. Both simulations

and reduced‐scale screening experiments can be performed to find the values of each variable

necessary for inhibition rather than explosion. The focus of this work is to understand the effects of

temperature, pressure, and humidity on the behavior of a range of representative compounds (e.g.,

hydrofluorocarbons HFCs, hydrofluoroolefins HFOs, inerts, etc.).

Comments

Even in the absence of a new, effective agent, surrogates can be used to assess the potential of a

new agent to work in the FAA‐ACT. For example, blends of C2H2, CF3Br, and N2 were found to be

good surrogates for 2‐BTP. By performing screening tests and numerical simulations using

surrogates, the parameters of chemical activity, inert activity, and fuel activity can be varied. For

example, by starting with 2‐BTP, an agent with added chemical activity can be simulated by adding

Br2 (which has nearly a pure chemical effect in the flame), N2 (inert), or C3H8 (fuel). One can then

answer whether an agent, with various amounts of Cl, F, Br, I or other element, combined with

various amounts of hydrocarbon, HFC, or HFO, can likely work.

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2. Issue

2‐BTP has varying effectiveness in different flame types and experimental configurations.

Need

Develop a better understanding of why 2‐BTP behaves so differently in different flame types.

Background

Good understanding of the behavior of 2‐BTP in premixed methane‐air flames of various

stoichiometries has been obtained through modeling and reduced‐scale experiments. The reasons

for the enhancement have been postulated, and it would be good to test them for other fuels and

flame types. For example, the relative importance of combustion enhancement needs to be

assessed for more typical flames (e.g., diffusion flames), different fuels, elevated temperatures and

with water vapor.

Comments

This need addresses whether the properties of 2‐BTP observed in the FAA‐ACT are generally relevant,

or specific to the FAA‐ACT.

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3. Issue

Existing agents have all failed the FAA Aerosol Can Test for their use in aircraft cargo bay fire

protection. Is a new agent possible?

Need

Perform a comprehensive exploration of all the possible molecules which might meet the system

requirements (vapor pressure, toxicity, over pressure, flame suppression, etc.) in the FAA‐ACT.

Background

Developing a new fire suppressant molecule is challenging because of the multiple requirements for

the agent, including fire suppression effectiveness (in a variety of tests), low toxicity, low ODP, low

GWP, acceptable cost and weight, material compatibility, high vapor pressure, and low residue.

There was active research in the 1990s to find a halon replacement, and that work resulted in the use

of the current agents. However, with potential GWP restrictions, and failure of the agents in the

FAA‐ACT, new agents with additional features are now required. There was work to explore new

agents and approaches, supported by the Next Generation Project; however, that program was

discontinued due to a change in funding priorities.

Comments

It would be of value to review the recommendation of the NGP project to assess the potential of any

chemicals or classes of chemicals suggested. Further, there has recently been work done at NIST

Boulder to explore the entire range of possible chemicals for use as refrigerant working fluids. A

similar approach to explore the range of possible options for chemically acting fire suppressants

would be of value.

20
 
   

                                 

  

                   

                         

                        

                   

                                      

                       

                        

                              

                         

                       

                         

                                

                                    

                          

                     

                             

                         

                                  

                                

                            

                       

                           

                          

                               

                              

                                 

                            

                               

                             

                               

                            

                     

   

4. Issue

All agents tested, except CF3Br, have failed the FAA‐ACT, so a new agent (or approach) is necessary.

Need

Determine if blends of agents can work in the FAA‐ACT.

Background

The halogen‐based halon replacement agents work by lowering the reactivity of the reacting mixture

through the interaction of the halogen‐containing species with the normal fuel chemistry. The

halogen‐containing species reduce radical concentrations either through gas‐phase catalytic cycles

(Br, I, and to some extent Cl), or by trapping H atoms to form HF). Unfortunately, the halogen atoms

are typically attached to hydrocarbon molecules, which have a fuel‐like character, increasing the

flame temperature (in fuel‐lean mixtures) and increasing reaction rates. Hence, there is competition

between these two effects, and which predominates depends upon the fire scenario. It is possible

that mixtures of inert agents with the halon replacement might overcome the higher temperature

caused by the agent, and hence be effective in the FAA‐ACT.

Comments

The effectiveness of the blends can be explored either through reduced‐scale tests or kinetic

calculations. These would likely give good indication as to the potential of the blends in full‐scale

tests in the FAA‐ACT. The FAA tested mixtures of CF3Br and N2 in the FAA‐ACT, and found conditions

(concentration of each component, CF3Br or N2) for which the explosion was suppressed. Using

stirred‐reactor simulations, this boundary was subsequently predicted via numerical simulations.

This procedure can be repeated for the halon replacements with inert compounds: the locus of

conditions bounding flammable vs. non‐flammable can be found for the concentration of each

component (agent and inert; e.g., 2‐BTP and N2) for the compounds of interest. The effect of the

inert is likely to vary from agent to agent, since the mechanism of inhibition is different. These

predictions can then be tested using the reduced‐scale screening methods recently developed. If the

results are promising, tests can then be conducted in the FAA‐ACT.

The approach described above for adding inert compounds can also be repeated for chemically

active compounds. For example, if the 2‐BTP molecule had a little more chemical inhibition

character, it might suppress the FAA‐ACT at a concentration low enough such that the fuel effect

(and ensuing pressure rise) of the 2‐BTP was not relevant. The boundaries of the desired behavior

can be explored by added a nearly purely‐acting chemical additive (e.g., Br2) to mixtures of 2‐BTP and

the FAA‐ACT fuel, thereby simulating a 2‐BTP molecule with higher chemical activity. Exploring the

range of behavior of such mixtures will allow one to understand the ultimate potential of new

compounds, which still have a hydrocarbon backbone, but have a higher chemical activity than does

2‐BTP. The work would answer a question such as: How much chemical inhibition character is

required for a given amount of hydrocarbon character? Such information would be very helpful for

understanding the potential of new compounds which might be developed.

21
 
   

                 

  

                 

                 

                                 

                              

                            

                  

                       

                                   

                               

             

                              

                       

                                

                             

   

5. Issue

Flammability behavior of halogenated hydrocarbon fire suppressants in non‐premixed flames.

Need

Understand the flammability behavior of halogenated hydrocarbon fire suppressants in non‐

premixed flames representative of fire threats (i.e., diffusion flames).

Background

Most practical fires to suppress are diffusion flames, but most of the work to understand the agents

has been done in premixed systems. In the premixed systems, the combustion enhancement by the

alternative agents depends strongly upon the proportions of fuel and air in the mixture. For

explosion suppression, premixed flames represent a worst‐case scenario. Nonetheless, the

importance of the enhancement effect for many practical applications (e.g., nacelle fires) depends

upon the particular configuration of the fire to be suppressed. Since many fires to be suppressed are

diffusion flames (fuel and oxidizer initially separate), more work needs to be done to understand any

potential combustion enhancement for those situations.

Comments

This work can be done using either calculations or experiments, or both. Useful flame types are cup‐

burner flames and counterflow diffusion flames, both of which are experimentally and

computationally tractable. An approach would be to add agent to either the fuel or air stream, at

varying concentrations, and assess its effect on flame extinction and the rate of total heat release.

22
 
   

         

                        

                                      

                               

                              

                          

                   

                           

                    

                               

                       

                          

                   

      

   

6. Issue:

Fluid mechanics of agent dispersion.

Need:

Improve the understanding of the fluid mechanics of agent dispersion and distribution.

Background:

With Halon 1301, the agent was so effective that system design did not have to be optimized as well.

Since use of the alternatives requires more agent, agent distribution efficiency has a larger effect on

weight and performance. This is especially true for agents with lower vapor pressure (i.e., higher

boiling points). Finally, poor distribution and mixing of the agent can lead to sub‐inerting

concentrations, in which exothermic reaction of the agent can occur.

Comments:

Many of the issues with overpressure at sub‐inerting concentrations might be overcome with good

system design (nozzle design, placement, discharge location, effects of obstructions, etc.).

Temperatures in protected spaces can vary from ‐40°F to 110°F, and pressure is lower at altitude.

For effective system design, better understanding of the effects of temperature, pressure, and

geometry on agent dispersion would be useful, particularly for low vapor pressure agents. An

understanding of how venting requirements change with concentration non‐uniformities would be

useful.

23
 
   

   

               

                           

                            

                  

                         

                        

                           

                                

                            

                                

                                   

                           

                               

           

8.2 Refrigerant Flammability Research Recommendations

1. Issue

Roadmap for the safe implementation of marginally flammable refrigerants.

Need

Develop a roadmap outlining the information and steps required for the safe implementation of

marginally flammable refrigerants. This would include an understanding of all of the components of

a risk assessment for the use of the compounds.

Background

The fire and explosion risk from marginally flammable refrigerants depends upon many factors,

including: the refrigerant reactivity, temperature, and concentration; the volume of the equipment

space, ventilation rates, and humidity; the ignition sources; and the presence of other flammable

materials, among others. A risk model attempts to quantify the probability of an event and its

severity, and make some determination of acceptable overall risk. This is a multifaceted problem,

and accurate specification of the various elements is very helpful. It was suggested that a roadmap

for the risk model would be a useful starting point to solve the engineering problems posed, to focus

activity, and start the necessary communication required for the industry to move forward.

Comments

Phil Johnson provided a roadmap (attached below) to serve as a starting point for discussion, or

perhaps formation of a working group.

24
 
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2. Issue

Scenario definition .

Need

Develop a list of possible, plausible, and most common scenarios in which a refrigerant‐air mixture

might be ignited, so that the risk and consequences can be determined.

Background

There was concern among the participants that the possible scenarios for refrigerant leakage and

ignition in residential settings was almost infinite, making it difficult to quantify the risks and develop

methods to ameliorate them. Hence, they saw value in trying to develop a list of plausible scenarios,

and then choose some as base‐case examples, representing the entire range of those that might be

encountered in practice. To do this, it would probably be necessary to use numerical modeling to

understand the controlling parameters of the full‐scale experiments, so that the examples are both

representative, and conservative.

Comments

Typically, refrigerant charges are released as jets, and for marginally‐flammable compounds, the jets

can be ignited, but then produce weak flames that are very unstable. On the other hand, most of the

risk is from the explosion potential of premixed refrigerant‐air mixtures. Any degree of stratification

will produce non‐premixed conditions, and the flame propagation rates will be lower. Hence, while

it certainly is necessary to understand the explosive behavior of premixed gases, this condition may

be a special case, rather than a typical one. Nonetheless, the presence of turbulence greatly

increases the propagation rate of the deflagration and the rate of pressure build up, but the

generation of turbulence is very configuration dependent. Hence, the difficult but important task

represented here is to come up with possible, representative, and conservative scenarios that

represent the range of risks in different room configurations with different equipment types. By

exploring both typical and worst‐case scenarios, performing full‐scale experiments, and then

analyzing the results with numerical modeling, the important parameters can be determined. From

these, it is believed that the large range of potential scenarios can be reduced to some model cases,

from which the relevant codes and standards can be written.

26
 
   

             

  

                         

               

                               

                                  

                                   

                              

                                  

                   

                         

                        

                         

                                 

             

   

3. Issue

Behavior of halogenated hydrocarbon refrigerants in non‐premixed flames.

Need

Perform experiments and analyses to understand how the flame type (e.g., premixed vs. diffusion)

influences the safe use of marginally flammable materials.

Background

As a refrigerant leak occurs, the potential fuel (the refrigerant) and oxidizer (air) are separate, and

any flame would be a non‐premixed (i.e., diffusion) flame. For jet release of the agent, and with

time, however, the air and fuel mix such that the flame (if stable) might eventually be a premixed

flame. Hence, it is important to understand both premixed and diffusion flame behavior of the

compounds. Also, turbulence is important since it has a large effect on ignition, mixing of the fuel

and oxidizer, and the subsequent propagation of the premixed flame.

Comments

There is experimental evidence for combustion of these mildly flammable refrigerants, particularly in

premixed systems. Very limited data exist, however, on their behavior in non‐premixed (i.e.,

diffusion flame) systems. Future rules, guidelines, and standards need to be based on representative

scenarios. Hence, there is a need for more data on the behavior of these compounds in non‐

premixed systems, with and without turbulence.

27
 
   

     

                   

                                 

                                

                                 

   

                                 

                 

   

4. Issue

Refrigerant leakage rates.

Need

Develop a database of refrigerant leakage rates in the field.

Background

In order to design equipment spaces in which the flammability risk has been mitigated, it is necessary

to know the leakage rate of the working fluid. This is important for understanding the subsequent

dispersion of the agent, as well as the ventilation requirements to keep the space below the lean

flammability limit.

Comments

The industry does not collect data on leakage rates, so while this information would be useful, actual

field data might be hard to come by.

28
 
   

               

                           

                         

                             

                          

                          

                                  

                   

                                 

                             

           

   

5. Issue

Ignition properties of marginally flammable refrigerants with air

Need

Determine the ignition properties of marginally flammable refrigerants with air (i.e., the ability of

different ignition sources to initiate a flame of marginally flammable refrigerants with air).

Background

One approach to limit the risk from marginally flammable refrigerants is to control the ignition

sources. Flames of these compounds generally have much higher minimum ignition energy than

those of hydrocarbons. Hence, certain types of ignition sources which are important for

hydrocarbons may not be of concern for the refrigerants. Thus, there is a need to characterize the

ability of different types of ignition sources to create flames.

Comments

The need appears to be an understanding of the ability of practical ignition sources, such as hot

surfaces, contactors, flames, etc., to ignite these compounds, and a determination of which of the

myriad ignition sources are of concern.

