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ACT Rural Fire Service

Bushfire CRC

Summer Vacation Project - February 2006

Aerial Suppression Project – Draft Report

AN ASSESSMENT OF DROP PATTERNS, PENETRATION AND PERSISTENCE OF WATER AND FOAM FROM MEDIUM AERIAL PLATFORMS IN GRASSLAND, OPEN WOODLANDS AND PINE FOREST IN THE ACT.

PAUL KILLEY1 AND GUY BARRETT1.

1 ACT RURAL FIRE SERVICE / BUSHFIRE CRC SUMMER STUDENT.

2

Executive Summary. The aim of this project was to test the effect of canopy type and foam concentration on the

penetration and persistence of aerially applied fire suppressant. Eucalypt woodland and

plantation pine canopy were used as they represent the typical canopy types of the Canberra

region. Fire suppressants tested were water, 0.3% and 0.5% class A foam. Three 50x30 m

plots were set up in grassland (no canopy), eucalypt woodland and plantation pine, making a

total of 9 plots. A 5 metre grid was marked out on each plot and collection containers placed

at each grid intersection. A Bell 212 helicopter using a Simplex 304 belly-tank was used to

deliver the suppressant. The pilot was instructed to perform each drop at a height of 80 –100

feet and a speed of 40 knots using both side doors of the tank (full salvo). Fluid collected in

each container was measured and the fuel moisture content (FMC) of surface samples from a

selected transect across each plot were determined.

‘Drier’ or more concentrated foam solutions have been observed to ‘stick’ in canopies, with

the expectation that this would reduce canopy penetration. However, the results of this study

indicate that increasing foam concentration increases the penetration of suppressant through

both the pine and eucalypt canopies within the range of foam concentrations tested. It is

possible that the increase in volume afforded by foam may allow a greater quantity of

suppressant to penetrate the canopy. In addition, the reduction in surface tension and

increase in adhesion to fuels may have contributed to the observed result. However, a

rigorous explanation of this result requires further investigation.

As expected, the denser pine canopy intercepted more suppressant. On average across the

three suppressants used, an increase in the mean canopy density by 42% reduced the mean

volume penetrating to the surface fuels by 59%. Foam suppressants reduce the evaporation

of water from fuels (Goodwin, 1936; Gould et al, 2000; Schlobohm and Rochna, 1988).

However, in this experiment, no difference was found in the persistence of the different

suppressant. This may have been due to the limited sampling of fuels necessitated by the

available resources.

Some difficulties were encountered in the collection of data. Notably, a number of factors

combined during the grassland drops that made the data from this site less reliable. These

problems were largely a result of performing a complex experiment for the first time with

limited resources and time. Further experimentation is required to confirm and expand on

these results. Repetition of the current study would help to confirm that these results did not

occur by chance and enable a reliable comparison of the two canopy types with a no canopy

(control) situation. The inclusion of higher foam concentrations in future studies would clarify

the relationship between foam concentration and canopy penetration. Given greater on-

ground resources, a more comprehensive fuel moisture sampling regime would produce more

reliable information about the relationship between foam concentration and the persistence of

suppressant.

3

Acknowledgements. This project was made possible through a Summer Student Scholarship from the Bushfire

Cooperative Research Centre (CRC). It was developed and executed under the supervision

of Matt Plucinski of ENSIS (CSIRO) Bushfire CRC. Matt also made a significant contribution

to this report through comments on the draft. In addition, a number of individuals provided

support and assistance during the project. The staff of the ACT Rural Fire Service (RFS)

provided considerable advice and expertise. The pilots provided valuable advice and

demonstrated their skill in making the drops. Leigh Douglas of ENSIS (CSIRO) Bushfire CRC

worked tirelessly in assisting with data collection. This project could not have proceeded

without the cooperation of Environment ACT Conservation and Land Management (ACT

Forests) staff who authorised the use of Kowen Forest for the drops and assisted in locating

suitable sites. I would also like to thank Peter Dunn, Commissioner of ACT Emergency

Services for his encouragement and facilitation of this project.

4

Contents.

Executive Summary…………………………………..………………………….……….2

Acknowledgements…………………………………………..……………….…..……….3

1. Introduction and Aims………………………………….…………………..….….……5

2. Experimental Procedure…………………………………………………..….………..7

3. Results………………………………………………………………………..…..…….11

4. Discussion………………………………………………………………..……….…....25

5. Conclusion………………………………………………………………..…………….29

6. References…………………………..…………………………………..……………..30

Appendix 1: Data collection sheets.……………………………………....…………….31

Appendix 2: Canopy data.………………..……………………………….…..…………33

Appendix 3: Volumes per unit area statistics.…………………………………….……35

Appendix 4: Drop patterns……………………..………………………..………….……36

Appendix 5: Fuel moisture samples……………………..………….………………..…40

Appendix 6: Within-site canopy density and penetration correlations………………44

5

1. Introduction and aim. 1.1. Aim.

To investigate the effects of canopy and foam proportion on the drop pattern, penetration and

residence time of foam delivered from a Bell 212 helicopter using a Simplex 304 belly tank

during days of elevated fire danger.

