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NBS

PUBLICATIONS NISTIR 88-3880

Study of the Ignition

Inhibiting Properties of

Compressed Air Foam

Daniel Madrzykowski

U.S. DEPARTMENT OF COMMERCE

Nationl Institute of Standards and Technology

(Formerly National Bureau of Standards)

Center for Fire Research

Gaithersburg, MD 20899

October 1988

National Bureau of Standards became the

National Institute of Standards and Technology

on August 23, 1988, when the Omnibus Trade and

Competitiveness Act was signed. NIST retains

all NBS functions. Its new programs will encourage

improved use of technology by U.S. industry.

Sponsored by:

U.S. Fire Administration

Emmitsburg, MD 21727

QC

100

U56

#88-3880

1988

c.2

U.S. DEPARTMENT OF COMMERCE

C. William Verity, Secretary

NATIONAL INSTITUTE OF STANDARDS

AND TECHNOLOGY

Ernest Ambler, Director

NISTIR 88-3880

CitfOO

UCl

Study of the Ignition

Inhibiting Properties of

Compressed Air Foam

Daniel Madrzykowski

U.S. DEPARTMENT OF COMMERCE

Nationl Institute of Standards and Technology

(Formerly National Bureau of Standards)

Center for Fire Research

Gaithersburg, MD 20899

October 1988

Sponsored by:

U.S. Fire Administration

Emmitsburg, MD 21727

75 Years Stimulating Asrtmca • Prograaa

i»i)

TABLE OF CONTENTS

Page

LIST OF FIGURES iv

ABSTRACT 1

1.0 INTRODUCTION 2

2.0 EXPERIMENTAL APPROACH 4

2 . 1 Foam Generating Apparatus 4

2.2 Test Methods 4

2.3 Ignition Retardation Test 5

2.4 Mass Retention Test 7

3.0 RESULTS AND DISCUSSION 7

3.1 Ignition Retardation Test 7

3.2 Mass Retention Test 9

4.0 CONCLUSIONS 10

5.0 RECOMMENDATIONS FOR FURTHER STUDY 11

6.0 ACKNOWLEDGEMENTS 11

7.0 REFERENCES 12

iii
LIST OF FIGURES

Page

Figure 1. Basic compressed air foam system 13

Figure 2 . Laboratory foam generator 14

Figure 3. Schematic of improver 15

Figure 4. Side view and plan view of radiant panel and

specimen arrangement . * 16

Figure 5. Time to ignition curves for Tl-11 plywood siding .... 17

Figure 6. Effectiveness of water in delaying ignition of Tl-11

plywood siding 18

Figure 7. Effectiveness of unaerated water - foaming agent solution

relative to plain water in delaying ignition of Tl-11

plywood siding 19

Figure 8. Effectiveness of foam relative to plain water in delaying

ignition of Tl-11 plywood siding 20

Figure 9. Mass retention test results 21

iv
Study Of The Ignition Inhibiting Properties

of Compressed Air Foam

Daniel Madrzykowski

ABSTRACT

This report describes an initial step to quantify the effectiveness of waterbased compressed air foam (CAF) generated with a synthetic hydrocarbon-based

surfactant. Two series of tests were conducted with the synthetic hydrocarbon

surfactant based CAF: ignition retardation tests and mass retention tests.

The ignition delaying capability of the foam was twice that of water when

protecting a Tl-11 plywood surface irradiated from an external source in the

range of 15 kW/m2 to 60 kW/m2

. The mass retention test, conducted on Tl-11

plywood siding, exhibited an initial retention efficiency for the foam of

approximately 20 times the efficiency of water. This type of foam may have

potential for improving performance of fixed fire suppression systems, such as

residential sprinkler systems. Further study is recommended to generalize the

results of these tests and to quantify the extinguishing capabilities of the

CAF relative to water.

Key Words: compressed air foam (CAF); foam; foam generator; ignition

inhibiting; mass retention; residential sprinkler systems; retention

efficiency; surfactants.