29
 
   

         

                   

                 

                                    

                           

                             

                              

                             

                      

             

                             

                               

                               

   

6. Issue

Venting requirements to reduce overpressure from refrigerant‐air deflagration.

Need

Develop accurate, validated correlations and modeling capabilities for specifying venting

requirements to prevent overpressure from flames of marginally‐flammable refrigerants.

Background

If a deflagration occurs in an enclosure, venting can be used to limit the overpressure to safe values.

For combustion of typical hydrocarbons with air, which have high laminar burning velocities, there

exist correlations (for example, those used in NFPA‐68) and modelling tools (e.g. FLACS) which are

accurate for design purposes. However, these correlations are known to be poor for low burning

velocity fuels, or near the end of the propagation, when quenching (i.e., heat loss) becomes

important. Accurate, validated correlations and modeling capabilities are needed for specifying

venting requirements to prevent overpressure of marginally‐flammable compounds.

Comments

Tests need to be conducted to see if the existing correlations are accurate for low‐burning velocity

compounds. If not, new correlations need to be developed. The whole question of quenching, and

how is may be more important for low burning velocity compounds needs to be addressed.

30
 
   

                

               

  

                       

                   

                 

                               

                           

                                  

                             

                           

                                    

                       

                   

                               

                                        

                           

                                  

                              

                   

    

7. Issue

Accuracy of overpressure correlations/calculations for marginally‐flammable compounds in air.

Need

Improve the accuracy of overpressure correlations/calculations for marginally‐flammable compounds

in air.

Background

There are design tools and numerical codes for predicting venting requirements for hydrocarbon

explosions. These are empirically‐based, and require experimental validation (or benchmarking).

Their applicability to low flame speed fuels is unknown.

Comments

This is an extension of the previous issue: the need for guidelines for venting requirements. What

system manufacturers ultimately need, however, is a way to predict the flammability behavior of a

given chemical in a given configuration. One might envision this, for example, as using the NIST Fire

Dynamics Simulator (FDS) program to predict the growth of a fire ball, and the resulting

overpressure, for a particular room in a building, with given dilution, suppression, and venting

systems. For a given leak rate and type, it would include the provision for describing the mixing of

the agent with the air, dilution and settling, leak detection, system response, dilution/ventilation,

ignition, flame growth, turbulence generation, turbulent flame propagation, overpressure, and vent

activation. This is undoubtedly, a longer‐term project, but one which is possible within the near

future, and which would be of great value. While it may seem daunting, it is not unlike the needs in

industry, where useful codes have been developed based on a combination of empirical rules, full‐

scale calibration, and first principles. That approach is not unlike what is done in FDS (for example,

with radiation from soot, among many other examples). The goal here is to improve our

understanding of the various phenomena participating in the overall process.

31
 
   

               

                             

                            

                             

                            

                               

                                

                                      

                                    

             

                             

                           

                   

   

8. Issue

Existence of critical burning velocity for explosion risk

Need

Determine if there exists a critical burning velocity, below which heat losses will prevent turbulent

enhancement of the laminar flame speed and large increase in the flame propagation rate.

Background

Turbulence, caused by inherent flame instabilities and by clutter in the flow field, greatly increases

the propagation rate of a deflagration. Under certain conditions, however, the overall reaction rate

(which can be measured by the laminar burning velocity), is too low to support any flame

propagation. This is caused by the combination of the low reaction rate and radiant or conductive

heat loss from the flame. It would be of value to determine if there is a fundamental burning velocity

below which, there is no risk of explosion. (Analysis of the FAA Aerosol Can Test result with added

fire suppressants implies that this is true.)

Comments

Understanding the existence of such a limit, and how it varies with fuel, stoichiometry, lubricant,

temperature, and pressure, as well as configuration, will provide insight useful for designing new

refrigerant mixtures which do not have an explosion risk.

32
 
   

                   

                             

                         

                              

                              

                           

                           

                     

                           

         

                       

                             

                            

                               

                 

9. Issue

Flammability of Mixtures of R32, R290, CO2, and 1234yf, 1234ze(E)

Need

Develop the capability to predict the flammability of mixtures of R32, R290, CO2, 1234yf, and

1234ze(E).

Background

The Alternative Refrigerant Evaluation Program (AREP) considers about forty fluids, which are mostly

mixtures of R32, R290, CO2, 1234yf, and 1234ze(E). The NIST database RefProp and RefLeak describe

the thermodynamic and physical properties of the mixtures, and their behavior in leaks. It would be

of great value to have a similar program, perhaps RefFlam, which would describe the flammability

properties of arbitrary mixtures of these compounds. Parameters to include would be the adiabatic

flame temperature, maximum pressure rise, laminar burning velocity, and minimum ignition energy

for arbitrary mixtures of these compounds, as functions of temperature, pressure, and humidity, for

their most reactive mixture.

Comments

The database would be experimentally based, with numerical simulations used to develop

correlations for mixtures and their P, T, and humidity dependence, so that a tractable number of

tests could be performed. In order to perform the numerical simulations, detailed kinetic models

would be used, or developed as necessary. These would describe the elementary rates of chemical

reactions occurring in the chemical system of interest.

33
 
   

       

                       

                       

                       

                        

                                

                         

                               

                                  

                             

   

10. Issue

Standard Test(s) for Refrigerant Flammability

Need

Determine the most appropriate standard test(s) for ranking the flammability of alternative

refrigerants, to be used in specifying the safety requirements for their use.

Background

Current flammability rankings of refrigerants are based on the heat of combustion, lower

flammability limit, and laminar burning velocity. While these are clearly important parameters, there

may be others that would be useful to properly evaluate the explosion risk. These include the

minimum ignition energy, the maximum explosion pressure, and the turbulent explosion index.

Comments

It was noted that while additional indices would be useful, they (for example, the explosion pressure)

are often dependent upon the ignition source. The work here would be to determine which of the

available (or possible) tests would be most useful for specifying safe use of the materials.

34
 
   

           

                                     

             

                           

                                    

                         

                                

                       

   

11. Issue

HF formation from refrigerant flame reactions

Need

Develop and understanding of how to deal with HF formation (which will occur if there is a flame of

air and a fluorine‐containing marginally flammable refrigerant).

Background

Flame reactions of hydrofluorocarbon agents produce large quantities of HF (for example, there is

about 30% HF in the product gases of a stoichiometric R32‐air flame). HF is toxic and corrosive, and

there need to be approaches developed for dealing with its adverse properties.

Comments

HF gives a citrus smell, which is easily detected. Nonetheless, it is a new, potentially dangerous

byproduct for which safe responses and codes need to be developed.

35
 
   

                 

                      

                           

                                

                             

                     

                        

                               

              

                             

           

12. Issue:

Better detection of refrigerant gases or their decomposition byproducts

Need:

Improve sensors for detection of refrigerants or their decomposition byproducts. This would

increase safety by allowing automated venting upon their detection, reducing the hazard from their

presence.

Background

An explosion of a flammable mixture has a lower likelihood but a larger consequence. Explosion can

be prevented with rapid venting and dilution of the refrigerant‐air mixture, bringing the space into

the non‐flammable regime. Present detectors are somewhat expensive and not very sensitive.

Increased sensitivity and lower cost would facilitate prevention of the explosive mixtures. Similarly,

HF is a toxic byproduct of combustion of the refrigerants; more sensitive and rapid detectors would

facilitate venting of the space, increasing safety.

Comments

Detectors exist for both, but improvements are needed to achieve the rapid, economical, removal of

the compounds from the occupied space.

36
 
      

                                    

                         

                               

                                 

           

          

                         

                                    

                           

                              

                       

                              

                             

                    

                                 

                 

                         

                     

                     

                           

                             

                           

                        

                   

                 

                 

                       

         

                     

                                     

                                 

                                  

                                

                       

                          

9.	 SUMMARY/CONCLUSIONS / FOLLOW‐UP

The research needs in the above section are the core outcome of the workshop. There was a general

consensus that the problems in both industries (related to the exothermic reaction of halogenated

hydrocarbons) are complex and more research would help to delineate the problem and aid in designing

around any adverse properties of the materials (when that is possible). The results of two the breakout

groups are summarized separately below.

9.1 Aircraft Fire Suppression Summary

The research recommendations developed in the Aircraft Fire Suppression breakout group (described in

the previous section) are listed in Table 1 below. As the table (and the previous section) describes, most

of the recommended work involves improving the understanding of the behavior of potential new

compounds and blends of existing compounds. For the FAA Aerosol Can Test, the needed information

involves understanding how the molecular structure (or combination of compounds) affects the tradeoff

between inhibition and enhancement of the explosion, and how this is affected by other parameters.

For other aircraft fire suppression applications, this same information would be useful, as well as an

understanding of how the different flame environments affect the overpressure/inhibition tradeoff. In

particular, it would be useful to understand if the overpressure caused by some agents in the FAA‐ACT

can possibly occur in other configurations (e.g., diffusion flames).

Table 1 ‐ List of research needs developed in the Aircraft Fire Suppression breakout group.

1.	 Improve the understanding of the parameters (e.g., humidity, temperature, pressure, active

chemical moiety) affecting agent chemical inhibition and enhancement, to provide guidance on

the necessary properties of new compounds, or blends, for effective suppression of the FAA‐ACT.

2.	 Develop a better understanding of why 2‐BTP behaves so differently in different flame types.

3.	 Perform a comprehensive exploration of all the possible molecules which might meet the system

requirements (vapor pressure, toxicity, over pressure, flame suppression, etc.) in the FAA‐ACT.

4.	 Determine if blends of agents can work in the FAA‐ACT.

5.	 Understand the flammability behavior of halogenated hydrocarbon fire suppressants in non‐

premixed flames representative of fire threats (i.e., diffusion flames).

6.	 Improve the understanding of the fluid mechanics of agent dispersion and distribution.

9.2 Marginally Flammable Refrigerants Summary

The research recommendations developed in the Marginally Flammable Refrigerants breakout group

(described in the previous section) are listed in Table 2. It was generally agreed that the problem is

likely to be solvable, but that it is complex because it involves many different components and possible

scenarios. Hence, the group embraced the value of a roadmap to delineate the different parts of the

problem that need to be addressed. The research needs emphasized at the workshop highlight some of

the elements of the roadmap, including scenario definition, flammability properties of the compounds,

pressure rise, as well as HF formation and detector improvements. The flammability properties (e.g.,

37
 
                       

                         

                            

                           

                         

                         

                                

                         

                                

                               

             

                                     

                           

                          

                           

                 

                                 

                             

                   

   

                         

   

                         

                     

                       

                 

                   

                   

                   

                 

           

      

                 

                             

response to different ignition sources, flammability limits, minimum ignition energy, burning velocity,

turbulent flame acceleration, overpressure, and critical burning velocity for inertion) are related to the

reactivity of the mixture. The participants affirmed the value of flame measurements and simulations

that improve the understanding of the various parameters influencing the chemical reaction rate, which

ultimately affects flammability. These parameters include the effects of different chemical moieties,

humidity, temperature, and flow‐field on the overall reaction rate; in particular, the importance of

understanding the reaction rate (i.e., burning velocity) of blends of compounds was noted. The need for

improved theoretical and computational tools for predicting pressure rise was endorsed, particularly for

low burning velocity systems, for which current capabilities are known to be limited. Finally, the need

for understanding HF formation and its fate was described, as was better and less expensive sensors for

HF (and for the refrigerants themselves).

It is important to keep in mind that the scope of the workshop was limited to research questions related

to the exothermic reaction of halogenated hydrocarbons when used for aircraft fire suppression, or as

refrigerant working fluids. Thus, research recommendations related to the larger questions (e.g., such

as developing or using other, non‐reacting working fluids, or fire suppressants) were not specifically

addressed, but would supply additional areas needing investigation.

Participants in both industries felt that follow‐up meetings on a regular basis would be helpful, and that

we should move forward to identify the resources and expertise required to solve the problems

discussed.

Table 2 ‐ List of research needs developed in the Marginally Flammable Refrigerants

breakout group.

1.	 Develop a roadmap outlining the information and steps required for safe implementation of

marginally flammable refrigerants.

2.	 Develop a list of possible, plausible, and most common scenarios in which a refrigerant‐air
 

mixture might be ignited, so that the risk and consequences can be determined.
 

3.	 Perform experiments and analyses to understand how the flame type (e.g., premixed vs.
 

diffusion) influences the safe use of marginally flammable materials.
 

4.	 Develop a database of refrigerant leakage rates in the field.

5.	 Determine the ignition properties of marginally flammable refrigerants with air.

6.	 Develop accurate, validated correlations and modeling capabilities for specifying venting
 

requirements to prevent overpressure from flames of marginally‐flammable refrigerants.
 

7.	 Improve the accuracy of overpressure correlations/calculations for marginally‐flammable
 

compounds in air.
 

8.	 Determine the existence of critical burning velocity for explosion risk.

9.	 Develop the capability to predict the flammability of mixtures of R32, R290, CO2, 1234yf, and

1234ze(E).

38
 
             

                   

                     

   

10. Determine the best standard test(s) for refrigerant flammability.

11. Understand the formation of HF from refrigerant / flame reactions.

12. Improve sensors for detection of refrigerant gases or their decomposition byproducts.

39
 
         

                              

                                      

           

10. APPENDIX: PRESENTATIONS CLEARED FOR GENERAL RELEASE

The presentations (as pdfs) are presented below. When the talk was cleared or general release, the

entire talk is given, otherwise, only the title page is given. Many of the talks had embedded videos, and

they are not reproduced here.