1.2. Project background.

While medium platforms have been used widely in other jurisdictions for a number of years for

firefighting, the opportunity to undertake tactical and strategic training with them in the ACT

has been limited. Under the NAFC agreement, a medium platform (Bell 212 with belly tank) is

stationed in the ACT for the peak fire danger period This project provided the opportunity for

research to be conducted on in the use of these appliances in fuels typical of the ACT region

as part of an assessment of their capability.

1.3. Experimental design.

The main intention was to compare the effects of foam concentration and canopy type on

penetration and persistence of suppressant (Table 1). As only three drops could be achieved

each day, drops of water, 0.3% and 0.5% foam were performed in a single canopy type on a

drop day.

Other factors with the potential to influence the results included the weather (wind speed and

direction, temperature and relative humidity), site factors such as slope, aspect and

orientation, and aircraft delivery (speed, height and tank door combinations. All of these

factors were kept as consistent between each drop as possible. Typical fire weather

conditions (high temperature, low humidity and moderate winds) were targeted, although

there was some variation between the days of each drop. Fire weather danger rating and

microclimate conditions were recorded to assist data analysis. Site factors were standardised

as much as possible across the three sites. The helicopters speed and height were held as

constant as possible across all drops with the pilot being instructed to perform each drop at a

speed of 40 knots and height of between 80 and 100 feet. Both side doors were opened for

each drop to empty the tank quickly as possible.

6

TABLE 1. Experimental factors tested for their effect on drop penetration and persistence durability.

1.4. Aircraft and delivery system.

The aircraft used was a Bell 212 (Helitack 273) fitted with a Simplex 304 belly tank. The

specifications of this belly tank are outlined in Table 2.

The foam injection system on this tank consists of two collapsible bags located internally on

the mid-left side of the main tank. The bags have exterior fill ports and an electrically

operated pump for injecting the chemical into the water load through two injection tubes.

Biggs (2004) has suggested that foam percentage in older Simplex 304 tanks was higher than

the injection setting indicated, a problem that has been rectified on all tanks delivered since

April 2000 by modifying the foam delivery hoses. The tank used for these drops was

delivered after April 2000 and should therefore have these modifications.

TABLE 2. Specifications of Simplex Model 304 Fire Attack System Belly Tank (From Biggs, 2004).

Belly Tank Volume 1420 litres Maximum water volume 1275 litres Tare Weight of System 179.2 kg Gross Weight of System (fully loaded including foam concentrate)

1598 kg

Number of Drop Doors 3 Gross dimensions of main door aperture (each) 2140 mm x 180 mm Distance between main drop door apertures 690 mm Area of third (middle) door 900 mm x 180 mm Drop door combination Both, right hand or centre door. Drop door evacuation Adjustable flow rate not available Drop door opening sequence No sequence Drop door actuators Hydraulic Flow rate maximum Not stated Hover fill system Hydraulic or electric Hover fill time Full tank – 80 –90 seconds Foam concentrate reservoir capacity (internal) 143 litres

Factor Levels Comments

Foam concentration 3 Three foam concentration levels were tested; 0% (plain water), 0.3% and 0.5%.

Vegetation type/

Canopy

3 Three canopy types were investigated; 1. No canopy – open grassland (control) 2. Moderate canopy - open eucalypt woodland 3. Thick canopy - radiata pine forest (~15 years old). These types represent the canopies in the ACT region and can be applied across Australia. It was expected that these canopies would influence microclimates and therefore residence time of the water/foam as well as altering drop pattern due to interception of the water/foam.

7

2. Experimental procedure 2.1. Site selection and appraisal.

Three sites were selected in Kowen Forest, east of Canberra. Each site represented one

vegetation type. Kowen Forest is part of the ACT Forests estate and was used because of its

proximity to the helicopters base of Canberra airport and it contained suitable sites of the

three canopy types required for this experiment. The following criteria will be used to select

the sites.

• Each site needed to be able to contain 3 areas of 30 x 50 metres (total area of 450

m2;

• A uniform canopy cover;

• As level as possible;

• Limited elevated fuels (shrubs);

• Suitable road access for the delivery of equipment.

Once appropriate sites were identified, the following parameters were recorded:

• Location (map or GPS reference)

• Slope

• Aspect

• Vegetation type

• Estimated canopy cover

• Surface fuels .

Site assessment and surveying were done prior to the drop test day.

2.2. Grid alignment and marking out.

In each site, three drop plots were set out using two 100 m tapes and a compass. Each plot

was 30m wide and 50m long (Figure 1). The corners of each plot were then marked with

pickets and flagging tape and a 5 m grid was then marked on the ground with line marking

paint.

Each grid was aligned with its long axis along a NE -SW axis. This was to allow the aircraft to

fly along this axis, perpendicular to the expected wind direction (typically NW). This was done

to replicate a common tactic used during bushfire suppression activities and to capture the

lateral spread effect of a crosswind.

8

FIGURE 1. Grid layout.