1
1 . 0 INTRODUCTION

Two recent developments in foam technology have stimulated the interests of

firefighters and fire agencies across the country and around the world. The

first technological breakthrough was the development and use of the compressed

air foam system (CAFS) by the Texas Forest Service in 1977. This type of foam

generator creates mechanical foam by injecting compressed air into a solution

of water and foaming agent while it is being pumped through a hose. Dependent

on the foaming agent and the CAFS ' s capabilities, the water- foaming agent

solution may be expanded up to 50 times the original volume [1]. While this

system is effective for increasing the amount of fire fighting material

available from a limited water supply, it did not alleviate the problem of

carrying large quantities of foaming agent. At that time, commercially

available foaming agents had to be mixed at concentrations of 3 to 6 percent

or 3 to 6 gallons of foaming agent for every 100 gallons of water.

The second development was a new type of synthetic hydrocarbon surfactant

foaming agent that was introduced in Canada in 1985. The recommended

concentration for foaming solutions with this agent is 0.3 to 0.7 percent,

reducing the amount of the agent required by a factor of 10. Currently four

foaming agents of this type are commercially available and qualified under the

United States Department of Agriculture interim requirements for wildland fire

foam [ 2 ]

2
The Bureau of Land Management (BLM) , the U.S. Forest Service (USFS) , the Texas

Forest Service and a few municipal and state fire agencies have combined the

advantages of these recent developments and have built CAFS units to generate

synthetic hydrocarbon-based foam (Figure 1) . Operational experiments have

been conducted on both the CAFS and the foaming agents by the BLM and the USFS

[1], Initial firefighter testimonials indicate that the foam is superior to

water in a variety of forest fire fighting situations as well as in structure

protection. [ 3

It seems that this new generation foam may have potential uses in other fire

suppression systems, such as improving the performance of residential

sprinkler systems, and especially in self-contained systems which have a fixed

water supply held in a tank. These systems are used primarily in areas with...

low domestic water supply pressures. This study was undertaken as an initial

step in evaluating that potential.

This report describes an initial step in an effort to evaluate the

capabilities of CAF for use in residential sprinkler systems. This study was

limited to the ignition inhibiting properties of CAF although other factors

need to be evaluated to fully assess CAF's capabilities for use in residential

sprinkler systems. Two types of tests were conducted; an ignition inhibiting

test and a mass retention test. In both cases a vertically oriented sample

was used to simulate foam application to a wall.

3
2.0

EXPERIMENTAL APPROACH

2.1

Foam Generating Apparatus

To enable the study of the synthetic hydrocarbon surfactant foam (hereafter

referred to as the foam) a laboratory scale foam generator was

constructed, since a field operational CAFS unit is not suited to the

laboratory environment. After several iterations, the design of the foam

generator evolved into a unit similar to a Water Expansion System (WES) , a

predecessor of CAFS. The components of the foam generator are; a pressure

vessel, a compressed gas cylinder, flow meters, a mixing tee, an improver ^

(mixing device) and hose (Figure 2) . An improver was required since the

natural turbulence in the hose of the lab foam apparatus was insufficient to

produce the same quality of foam used in the field. The improver is similar

to the one built by Fry and French in 1951 [4] (Figure 3) . When used in

conjunction with a 12 m (40 ft) length of 5 mm (3/16 inch) diameter tubing, it

provides foam representative of that used in the field with an expansion

capability up to 20.

2.2

Test Methods

Since the performance of the foam is dependent on its characteristics, the

following characteristics were fixed in this study:

4
• A 0.3% foaming agent concentration was used in all of the tests. This

is within the manufacturer's recommended range for ground application.

• Only one brand of foaming agent was used. It is representative of the

commercially available foaming agents of this type.

• A foam expansion of 14 ± 1 was used for all of the tests.

• All of the tests were performed on 152 mm (6 inch) square specimens of

Tl-11 siding material (conditioned to constant moisture content at a

temperature of 23 ± 2 °C (74 ± 4 °F) and a relative humidity of 50 ±

10%). Tl-11 is a textural exterior plywood, which is composed of

southern pine and phenolic adhesives.

