Development of a New Test Procedure for Aqueous Film-Forming Foam

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Development of a New Test Procedure for Aqueous Film-Forming Foam Kim, A. K.; Taber, B. C.

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Internal Report No. 679

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DEVELOPMENT OF A NEW TEST PROCEDURE FOR AQUEOUS FILM-FORMING FOAM

by

Andrew Kim and Bruce Taber ABSTRACT

A project was undertaken to develop a new test procedure for Aqueous Film- Forming Foam (AFFF). The basis for the new test procedure was the CGSB-28.74-M90

"Standard for: Liquid Concentrate, Fire Fighting, Aqueous Film Forming Foam",

modified to apply the foam from a fixed nozzle. Repeatability of the new test procedures.

as well as acceptance criteria, were evaluated.

A series of tests was conducted to investigate a number of variables including the quantity of water used as a base, the quantity of fuel and the foam application time. The project was eanied out in three phases.

The NFL's results of three phases of tests showed that: Phases 1 and

2

provided repeatable, consistent test results. The test results in Phase 3 were inconsistent and showed very little agreement with the previous results. Although there is no conclusive evidence as to the reason for this, the agc of thc foam concentrates seems to be the most likely cause. Reviewing the test results from the other laboratories involved in the Phase 3

r o d robin testing will-provide the first step in locating the cause of the inconsistent results obtained in Phase 3.

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DEVELOPMENT OF A NEW TEST PROCEDURE FOR AQUEOUS FILM-FORMING FOAM

by

Andrew Kim and B N C ~ Taber INTRODUCTION

CGSB 28-GP-74M "Standard for Liquid Concentrate, Fire Fighting, Aqueous Film Forming Foam" is the current test standard used by the Department of National Defence (DND) and Transport Canada for evaluating the quality of Aqueous Film-Forming Foam (AFFF). This standard requires an operator to apply foam to a liquid pool fire.

Experience has shown that test results can vary due to the skill of the operator.

A project was undertaken on behalf of DND to develop a new test procedure for AFFF. The basis for the new test procedure was to be the CGSB-28.74M90 [I]

standard, modified to apply the foam from a fixed nozzle.

The project was camed out in three phases. The first phase consisted of a series of tests conducted between October 1989 and January 1991. During that phase, a number of variables were investigated including the quantity of water used as a base for the fuel, the quantity of fuel, and the foam application time. The results of these tests indicated that a larger database was required be&e a new test procedure could be recommended. As a result, a second series of tests was conducted at the National Fire Laboratory between April and November 1992. These test results, together with the results of the first phase tests, were used in making recommendations for a new standard test method.

The third phase of the project was a "Round Robin" test series to confirm the repeatability of the recommended test method. A series of tests, using four different foams, would be conducted at six laboratories. Three of the laboratories would conduct the tests outdoors. They are 3M Laboratories in Alabama, the Angus Fire Armour facility in Thurso, Quebec and the P.E.T.E. test field in Nicolet, Quebec. The other three test series would be conducted indoors at Underwriters' Laboratories of Canada in

Scarborough, Ontario, Ansel in Marinette, Wisconsin and the National Fire Laboratory (NFL) in Almonte, Ontario. The NFL has completed its "Round Robin" test series and the results are included in this report.

TEST EQUIPMENT

1. Test pan: 2.4 m diameter pan, 200 mm depth, fabricated from 2.5

mm

thick steel.

2.

Burnback pot: 300 mm diameter pot, 250 mm high, fabricated from 2.5

mm

thick steel.

3. Foam nozzle: UNI-86 design, 11.4 Llmin output at 700 kPa operating pressure. 4. Fuel: n-heptane.

BASIC TEST PROCEDURE

The test procedure was based on CGSB-28.74M90. Details included here are those which differed from the standard procedure.

1. A specified quantity of fuel is added to a specified quantity of water base in the test Pan.

2. The foam nozzle in the horizontal position is fixed to a tripod, 1 m above the bottom of the pan. It is placed along the diameter of the pan at a distance such that the foam

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stream will impinge on the surface of the fuel at a point 1 m from the far side of the _{- -} Pan.

3. 2 L of fuel is put in the bumback pot.