40
 
 

 

 

A Perspective on Lower 

GWP Refrigerant 

Performance Tradeoff’s vs 

Open Flammability 

Knowledge Gaps for 

HVACR Products 

Steve Kujak 

Ingersoll Rand 

Refrigerant Technology Leader 

1 
 

 

 

Fluorocarbons as Gaseous Fire 

Extinguishing Agents
 

by
 

Joe Senecal
 

Senior Fellow, UTCFS
 

Kidde-Fenwal, Inc.
 

NIST Workshop on the Exothermic Reaction 

of Halogenated Hydrocarbons
 

October 27, 2014
 

1 
Barriers to using flammable 

refrigerants
 

NIST workshop
 

October 27, 2014
 

Robert Richard
 
 

 

 

 

Problem 

•	 Nearly Everybody Knows 

–	 Flammable hydrocarbons explode. 

–	 Flammable liquids make for big fires that spreads rapidly. 

–	 The flame triangle. 

•	 Professional Knowledge 

–	 Fire marshals – fire fighters 

–	 Chemical process safety 

–	 Academia 

•	 Unknowns 

–	 Fear of not knowing what you don’t know 

–	 The border between small controlled fires and large catastrophic 

events 

What's new about halogenated material and what 

difference does it make? 
 

 

 

 

 

Questions/Outline
 

•	 What is the risk of using flammable refrigerants? 

•	 What have experimenters observed? 

•	 What is needed to mitigate the risk? 

•	 What should be the safety factors employed? 

•	 What is the importance of confinement-congestionunrestricted on vapor cloud ignitions? Leaked/spilled 

refrigerant. 

•	 What is the role of flame stability in ignition, flame 

propagation and extinguishment? 

•	 What can be and to what extent can it be relaxed for 

ASHRAE/ISO flammable class 2L (Su< 10cm/s)? 
 

 

 

 

Observations
 

•	 We need environmentally friendly refrigerant. 

•	 Blends have been employed to meet the required properties 

and still be nonflammable. 

•	 Experience and experimental investigation show that not all 

flammables materials/mixtures have the same hazard. 

–	 The general trend is well described using burning velocity. 

•	 This parameter (burning velocity) is used for classification but 

is not used in designing mitigation for HVAC&R systems. 

Why is burning velocity important
 

and how can/should it be used?
 
 

 

Borderline-Fire suppressant?
 

Lower and upper 

Flame Limit 

R134a can become flammable at higher 

pressures or temperatures if sufficient 

oxygen and an ignition source is present 

R-134a Flammability as f (P)T 

Temp (oC) Pressure (Bars) 

280 1 

25 8 
The risk of using flammable 

refrigerants.
 

• Light 

• Sound 

• Consumption of oxygen 

• Stabilized flame and secondary fires 

• Blast damage – projectiles, structural failure
 
 

 

 

 

 

 

What is needed to mitigate the 

blast risk or risk of a stable flame.
 

• Avoid flammable concentrations (but a leak is at a 

concentration of 100%, flammable zone ATEX )
 

• Eliminate Ignition source (but open flames are common) 

•	 Reduce quantity that leaks 

–	 Reduce total amount, limit charge. 

–	 Mix to uniformly distribute. Allowing larger quantities of flammable to 

be release before exceeding the LFL. 

•	 Use the fact that the minimum ignition energy is high 

•	 Use the fact that flames are buoyant and are unstable. 
 

 

 

 

 

 

 

 

 

What should be the safety factor
 

employed.
 

•	 The greater the hazard of event the greater the effort 

to avoid it should be. The greater the probability of a 

severe event the larger the safety factor. 

– Currently 20% or 25% of LFL if total charge is released and 

uniformly mixed. To account for pooling or unknowns.
 

– Accidental release an concentration that peak ; 75% of LFL 

for short periods of time. 

–	 Design for pooling and concentrations up to the LFL. 

What is the relationship between 

hazardous event and safety factor? 
 

 

 

 

The importance of Confinement
 

•	 The energy of combustion is nearly the same 

for all material of interest. 

•	 The difference is in the rate of release and 

efficiency of the release of this energy, i.e., 

burning velocity and completeness of 

propagation. 
 

 

 

 

What is the role of flame stability
 

in ignition, flame propagation and 

extinguishment.
 

• How can this be used in safety standards,
 

equipment standard, and codes etc.?
 

• Does this allow for relaxation of safety rules?
 

Proper consideration of flame
 

stability
 
 

 

 

 

 

Research Needs
 

•	 Blast models assume rapid kinetics; we need 

models that properly model and are validated 

for slower reacting materials and pneumonia. 

•	 Relationship between reaction rate (burning 

velocity) and severity - probability leading to 

safety factors 

•	 Flame stability has important influence on 

ignition, propagation, extinction, efficiency of 

energy release. 
 

 

 

 

Clean Agents in Explosion Inerting
 Behaviour of fluorinated compounds at
 

sub-inert concentrations in
 

explosion suppression
 

NIST Workshop on the Exothermic Reaction of Halogenated Hydrocarbons
 

Gaithersburg, MD Oct 27-28, 2014
 

Work Carried out by Josephine Gatsonides; Presented by Adam Chattaway
 
 

 

 

 

 

 

 

Flammability Testing in HVAC Configurations using Low
 

GWP, Alternative Refrigerants
 

Presented by Paul Papas 

NIST Workshop on the Exothermic Reaction of Halogenated Hydrocarbons 

October 27-28, 2014 

© 2014 Carrier Corporation. All Rights Reserved. 

No further copies or distribution of, or reference to these materials and content is permitted without Carrier Corporation’s express written permission. The information in these 

slides is provided AS IS; Carrier Corporation makes no warranty with respect to its accuracy and disclaims all liability arising out of use, copying, distribution and/or 

reliance upon information and test results or with respect to reproduction of tests. 
 

Inhibition of Vapor Cloud Explosions
 

Workshop on Exothermic Reaction of Halogenated Hydrocarbons 

27-28 October 2014 

NIST, Gaithersburg 
Fire Safety Journal 71 (2015) 58–68

Contents lists available at ScienceDirect

Fire Safety Journal

journal homepage: www.elsevier.com/locate/firesaf

Quenching distance measurement of highly to mildly flammable

compounds

Kenji Takizawa n, Naoharu Igarashi, Shizue Takagi, Kazuaki Tokuhashi, Shigeo Kondo

National Institute of Advanced Industrial Science and Technology (AIST), Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan

article info abstract

Article history:

Received 20 April 2014

Received in revised form

19 November 2014

Accepted 23 November 2014

Keywords:

Low GWP alternatives

Refrigerants

Quenching distance

Minimum flame radius

Minimum ignition energy

Burning velocity

Microgravity

Quenching distance measurements were carried out for 11 highly to only mildly flammable gases (which

include alkanes, fluorinated alkanes and alkenes, and ammonia) to elucidate the ignition and quenching

characteristics of low-GWP (global warming potential) alternative materials. For buoyant flames of

mildly flammable compounds, conventional 25 mm diameter parallel plates in the vertical position

provided significantly smaller quenching distance (dq) than 100 mm diameter plates in the horizontal

position. A good correlation was obtained between the quenching distance (dq,h in mm) measured by the

latter test apparatus and the maximum burning velocity (Su0,max in cm s1

) for these compounds: −0.926 dq,h = 58.12(ρuSu0, max ) , where ρu is the unburned gas density. The mildly flammable compounds that

have Su0,max below 10 cm s1 have a dq more than three times larger than that of propane. Initial development of the schlieren flame radius was observed for mildly flammable CH2F2/air mixture using thin

electrodes and a variety of spark energies. It was confirmed that the parallel plate quenching distance

was essentially equal to the minimum flame diameter in a free space. By applying the measured dq,h and

Su0,max in the simplified heat loss theory, the minimum ignition energy (Emin in mJ) was expressed by

Emin1⁄40.0712dq,h2.97. The results showed that the mildly flammable compounds have Emin that is more

than an order of magnitude greater than that of propane.

& 2014 Elsevier Ltd. All rights reserved.

1. Introduction

In order to reduce environmental impacts, phase-out of high

global warming potential (GWP) materials is currently a very important issue for the industries related to refrigerants, insulating

foaming agents, and blowing agents. Regulations for the phase-out

of R-134a (CH2FCF3) as a refrigerant of automotive air conditioning

system has already come into effect in the EU and are anticipated to

spread to other regions and applications. Because high-GWP compounds are stable in the atmosphere, the less stable compounds are

now taken into consideration as lower-GWP alternatives. The

properties that make the new compounds have higher reactivity in

the atmosphere also make them more flammable. Considering this

risk tradeoff, low-GWP compounds with mild flammability appear

to be alternatives that provide the optimum balance of acceptable

safety properties and environmental performance. Thus, risk assessments of mildly flammable compounds will need to be made

before they are used in practical applications. (Hereafter, a compound whose maximum burning velocity (Su0, max) is not higher

than 10 cm s1 is called “mildly flammable compound”).

n Corresponding author. Fax: þ81 29 861 4770.
 

E-mail address: k.takizawa@aist.go.jp (K. Takizawa).
 

http://dx.doi.org/10.1016/j.firesaf.2014.11.013

0379-7112/& 2014 Elsevier Ltd. All rights reserved.

Considering the probability of fire hazard due to flammable

gases, minimum ignition energy and quenching distance are some

of the most important indices. Experimentally, minimum ignition

energy (Emin) is the lowest spark discharge energy that can ignite a

flammable gas mixture at the most ignitable concentration. Parallel plate quenching distance (dq) is the minimum distance between two surfaces above which self-sustained propagation of a

flame is achieved. A standard test method for determining Emin

and dq is specified in ASTM E582 [1]. These parameters, if obtained

appropriately, are useful for designing the electrical equipment

that may be deployed in areas with a potentially flammable gas

atmosphere. Table 1 summarizes the published data of Emin and dq

for compounds relevant to this study [2–17]. For propane, the reported Emin range from 0.247 mJ [3] to 0.48 mJ [9]. For mildly

flammable compounds, the reported Emin vary widely from

o10 mJ to 410 J. This makes assessing the fire risk based on Emin

very difficult. The difficulty in determining the reliable Emin is that

it is very dependent on the electrode size, the gap between the

electrodes, and the ignition spark density and duration [3,5,

18–20].

Compared to measuring Emin, measuring dq seems to be much

easier, and provides reliable data on mildly flammable compounds. As listed in Table 1, the reported dq of propane range from

1.7 to 1.9 mm; i.e., they are in good agreement. For mildly
 

 

 

 

 

 

 

 

 

 

 

 

 

2672, Page 1 

Ignition of R-32 and R-410A Refrigerant Mixtures with Lubricating Oil 

Adam BOUSSOUF1, Vivien R. LECOUSTRE2, Hao LI3, Robert BY4, Peter B. SUNDERLAND5,* 

1

University of Maryland, Department of Fire Protection Engineering,
 

College Park, Maryland, USA
 

(+1 301 526 5678, +1 301 405 9383, adamb417@umd.edu)
 

2

University of Maryland, Department of Fire Protection Engineering,
 

College Park, Maryland, USA
 

(+1 301 405 8540, +1 301 405 9383, vlecous1@umd.edu)
 

3

Goodman Manufacturing
 

Houston, Texas, USA
 

(+1 713 263 5650, +1 713 861 5428, Stephen.Li@Goodmanmfg.com)
 

4

Goodman Manufacturing
 

Houston, Texas, USA
 

(+1 713 263 5621, +1 713 861 5428, Robert.By@Goodmanmfg.com)
 

5

University of Maryland, Department of Fire Protection Engineering,
 

College Park, Maryland, USA
 

(+1 301 405 3095, +1 301 405 9383, pbs@umd.edu)
 

* Corresponding Author
 

ABSTRACT 

This study examines the flammability risk of refrigerant and oil mixtures. The flammability risk associated with 

refrigerants is an important property to consider prior to their use in residential and commercial HVAC systems. This 

research was conducted to compare the ignition characteristics of R-32 with R-410A, and the effects of lubricating 

oil. Unpiloted hot-plate ignition tests and computational fluid dynamics (CFD) were used to determine the autoignition 

temperature and ignition probability data. The results indicate that the ignition temperature of R-32 impinging a hot 

plate is 764 o

C. This is 116 oC higher than the reported autoignition temperature of R-32, but it is very close to the 

reported open top autoignition temperature. R-410A was found to ignite at a slightly higher temperature than R-32: 

790 o

C. Tests with polyolester (POE) oil indicate that the R-32 ignition temperature is reduced to nearly that of the 

ignition of oil alone. CFD predictions for a jet of R-32 impacting a hot plate at a temperature close to autoignition 

temperature of R-32 show that ignition should happen only away from the jet point of impact and in rich regions. 

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2672, Page 2 

1. INTRODUCTION
 

Two important risks associated with refrigerants are their environmental impact and their flammability. 

Difluoromethane, or R-32 (CH2F2) is a non-ozone depleting refrigerant with a global warming potential (GWP) of 

675. R-32 is slightly flammable, with flammability limits of 13.3 – 29.3% by volume in air, has a laminar flame speed 

of 6.7 cm/s (Jabbour, 2004), and has a heat of combustion of 9.4 kJ/g. It is classified as a 2L refrigerant (Hihara, 2012). 

R-410A is a mixture of R-32 (CH2F2) and R-125 (pentafluoroethane, formula CH2F2CF3); it is a non-ozone depleting 

working fluid with a GWP of 2088, which is more than three time that of R-32. R-32 has entered service in Japan and 

is being considered for service in the US. However, its adoption is being hindered by its slight flammability in air. 

This work is motivated by the possibility of an accidental release of working fluid within a refrigeration system. Under 

certain conditions, this release may produce mixtures with localized flammable concentrations of refrigerant vapors 

in the surrounding air. This scenario may lead to a subsequent fire if this flammable gas comes into contact with an 

ignition source. Because the vapors are heavier than air, higher concentrations may develop near the floor or near the 

bottom of a refrigerant unit, and this region may remain flammable for an extended period of time. 