2.3 Ignition Retardation Test

The ignition retardation tests were performed on the Lateral Ignition and

Flame Spread Test (LIFT) apparatus [5]. The key component of this device is a

gas fired radiant panel (Figure 4). Prior to testing, the apparatus was

calibrated as specified in "New Concepts for Measuring Flame Spread

Properties" [5]. This test was performed by exposing a vertically-oriented

sample to constant and nearly uniform irradiation from the radiant panel and

recording the time until piloted ignition. This test simulates a wall

exposure situation. The heat flux from the radiant panel was varied from 60

kW/m2 down to a flux where ignition would not occur. Testing in this fashion

yields a curve of time to ignition versus the heat flux. To find a basis on

5
which to gauge the foam's performance, 4 treated samples were tested at each

flux level. The treatments are as listed below:

1. Untreated Tl-11

2. Tl-11, test surface sprayed with approximately 9 ml (3 f 1 . oz .

)

of

water

3. Tl-11, test surface sprayed with approximately 9 ml (3 f 1 . oz .

)

of

water and 0.3% foaming agent (unfoamed).

4. Tl-11, test surface covered with a 6 mm (1/4 in.) blanket of foam„

The 6 mm (1/4 in.) thick foam cover contains approximately the

same amount of water as in treatments 2 and 3.

The quantity of water to be used was determined empirically by observing the

amount of water the Tl-11 surface would hold without dripping, when oriented

in a vertical position. At 9 ml, no dripping from the sample occurred. It

should be noted that the samples were treated in a horizontal position and

then immediately (under 10 seconds) oriented vertically and positioned in the

LIFT apparatus (Figure 4) . A set of the treated samples was tested at the

following heat flux levels; 60, 50, 41, 30, 25, 20 and 15 kW/m2

. The time to

ignition was recorded for each sample.

6
2.4 Mass Retention Test

The scenario represented by this experiment is that of foam application to a

wall. A vertically oriented Tl-11 sample, of known mass, was subjected to a

constant flow rate stream of water applied to its textured surface for a fixed

amount of time. Immediately after the application period, the sample was

weighed to determine the amount of water which remained with the sample. With

a new sample placed in position, the test was repeated for a longer period of

time. This cycle was repeated until the sample's change in weight was

negligible. The test sequence was then repeated applying foam to the sample

instead of water. This experiment provides an indicator as to the efficiency -

of application of foam to a vertical surface.

3.0 RESULTS AND DISCUSSION

3.1 Ignition Retardation Test

The ignition retardation tests were performed over a heat flux range

which represents heat flux exposures associated with a developing room fire,

15 kW/m2 (panel temperature ~ 440 °C (830 °F)), up through a fully developed

room fire, 60 kW/m2 (panel temperature « 740 °C (1370 °F)). The results are

shown in Figure 5

7
To study the overall effectiveness of the various treatments, relative

comparisions of ignition times were made. Using the ratio of ignition times

(water/untreated), at the same radiant flux, Figure 6 exhibits the

effectiveness of water in delaying ignition of the Tl-11 plywood siding. At

low radiant flux exposure, the water increased the time to ignition by about

20 percent. At higher radiant flux exposures the time to ignition was

doubled. The reasons for the difference in behavior at low and high incident

radiant flux are unknown.

The effectiveness of the foam, and the unaerated water - foaming agent solution

were determined relative to the ignition times for the water treated plywood,-*

siding. Figure 7 shows the relative performance of the unaerated waterfoaming agent solution compared with water as the ratio of ignition times

(water+/water) . The data show considerable scatter. The average of the

entire data set is approximately 1. This means that on the average there is

no increase in the ignition delay for unaerated water- foaming agent solution

over that provided by plain water treatment. It may be significant that there

was a decrease in ignition time for the unaerated water- foaming agent solution

compared to plain water at the lowest radiant flux exposure measured (15

kW/m2

) . In the two measurements performed, the plywood siding treated with

the unaerated water- foaming agent solution ignited in half the time required

for the water treated siding. The reasons for this behavior are not clearly

understood. As unaerated water- foaming agent solutions may be used in the

field, this detrimental performance with regard to ignition retardation should

be investigated further.

8
Figure 8 shows the relative performance of the foam compared with water, as

the ratio of ignition times (water/foam) . The average of the entire data set

is approximately 2. This indicates that on the average, the foam treatment

yielded ignition delay times twice as long as the delay provided by the water

treatment. It should be noted that the layer of foam used in these tests was

thin (6 mm) to enable the direct comparision of the foam relative to water on

a mass basis. In practice, the foam is applied liberally, yielding a thicker

coating of foam than those used in the ignition inhibiting tests. A thicker

coating of foam, with a similar expansion ratio, on a surface means more water

mass is retained by the surface, possibly furthering the foam's capability to

inhibit ignition. The amount of foam or water that could be retained by a -,~

sample in a specific time period was investigated in mass retention tests.