4. The fuel in the test pan is ignited and allowed to burn for 60 s.

5. The foam application commences following the 60 s pre-burn and continues for a specified length of time.

6. The nozzle pressure is maintained at 700 kPa throughout the application. 7. The "Extinguishment Time" is recorded.

8. The bumback pot is placed gently in the centre of the test pan shortly after

extinguishment. Five minutes after the end of the foam application, the bumback pot is ignTted.

9. The burnback pot is allowed to bum until 25% of the surface area of the test pan (measured visually) is involved in fire. This time is recorded as the "25% Burnback PHASE 1 TESTS

In this phase, four different foam concentrates were used to assess the effectiveness of the new test method in evaluating the quality of foam, and also to determine the

acceptance criteria for the new test method. Ninety-one tests were conducted at t h e m in which two test parameters were varied. The duration of the foam application was varied from 3 min to 45 s. Also, two different hewwater ratios were used in the test pan. The first was 50 L of n-heptane on a 100 L water base (Fuel Condition A) and the second was 75 L of n-heptane on a 75 L water base (Fuel Condition B).

The four foam concentrates were also tested according to the CGSB 28-GP-74M test method at a DND test facility in Nicolet, Quebec using a skilled operator to determine the quality of each of the foams based on currently-acceptable test criteria.

PHASE 1 TEST RESULTS

The Phase 1 test results are summarized in Tables 1-8 as follows: Table 1 - CGSB 28-GP-74M Test Results from DND test facility

Table 2

-

Fixed Nozzle Test Results, Foam Sample 1 Table 3 - Fixed Nozzle Test Results, Foam Sample 2 Table 4 - Fixed Nozzle Test Results, Foam Sample 3 Table 5

-

Fixed Nozzle Test Results, Foam Sample 4 Table 6

-

Application Times

Table 7

-

99% Extinguishment Times Table 8 - Average Extinguishment Times PHASE 1 OBSERVATIONS

The CGSB Standard test results (Table 1) show that Samples 1 , 2 and 3 were acceptable foams with Sample 2 providing the best results. Sample 4 was a slightly inferior foam whose quality was v e v close to the minimum acceptable level.

The fixed nozzle test results (Table 6) indicate that Sample 4 is consistently the least effective of the four samples with regard to its 25% bumback time. The results also show that Sample 2 provided ihe best resdts in most cases

The two fuel conditions that were used showed that both the extinguishment time and the burnback time were affected by this variable. By increasing the amount of fuel

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(Fuel Condition B), the extinguishment time was increased in most cases and the burnback tirnc dccreascd. In terms of rating thc foams in order of quality based on cxtinguishmcnt and burnback times, thcrc was no appreciable differcnce bctwccn the two fuel conditions.

There was a substantial variation in the extinguishment times throughout the test series. In all cases, the last portion of the flame to extinguish was a small area, less than 1% of the fuel surface area, located along the hot edge of the test pan closest to the applicator nozzle. This area was the last to be covered by the foam as it expanded over the fuel surface. This small flame extinguished relatively quickly in some cases and burned persistently in others, resulting in large variations in the extinguishment times. For tests conducted with application times of 1 min 45 s and 1 min 35 s, the 99% extinguishment times are recorded (Table 7). These times show much more consistent results.

The average extinguishment times (Table 8) indicate that there is a trend towards shorter extinguishment times as the application time is shortened. Based on this

observation, it was concluded that the forceful application of the foam with the fixed nozzle affected the test results. The sooner the foam application was stopped, the sooner the fire was extinguished by the expanding foam blanket, if sufficient foam had been applied. Fire extinguishment depended more on the rapid expansion of the foam layer over the fuel surface than on the amount of foam applied. The test results showed that an application time of 45 s was not sufficient to extinguish the fire in most cases. An

application time of 1 min 10 s resulted in consistent extinguishment of the fire by all the foams tested.

Due to the lack of a significantly inferior foam sample in this phase, it was difficult to recommend an acceptance criteria for the extinguishment time and the 25% bumback time. As such, tests were canied out in the second phase of the project using an inferior foam sample.