The autoignition temperature of a fuel, or AIT, is the lowest temperature at which quiescent isothermal fuel/air mixture 

will spontaneously ignite unaided by an external ignition source. Ignition occurs when the rate of heat produced 

exceeds the rate at which heat is dissipated. 

This study was conducted to better understand ignition risks due to an accidental refrigerant leak within a system using 

R-32 or R-410A. Past research has examined the flammability of pure refrigerants without considering the effects of 

the presence of lubricating oil. The concentration of oil released in a refrigerant leak can vary depending on the location 

of the leak and the operating state of the equipment. In this study, mixtures of R-32 and R-410A with lubricating oil 

are impinged onto a hot horizontal metal surface to examine ignition behavior. The ignition temperatures of R-32 and 

R-410A were determined using hot surface ignition test methods. Additionally, computational fluid dynamics (CFD) 

simulations were performed to provide physical insight associated with hot-plate ignition, to validate ignition 

chemistry, and to aid a systematic risk assessment in various configurations. 

2. METHODS 

The most widely used method to measure the autoignition temperature of liquid fuels is ASTM E659, the Standard 

Test Method for Autoignition Temperature of Liquid Chemicals. This standard provides the conditions for sustained 

combustion of a quiescent, isothermal, homogeneous mixture (simulating a perfectly stirred reactor). In such 

conditions, the reported AIT for R-32 is 648 °C (Goetzler, 1998). However, the original source of this measurement 

is a personal communication with no documentation. In terms of risk analysis, these conditions are unlikely to occur 

in practice and therefore can be considered as conservative. 

The present tests aim to characterize the ignition temperature (IT) of refrigerants through contact with an isothermal, 

hot metallic surface. Figure 1 illustrates the design and components of the isothermal hot plate. The apparatus consisted 

of two 20  20 cm square copper plates. The top cover plate, used as the testing surface, was 6.35 mm thick; the 

bottom plate was 3.175 mm thick. Copper was chosen due to its good thermal conductivity and its resistance to 

oxidation. The test plate was heated using four cylindrical electrical heaters with a diameter of 9.5 mm. Each heating 

element operated at a maximum power density of 11 W/cm2

. The maximum operating temperature of the heating 

elements indicated by the manufacturer is 1150 °C. The four heating elements were powered by two variable 

autotransformers, delivering 120 V and up to 33 A. Exposed sections of the apparatus were insulated with kaowool 

insulating panels (on the sides) and a thick mineral wool insulator minimized the heat losses from the sides and from 

the bottom plate. Additionally, insulation was placed on top of the hot plate surface, providing a 3 cm tall draft shield 

along the outer perimeter of the hot plate. With these precautions, the test plate was kept isothermal, and elevated 

temperatures (up to 900 °C) was reached. The temperature of the hot plate could then be controlled by varying the 

power delivered by the autotransformers. 

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2672, Page 3 

Figure 1: Hot plate schematic. 

The temperature of the hot plate was monitored using two type-K thermocouples. Two small bead thermocouples 

were used, one peened into the center of the plate and the other fixed to the plate edge. The center thermocouple was 

directly under the discharge nozzle and the second thermocouple was used to verify temperature uniformity away 

from the center. The temperatures were recorded with a data acquisition software at a frequency of 10 Hz. The 

experimental uncertainty of the measured temperatures was ± 10 o

C. At elevated temperatures (above 500 °C), 

measurable temperature fluctuations were observed. This is attributed to the increased turbulent motion caused by 

natural convection. 

R-32 and R-410A were delivered in the gas phase at ambient temperature through an aluminum circular nozzle, with 

an inner diameter of 1.58 cm. The delivery assembly consisted of refrigerant hose tubing, a solenoid valve, a singleshot timer relay, a needle valve, soft silicone rubber tubing, and an aluminum discharge tube. Prior to each discharge, 

the programmable timer relay was set to the desired discharge time, between 1 – 2 s, and the needle valve was set to 

the desired flow rate. For each discharge, the release of refrigerant was initiated with a switch, opening the solenoid 

valve. The vertical discharge nozzle was 5 cm above the hot plate. Figure 2 illustrates the experimental apparatus. 

Figure 2: Color image of hot plate. 

Four different cases were tested: pure R-32, pure R-410A, POE oil, and R-32 mixed with oil. Flow rate tests showed 

a negligible influence of the gas flow rate on the observed ignition temperatures. To reduce excessive refrigerant 

release, all subsequent tests were conducted with a constant refrigerant mass flow rate discharge of 1.1 g/s. Pure 

refrigerant was delivered in the gas phase. While the refrigerant supply tank was kept at ambient temperature, some 

frost was noted at the end of each refrigerant injection. For each test, the hot plate was first covered and heated to 800­

900 o

C and maintained for approximately 30 minutes to ensure an even temperature distribution. Once steady state 

was reached, the plate temperature was slowly reduced by either removing the cover insulation or by reducing the 

power supplied to the heating elements. The occurrence of refrigerant mixtures ignition was determined by visual 

inspection and the tests were recorded by video for later analyses. For tests involving a mixture of refrigerant/oil, POE 

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2672, Page 4 

oil was introduced manually using a tube and syringe assembly discharging roughly 0.02 mL of oil. This corresponds 

to an oil-to-gas ratio of approximately 1% by volume. For each refrigerant mixture tested, the test was repeated at 

least three times. In total, approximately 150 tests were conducted. 

3. RESULTS 

Figures 3a, 3b, and 3c show photographs of R-410A, R-32, and POE oil ignition, respectively. They were captured at 

temperatures slightly above their critical ignition temperatures. Several differences in the burning characteristics of 

the fuels were observed: the refrigerants ignited more rapidly than oil, but combustion did not sustain burning after 

injection, whereas oil ignited with a slight delay but combustion lasted longer. A similar relationship was observed 

when oil and refrigerant are introduced simultaneously. For hot plate temperatures above the pure refrigerant critical 

IT, the refrigerant vapor and POE oil mixture ignited simultaneously. For hot plate temperatures below the refrigerant 

IT, oil ignited before the refrigerant. 

(a) (b) (c) 

Figure 3: (a) R-410A ignition at 820 o

C, (b) R-32 ignition at 789 oC, and (c) POE oil ignition at 654 oC. 

For both R-410A and R-32, orange flames were observed close to the plate surface and blue flames were observed at 

the periphery of the burning region. A similar phenomenon was documented in the hot plate ignition report done by 

Bannister et al. (2005), where they described the blue flame regions of fuel/air mixtures as being lean, or oxygen rich, 

but lacked the heat to sustain ignition. This phenomenon is evident in R-32 and R-410A combustion tests. When 

unburned fuel vapors escape the heated plate area, the heat flux provided by the combustion reaction alone was 

insufficient to propagate to unburned vapors and thus the flame self-extinguished. 

Table 1 reports the critical ignition temperatures recorded and compares them with published values. The lowest R32 IT observed was 764 o

C, which is 116 oC higher than the published, albeit in a different setup. Richard (2012) 

reported that the autoignition temperature was above 700 o

C in an open top measurement. This measurement is closer 

to ours. 

The lowest R-410A IT was observed at 790 o

C. POE lubricating oil ignited at 645 oC. Differences between the 

observed IT values and those in the literature arise from the differences in the test conditions or methods used, as 

explained by Affens (1974). Smyth and Bryner (1997) further discussed this, and highlighted the IT dependence on 

the fuel structure, surface material properties, surface temperature, fuel/air stoichiometry, surface size, surface 

orientation, and ambient pressure conditions. 

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2672, Page 5 

Table 1: Present work observed ignition temperature along with values reported in literature. 

Ignition Temperature, in °C 

Fuel 

Present work Literature 

R-32 764 (+/- 10) 648a to >700b 

R-410A 790 (+/- 10) ­

POE Oil 645 371-427c 

R-32 mixed with POE 649 ­ Oil 

a Ref (Airgas, 2010)
 b Ref (Richard, 2012)
 c Ref (Kuchta, 1968)
 

Many literature sources report R-410A as a non-flammable refrigerant, but it was found here to burn. The measured 

critical ignition temperature of pure R-410A is 26 o

C higher than pure R-32. Furthermore, the addition of 1% POE oil 

lowers significantly the IT of R-32 refrigerant/oil mixtures, to a value very close to the ignition temperature of the oil. 

In this study, we found that the ignition temperature of the POE oil is 645 o

C. Tests show that when mixed with this 

oil, the ignition temperature of R-32 is reduced to 649 o

C; a decrease of 125 oC .The oil provides sufficient energy to 

ignite the refrigerant vapors. Further results are depicted graphically in Figure 4. 

Figure 4: Hot-plate ignition temperature for pure R-32, POE oil alone, and a 1% mixture of R-32-oil. 

4. CFD MODEL 

To provide an improved understanding of the experiments, a LES code, the Fire Dynamics Simulator (FDS, 

McGrattan, 2013) was employed. This section presents results predicted for the configuration of pure R-32 injected 

at a mass flow rate of 1.1 g/s and impinging the hot plate set at a temperature corresponding to the measured ignition 

temperature of R-32, 764 o

C. Note that while the code features combustion capabilities, these were not used here. 

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2672, Page 6 

The Fire Dynamics Simulator (FDS) is an open-source Fortran program written by the National Institute of Standard 

and Technology (NIST) and it is widely used in the fire modeling. FDS is a Large Eddy Simulation solver that solves 

the Navier-Stokes equations with the Low Mach Number assumption. See McGrattan et al. (McGrattan, 2013a) for a 

complete description of the code. 

The numerical configuration for this work is similar to that of the experiment. The mesh consists of 130 points in the 

x and y directions and 49 points in the z-direction, taken as the vertical direction. The mesh spacing is 1.75 mm in the 

x and y direction and 1.25 mm in the z-direction. The dimensions of the computational domain are 227.5 mm in x and 

y directions, and 61.25 mm in z direction. The computational description is illustrated in Figure 5. The injection nozzle 

outlet is modeled with 8 points across in both directions. Due to the limitation of FDS, which can only model regular 

Cartesian geometry, the nozzle is modeled as a rectangular parallelepiped instead of a cylinder. The dimensions of the 

nozzle outlet (injection zone) were adjusted to match the area of the cylindrical nozzle used in the experiment. The 

mass flow rate of injected R-32 is set to 1.1 g/s. This corresponds approximately to an injection velocity of 2.8 m/s. 

The nozzle temperature is set to 0 o

C, as it was observed during the experiment that some frost was forming on the 

nozzle during the injection of R-32. The nozzle is located 55 mm above the hot plate. The hot plate spans 203 mm in 

x and y directions and it is flanked by an insulated 30 mm high draft shield. The hot plate is modeled as an isothermal 

surface with a surface temperature of 764 o

C. The insulated draft shield is also modeled as an isothermal surface, with 

a surface temperature of 394 o

C. This value was chosen to account for the heat addition that originates from the hot 

plate. Open boundary conditions are applied in Z = Zmax, and on the vertical sides. A rough wall log-law is used as a 

wall model to describe the interactions flow/hot plate. 

Isothermal insulation, T = 394°C 

Isothermal nozzle, T = 0°C 

Isothermal hot plate, T = 764°C 

Figure 5: Geometrical description of the FDS computational domain. Open boundary conditions are used. 

The simulation was initialized with still air at ambient condition (25 o

C and 1.01 bar) and was run for 2.0 s prior to R32 discharge to simulate the development of a turbulent buoyant flow generated by the presence of the hot plate. The 

injection of R-32 at a mass flow rate of 1.1 g/s was imposed for 1.5 seconds using a progressive linear ramp of 0.1 s. 

It was maintained steadily until 3.5 s, after which time it was stopped, again using a linear ramp. The simulation was 

stopped at 5.0 s, as it was of interest to study the presence of R-32 after the injection. 

The near-wall resolution on the hot plate was verified a posteriori by checking the value of y+ at the first grid cell 

above the hot-plate. Its maximum value is 6, which corresponds to a considered highly resolved simulation 

(McGrattan, 2013b). An additional a posteriori test was performed to measure the error associated with the mesh 

discretization on the velocity and scalar fields. It consists of assessing the fraction of unresolved turbulent kinetic 

energy over the whole turbulent kinetic energy, referred to as the measure of turbulence resolution (Pope, 2004). This 

dimensionless criterion takes the value of 0 for a perfect resolution and 1 for a poor resolution. A recommended 

practice is to keep this value lower than 0.2. It is found that this criterion is observed everywhere in the domain except 

in a ring located between 1 – 2 nozzle diameters away from the point of impact of the jet with the hot plate (or 

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2672, Page 7 

stagnation point, located at the origin), where the maximum value is 0.3. This is considered satisfactory for this 

simulation as the area of interest is located away from the stagnation point. 

Figure 6: Cross section (at y = 0) of the temperature field and the contours of constant R-32 concentration at different 

times. The injection of pure R-32 from the nozzle starts at t = 2.0 s and continues for 1.5 s, until t = 3.5 s. The 

simulation ends at 5.0 s. Figure (a) plots the instantaneous conditions prior to R-32 injection at t = 1.9 s, (b) plots 

instantaneous conditions at t = 3.0 s during R-32 injection from the nozzle at x = 0 cm and z = 5.5 cm, (c) plots 

averaged conditions during R-32 injection between 3 and 3.5 s, and (d) plots the instantaneous conditions at the end 

of the simulation (t = 5 s), which is 1.5 s after the end of the R-32 injection. The solid line corresponds to where the 

R-32 concentration is at the lower flamability limit (13% in volume) and the dashed line corresponds to where the R32 concentration is at the upper flamability limit (30% in volume). Neither (a) nor (d) has significant R-32 

concentration levels. 