One litre rectangular take away food containers were used to select a sample of drop

coverage (width=119mm, length=173mm, depth=65mm; top opening surface area=0.019m2)

at each of the grid intersections. Each container sat inside an identical base container. The

base containers were fixed to the ground with a 10cm roofing nail. Collection containers were

labelled according grid position (column : row).

2.3. Fuel load sampling.

Fuel samples were collected from each site to assess fuel load and grass curing. These

samples consisted of three 0.25m2 destructive samples at each site. The quadrat sites were

selected to represent fuels within each drop zone.

Grassland: Fuels were collected by cutting down to mineral earth. These samples were then

separated into cured and green portions within 24 hours of sampling to estimate grass curing.

Woodland: All fine fuels within each quadrat were collected. This included decomposing

litter.

Pine: Top litter and decomposing (duff) organic matter were both collected but placed in

separate bags.

All samples were then oven dried for 24 hours. Oven dry weight of each sample was then

measured and estimates of fuel loads were then calculated.

2.4. Canopy assessment.

Photographs of the canopy were taken at each grid intersection. At each of these points, a

camera was placed on the ground and held as level as possible with the lens facing vertically.

50m (Rows)

30m (Columns)

9

A photograph of the canopy was then taken. These photographs were then assessed against

the standard estimates of crown cover provided by McDonald et al (1990, p.71). Each

photograph was rated for percentage cover category, providing an estimate of the crown

cover at each grid intersection. The grassland site did not have a canopy and therefore the

suppressant dropped with no interception.

2.5. Weather station.

In order to have local weather data, a portable weather station was placed near to the drop

sites in an area representative of the particular canopy. This was set to log data at one

minute intervals.

2.6. Video camera.

A video camera was placed on a tripod ahead of the plot facing the oncoming aircraft. A

second video camera was positioned at the side of each plot. The videos were time

synchronised with the GPS to allow accurate estimation of the flight variables of each drop.

2.7. Drops.

The pilot was briefed prior to each flight on the location, alignment and intention of each drop.

The flying pattern for each drop was standardised as much as possible (40 knots, 80-100

feet) along a SW to NE axis. Water was dropped first. After refilling, the pilot added foam to

approximately* 0.3% and this was dropped on the second plot. The pilot then refilled and

flushed the tank before refilling and adding foam to approximately* 0.5%. On each run, the

two outside doors were opened to empty the tank as quickly as possible.

During the drops, crews were positioned at a safe distance from the drop zone but with a

good view to allow video recording. Communication with the pilot was maintained for the

duration of the drop through the ACT RFS radio network.

* The operational capacity of the belly tank was reduced from its maximum due to the aircraft carrying a full fuel load. The pilot estimated that the tank would be filled to ¾ capacity (750 litres) for each drop. To compensate for the reduced belly tank volume, a foam injection setting of 0.2% was chosen to make the 0.3% solution and an injection setting of 0.4% was chosen to make the 0.5% solution. If the belly tank is at maximum capacity (1275 l) then a 0.1% foam solution will require an injection of 1.275 l of concentrate. An injection setting of 0.2% will, therefore add 2.55 l of concentrate to the tank. If it were assumed that the tank was holding 750 l, this would make a 0.34% solution. Similarly, an injection setting of 0.4% would deliver 5.1 l of concentrate, which would make a 0.68% solution with 750 l of water.

10

2.8. Drop pattern and canopy penetration.

After each drop, lids were placed on the containers that had captured suppressant. This was

done as quickly as possible to prevent any loss through evaporation. These containers were

then collected and weighed, giving a measure of the volume of suppressant collected.

2.9. Fuel moisture monitoring.

Fuel moisture content was monitored in each of the drop sites. A transect across the drop

zone was selected according to a visual estimate during the drops of the region of each plot

that received the greatest amount of suppressant. Fuel samples were collected along this

transect, one from each grid square, in a continuous cycle across the three plots. Each fuel

sample consisted of a few handfuls of surface fuels. In the grassland, only cured standing

grasses were collected. In pine and woodland sites, surface, undecomposed litter was

collected. These samples were then weighed immediately, to give a wet weight, and then

oven dried (24 hours at 950) to give a dry weight. From this, fuel moisture content (FMC) of

each sample was calculated [ (wet weight-dry weight)/dry weight ] and the evaporation of

suppressant from the time of each drop was graphed. Data collection sheets for container

weights and fuel samples are presented in Appendix 1.

2.10. Microclimate.

Ground level temperature and humidity measurements were made with an Assman

psychrometer. These measurements were taken along the same transects as the FMC

samples.

2.11. Post flight follow up.

All available tracking information from the aircraft’s GPS was downloaded from the aircraft in

order to compare air speed and altitude of the drops.

2.12. Site clean up.

Once all data has been collected, the site was cleaned up and all rubbish removed including

marker posts and flagging tape.

11

3. Results. 3.1. Site information.

Selection of three sites of suitable size and canopy cover resulted in some compromise in the

desired site qualities. Notably, all three sites had different aspects. In addition, the slope

varied between the sites. However, these differences do not affect a comparison between the

three different suppressant within each site. In terms of the required site variables, the sites

were individually as homogenous as possible.