PHASE 2 TESTS

A fifth foam sample (Sample 5) was added to the test series. This foam was tested using the CGSB 28-GP-74M test method and was shown to be substantially inferior to the other four foam samples. The extinguishment times were consistently longer than 1 min and the 25% bumback times were consistently shorter than 5 min 30 s, which indicated that the sample was not acceptable according to the CGSB method.

Two additional fuellwater ratios were also used in this test series. They were 144

L

of fuel on 90 L of water and 75 L of fuel on I00 L of water.

Twenty-seven tests were conducted in this phase. The foam was applied for 1 min 10 s for all tests.

To obtain the 25% burnback time for the tests in which extinguishment was not achieved, the fires were manually extinguished 2 min after the end of the foam application. The small remaining flame was extinguished by blowing on it, with very little effect on the foam blanket.

PHASE

2

TEST RESULTS

The Phase 2 test results are summarized in Tables 9-14 as follows: Table 9 - Test Results for hellwater ratio of 144 L fuel on 90 L water Table 10

-

Test Results for fueVwater ratio of 75 L fuel on I00 L water

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Table 11

-

Test Results for fueVwater ratio of 75 L fuel on 75 L water Table 12 - Test Results for fueVwater ratio of 50 L fuel on 100 L water Table 13 - Extinguishment Times for various fueVwater ratios

Table 14 - 25% Bumback Times for various fueWwater ratios PHASE 2 OBSERVATIONS

To recommend an acceptable 25% bumback time, it is important to take the fuel condition into consideration. It can be seen in Table 14 that the bumback times were affected by the fueVwater ratios.

There are two factors that may contribute to these different bumback times. The first is the depth of the fuel layer. A deeper fuel layer may result in more fuel being picked up by the foam as it impinges on the fuel surface during application. The more fuel that is picked up and held by the foam layer, the faster the foam layer will break down during bumback. The results, shown in Table 14, indicate that as the amount of fuel used decreases from 144 L to 50 L, the bumback times increase.

The second factor is the height of the fuel layer relative to the bumback pot (see Figure 1). The fuel depth in the bumback pot before ignition is 28

mm.

Therefore, the bottom 28 mm of the bumback pot will remain cool while the walls above that point will become hot. The larger the surface area of the fuel (depth times perimeter) in the test pan that is exposed to the hot portion of the bumback pot, the faster the fuel will vaporize and contribute to the breakdown of the foam layer.

The depth of the fuel in contact with the hot bumback pot depends on both the amount of water and the amount of fuel used in the test pan. Figure 1 shows the depth of the fuel exposed to the hot portion of the bumback pot for each of the fuel conditions. Table 14 indicates that the bumback time decreases as the area of fuel exposed increases.

Table 14 also shows that, even though the 25% bumback time was affected by the fuel condition used, the ranking of the foams, based on their burnback time, remained the same regardless of the fuel condition used. The ranking of the foams in descending order, based on their burnback times, was: Sample 2, Sample 1, Sample 3, Sample 4, for all fuel conditions. This ranking was the same as the one obtained by the CGSB 28-GP-74M test method (see Table 1). Burnback times of Sample 5 were not considered in the ranking, because Sample 5 consistently failed to extinguish the fire within the specified time (2 min).

Based on the results shown in Table 14, a critical bumback time, consistent with the CGSB results (Samples 1-3 pass, but Sample 4 fails) can be determined for each fuellwater ratios as follows:

hellwater ratio 25% Bumback Time (rnin:s)

The CGSB results showed that Samples 1-3 consistently extinguished the test fire

within 1 min of foam application which indicates a pass, while Sample 5 did not extinguish the fire within 1 min, indicating a failure. Sample 4 extinguished the test fire within 1 min in two tests, while it took more than 1 min to extinguish the fire in other tests, indicating that it was 'borderline'.

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Table 13 shows that tests with a fueVwater ratio of 75/75 resulted in

extinguishment times that are the most consistent with the CGSB results. Based on the results of Pbases 1 and 2, the final recommendations for the test method were as follows:

1) Foam application time of 1 min 10 s

2) A fueWwater ratio with 75 L of fuel on a 75 L water base

3) Acceptance criteria based on extinguishment time of 1 min 40 s (30 s after the end of foam application)

4) Acceptance criteria based on the 25% Burnback Time of 5 min 30 s

PHASE 3 TESTS

In Phase 3, tests were conducted as a part of the 'Round Robin' to confirm the repeatability of the recommended test method. Four of the five foam samples

(Samples 1-3 and 5) were used in this test series. The temperatures of the fuel, the water base, the foam and the ambient air were maintained as close to 20°C as possible for these tests.