Figure 6 plots the temperature fields and the contours of constant R-32 concentration corresponding to the ambient 

lower flammability limits (13% in volume) and the ambient upper flammability limit (30% in volume) of R-32 in air. 

The fields depicted correspond to the cross-section along the x and y directions at the location of y = 0 mm. Figure 6a 

plots the instantaneous fields prior to the R-32 injection, at 1.9 s. The turbulent nature of the buoyancy induced flow 

can be readily seen. As the air near the hot plate is heated, it rises and induces a turbulent motion, with a maximum 

vertical speed of 0.5 m/s. Some pockets of hot air are present in the domain. Figure 6b plots the instantaneous 

temperature field and the contours of constant R-32 concentration at t = 3.0 s. This is 0.5 after the start of injection 

and it corresponds to a turbulent steady state behavior. Figure 6c plots the average temperature field and contours of 

constant R-32 concentration over 0.5 s between 3.0 and 3.5 s. This plot illustrates the motion of the flow during the 

experiment. As the flow impinges the hot plate, it is conveyed toward the edge of the plate. During this process, it is 

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2672, Page 8 

heated and its temperature rises above 600 °C near the draft shield, more than 9 cm away from the point of impact. 

Near the draft shield, a stagnant zone exists, which is characterized by elevated temperatures and slow velocities. This 

implies that conditions propitious to R-32 ignition are to be expected near the draft shield and away from the jet point 

of impact. Figure 6d plots the temperature field at the end of the simulation. The discharge of R-32 had stopped 1.5 s 

earlier. Similar to Fig. 6a, buoyant turbulent structures can be readily observed. No significant concentration of R-32 

remains; the concentration of R-32 falls below the lower flammability limit (13% in volume) about 0.9 seconds after 

the end of R-32 injection. 

To gain a better understanding of the temperature variations with the distance from the jet point of impact (located at 

x = 0), values of temperature along the contours of constant concentration corresponding to the ambient lower 

flammability limit (XR-32 = 0.13), stoichiometry (XR-32 = 0.174) and the ambient upper flammability limit (XR-32 = 

0.30) were extracted from Fig.6c. Figure 7 plots these data along the location in the x direction. Away from the jet 

point of impact, the temperature increases with the concentration of R-32 (higher concentrations correspond to higher 

gas temperature) and, for a given concentration, the temperature increases away from the jet point of impact. Figure 

7 shows that temperature at constant concentration reaches its maximum near the draft shield. Figure 7 indicates that 

conditions corresponding to the greatest R-32 concentration, XR-32 = 0.30, has the highest temperature, 270 o

C, at |x| 

= 0.09 mm. This indicates that ignition is likely at locations in refrigerant rich conditions, i.e., at locations where the 

R-32 concentration is above the stoichiometric value and far from the center of the plate and near its edges. 

Figure 7: Temperature profiles along the x direction of different contours of constant R-32 concentration: 0.13 

(which corresponds to lower flammability limit at ambient conditions) in red, 0.174 (stoichiometric) in black, and 

0.3 (which corresponds to upper flammability limit at ambient conditions) in blue. Data were extracted from Figure 

6c and correspond to averaged values over 0.5 s. 

5. CONCLUSIONS 

The experimental ignition temperatures of pure R-32 and R-410A refrigerants along with the ignition temperature of 

these refrigerants mixed with liquid POE oil were studied using a hot-plate configuration with a surface temperature 

varying from 200 – 900 o

C. The hot-plate ignition temperature of R-32 was found to be 764 oC (± 10 oC), while that 

for R-410A was found to be at 790 o

C (± 10 oC). When mixed with POE oil, the ignition temperature of the R-32 

refrigerant/oil mixture was found to be very close to that of the POE oil (649 o

C) employed in this study. The presence 

of ignited oil was found to be a driving factor of subsequent refrigerant ignition. CFD simulations using a LES code 

were performed to simulate the discharge of pure R-32. Simulations at 764 o

C suggest that ignition begins away from 

the jet point of impact and for R-32 concentrations above that of stoichiometry. This work is a first step in providing 

an extensive fire risk assessment associated with the use of R-32 in HVAC systems as a replacement for R-410A. 

15th International Refrigeration and Air Conditioning Conference at Purdue, 2014 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2672, Page 9 

ACKNOWLEDGEMENTS
 

The authors would like to thank Reinhard Radermacher, Jan Muehlbauer, Masoud Pourali, and Olga Zeller for their 

guidance, support, and help. Special thanks to Tyler Pierce for his laboratory assistance. The authors are also grateful 

to Dr. Chun-Cheng Piao of Daikin R&D for his sponsorship of this research and for his review of this paper. 

REFERENCES 

Affens, W., et al., 1974, The Determination of Autoignition Temperatures of Hydrocarbon Fuels, Naval Research 

Laboratory, Washington D.C. 

Airgas Inc., 2010, Difluoromethane R32, Material Safety Data Sheet, MSDS # 001054 

Bannister, W., Donatelli, A., Bonner, F., Lai, F., Kurup, P., Egan, J., Jahngen, E., Muanchareon, P., Paramasawat, W., 

Sriseubsai, W., Chiang, S., Kongkadee, V., Sengupta, S., Nagarajan, R., Euaphantasate, N., Parma, V., 

Cazeca, M., Chen, E., and Morales, A., 2005, Anionic Effects in Hot Surface Combustions. 

Bennett, C., 2011, Laminar Burning Speed and Flame Structure of 1,1-Difluoroethane (HFC-152A)/Air and 

Difluoromethane (HFC-32)/Air Mixtures, The Department of Mechanical and Industrial Engineering, 

Northeastern University, Boston, MA. 

Goetzler, W., Bendixen, L., Little, A., 1998, Risk Assessment of HFC-32 and HFC-32/134a (30/70 wt. %) in Split 

System Residential Heat Pumps Final Report, The Air Conditioning and Refrigeration Technology Institute. 

Hihara, E., 2012, Risk Assessment of Mildly Flammable Refrigerants, Graduate School of Frontier Sciences, The 

University of Tokyo, p. 1-8. 

Jabbour, T., 2004, Flammability refrigerant classification based on the burning velocity, Ph.D. thesis in Energy 

Science, Ecole des Mines de Paris, Paris, France. 

Kataoka, O. 2013, Safety Considerations When Working With 2L Flammability Class Refrigerants, The Institute of 

Refrigeration. 

Kuchta, J., 1968, Review of Ignition and Flammability Properties of Lubricants, Bureau of Mines, Air Force 

Propulsion Laboratory Research and Technology Division, Wright-Patterson Air Force Base, Ohio. 

McGrattan, K., McDermott, R., Weinschenk C., Overholt K., Hostikka S., Floyd J., 2013, Fire Dynamics Simulator 

Technical Reference Guide, NIST Special Publication 1018, 6th edition. 

McGrattan, K., Hostikka, S., McDermott, R., Floyd, J., Weinschenk, C., Overholt, K., 2013, Fire Dynamics Simulator 

User’s Guide, NIST Special Publication 1019, 6th edition. 

Pope S.B, 2004, Ten questions concerning the large eddy simulation of turbulent flows. New Journal of Physics, 6:1­

24. 

Richard, R., Spatz, M., Yana Motta, S., 2012, Hot Surface Ignition with 2L Refrigerants, Honeywell Buffalo Research 

Laboratory. 

Smyth, K., Bryner, N., 1997, Short-Duration Autoignition Temperature Measurements for Hydrocarbon Fuels Near 

Heated Metal Surfaces, National Institute of Standards and Technology, Building and Fire Research 

Laboratory, Gaithersburg, MD. 

15th International Refrigeration and Air Conditioning Conference at Purdue, 2014 
 

Laminar Flame Speeds of 

Hydrofluorocarbon-Air Mixtures
 

Experiments and Modeling
 

Paul Papas, Shiling Zhang, WonWook Kim, Steve Zeppieri, 

Med Colket, Parmesh Verma
 

Presented by Med Colket (retired)
 

United Technologies Research Center
 

E. Hartford, CT 06108
 

NIST Workshop on the Exothermic Reaction 

of Halogenated Hydrocarbons
 

Gaithersburg, MD
 

October 27-28, 2014
 

© 2014 Carrier Corporation. All Rights Reserved.
 
 

 

 

 

 

 

for Understanding Explosive 

Behavior of Mildly Flammable 

Experimental and 

Numerical Approaches 

Combustible Gases 

Scott Davis, PhD, PE 

NIST Workshop – October 27, 2014 
 

 

 

 

Outline 

• Background of explosion risk and consequences 

• Bench scale experimental tests 

• Large scale experimental tests 

• Numerical modeling of consequences 

© GexCon 2 www.gexcon.com 
 

	
   	
   	
   	
   	
  

	
   	
  

-­‐ 	
   	
  

	
   	
   	
   	
  

	
   	
  

Gas explosions: chain of events
 

Release Gas or

Liquid

Flammable /

Combus@ble	
  

No Igni@on	
  

Immediate Igni@on	
   Fire

Forma@on of

Combus@ble	
  

Fuel air Cloud

(premixed)	
  

Delayed Igni@on

Gas	
  Explosion

No Damage

Fire

Damage	
  or	
  

Injuries	
  

Fire, BLEVE,

Escala@on	
  

Flash fire

© GexCon 3 www.gexcon.com 
Explosion Risk 

Probability x Consequence

• Loss of containment	
   • Fuel type -­‐ reacGvity

• IgniGon source – probability • ConcentraGon of fuel

• Gas cloud accumulaGon • Layout	
  

• Mechanical venGlaGon • Obstacle density “congesGon”

• Pipe size and inventory • Type of gas cloud

• VenGng present	
  

© GexCon 4 www.gexcon.com 
 

 

Basic Parameters – combustion 

properties 

• Flammability limits or explosivity limits 

• Laminar burning velocity – reactivity 

• Ignition 

• Minimum ignition energy 

• Auto-ignition temperature 

© GexCon 5 www.gexcon.com 
Explosive part of the cloud 
 

© GexCon 

www.gexcon.com 6 
© GexCon 

Laminar burning velocity 
 

7 www.gexcon.com 

R32, ammonia	
  

Su ~ RR1/2
 

 

 

 

 

Ignition – what is it 

•	 A process where a sufficiently amount of energy is 

transferred into a small volume of explosive atmosphere 

to initiate self sustaining flame propagation. 

Heatin + radical spicesin > Heatout + radical spicesout 

© GexCon 8 www.gexcon.com 
Ignition energy (electric spark) 

§ Hydrocarbons: MIE = 0.1 – 0.3 mJ

§ R32: MIE ~ 15 mJ, Ammonia: MIE ~ 21 mJ

© GexCon 9 www.gexcon.com 
 

 

 

 

 

 

 

 

Auto-ignition temperature 

•	 Theoretical lowest temperature of a hot surface at which 

a mixture of fuel and air can ignite 

•	 Methane 537°C c 

•	 Propane 450°C c-c-c (linear) 

•	 N-heptane 206°C 

•	 iso-octane 415°C (branched) 

•	 R32 648°C 

•	 Ammonia 651°C 

c-c-c-c-c-c-c (linear) 

© GexCon 10 www.gexcon.com 
 

Explosions 

• Rate of pressure rise vs. rate of venting gases 

© GexCon 11 www.gexcon.com 
 

 

Turbulent combustion 

•	 Turbulence causes an increase of burning velocities due 

to an increased flame surface area 

Flame speeds (expansion +

combusGon) can vary from 5

to more than 600 m/s

© GexCon 12 www.gexcon.com 
 

 

Experiments – cross flow 

obstructions - no confinement 

© GexCon 13 www.gexcon.com 
Experiments – congested vs. 

uncongested 

© GexCon 14 www.gexcon.com 
15 © GexCon

www.gexcon.com 

Venting 
16 © GexCon

www.gexcon.com 

Bench scale tests 

• Flammability limits (LEL – UEL) 

• Ignitibility tests 

• MIE – for very low LBV may suffer from “flame quenching” 

• AIT 

• Laminar burning velocity – reactivity 

• Deflagration indexes: Kg (quiescent) or KSt (turbulent) 
17 © GexCon

www.gexcon.com 

Ignition tests 

• For very low LBV may suffer from “flame quenching” 

• May differ from the actual release/environment 
18 © GexCon

www.gexcon.com 

Laminar burning velocity 

• Buoyancy has a great effect for mildly burning fuels 

• Difficult to overcome in 1g environments 
19 © GexCon

www.gexcon.com 

Explosivity tests – 20 liter sphere 

dP

dt	

max	

Pressure	

Time	

Pmax	

Kg	or	KSt=dP/dt[max]	V1/3			Op;mum	concentra;on	
20 © GexCon

www.gexcon.com 

20 liter 

• Confined (no venting) 

• Can evaluate effects of turbulence 

Pressure

Time	

High	reac4vity medium

Low	reac4vity
21 © GexCon

www.gexcon.com 

Large Scale tests - modeling 

• Validate the “actual” effects at the large scale 

• Evaluate rate of pressure rise versus venting 

• Evaluate ignition 

• Validate turbulence effects 

• Enhancing or inhibiting 

• Validate CFD models 
22 © GexCon

www.gexcon.com 

Geometry 
23 © GexCon

www.gexcon.com 

Low vs. High Momentum Release 
24 © GexCon

www.gexcon.com 

Laminar Burning Velocity 
25 © GexCon

www.gexcon.com 

Unvented 

Typical	Burning		

Velocity	

Low	Burning		

Velocity	
26 © GexCon

www.gexcon.com 

Unvented 

Similar	Peak		

Pressures	

Longer	Build	Up	Time	

Shorter	Build		

Up	Time	
27 © GexCon

www.gexcon.com 

0.25 m2 Vent 

Typical	Burning		

Velocity	

Low	Burning		

Velocity	
28 © GexCon

www.gexcon.com 

0.25 m2 Vent 

Higher	Peak		

Pressures	

Low	Peak		

Pressures	
29 © GexCon

www.gexcon.com 

0.25 m2 Vent With Congestion 

Higher	Peak		

Pressures		

Lower	Peak		

Pressures	

Peak	Pressure		

Almost	Double	From	

	the	Uncongested	Case	
30 © GexCon

www.gexcon.com 

0.25 m2 Vent With Congestion 
31 © GexCon

www.gexcon.com 

Rich Layer 
32 © GexCon

www.gexcon.com 

Rich Layer 
33 © GexCon

www.gexcon.com 

Summary 

• Explosion risk is based on both the likelihood of having 

an event and its potential consequences 

• Need to develop a method of evaluating the relative risk 

of mildly burning combustible gases 

• Based on “standard” bench scale tests 

• Validated on large scale 

• Incorporated into advanced 3D models. 