Site 1.

Location: Kowen Forest, Grid reference 710500:6090500

Vegetation Type: Grassland

Vegetation Height: 0.4 –0.5 m

Slope: 0

Aspect: North (flat)

Site Description: Open native grassland.

Tenure: ACT Forests

Access: McInnes’ Rd

FIGURE 2. Grassland site.

12

Site 2.


Vegetation Type: Open eucalypt woodland, dominated by Eucalyptus rossii, E. macrorhynca,

and E. mannifera.

Vegetation Height: Upper canopy 10 – 12 m

Slope: 30-50

Aspect: South west

Site Description: Remnant native woodland.

Tenure: ACT Forests

Access: Fernside Way

FIGURE 3. Eucalypt woodland site.

13

Site 3.


Vegetation Type: Pine forest (Pinus radiata).

Vegetation Height: 12 – 15 m

Slope: 30-50

Aspect: East north-east Site Description: Un-thinned pine forest

Tenure: ACT Forests

Access: Charcoal Kiln Rd

FIGURE 4. Plantation pine site.

14

3.2. Canopy density.

Table 3 summarises the estimates of the Pine and Euaclypt Woodland canopy densities. The

sites were chosen because they appeared to have a relatively uniform canpopy. This was

confirmed by the formal canopy assessment. All of the plots at each site had very similar

mean canopy densities. Standard error and standard deviation from the mean were also

comparable within each site. Graphs of the canopy data are provided in Appendix 2.

TABLE 3. Summary of the canopy estimates at each grid intersection.

WOODLAND

Water Plot

0.3% Foam

Plot

0.5% Foam

Plot

Mean density 41.8 41.0 44.4

Standard error 0.82 0.71 0.61

Standard deviation 7.2 6.2 5.4

Median density 40.0 40.0 45.0

Minimum density 10.0 20.0 35.0

Maximum density 55.0 55.0 60.0

PINE PLANTATION

Mean density 72.3 73.2 71.4

Standard error 0.53 0.32 0.62

Standard deviation 4.7 2.8 5.5

Median density 75.0 75.0 75.0

Minimum density 50.0 65.0 50.0

Maximum density 75.0 75.0 80.0

15

3.3. Fuel variables.

The measuredd fuel variables were:

Grassland:

Fuel Load = 2.3 t/ha (SD=0.14; SE =0.08)

Curing = 93.8% (SD = 1.5%; SE = 0.9%)

Maximum fuel height estimated to be approximately 0.5 m

Eucalypt woodland:

Total fine fuel load = 23 t/ha (SD = 9; SE = 5.2)

Pine plantation:

Surface fuel load = 2.5 t/ha (SD = 0.2; SE = 0.1)

Duff load = 17 t/ha (SD = 2; SE = 1.1)

Total (surface + duff) load = 17.8 t/ha (SD = 2.7; SE = 1.6)

The sampling of the eucalypt woodland fuel did not distinguish between surface and

decomposing (duff) litter. This site did not have any signs of recent fire, and the fuel load had

probably reached equalibrium. There was considerable variation in the Eucalypt woodland

fuel load, with much higher loads observed near the trunks of gum barked trees. In

comparison, the Pine fuel load was relatively uniform.

16

3.4. Weather variables.

Although high fire danger weather was considered desirable for this experiment, time

constraints and aircraft availability limited the ability to select weather that was consistent

between the three drop days. Although the temperature was similar on all three days, the

relative humidity was considerably lower and wind speed higher on the grassland drop day

than on the other two days. The wind direction was not consistent between the days. The

wind strength and direction caused considerable difficulty during the grassland drops. In

addition, fuel sampling after the Pine plantation drops was ceased when it started to rain.

The portable weather station malfunctioned on two of the three days resulting in the data

collected being of little value. Instead, the data presented is from the Bureau Meteorology

(BOM) station at Canberra Airport, approximately 11km to the west of the sites. Although this

does not give local conditions, it provides a reasonable estimate of the weather conditions

experienced during the drops and subsequent fuel sampling. Figures 5, 6 and 7 show the

BOM weather data.

The KBDI ranged from 74.3 to 79.2 during the period of data collection (13 - 24/2/06).

Weather Data - Grassland Drop (13/2/06)

0

5

10

15

20

25

30

35

14:09 15:21 16:33 17:45

Time

Wind SpeedTemperatureRHGFDIWater Drop0.3% Foam Drop0.5% Foam Drop

FIGURE 5. BOM weather data (Canberra Airport) for the period of the grassland experiment. GFDI has been calculated from the supplied data using the grass curing rate of 93.84%. Wind direction during this period was NW to WNW.

17

Weather Data - Woodland Drop (15/2/06)

0

10

20

30

40

50

60

13:40 14:52 16:04 17:16

Time

Temperature

RH

Wind Speed

FFDI

Water Drop

0.3% Foam Drop

0.5% Foam Drop

FIGURE 6 . BOM weather data (Canberra Airport) for the period of the woodland experiment. FFDI has been calculated form the supplied data. Drought factor on the 15/2/06 was 9. Wind direction during the test period was N until15:30, NW from 15:30 to 16:40, and SE after 16:40.