3.2 Mass Retention Test

The mass retention test was performed with a water mass flow rate of 760 grams

per minute (gpm) and a foam flow rate of 190 gpm. The water application rate

was set at 760 gpm, which was the lowest value capable of delivering a steady

water stream from the unit. This meant that the mass flow rate of water being

applied to the sample was 4 times the mass flow rate of the foam. The initial

measurements were performed after 5 seconds of application time. The plot for

water in Figure 9 represents the averages of the three water tests,- with the

9
exception of the 60 second water test for which only one trial was conducted.

Since measurements were only taken at two time periods for the foam, the data

points are shown without a curve fit. The initial fraction of water mass

retained by the sample, after 5 seconds of application, was 0.045. This was

determined by dividing the average mass gain by the mass applied (the product

of flow rate and time) {2.9g/[(l/12 min) (760 g/min) ] } . The initial

percentage of foam retained by the sample was calculated in the same way and

yielded 0.88 {14g/[(l/12 min) (190 g/min)]}. This represents an initial

retention efficiency for foam approximately 20 times greater than plain water.

Prior to the initial measurement at 5 seconds the foam treated sample had

reached its virtual steady state weight. The foam applied after the initial

coating of the sample simply sheared off, leaving a residual foam layer

approximately 12 mm (1/2 in.) to 19 mm (3/4 in.) thick on the sample. After

60 seconds of application time, the water sample still yielded a slight weight

gain. The water weight gain after 60 seconds was 72% of the weight gain of *

the foam treated sample at 5 seconds (Figure 9)

4.0 CONCLUSIONS

A 6 mm (1/4 inch) thick layer of foam exhibited an ignition- inhibiting

capability twice that of an equal mass of water for Tl-11 plywood siding

irradiated from an external source. The synthetic hydrocarbon surfactantbased CAF displayed a retention efficiency approximately 20 times the

efficiency of water on the test samples. Considering the results of both the

tests, water in the form of foam should be more efficient than plain water at

retarding the ignition of combustibles in room fires. Foam could be

10
beneficial for use in residential sprinkler systems, especially residential

sprinkler systems that draw on a small, tank held water supply.

5.0 RECOMMENDATIONS FOR FURTHER STUDY

To evaluate fully the potential use of this technology in residential

sprinkler systems, the direct extinguishing capabilities of the foam relative

to water spray must be studied. Further testing must be performed on

different materials to generalize the results of the ignition inhibition

tests, mass retention tests and any future fire extinguishment tests. In

addition, understanding of the basic physical processes involved in the action

of the foam for ignition inhibition and fire extinguishment should be ...

addressed to determine the generality of findings and to allow optimal use of

the agent

6 . 0 ACKNOWLEDGEMENTS

Appreciation is extended to David Evans, Margaret Harkleroad, Roy McLane , Gary

Roadarmel, David Stroup and Bob Vettori of the Center for Fire Research and to

Ron Rochna and Paul Schlobohm of the Bureau of Land Management for their

assistance in the performing of this study. Appreciation is also extended to

Ed Wall, Roger Lanahan and Tom Smith of the U.S. Fire Administration for their

support of this project.

11
7 . 0 REFERENCES

[1] Hill, P.R. & McKenzie, D.W., Engineering Analysis of Threshold

Compressed Air Foam Systems (CAFS) , Project Report 8751 1202, U.S.

Department of Agriculture, Forest Service Technology and Development

Center, 444 East Bonita Ave . , San Dimas, CA 91773 (1987).

[2] Hill, P.R., Manufacturer Submission Procedures for Wildland Fire Foams,

Foam Applications for Wildland 6c Urban Fire Management, Vol 1, No

2 , U.S. Department of Agriculture, Forest Service Technology and

Development Center, 444 East Bonita Ave., San Dimas, CA 91773 (1988).