• Update predictive 3D models to accurately predict the 

potential consequences of release events 
GexCon 

sgdavis@gexcon.com
Review of Regulations, Standards, and Codes related 

to reductions in Global Warming Gas Emissions and 

to Support the Use of New Refrigerant Options 

NIST Workshop- October 27-28, 2014 

Richard Lord – Carrier & ASHRAE Fellow 

Revision 3 

© 2014 Carrier Corporation. All Right Reserved 
The Use of Thermodynamic and Chemical Kinetic Models to 

Understand Explosive Behavior of Mildly Flammable 

Combustible Gases 

NIST Workshop on the Exothermic Reaction of Halogenated Hydrocarbons

Gaithersburg, MD Nov. 27-28, 2014

Greg Linteris*, NIST Fire Research 

Jeff Manion / Wing Tsang / Don Burgess, NIST Chemical Kinetics

Valeri Babushok, (NIST GR)

Vish Katta, Innovative Scientific Sol. Inc. 

Fumi Takahashi, Case Western Reserve Univ. 

Peter Sunderland, John Pagliaro Univ. of Maryland

 

*Presenter 

The work was supported by The Boeing Company, NIST Internal Funds, ARRA Grant. 

Kinetics

Flame modeling

Experiments
FAA-Aerosol Can Test (FAA-ACT)

Goal: Understand the overpressure 

phenomena in the FAA Aerosol 

Can Test

1. Why is the overpressure occurring 

with the added suppressants—

which were expected to inert the 

explosion?

2. Connection to refrigerants?

1. Pressure vessel (v= 11.4 m3) 

2. Pinit ≈ 1.01 mPa ; Tinit =13 ± 9 oC

3. Fuel: ethanol+propane+water 

spray. 

4. Ignition: constant high-voltage 

DC arc, (max 10 kV, 20 mA). 

FAA Aerosol Can Test Chamber

η 
2-BTP

Novec 1230

HFC-125

No agent

1301

FAA-Aerosol Can Test (FAA-ACT)

When added at sub-inerting concentrations, pressure rise is higher than with no agent. 
Pressure rise in FAA-ACT with added suppresants
Pressure rise in FAA-ACT with added suppresants
Pressure rise in FAA-ACT with added suppresants
Pressure rise in FAA-ACT with added suppresants
Pressure rise in FAA-ACT with added suppresants

=> Can we understand the reasons for 

the different pressure rise with the 

different agents? 
To Estimate Pressure Rise: Use Thermodynamics

Assume fuel and oxidizer mix in ratio which gives peak temperature (like a typical 

diffusion flame).

η − fraction of chamber oxidizer that reacts. 

1-η − fraction of chamber oxidizer that is inert.

Find η as that which gives peak Tad. 

Let reacting (η)fraction go to equilibrium products.

Mix with inert (1-η) fraction. 
Halon 1301: Adiabatic Flame Temperature (Tad) Thermodynamic Equilibrium Calculations

1000

1500

2000

0.0 0.2 0.4 0.6 0.8 1.0

Taft / K Xi

η

0.118

0

e.)

1000

1500

2000

0 1 2 3 4 5 6

0.0

0.1

0.2

0.3

0.4

Taft,max / K 0.5

η ( 

Taft,max )

X I Fraction of Vessel Air Involved in Combustion, η f.) (%) Inhibitor Volume Fraction in Oxidizer, Xi (%)
HFC-125: Adiabatic Flame Temperature (Tad) Thermodynamic Equilibrium Calculations

1000

1500

2000

0.0 0.2 0.4 0.6 0.8 1.0

Taft / K

Xi 

0

Fraction of Chamber Volume Involved in Combustion, η

0.144

0.072

a.)

1000

1500

2000

0 5 10 15

0.0

0.2

0.4

0.6

0.8

1.0

Taft,max / K 1.2

η (

Taft,max )

Inhibitor Volume Fraction in Oxidizer, Xi b.) (%) Inhibitor Volume Fraction in Oxidizer, Xi (%)
0

1

2

3

4

5

1000

1500

2000

0 2 4 6 8 10

Tad, max / K

ηmaxT

Inhibitor Volume Fraction in Oxidizer, Xinh (%)

10 %

1000

1500

2000

0.0 0.2 0.4 0.6 0.8 1.0

Tad / K Xinh 

η

0

0.100

0.027

0.053

Fraction of Vessel Air Involved in Combustion, η 

Tad / K Tad, max X / K inh

η Xinh

ηmaxT

Novec 1230: Adiabatic Flame Temperature (Tad) Thermodynamic Equilibrium Calculations
For most agents, pressure rise can be predicted based on thermodynamics.

- Thermodynamics determines possible pressure rise.

- Kinetics determines fraction of pressure rise achieved.

- For the alternative agents, kinetics is generally not important except at the inertion point. Return

0

2

4

6

8

0 5 10 15

Pressure Rise at η {ypeak Pressure Rise at η {y } / bar peak Pressure Rise at ηmax / bar } / bar

2-BTP

HFC-125

halon 1301

Inhibitor Volume Fraction in Air 

Novec 

1230

----- lines: Predictions.

 ● circles: FAA Experimental Results
Predicted vs. measured pressure rise in FAA-ACT with added suppresants
Predicted vs. measured pressure rise in FAA-ACT with added suppresants
Predicted vs. measured pressure rise in FAA-ACT with added suppresants
Predicted vs. measured pressure rise in FAA-ACT with added suppresants
Predicted vs. measured pressure rise in FAA-ACT with added suppresants

⇒ When is ∆P not predicted well?

⇒ Look at kinetics. 
Kinetic limitations to pressure rise in FAA-ACT

Estimate variation in overall reaction rate with:

- Agent type

- Xinh

− η 

To do this, we need:

- A kinetic mechanism.

- A reaction rate measure.

- The reactants. 
Kinetic Mechanism* 

Aerosol Can Test Kinetic Model Species Reactions Type

C3-C4 Hydrocarbon mechanism (Wang et al.) 

with C2H50H reactions (Dryer et al.) 116 820 Acquired

NIST C1, C2 HFC, for hydrocarbon flame 

inhibition + update for pure flames

171 1467 Updated,

Developed

FM200 178 1504 Updated

Novec 1230 181 1513 Developed

CF3Br 181 1568 Updated

CF3I 181 1563 Updated

2-BTP 188 1609 Developed

HCFC-123 242 1959 Developed

* It should be emphasized that the mechanisms adopted for the present calculations should be considered only as a 

starting point. Numerous changes to both the rates and the reactions incorporated may be made once a variety of 

experimental and theoretical data are available for testing the mechanisms.
Many available.

We use: 

- Laminar burning velocity (SL) 

- Perfectly-stirred reactor (PSR) overall rate (ωpsr).

(these are related).

Both: 

- measured or 

- calculated 

Using:

- detailed kinetic mechanisms and 

- conservation equations. 

Reaction Rate Measure
0

500

1000

1500

2000

2500

0.0001 0.001 0.01 0.1 1 10

 Residence Time / s

Reactor Temperature / K

XC2HF5 = 0 %

7.7

14.4

η ≈ 0.65

50 % r.h.

0.43 2.4 τ = 32 ms

i in

i in

h

Y

m

,

,



outi

outi

h

Y

m

,

,

V 

P

T

Yi

Just above the blowout flow rate, 

τchem= τres 

 ωpsr = 1 / τres = 1/ τchem 

(estimate of overall chemical rate at T).

To find the blow-out condition:

- calculate Tpsr at decreasing values 

of the residence time, τres. 

- Tpsr drops to inlet temperature at 

blow-out). 

Overall Chemical Rate from PSR (ωpsr) 
Reactants:

Get from:

- initial loading of agent Xinh (specified)

- fuel-oxidizer ratio (η) (from that which gave peak Tad) 
How does reaction rate of system vary with η and Xinh? 

Perform PSR simulations over range of :

- Agent type

- Xinh

− η 
- Adding 1301 always lowers ωchem (for all η)

- ωchem falls off very steeply with η (for all Xinh; follows temperature results).

Perfectly-Stirred Reactor (PSR) Overall Chemical Rate with 1301

1

10

100

1000

10000

0.0 0.2 0.4 0.6 0.8 1.0

Xinh

0

η

0.024

ωpsr / s-1 

0.046

CF3Br
- Adding R-125 lowers ωchem for rich mixtures (low η), but raises (then lowers) it for lean mixtures (high η). 

−η has a big effect on overall chemical rate at low Xi

, less effect at high Xi (follows temperature results).

- i.e., for higher Xi

, these curves flatten ( ωchem is insensitive to η for η > 0.4 ).

Perfectly-Stirred Reactor (PSR) Overall Chemical Rate with R-125

1

10

100

1000

10000

0.0 0.2 0.4 0.6 0.8 1.0

Xinh

0

η

0.072

ωpsr / s-1 

0.133

C2HF5
Perfectly-Stirred Reactor (PSR) Overall Chemical Rate with Novec

1

10

100

1000

10000

0.0 0.2 0.4 0.6 0.8 1.0

0.00

0.55

1.09

1.63

2.16

2.69

3.20

3.72

4.23

4.73

5.23

5.72

6.21

6.69

7.17

7.64

8.11

8.58

9.04

ωpsr / s-1

Fraction of Vessel Volume Involved in Combustion, η

Xinh

C6F12O

0

0.100

0.011 0.037

0.042

0.047

Xinh
Perfectly-Stirred Reactor (PSR) 2-BTP Use Pressure Rise to get η 

1

10

100

1000

10000

0.0 0.2 0.4 0.6 0.8 1.0

Xinh

0

η

0.04

0.02

ωpsr / s-1

0.06

CH2CBrCF3

1.8 1.3 1.0 0.8 0.7 0.6 0.5 0.4 0.3
1

10

100

1000

10000

0.0 0.2 0.4 0.6 0.8 1.0

Xinh

0

η

ωpsr / s-1 C6F12O

0.100

0.011

0.037

0.042

0.047

0.052

Green dots: η = η(Tad,max) 

ωpsr,critical = 16 s-1 

(Xinh=0.08, η = 1)

η 

Perfectly-Stirred Reactor (PSR) Novec 1230 Use Pressure Rise to get η 
=> Want to compare ωpsr of alternative agents with that of CF3Br.

But! We don’t know η for CF3Br.

Kinetic Limitations to Pressure Rise
1

10

100

1000

10000

0.0 0.2 0.4 0.6 0.8 1.0

Xinh = 0 % 

ωpsr / s-1 

η 

ωpsr / s-1 

XC2HF5 = 7.2 %

XC2HF5 = 13.3 %

Overall Reaction Rate with Added HFC-125 (η from ∆P)
1

10

100

1000

10000

0.0 0.2 0.4 0.6 0.8 1.0

Xinh = 0 % 

ωpsr / s-1 

η 

XCF3Br = 2.4 %

ωpsr / s-1 

XCF3Br = 4.6 % XC2HF5 = 7.2 %

XC2HF5 = 13.3 %

Overall Reaction Rate with Added CF3Br (η ?)
But we can get η from experiments with CF3Br / N2 mix in FAA-ACT.
0 00

0 00

000 0 0

0 0 0 0 0

0 0

0

0

0 0 0 0

0 0

0

0 0

0 0 0 00

0 0

0 0

0

0

0

0 0

1 1

1

1 1

1 1

1

3

3

3

3

8

8

8

8 8

12

12

12

12

12

18 18

18 18

18

18

18

18 18

18

25

25

25

25

y = 0.0615x2 - 1.6472x + 11.057

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

10 12 14 16 18 20

O2 Mole Fraction in Air / %

CF

3Br Mole Fraction in Air / %

Flammable

non-Flammable

FAA-ACT with CF3Br with Varying XO2,ox
Inertion Cond. of Mixtures of CF3Br and N2 all imply ≈ same value of η and ωpsr

1

10

100

1000

10000

0.0 0.2 0.4 0.6 0.8 1.0

21 / 3.5 

16 / 0.5

17 / 1.0

18 / 1.6

19 / 2.2

20 / 2.8

15 / 0.0

% O2 / %CF3Br

Fraction of Chamber Volume Involved in Combustion, η

ωpsr / s-1

XCF3Br/N2 Blends 
1

10

100

1000

10000

0.0 0.2 0.4 0.6 0.8 1.0

21 / 3.5 

16 / 0.5

17 / 1.0

18 / 1.6

19 / 2.2

20 / 2.8

15 / 0.0

% O2 / %CF3Br

Fraction of Chamber Volume Involved in Combustion, η

Xinh = 0 % 

ωpsr / s-1

XCF3Br/N2 Blends 

XC2HF5 = 13.3 %

XC6F12O= 8.1 %

CF3Br / N2 Mixtures Show 

that in Turbulent Zone, 

the overall reaction rate 

must be lowered below 

about 1800 s-1 for inerting 

(i.e., lower rxn rate by 5x)

Whereas with added R125, 

Novec, or 2-BTP, the 

overall reaction rate must 

be lowered to about 20 s-1

for FAA-ACT extinction 

(i.e., 100x lower reaction 

rate than in the turbulent 

zone).