Weather Data - Pine Drop (24/2/06)

0

5

10

15

20

25

30

35

40

13:40 14:52 16:04 17:16

Time

Wind SpeedTemperatureRHFFDIWater Drop0.3% Foam Drop0.5% Foam Drop

FIGURE 7. BOM weather data (Canberra Airport) for the period of the pine forest experiment. FFDI has been calculated form the supplied data. Drought factor on the 24/2/06 was 9. Wind direction during the test period was W or WSW until 17:00 when it became E. Although not recorded at the airport, rain fell on the pine site at approximately 16:30. Fuel moisture sampling ceased at this time.

18

3.5. Drop volumes.

The container weight data was converted into volume per square metre by the following

process:

• An average container weight was calculated by measuring the weights of 40 containers and 40 lids. This produced a mean container weight of 33.95 g (SD = 0.33; SE = 0.07).

• This average container weight was then subtracted from the measured weight to give the weight in grams (and therefore volume in mls) of fluid collected in each container;

• The collection area of the containers was measured and found to be 0.019 m2. • The volume in litres was then divided by the area of a container to give a volume

per unit area (lm-2).

A considerable number (water plot = 3%; 0.3% foam plot = 39%; 0.5% foam plot = 54%) of

the grassland containers were cracked during the application of the lids. An unknown

quantity of suppressant had leaked from these containers, making this data unreliable. It is

presented here only for completeness. Modification of the method of putting on container lids

prevented any further cracking of containers in the subsequent drops.

The collected volume of suppressant shows a consistent trend in both the eucalypt woodland

and plantation pine drops. The amount of fluid collected was highest in the 0.5% foam plot

and lowest in the water plot. This trend remains the same if all containers registering more

than a trace of fluid are considered (Figure 8), and if only the top 5 (Figure 9) containers are

compared. Data for Figure 8 is presented in Appendix 3.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Grassland Woodland Pine

lm-2

Water

0.3 % Foam

0.5% foam

FIGURE 8. Mean volume per square metre of all containers registering more than a trace of fluid across the three sites demonstrating an increase in penetration with increasing foam concentration. Standard error bars are shown.

19

0

0.5

1

1.5

2

2.5

3

Grassland Woodland Pine

lm-2

Water

0.3% Foam

0.5% Foam

FIGURE 9. Mean value of the top 5 recorded volumes per unit area.

Standard error bars are shown.

3.6. Drop pattern.

The footprint pattern for each drop varied considerably. The wind direction and speed on the

day and the reduced plot length made the grassland drops particularly difficult. Similarly, the

dense nature of the pine canopy presented particular problems for the pilot in identifying the

drop zone. Not all drops, therefore hit the centre of the target. This is another level of

variance between the drops that needs to be considered in interpreting the data. Each drop

pattern is graphically presented in Appendix 4.

3.7. Flight data.

Data recorded by a GPS mounted in the aircraft was downloaded and analysed to give the

speed and height during each of the drops. Considerable variation was observed in the

height of each drop, with the maximum variation being 40%. Speed was more consistent with

the maximum variation being 23%. Table 4 details the flight variables for each drop.

TABLE 4. Flight variables for each drop.

Site Suppressant Height (ft) Speed (kn) Grassland water 134 54.2 0.3% foam 96 52.6 0.5% foam 152 57.6 Woodland water 137 53.8 0.3% foam 97 46.9 0.5% foam 135 44.7 Pine water 160 50.4 0.3% foam 121 50.9 0.5% foam 131 44.2

20

3.8. Fuel moisture duration.

Fuel moisture samples were taken from each plot to determine the longevity of each drop.

The resources available limited the extent of sampling with only one sample taken from each

grid square along the chosen transect during each sampling cycle. Using only a single

sample has resulted in considerable variation in the results. However, trend lines fitted to the

data give an indication of the rate of evaporation from each plot. The complete set of data

points and trend lines is presented graphically in Appendix 5.

The results presented below are distilled to give a clearer idea of the evaporation rate from

each plot. Figures 10, 11 and 12 show the results from the single grid square along each

transect that had the highest FMC at the start of the sampling period. The associated Tables

(Tables 5, 6 and 7 respectively) detail the FMC at the start and end of the sampling, the

change in FMC during this period, the length of time of this change and the equation

calculated for the trendline displayed in the graph.

In the graphs presented, there is no clear trend demonstrated in the relative persistence of

the three suppressants. It should be noted that the humidity was much lower during the

grassland sampling cycle, and rainfall ended the pine sampling cycle (Section 3.4).

Grassland - Fuel Moisture Duration

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0:00 0:28 0:57 1:26 1:55

Time since drop (hours:minutes)

FM

C (

%)

Water

0.3% Foam

0.5% Foam

Ref.

Expon. (0.3% Foam)

Expon. (Water)

Expon. (0.5% Foam)

Expon. (Ref.)