PHASE 3 TEST RESULTS

The test results for Phase 3 are shown in Table 15.

PHASE 3 OBSERVATIONS

The results of Phase 3 were very inconsistent. Three of the foams had

extinguishment times greater than the acceptable limit of 1 min 40 s in two of the three tests. Only Sample 3 bad extinguishment times that were acceptable. The bumback times also showed inconsistent results.

In reviewing the test results from Phase 1 (Table 1 1) for the same fuel condition and application time, there were consistent results indicating a high degree of repeatability. There are two factors that may be the cause of this change in the test results.

The first factor could be the difference in ambient temperature between the two test series. The earlier results were obtained from tests that were conducted in November and December 1990. The temperature of the air, foam concentrates, water and fuel were not independently monitored but it can be assumed that they were approximately the same as the ambient air temperature which was 5-10°C. The tests in Phase 3 (Table 15) were conducted in September 1993 and the temperatures were maintained at approximately 20°C. This difference in ambient temperature may affected extinguishment and bumback times, but it is unlikely that it alone can explain the inconsistency in the Phase 3 results.

The second factor is the age of the foam concentrates. The dates of manufacture of the various foams used were as follows:

Sample 1 October 1989 Sample 2 August 1987 Sample 3 March 1989 Sample 5 February 1992

The tests for Phase 1 were conducted in November and December 1990 while those for Phase 3 were conducted in September of 1993. The age of the foam and the 3-year time span between the test series may have had an adverse affect on their quality and may explain the inconsistency of the Phase 3 results.

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At present, three other laboratories are conducting tests as part of the round-robin to evaluate the proposed test method. They are 3M Laboratories, Underwriters'

Laboratories of Canada and P.E.T.E. Once the round-robin tests are completed, the test results will provide the necessary information in locating the cause of the inconsistent results obtained in Phase 3.

CONCLUSIONS

A new test procedure to evaluate the quality of aqueous film-forming foam was proposed. The new test procedure is based on the current CGSB-28.74-M90 standard modified to apply the foam from a fixed nozzle. Repeatability of the new test procedure as well as acceptance criteria were evaluated by the NFL, which canied out full-scale fire test in three phases. Currently, there is an on-going round-robin organized by

Underwriters' Laboratories of Canada. The round-robin test results will provide the necessary information for the accuracy and bias of the proposed test method.

The NFL's results of three phases of tests showed that: Phases 1 and 2 provided repeatable, consistent test results. The test results in Phase 3 were inconsistent and showed very little agreement with the previous results. Although there is no conclusive evidence a s to the reason for this, the age of the foam concentrates seems to be the most likely cause. Reviewing the test results from the other laboratories involved in the Phase 3 romd-robin testing wiliprovide the first step in locating the cause of the inconsistent results obtained in Phase 3.

An additional test series to address the factors of aging of the foam and ambient temperature of the test would be of value. That series of tests with new and old foam samples at both the higher temperature (20-25OC) and the lower temperature (5-10°C) would provide insight into these two potential problem areas.

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TABLE 1

CGSB 28-GP-74M Results from Tests Conducted at DND Test Facility in Nicolet, Quebec

Sample 1 2 3 4 Extinguishment Time (min:s) 0:47 051 0 5 5 0:44 0:44 0:46 0:44 0:39 0:49 1:15 058 1:02 0:46 25% Burnback Time (min:s) 7:35 7:17 7: 10 8:18 11:02 8:05 7:21 7:19 7:20 4:41 236 5:46 5:45

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TABLE 2

NRC Fixed Nozzle Test Results

-

Foam Sample 1

*

Tests conducted with Fuel Condition B. All other tests were conducted with Fuel Condition A. Duration of Application (min:s) 3:OO 2:30 2:OO 1:45 1:35 1:lO 1:00 0:45 Extinguishment Time (min:s) 0 5 4 1:lO 0:58 0 5 3 1:11 1:14 1:lO 1:lO 1:21 1:09 1:07 1:14 1:18 1:00 1:13 1:05 1:05 1:02 1:28 1:05 No extinguishment 25% Bumback Time (min:~) 17:30 16:47 1552 16:55 15:14 13:39 1 1:29 13:37 9:17* 12:25 11:27 7:40* 13:12 10:09 8:56* 1355 14:19 12:49* 13:OO 15:19 NIA*

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TABLE 3

NRC Fixed Nozzle Test Results

-

Foam Sample 2

*

Tests conducted with Fuel Condition B. All other tests were conducted with Fuel Condition A.