Return

For inertion of the FAA-ACT, HFC-125, 2-BTP, or Novec 1230 must lower the reaction 

rate 100 x more than CF3Br/N2 mixtures

Uninhibited flames have 

a reaction rate of about 

9000 s-1. 
Strain rate varies over chamber domain

Droplet evaporation, 

turbulent pre-mixing

Arcing igniter

The core region near 

the fuel spray is high 

strain, and easy to 

extinguish.

Air - agent 

mixture

Fuel discharge port 

(propane/ethanol/water)

Secondary reaction 

of the agents with air 

occurs at low strain, 

and is hard to 

extinguish.

=> Adding a mildly flammable agent creates low-strain regions that are harder to extinguish 
These mixtures, nearly pure suppressant and air, were burning at conditions at which 

their burning velocity was only about 1 cm/s*. 

If you have something that is mildly flammable, and you get it burning with some 

other strong ignition source, it can burn, even at very low SL, if the conditions are right, 

and create overpressure. 

=> Does this matter for the safe use of 2L refrigerants?

⇒ Does this matter in the use of fire suppressants in systems other than aircraft cargo 

bays? (e.g., engine nacelles, flammable liquid storage areas, battery backup rooms, 

energized electrical equipment, etc.)

⇒ Simple analyses based on fundamental thermodynamic and kinetic considerations 

can teach us a lot about the dynamics of these systems. 

* More calculations are necessary to really pin down this number.

Moral of the Story
Reduced-Scale Experiments for Screening, Model 

Validation and Understanding Full-Scale Results of 

Marginally-Flammable Mixtures

JOHN PAGLIARO

DEPARTMENT OF MECHANICAL ENGINEERING

UNIVERSITY OF MARYLAND

SPONSORS: BOEING, ARRA GRANT

CONTRIBUTORS: G. T. LINTERIS, V. I. BABUSHOK, P. B. SUNDERLAND, P. BAKER
Outline

1. Experiments

a. Devices

b. Results

c. Screening

2. Model Validation

a. Models 

b. Approach

c. Results
Used to measure: 

1. Flammability limits

2. Max explosion pressure

3. Rate of pressure rise (dP/dt) 

4. SL 

2 L Constant V Chamber => Pressure Rise

CH4-air 

SL = R

3 1 − 1 − x

P0

P

1

γu �

−2

3�

P0

P

1

γu � dx

dd

Pros:

1. Provides burning velocity for a range of 

temperature and pressure from one experiment 

SL determined from the pressure-time trace

Ignition methods:

1. Variable cap discharge 

2. Fused wire 
Sb from flame front tracking

30 L Chamber: Shadowgraph Image of Flame => SL 

Flame front tracking illustration

Vf = Sb + ub

0 from symmetry

Nonlinear extrapolation

sb

sb

0

2

ll

sb

sb

0

2

= −2

Lmκ

sb

0

Linear extrapolation

Sb = Sb

0 − LMk

Continuity across flame

Su

0 =

ρb

ρu

Sb

0

Vf =

dRf

dd

k = Stretch rate

1

A

d

dd

=

2

Rf

dRf

dd

4 ms 8 ms 12 ms 16 ms

Pros:

1. Straightforward method for obtaining unstretched 

burning velocities and effects of stretch 

2. Can go to lower SL than 2 L chamber.
Adding Fire Suppressants can Increase Pressure 

Rise

Agents added to premixed CH4-air at Φ = 1.0 and 0.6

T=298 K and P=1 bar
Agents added to premixed CH4-air at Φ = 1.0 and 0.6

T=298 K and P=1 bar

Adding Fire Suppressants can Increase Burning 

Velocity
Higher Initial Temperature Reduces Effectiveness

Agents added to premixed CH4-air at Φ = 1.0 and 0.6

T=400 K and P=3 bar
H2O increases pressure rise at certain conditions

C3H8-air, Φ=0.6 with added C2HF5 (R-125)
Screening technique

Agents added to premixed CH4-air at Φ = 1.0 and 0.6

T=298 K and P=1 bar
Outline

1. Experiments

a. Devices

b. Results

c. Screening

2. Model Validation

a. Models 

b. Approach

c. Results
Models
Can use SL to validate mechanisms

Can solve the steady, 1-D flame equations with full chemistry (Chemkin PREMIX)

Can measure SL and compare with calculation 

SL is:

• A distinct property of a combustible mixture

• A measure of reactivity, diffusivity, and exothermicity

• steady, 1-D, planar, adiabatic flame 
Model Validation – CH4-air + C2HF5 (R-125)
Model Validation – CH4-air + C2HF3Cl2 (R-123)
Model Validation – CH4-air + C6F12O (Novec 1230)
Model Validation – C3H8-air + C6F12O (Novec 1230)
Model Validation – CH4-air + C3H2F3Br (2-BTP)
Model Validation – C3H8-air + C3H2F3Br (2-BTP)
Similar overpressures as observed in the FAA-ACT were seen in small-scale 

premixed tests, particularly at lean conditions

Constant-volume spheres offer screening potential for agent performance in 

the FAA cargo bay test 

Adding R-125 and Novec 1230 to lean mixtures not only increases heat 

release, but reactivity (SL) as well

Suppressant influence on reactivity of lean flames is even worse at elevated 

temperature

Validation data is in excellent agreement with models considering they are not 

“tuned”

Now that mechanisms have been tested, we have improved confidence in the 

previous findings and in what we can learn from them in the future

Conclusions
Measurements & Data for Fundamental 

Kinetic Modeling of Halocarbon Flammability

Jeffrey A. Manion

Contributors: David Sheen, Don Burgess, Iftikhar Awan, 

Valeri Babushok, Greg Linteris 

National Institute of Standards and Technology

Gaithersburg, MD 20899

 Workshop on the 

Flammability of Halogenated Hydrocarbons 

Gaithersburg, Maryland

October 28, 2014
Challenges of Multi-Scale Problems

System-level Microscopic 

0

t

ρ ρ∂ +∇⋅ =

∂

u

( ) 2

p

t

ρρ μ

∂ + ⋅∇ = −∇ + ∇

∂

u

uu u

RT P

M

ρ=

( ) ,chem

k 1

k kk k

Y Y Y

t

ρ ω

ρ

∂ + ⋅∇ = ∇⋅ +

∂

u u

( ) ( )

,chem

1 1

k k k k

k k k

e e T eY

t

e w

λ ρ

ρ ρ

ω

∂ + ⋅∇ = ∇⋅ ∇ − ∇⋅

∂

+ −

∑

∑

u u



[ ]

,chem [ ][ ] X

X Y exp n

X

d E AT

dt T

ω

  − = = −    

X + Y → C + D

Can we predict (or develop useful insight on) the behavior of a 

human-scale system based on fundamental molecular properties?
Understanding Flammability – The Role of 

Fundamental Chemical Kinetic Models & Data

 Engineers require design tools to answer technological questions. 

 Fire Suppressants: How much agent do I need? What are the failure modes? 

What happens with different fuels? Can I design a better agent? 

 Refrigerants: Does it burn? How fast? What safety standards are needed? 

Can I design a better, safer refrigerant? 

 What happens if ...? 

 Engineering tools have an wide range of sophistication:

 Empirical approaches & correlations (Edisonian) 

 Fundamental understanding and science-based insight

 Realistic accurate computer based models of complex systems 

• Best designer is probably the one with the best tools

• More realistic, accurate models will be developed

• Question is when and by whom? 

• How can NIST help? 
Outline

 Some Fundamental Property Databases at NIST

 Data Informatics

 Development of a chemical kinetic model for 2-BTP

 Strategies for improving models

 Concluding Remarks
Some Fundamental Property Databases at NIST

 General Chemical Properties. 

 NIST Webbook: (Peter Linstrom) webbook.nist.gov

 Physical Properties: 

 REFPROP (Fluid Properties): (Eric Lemmon) www.nist.gov/srd/nist23.cfm

 Molecular Properties. 

 TRC Thermodynamics Database: (Michael Frenkel) trc.nist.gov 

 Gas Phase Kinetics: (Jeff Manion) kinetics.nist.gov 

 Quantum Chemical Calculations: (Russ Johnson) cccbdb.nist.gov/
Data Standards & Informatics – Organizing and 

Mining Chemical Kinetic Information

 NIST Kinetics Database (60,000+ rate constants) 

 How to search for relationships and evaluate the data?

 InChI-ER: New unique electronic identifier for elementary reactions: 

 Extension of existing InChI: a computer-generated slash delimited string

 InChI String Molecular Structure

 InChI-ER is a unique identifier for reaction identification and classification, 

 Will facilitate data sharing, data mining, evaluation, model comparison

“Data Formats for Elementary Gas Phase Kinetics: Part 1. Unique Representations of Species at the Molecular 

Level” D.R. Burgess, J.A. Manion, and C.J. Hayes, Intern. J. Chem. Kinetics. 46(10), 640-650, 2014. 

“Data Formats for Elementary Gas Phase Kinetics: Part 2 Unique Representations of Reactions” D.R. Burgess, 

J.A. Manion, and C.J. Hayes, submitted IJCK, under peer review, 2014. 

“Data Formats for Elementary Gas Phase Kinetics: Part 3. Reaction Classification” D.R. Burgess, J.A. Manion, 

and C.J. Hayes, submitted IJCK, under peer review, 2014. 

algorithm

HOCH2CH3 is the same as CH3CH2OH
Outline

 Some Fundamental Property Databases at NIST

 Data Informatics

 Development of a chemical kinetic model for 2-BTP

 Strategies for improving models

 Concluding Remarks
Chemical Data Needs for Detailed Kinetic Models

 Chemical Properties. 

 Thermochemistry of Molecules: 

 Kinetics: k(T, P)

 Mechanism (Reaction Set)

 Physical Properties:

 Transport properties, etc. 
Thermochemistry

Quantum Chemical

Calculations*

Experimental Data

(Literature)

Evaluation

* 2-BTP Model: Don Burgess 

Good & Bad 

ways of doing 

this!
Halocarbon Combustion and Inhibition: 

2-BTP Mechanism Development

Fuel

+ 

O2 

CO2

+ 

H2O 

A 

B + C

C 

D 

E 

H 

I + J 

F + G 

H ... 

Fuel Combustion

models exist

2-BTP

A 

B + C

C 

D 

H 

I + J 

F + G 

H 

... 

 Halocarbon chemistry 

partly known

 Augment with:

• Theory

• Experiment

“A Chemical Kinetic Mechanism for 2-Bromo-3,3,3-trifluoropropene (2-BTP) Flame Inhibition” D.R. 

Burgess, V.I. Babushok, G.T. Linteris, J.A. Manion, submitted to Intern. J. of Chem. Kinetics
Kinetics for 2-BTP

Quantum Chemical

Calculations*

Experimental Data

(Literature)

Evaluation

2-BTP Model: * Don Burgess; **Awan & Manion 

Experimental Data

(NIST Shock Tube)**

Evaluation

Evaluation
Shock Tube – A Pulse Heater for Gases

Characteristics:

 Pulse short duration heater – no surface induced interference

 Allows isolation of initial gas phase processes (not global reactions)

 Accurate product monitoring at sub-ppm levels (see all products)
Unimolecular Decompositions – 2-BTP and Related

 2-BTP is very stable (most stable compound to HBr elimination yet measured)

 Experimental reference data: needed to validate computational kinetics

Shock Tube Measurements : 

 Double bond lowers k by 100x

 CF3 lowers k an additional 100x

Br Br

CF3

Br

Br

Br

CF3

Br

Studies of structure/rate effects 
Bimolecular Attack by H atoms – 2-BTP and Related

 H atom induced decomposition of 2-BTP is similar to hydrocarbons

 Experimental reference data: validate computational kinetics

Shock Tube Measurements : 

 Only small variations; rates 

within about 3x at 1000 K. 

 

Studies of structure/rate effects 

F

F

F

Br

F

F

F

F

F

F
Decomposition of Fuel Radicals

Our technique resolves complex behavior and minor channels 
NIST Reference Data – Fuel Radical 

Fragmentation Patterns

Focus is reference data to fill data gaps 

Precise measurements - uncertainties are (5 to 10)% compared with (300 to 400)%. 