FIGURE 10. FMC trendlines for the single grid square with the highest recorded FMC in the three grassland plots.

21

TABLE 5. Detail of the data from Figure 10.

Woodland - Fuel Moisture Duration

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:00 0:28 0:57 1:26 1:55 2:24 2:52 3:21


FM

C (

%)

Water

0.3% Foam

0.5% Foam

Ref.

Expon. (0.5% Foam)

Expon. (0.3% Foam)

Expon. (Water)

Expon. (Ref.)

FIGURE 11. FMC trendlines for the top single grid square with the highest recorded FMC in the three woodland sites.


Drop Max. FMC% Min. FMC % % Change Time Period (min) Trendline Equation

Water 27.4 12.4 55 47 y = 40.514e-24.657x

0.3% Foam 28.4 13.4 53 46 y = 38.341e-24.541x

0.5% Foam 21.3 9 57 46 y = 26.992e-23.262x


Water 69 24 65 137 y = 0.6195e-9.083x

0.3% Foam 39 13 68 137 y = 0.553e-8.3771x

0.5% Foam 60 38 37 138 y = 0.6172e-5.6426x

22

Pine - Fuel Moisture Duration

0%

20%

40%

60%

80%

100%

120%

140%

0:00 0:36 1:12 1:48 2:24


FM

C (

%)

0.5% Foam

0.3% Foam

Water

Ref.

Expon. (0.5% Foam)

Expon. (Water )

Expon. (0.3% Foam)

Expon. (Ref.)

FIGURE 12. FMC trendlines for the top single grid square with the highest recorded FMC in the three pine sites.



Water 97 42 57 1:22 y = 1.1757e-13.721x

0.3% Foam 44 16 62 1:04 y = 0.7052e-22.332x

0.5% Foam 130 79 40 1:02 y = 1.6108e-11.751x

23

3.9. Post-drop Microclimate.

Figures 13, 13 and 15 display the relative humidity (RH) recorded at ground level on the

corresponding grid square as the fuel moisture duration data presented in Section 3.8. The

RH measured at ground level follows a similar pattern as the FMC data.

0

10

20

30

40

50

60

70

0:00 0:14 0:28 0:43 0:57 1:12 1:26 1:40


RH

(%)

Water

0.3% Foam

0.5% Foam

Ref.

Expon. (0.3% Foam)

Expon. (Water)

Expon. (0.5% Foam)

Expon. (Ref.)

F

FIGURE 13. Grassland microclimate (RH).

24

0

10

20

30

40

50

60

70

0:00 1:12 2:24 3:36


RH

(%)

Water

0.3% Foam

0.5% Foam

Ref.

Expon. (0.5%Foam)

Expon. (Water)

Linear (0.3%Foam)

Expon. (Ref.)

FIGURE 14. Woodland microclimate (RH).

0

10

20

30

40

50

60

0:00 0:28 0:57 1:26 1:55


RH

(%)

Water

0.3% Foam

0.5% Foam

Ref.

Expon. (0.5%Foam)Expon. (Water)

Expon. (0.3%Foam)Expon. (Ref.)

FIGURE 15. Pine microclimate (RH).

25

4. Discussion 4.1. Data collection problems.

As the grassland drops were the first performed for this experiment, there were a number of

‘teething’ problems encountered. These problems were able to be rectified for the following

drops. The problems encountered during the grassland experiment included:

• We did not take out enough containers to lay three complete 50m x 30m plots.

To compensate for this, all three plots were shortened to just 30m in length.

• The wind direction was behind line of run of the aircraft, making accuracy very

difficult for the pilot. This, combined with the shortened grids resulted in most of

the suppressant falling outside the grid on 2 of the three drops (see Appendix 4

for drop patterns).

• A considerable number of the containers were split by the base container holding

nail when the lids were applied. This resulted in the loss of an unknown quantity

of fluid form these containers. On subsequent drops, collection containers were

removed from the base containers when the lid was applied to prevent this

problem recurring.

The grassland data was intended to provide a ‘control’ comparison for the woodland and pine

canopy penetration. However, the problems detailed above mean that this comparison can

not be made. In addition, interpretation of the grassland duration data needs to be done with

caution.

The portable weather station also presented some problems with data collection. During the

woodland drop, the data logging reverted automatically to an hourly setting. During the pine

drop, the relative humidity sensor malfunctioned. These problems meant that little useful data

was recorded. As a result, the BOM data from Canberra airport is presented as a next best

approximation for local conditions.

Some of the above problems could have been prevented if more on-ground resources were

available to assist with the experiment and data collection. In addition, more on-ground

resources would have enabled increased fuel moisture monitoring and reduced the time lag

between drops.