Duration of Application (rnin:~) 3:OO 2:30 2:OO 1 :45 1:35 1:10 1:00 0:45 Extinguishment Time (min:s) 1:02 0 5 6 055 1:17 1:27 1:20 1:45 1:46 1:34 1:33 1:28 1:16 1:09 1:27 1 :24 1:08 3 5 2 12:13 No extinguishment No extinguishment No extinguishment No extinguishment 25% Burnback Time (min:s) 1253 1154 21:03 21:31 20:30 17:39 13:30 1459 11:37* 12:13 12:09 11:45* 1440 1521 14:06* 13:34 16:37 N/A* N/A N/A N/A* N/A*

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TABLE 4

NRC Fixed Nozzle Test Results - Foam Sample 3

*

Tests conducted with Fuel Condition B. All other tests were conducted with Fuel Condition A.

Duration of Application (min:~) 3:OO 2:30 2:OO 1:45 1:35 1:lO 1:00 0:45 Extinguishment Time (min:s) 1:11 1:02 0:59 1:07 1:32 1:15 1:27 1:20 1:25 1:07 1:16 1:27 1:13 1:16 1:18 1:17 1:07 1:03 No extinguishment No extinguishment No extinguishment 25% Burnback Time (min: s) 13:23 10:45 8:53 9:11 12:29 10:45 8:09 8:45 7:11* 8:5 1 8:57 8:39* 12:28 10:48 8:33* 12:14 19:30 10:06* NIA NIA NIA*

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TABLE 5

-

Foam Sample 4

*

Tests conducted with Fuel Condition B. All other tests were conducted with Fuel Condition A. Duration of Application (min:s) 2:OO 1 :45 1:35 1:10 1:OO 0:45 Extinguishment Time (min:s) 1:32 1:33 1:29 1:25 1 :44 3:17 1:03 1:03 1:31 1:08 1:15 1:27 0:58 0:57 1:13 No extinguishment No extinguishment No extinguishment 25% Burnback Time (min:s) 6:22 8:36 8:40 6:18 6:31 4:46* 6:47 6:43 4: 17* 7:47 5:56 5:30* 5:59 7:19 5:52* N/A N/A NIA*

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TABLE 6

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Table 6 (Cont.)

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14

TABLE 7

99% Extinguishment Time (Fuel Condition A)

Application Time (rnin:~) Sample # 1 2 3 4 1 2 3 4 99% Extinguishment Time (min:~) 1:Ol 0 5 9 1:05 1:16 0:59 1:08 l:oo 0 5 7 0 5 8 1:06 1:15 1:lO 1:03 1:08 l:oo 0 5 5

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TABLE 8

Average Extinguishment Time (Fuel Condition A)

Sample # 1 2 3 4 Application Time (min:s) 2:OO 1 :45 1:35 1:lO 1:00 2:OO 1:45 1:35 1:lO 1:00 2:oo 1:45 1:35 1:lO l:oo 2:OO 1:45 1:35 1:lO l:oo Average Extinguishment Time (min:s) 1:13 1:lO 1 :08 1:09 1:05 1:24 1:45 1:30 1:18 2:30 1:23 1:23 1:11 1:14 1:12 1:31 1:35 1:03 1:11 0:58

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TABLE 9

NRC Fixed Nozzle Test Results 144 L of Fuel on 90 L of Water Sample # 1 2 3 4 Extinguishment Time (min:s) 1:07 1:20 1:08 1:21 1:15 1 5 0 2:09 1:34 25% Burnback Time (min:~) 8:02 6:40 8:11 7:36 5:50 6:15 1:35 1:42