NIST studies are the ONLY direct measurements of fragmentation patterns at high T 

Product ratio: cyclopentyl Product ratio: n-pentyl Product ratio: 2-butyl 
Raw Measurements to Reliable Rates

Lab Experiments

Reaction log10 A (s-1) n Ea/R K

k1: c-C6H11 → c-C6H10 + H 12.97 0.8422 16381

k2: 1-C6H11-6 → C2H4+ C4H7-4 14.06 - 0.2308 14899

k3: 4-C6H11-3 → 1,3-C5H8 + CH3 13.29 - 0.2662 18201

k4: 1-C6H11-3 → 1,3-C4H6 + C2H5 14.28 -0.3962 17866

k5: c-C5H9-CH2 → CH2-c-C5H8 + H 11.98 1.283 15490

k6: 1-CH3-c-C5H8-3 → 4-CH3-c-C5H7 + H 12.69 0.8105 16861

k7: 1-CH3-c-C5H8-3 → 3-CH3-c-C5H7 + H 12.66 0.8104 16808

k8: 1-C6H11-5 → C3H6 + C3H5 (allyl) 13.89 - 0.3622 12029

k9: 2-CH3-4-C5H8-1 → C3H6 + C3H5(allyl) 13.78 - 0.6942 11831

k10: 1-C6H11-6 → c-C6H11 7.54 1.7491 2433

k-10: c-C6H11 → 1-C6H11-6 12.33 1.004 13605

k11: 1-C6H11-6 → 1-C6H11-3 8.83 2.596 6510

k-11: 1-C6H11-3 → 1-C6H11-6 10.50 2.015 14585

k12: 1-C6H11-6 → c-C5H9-CH2 8.13 2.171 4757

k-12: c-C5H9-CH2 → 1-C6H11-6 11.65 1.741 12554

k13: 1-C6H11-3 → 4-C6H11-3 9.77 3.032 12946

k-13: 4-C6H11-3 → 1-C6H11-3 8.99 3.665 13395

k14: c-C5H9-CH2 → 1-CH3-c-C5H8-3 9.47 2.758 9264

k-14: 1-CH3-c-C5H8-3 → c-C5H9-CH2 9.75 2.529 11802

k15: 1-CH3-c-C5H8-3 → 1-C6H11-5 12.39 1.346 14544

k-15: 1-C6H11-5 → 1-CH3-c-C5H8 8.53 2.178 5353

Reaction log10 A (s-1) n Ea/R K

k1: c-C6H11 → c-C6H10 + H 12.97 0.8422 16381

k2: 1-C6H11-6 → C2H4+ C4H7-4 14.06 - 0.2308 14899

k3: 4-C6H11-3 → 1,3-C5H8 + CH3 13.29 - 0.2662 18201

k4: 1-C6H11-3 → 1,3-C4H6 + C2H5 14.28 -0.3962 17866

k5: c-C5H9-CH2 → CH2-c-C5H8 + H 11.98 1.283 15490

k6: 1-CH3-c-C5H8-3 → 4-CH3-c-C5H7 + H 12.69 0.8105 16861

k7: 1-CH3-c-C5H8-3 → 3-CH3-c-C5H7 + H 12.66 0.8104 16808

k8: 1-C6H11-5 → C3H6 + C3H5 (allyl) 13.89 - 0.3622 12029

k9: 2-CH3-4-C5H8-1 → C3H6 + C3H5(allyl) 13.78 - 0.6942 11831

k10: 1-C6H11-6 → c-C6H11 7.54 1.7491 2433

k-10: c-C6H11 → 1-C6H11-6 12.33 1.004 13605

k11: 1-C6H11-6 → 1-C6H11-3 8.83 2.596 6510

k-11: 1-C6H11-3 → 1-C6H11-6 10.50 2.015 14585

k12: 1-C6H11-6 → c-C5H9-CH2 8.13 2.171 4757

k-12: c-C5H9-CH2 → 1-C6H11-6 11.65 1.741 12554

k13: 1-C6H11-3 → 4-C6H11-3 9.77 3.032 12946

k-13: 4-C6H11-3 → 1-C6H11-3 8.99 3.665 13395

k14: c-C5H9-CH2 → 1-CH3-c-C5H8-3 9.47 2.758 9264

k-14: 1-CH3-c-C5H8-3 → c-C5H9-CH2 9.75 2.529 11802

k15: 1-CH3-c-C5H8-3 → 1-C6H11-5 12.39 1.346 14544

k-15: 1-C6H11-5 → 1-CH3-c-C5H8 8.53 2.178 5353

Kinetics over 

P, T

500 to 2500 K

0.5 to 500 bar

Tuned Quantum 

Chemical 

Calculations & 

RRKM Analysis

Can’t measure everything:

Measure for prototypical species

Extend by reaction class

Team: Jeff Manion, Don Burgess, Iftikhar Awan 
Outline

 Some Fundamental Property Databases at NIST

 Data Informatics

 Development of a chemical kinetic model for 2-BTP

 Strategies for improving models

 Concluding Remarks
Data Evaluation – When the data disagree

 Evaluation of data is an important process 

 NIST shock-tube experiments can provide validating kinetic reference data

H + n-alkanes

Manion, Sheen, Awan, 2014

H + 1-alkenes

Manion, Awan, 2014
Models and Uncertainty – What Do 

We Really Know?

• Many models, none agree with 

each other or with experiment

• Without understanding 

uncertainty, model development 

is a non-converging process

= Density x Laminar Flame Speed

Burke, et al., 2010
Working Smarter – Better Models 

Through Uncertainty Analysis

Forward Uncertainty Quantification

(Propagation) 

Inverse Uncertainty Quantification

(Constraint) 
Experimental Design through 

Differential Information (1)

* obs

, obs *

j i

H ij

i j

S

σ σ

σ σ

∂ = ∂

This is the sensitivity of the model uncertainty 

in prediction j to uncertainty in measurement i 

Every measurement has 

• measurement uncertainty σobs 

• model uncertainty σ* 

Define an information sensitivity

( ) 2 2

, ,

1

Ne

r H ri H ir

i

S S =Φ= − ∑

Φr > 0 ↔ More information going out from measurement r to other conditions

Φr < 0 ↔ More information coming in from other measurements to condition r

Effect of experimental uncertainty of r on 

other experiments’ simulated uncertainty

Effect of other experiments’ experimental 

uncertainty on simulated uncertainty of r

cf. Information entropy (Shannon 1948)

Sheen & Manion, J. Phys. Chem. A, 118, 4929, 2014
Experimental Design through 

Differential Information (2)

Prior model:

• Predictions y, σ

Proposed measurements:

• Test Conditions

• Measured value yobs 

• Uncertainty σobs

Applications: 

• Modeled conditions

• No measurement info

Inverse Uncertainty Quantification

Posterior model:

y

*,σ*, Φ

Remove experiment 

with smallest

Φr < 0

Remaining measurements will 

• Be least correlated set

• Have best uncertainty

• Target chemistry relevant to applications

Sheen & Manion, J. Phys. Chem. A, 118, 4929, 2014
Experimental Design through 

Differential Information (3)

Application of EDDI 

• We have applied to complex chemical kinetic models 

and shock tube experiments

• However, method is general - applicable to any system 

with uncertain model parameters 

• May help answer “what experiments to do?”

Sheen & Manion, J. Phys. Chem. A, 118, 4929, 2014
Recap

 Some Fundamental Property Databases at NIST

 Data Informatics

 Development of a Chemical Kinetic Model for 2-BTP

 Strategies for Improving Models

 Concluding Remarks
Applying Fundamental Models to Flammability

 Fundamental Data / Models – What would be useful? 

 Standard Fuel Combustion Models? 

 Standard Models for Combustion of Refrigerants/Suppressants?

 Standard Tests? 

 Databases – what data, properties, etc.?

...? 
Assorted Properties of Mildly Flammable Systems

NIST Workshop on the Exothermic Reaction of Halogenated Hydrocarbons

Gaithersburg, MD Nov. 27-28, 2014

Greg Linteris*, NIST Fire Research 

Jeff Manion / Wing Tsang / Don Burgess, NIST Chemical Kinetics

Valeri Babushok, (NIST GR)

Vish Katta, Innovative Scientific Sol. Inc. 

Fumi Takahashi, Case Western Reserve Univ. 

Peter Sunderland, John Pagliaro Univ. of Maryland

 

*Presenter 

The work was supported by The Boeing Company, NIST Internal Funds, ARRA Grant. 

Kinetics

Flame modeling

Experiments
What we learned*

Low-strain regions can support low reactivity flames.

Once you get a flame going (e.g., with a stronger hydrocarbon-air flame), very weak 

mixtures can burn vigorously. 

Adding a suppressant to lean mixture beyond its flammability limit can make it 

flammable.

Adding a suppressant to cup-burner flame can increase the heat release.

The flammability behavior depends a lot on the ignition source.

Water vapor has a significant effect on halogen-rich systems.

If this is all true for some fire suppressants, then it is even more true for mildlyflammable refrigerants.

⇒ The behavior of a mildly-flammable compound depends a lot on the environment it 

is in (ignitions source, other flammables, flow-field, clutter, turbulence, etc.)

*Does this matter for the safe use of 2L refrigerants and fire suppressants?
Droplet evaporation, 

turbulent pre-mixing

Arcing igniter

The core region near 

the fuel spray is high 

strain, (i.e., high speed 

flow) and is easy to 

extinguish.

Air - agent 

mixture

Fuel discharge port 

(propane/ethanol/water)

Secondary reaction 

of the agents with air 

occurs at low strain, 

and is hard to 

extinguish.

=> Adding a mildly flammable agent creates low-strain regions that are harder to extinguish 

Low-strain regions can support very weak flames. 
Suppressant added to lean mixture beyond its flammability limit can make it flammable

HFC-125 with Aerosol Can Test Fuel, Tinit=298 K

1

10

100

0 5 10

Inhibitor Volume Fraction in Air (%)

Burning Velocity / cm/s 

φ=1.0 

φ=0.41

Adding suppressant to a stoichiometric flame 

slows the burning velocity.

Adding suppressant to a lean mixture can:

- increase the burning velocity, and 

- bring the mixture into a flammable regime.

A burning velocity of 5 cm/s is sometimes 

considered a criterion for the flammability limit. 

Return
Effect of suppressant on lean flames (CH4-air, φ=0.5) varies with the agent type

Return
Adding a suppressant to cup-burner flame can increase the heat release.
● Validation 

⇒Validated for various flame-flow phenomena, including couterflow flame 

extinction, vortex-flame interaction, blowoff, and suppression

⇒The predicted extinction strain rates for propane-air counterflow diffusion 

flames were within 7.5% of the measured values.

 Computational Method (UNICORN)

● Time-dependent axisymmetric governing equations

⇒Mass, momentum, species, energy conservation equations

⇒Thermo-physical properties from polynomial curve fits

⇒Optically thin-media radiation from CO2, H2O, CH4, CO, and CF2O, and soot

⇒Implicit QUICKEST scheme (momentum)

● Comprehensive reaction mechanism (177 species/2986 rxns)

⇒4-carbon hydrocarbon mechanism by Wang et al. (111 species/1566 rxn.)

⇒Ethanol reactions by Dryer et al. (5 species/72 rxns)

⇒CF3Br inhibition by Babushok et al. (10 additional species/148 rxns)

⇒A subset of NIST HFC mechanism (51 species/1200 rxns)
Cup Burner Flame Simulations

0

0.1

0.2

0.3

0.4

Br2 CF3Br CF3H Ar He N2 CO2 CO2

(mg)

Volume Fraction for Extinction

experiment

prediction

1. Detailed numerical simulation (solves Navier-Stokes 

equations) with full kinetics (177 species, 2986 reactions).

2. Time dependent, 2-D, axi-symmetric, full transport, gray thinlimit radiation model. 

1. The model has can predict extinction of the cup burner.

Return
Cup Burner Flame: Tmax, and Heat Release (total and at base)

ACT Fuel: Ufuel=0.853 cm/s Air + Agent: Uox= 10.7 cm/s

Base

z 

r 

Air+agent

added to coflow
HFCs added to Propane-air Flame Increases Heat Release, but HCFCs do not.

⇒ Total heat release increases (≈2 to 4 times) 

for C2H2F4 (HFC-134a)

 or C3HF7, (HFC-227ea)

 at concentrations just below extinction, 

=> but does not increase for Halotron 1 

 (mostly C2HCl2F3 ; i.e., R-123).

 

=> So this test also indicates that R-123 may 

work in FAA Aerosol Can Test. 

C2H2F4 C3HF7 

From: Holmstedt et al. 1994

Heat Release Rate Measurement

<= air and agent input

<= propane

(Increase agent concentration in air linearly in time.)
- some fire suppressants themselves may support flames (although very weak) in 

air at elevated temperatures. 

- burning velocity of CF3Br is < 0.15 cm/s at 500 K with O2 oxidizer.

Agent Formula Oxidizer

Initial 

Temperature, K

Peak Adiabatic 

Flame Temperature

K 

Burning 

Velocity, cm/s

HFC-23 CF3H air 400 1751 0.567

HFC-125 C2F5H air 400 1858 1.56

HFC-227ea C3F7H air 400 1874 2.48

2-BTP C3H2F3Br air 400 2033 2.14

Novec 1230 C3F7COC2F5 air 400 1864 0.367

Triodide CF3I oxygen 500 1528 1.33

halon-1301 CF3Br oxygen 500 1485 <0.15

Calculated Temperature and Burning Velocity of fire suppressant/air stoichiometric mixtures (1 bar)

Exothermic reaction of pure agents in air

(values down to 

≈1 cm/s can be 

measured. )

(Premixed burning velocity is a measure of the mixture’s overall reaction rate. ) 

Return
The flammability behavior depends a lot on the ignition source. 

⇒ To ignite mixtures that were burning in the FAA-ACT, we had to go to the Pt wire 

igniter. Could not do it with the high energy spark ignition.

⇒ That igniter implies different flammability limits (e.g. C3H8-air flame with 125)

 
Water Vapor Can Have a Significant Effect
Point of this talk:

This is what we learned from interpreting the FAA_ACT.

Does any of this matter for suppressants in other scenarios (than cargo bay)?

Are there any scenarios for refrigerants in which these properties matter?

(Oil burner, leak in A/C coil, etc.)

What is the limiting SL for inertion? What is the value of SL for safe use of the 

compounds and what are the environmental conditions that influence that value?