26

4.2. Canopy penetration and foam concentration.

Observation of previous aerial fire suppression activity had indicated that increasing foam

concentration resulted in larger amounts of foam clinging to the canopy and not penetrating to

the surface fuels. From these observations, it was hypothesised that increasing foam

concentration would reduce canopy penetration. The most significant result seen in this

experiment, therefore, is the increasing canopy penetration with increasing foam

concentration (Figures 8 and 9). Class A foam expands the volume of a quantity of water

through the formation of bubbles (Goodwin, 1939; Gould et al, 2000). One possible

explanation for result obtained is that this increase in volume allows a larger amount of

suppressant to fall through the canopy. Assuming that the area of each drop is consistent,

then the canopy area coated with suppressant would also be similar. Once the canopy was

was holding its maximum volume of suppressant, the remainder would continue penetrate

through to the ground. By increasing the concentration of foam, the volume of suppressant

has increased, thereby delivering a greater quantity to the ground. It is also possible that the

volume of successive drops increased as fuel was burned, increasing the carrying capacity of

the aircraft. A repeat of this experiment reversing the order of the drops (0.5%, 0.3%, water)

would investigate this possibility. Other factors that may contribute to increasing penetration

include the alteration in surface tension and adhesion properties of water through the addition

of foam. Therefore, a rigorous explanation of this observation would require further

investigation including replication.

This experiment tested only two proportions of foam, estimated to be 0.34% and 0.68%

(Section 2.7). No aerial photos were taken of these drops to record the amount of foam

visably remaining in the canopy. It may be that higher proportions of foam reduces canopy

penetration by allowing more foam to adhere to the canopy and by increasing sideways drift

of a ‘drier’ more aerated mix (Figure 16). That is, there is probably a limit to the effect of

increasing foam concnetration on canopy penetration Further experimentation is requried to

test this hypothesis.

Increasing foam concentration

Dro

p vo

lum

e on

gro

und

FIGURE 16. A hypothetical effect of increasing foam concentration on canopy penetration is that increasing foam concentration may eventaully reduce canopy penetration as more suppressant is held (sticks) in the canopy.

27

4.3. Canopy density and penetration.

There was a distinct correlation bet ween canopy density and suppressant penetration

between the woodland and pine sites. Across the three suppressant drops, the eucalypt

woodland with a mean canopy density of 42% received a mean volume of 0.41 lm-2 and the

pine plantation with a mean canopy density of 72% received a mean volume of 0.17 lm-2

(Figure 17). In this instance, increasing the mean canopy density by 42% reduced the mean

volume penetrating to the surface fuels by 59%.

Canopy density and penetration

0

0.1

0.2

0.3

0.4

0.5

0.6

0 10 20 30 40 50 60 70 80

Canopy Density (%)

Mea

n lm

-2

Water

0.3% Foam

0.5% Foam

FIGURE 17. Mean canopy density plotted against mean volume per square metre at the woodland and pine sites showing a distinct reduction in penetration with increasing canopy density.

Correlations between canopy density and penetration within each site were also performed

(Table 8). These are the correlations of the data at each grid point, and therefore are

influenced by the variation in volume delivered across the plot. The low correlations obtained

indicate that canopy density had less influence on penetration than the inherent variability in

the volume delivered to each point in a drop of this nature. The weak correlation in the pine-

water drop (R2 = 0.2424) reflects the relatively uniform canopy density in this plot

compressing the data into a more uniform pattern. These correlations are graphically

presented in Appendix 6. To adequately test the correlation between volume and density at

each grid point, a uniform volume would need to be delivered above the canopy.

TABLE 8. R2 values for the correlation between canopy density and penetration (container volume). Eucalypt woodland Pine plantation Water 0.0053 0.2424 0.3% Foam 0.0197 0.0352 0.5% Foam 0.0022 0.0485

28

4.4. Fuel moisture content and persistance.

In both the woodland and pine drops, the 0.5% foam to had the highest FMC. This may again

reflect the relative volumes of suppressant delivered to each plot under the influence of foam.

The 0.5% foam achieved higher FMC by allowing a greater volume of suppressant to

penetrate the canopy. However, this explanation would suggest that 0.3% foam should

produce a higher FMC than water. This was not observed in this experiment.

There was no clear trend discernable between the three suppressants in terms of

persistence. It was expected that foam suppressant would inhibit evaporation (Gould et al,

2000; Schlobohm and Rochua, 1988), slowing the loss of moisture from these plots. This was

not observed in this experiment. The majority of fuel moisture curves appear to follow a very

similar trend, with the exception of 0.3% foam in the pine site. This lack of observed

difference may be influenced by the limited fuel moisture sampling regime used. This issue

needs to be investigated in a more controlled environment such as in a laboratory where

inconsistencies in coverage and evaporation can be minimised.

4.5. Further research.

The opportunity to perform further research would help to confirm the results obtained in this

project, as well as answer some of the questions that inevitably arise from such experiments.

Suggestions for further research include:

• Repetition of the current project to confirm the trend of increasing canopy penetration

with increasing foam concentration. In addition, if the current experimental procedure

was repeated, more reliable grassland data would be available for comparison with

the other two canopy types;

• Repetition of this project might be able to incorporate multiple drops on the same

plots. This would increase the statistical power of the results and afford a level of

confidence beyond the indication obtained in this study;

• A larger range of foam concentrations would help to clarify the effect of increasing

foam concentration. Foam concentrations above the standard upper limit of 1%

would confirm or otherwise the hypothesis presented in Figure 15. This would also

help to determine the most effective foam concentration (in terms of canopy

penetration);

• Further experimentation into FMC persistence would be beneficial to study the effect

of foam on the evaporation of suppressant. If this is to be undertaken, then

appropriate resources (labour) would be required to take a more comprehensive set

of samples. A complementary set of laboratory experiments may be required to fully

investigate this issue.