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TABLE 10

NRC Fixed Nozzle Test Results 75 L of Fuel on 100 L of Water

*

Bumback time in parenthesis was obtained after manually extinguishing the fire at 3 min. Sample # 1 2 3 4

5

Extinguishment Time (min:~) 1:SO 1:OU 1:28 1:30 1:09 1:11 1:12 1:17 1:15 1:07 1 :29 1:37 No extinguishment 25% Burnback Time (min:s) 6:35 6:15 8:26 9:49 5:49 5:17 6:12 3 5 5 3:36 4: 14 6:16 5:13 (7:58)*

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TABLE 1 1

NRC

Fixed Nozzle Test Results 75 L of Fuel on 75 L of Water

*

Burnback time in parenthesis was obtained after manually extinguishing the fue at 3 min. Sample # 1 2 3 4 5 Extinguishment Time (min:s) 1:12 1:lO 1:13 1:18 1:11 1:24 1:18 1:12 1:11 1:11 1:18 1:27 1 5 6 No extinguishment No extinguishment 25% Burnback Time (minx) 8:46 9:lO 8:56 13:47 13:08 14:06 8:33 8 5 5 7:38 6:15 3:15 5:30 8:03 (7:52)* (7:33)*

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TABLE 12

NRC Fixed Nozzle Test Results 50 L of Fuel on 100 L of Water

*

Burnback time in parenthesis was obtained after manually extinguishing the fire at 3 min. Sample # 1 2 3 4 5 - Extinguishment Time (min:~) 1:18 1:OO 1:09 1 :27 1:13 1:16 1:08 1:15 1:17 1:16 1:16 No extinguishment 25% Burnback Time (min:s) 13:12 10:09 14:40 15:21 12:28 10:48 7:47 ,556 6:46 1144 11:02 (10:50)*

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TABLE 13

Extinguishment Times of Various FuelIWater Ratios (Fm-R)

Sample # 1 2 3 4 5 Fiw-R of 144 Ll90 L (min:s) 1:07 1:20 1:08 1:21 1:15 1 5 0 1:34 2:09 Fm-R of 75 LIlOOL (min:~) 1:08 1:lO 1:28 1:30 1:09 1:11 1:12 1 :07 1:15 1:17 No extinguishment 1:29 1:37 Fm-R of 75 Ll75 L (min:~) 1:10 1:12 1:13 1:11 1:18 1:24 1:11 1:12 1:18 1:11 1:18 1:27 No extinguishment No extinguishment 1:56 Fiw-R of 50 LI100 L (min: s) 1:00 1:18 1:09 1:27 1:13 1:16 1:08 1:15 1:17 No extinguishment 1:16 1:16

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TABLE 14

25% Burnback Times of Various FuelIWater Ratios (FIW-R)

*

Burnback time in parenthesis was obtained after manually extinguishing the fire at 3 min. Sample # 1 2 3 4 5 FN-R of 144 Ll90 L (min:~) 6:40 8:02 7:36 8:11 5 5 0 6:15 1:35 1 :42 No test conducted FIW-R of 75 LIlOOL (min:s) 6:15 6:35 8:26 9:49 5:17 5:49 6: 12 3:36 3:55 4 1 4 5:13 6:16 (7:58)* FIW-R of 75 L/75 L (minx) 8:46 8 5 6 9: 10 13:08 13:47 14:06 7:38 8:33 8 5 5 3:15 5:30 6:15 (7:33)* (7:52)* 8:03 FN-R of 50 L1100 L (min:s) 10:09 13:12 14:40 15:21 10:48 12:28 5:56 6:46 7:56 (10:50)* 1 1:02 11:44

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22 TABLE 15 NRCC Results (Phase 3) Sample # 1 2 3 5 Extinguishment Time (minx) 1:22 3:38 1 5 6 1:23 1 5 3 2:02 1:15 1:15 3:25 1 :47 1:38 25% Bumback Time (min:s) 13:ll 1456 8:38 15:ll 15:32 1 8 5 2 15:03 9:24 8:38 9:48 9:38

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Burnback Pot 144 L fuel

on

90 L water Burnback Pot 75 L fuel

on

100 L water Scale 5:l