[3] Rochna, R. & Schlobohm, P., An Evaluation of Foam as a Fire

Suppressant, Symposium on Wildland Fire 2000, U.S. Department of

Interior, Bureau of Land Management, 1717 Fabry Rd. S.E., Salem, OR

97306 (April 1987) .

[4] Fry, J.F. and French, R.J., A Mechanical Foam-Generator for Use in

Laboratories. Journal of Applied Chemistry, October 1951.

[5] Quintere, J. G. and Harkleroad, M. , New Concepts for Measuring Flame

Spread Properties. Fire Safety: Science and Engineering,

ASTM STP 882. T. Z. Harmathy, Ed., American Society for Testing and

Materials, Philadelphia, PA 19103 (1985).

12
1/4 Turn

Ball Valve

Figure 1. Basic compressed air foam system

13
pressure

gauge

compressed

air

pressure

vessel

(batch tank)

shut off

valve

fill

alve

V

c/

pressure

gauge

flow

meter

IT

compressed

air

flow

meter

•X

control

valve mixing

tee

improver

foam

Figure 2. Laboratory foam generator
1

INCH

XS

PIPE

15

Figure

3,

Schematic

of

improver
I k

162 mm

Plan View of Specimen - Panel Arrangement

Figure 4. Side view and plan view of radiant panel and specimen arrangement

16
T1-11

Plywood

Siding

O

CD

O

Tjo

CVJ

C\J

17

Figure

5.

Time

to

ignition

curves

for

Tl-11

plywood

siding
S3IAILL N0I1IN9I dO OllVd

18

Figure

6,

Effectiveness

of

water

in

delaying

ignition

of

11-11

plywood

siding
o

CD

O

ID

O

Tjo

CO

o

C\J

o

S3IAII1 AVI3 Q N0I1IN0I 30 OIJLVd

19

HEAT

FLUX

(kW/m

2)

Figure

7,

Effectiveness

of

unaerated

water-foaming

agent

solution

relative

to

plain

WATER

IN

DELAYING

IGNITION

OF

Tl-U

PLYWOOD

SIDING
o

CDO

Lf> OO

COo

C\J o

20

HEAT

FLUX

(kW/m 2)

Figure

8,

Effectiveness

of

foam

relative

to

plain

water

in

delaying

ignition

of

Tl-11

PLYWOOD

SIDING
T1-11

Plywood

Siding

(6) Q3NIVO SSVIN

21

Figure

9.

Mass

retention

test

results
form NBS-1 14A (REv.i 1-84)

U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date

BIBLIOGRAPHIC DATA

SHEET (See instructions)

REPORT NO.

NISTIR-88/ 3880 October 1988

4. TITLE AND SUBTITLE

Study of the Ignition Inhibiting Properties of Compressed

Air Foam

5. AUTHOR(S)

Daniel Madrzykowski

6. PERFORMING ORGANIZATION (If joint or other than N BS; see in struction s) 7. Con tract/Grant No.

National Institute of Standards

and Technology 8. Type of Report & Period Covered

U.S. Department of Commerce

Gaithersburg, MD 20899 I

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, State, ZIP)

U.S. Fire Administration

Emmitsburg, MD 21727

10.

SUPPLEMENTARY NOTES

_ Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

This report describes an initial step to quantify the effectiveness of waterbased compressed air foam (CAF) generated with a synthetic hydrocarbon-based

surfactant. Two series of tests were conducted with the synthetic hydrocarbon

surfactant based CAF: ignition retardation tests and mass retention tests.

The ignition delaying capability of the foam was twice that of water when

protecting a Tl-11 plywood surface irradiated from an external source in the

range of 15 kW/m2 to 60 kW/m2

. The mass retention test, conducted on Tl-11

plywood siding, exhibited an initial retention efficiency for the foam of

approximately 20 times the efficiency of water. This type of foam may have

potential for improving performance of fixed fire suppression systems, such as

residential sprinkler systems. Further study is recommended to generalize the

results of these tests and to quantify the extinguishing capabilities of the

CAF relative to water.

12.

KEY WORDS (Six to twelve entries ; alph abeti ca I order; capitalize only proper names; and separate key words by semicolon s) compressed air foam (CAF); foam; foam generators; ignition; mass retention;

residential building; sprinkler systems; retention efficiency; surfactants

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