• Performing multiple drops of the same suppressant on different canopy densities

would allow the quantification of the relationship between canopy density and

penetration of suppressant.

29

5. Conclusion. This study has investigated the effects of canopy and foam concentration on the penetration

and persistence of fire suppressant delivered by a Bell 212 helicopter using a Simplex 304

belly tank. As expected, increasing canopy density clearly reduced the penetration of

suppressant to the surface fuels. This was seen in the relative amount of suppressant

collected under the pine and woodland canopies. However, contrary to expectations,

increasing foam concentration was observed to increase canopy penetration. This may

simply be due to the expansion of volume caused by foam. There was no difference

observed in the evaporation of the three suppressants, although this may be due to the

limited sampling of fuel moisture that could be performed with the available resources.

Further experimentation is required to confirm these observations, and to further investigate

the effect of foam concentration and canopy density the penetration and persistence of aerial

fire suppressants.

30

6. References. Biggs, H. (2004). An evaluation of the performance of the Simplex 304 helicopter belly-tank . Research Report No. 71. Fire Management, Department of Sustainability and Environment, State of Victoria.

Godwin, D. (1939) Aerial and chemical aids. Fire Control Notes. Vol. 1(1), pp.5-10.

Gould, J., Khanna, P., Hutchings, P., Cheney, N. and R. Raison (2000). Assessment of the effectiveness and environmental risk of the use of retardants to assist in wildfire control in Victoria. Research Report No. 50. Department of Natural Resources and Environment, Victoria.

McDonald, R., Isbell, R., Speight, J., Walker, J. and M. Hopkins (1990). Australian Soil and Land Survey (2nd edn.) Department of Primary Industries and Energy, Canberra. Schlobohm,P. and R. Rochau (1988). An evaluation of foam as fire suppressant. Fire management Notes, Vol. 49 (2).

31

Appendix 1. Data collection sheets.

1. Container weights.

Site: Date: Time:

Location:

Vegetation type: Canopy Density: Canopy Height:

Foam concentration:

Fuel type: Fuel quantity (kg/m2):

A B C D E F G

1

2

3

4

5

6

7

8

9

10

11

32

2. Fuel Moisture samples.

Site: ________________________ Date:_____________

Bag # Time Field Weight (g) Dry weight (g) Bag weight (g)

33

Appendix 2. Canopy data.

1

3

5

7

911

ABCDEFG

10

20

30

40

50

60

CANOPY DENSITY (%)

WOODLAND CANOPY WATER

50-60

40-50

30-40

20-30

10-20

1

3

5

7

911

HIJKLMN

10

20

30

40

50

60

CANOPY DENSITY (%)

WOODLAND CANOPY 0.3% FOAM

50-60

40-50

30-4020-30

10-20

1

4

7

10

OPQRSTU

10

20

30

40

50

60

CANOPY DENSITY (%)

WOODLAND CANOPY 0.5% FOAM

50-60

40-50

30-40

20-3010-20

34

1

4

7

10

H I J K L M N40

50

60

70

80

90

CANOPY DENSITY (%)

PINE CANOPY - WATER

80-9070-80

60-70

50-60

40-50

1

4

7

10

O P Q R S T U40

50

60

70

80

90

CANOPY DENSITY (%)

PINE CANOPY - 0.3% FOAM

80-90

70-80

60-70

50-6040-50

1

4

7

10

A B C D E F G40

50

60

70

80

90

CANOPY DENSITY (%)

PINE CANOPY - 0.5% FOAM

80-90

70-80

60-70

50-60

40-50

35

Appendix 3. Volumes per unit area – descriptive statistics.

GRASSLAND DROP

Water 0.3% Foam 0.5% Foam Mean 0.49 0.23 0.30 Standard Error 0.08 0.06 0.05 Median 0.40 0.10 0.18 Standard Deviation 0.43 0.33 0.30 Sample Variance 0.19 0.11 0.09 Range 1.36 1.14 1.42 Minimum 0.01 0.00 0.02 Maximum 1.37 1.15 1.44 Sum 14.23 6.38 10.42 Count 29 28 35

WOODLAND DROP


PINE PLANTATION DROP


36

Appendix 4. Drop patterns.

The aircraft movement represented in these drop patterns is from bottom right to top left of

each graph. Row ‘1’ of containers was always at the start of the plot with the aircraft moving

from row ‘1’ towards row ‘11’. These graphs are the result of plotting the calculated

volume/unit area of each container that collected more than a trace of fluid.

37

Grassland plots.

A

C

E

G

1

4

7 00.51

1.5

2

2.5

lm-2

GrasslandWater Drop

2-2.5

1.5-2

1-1.5

0.5-1

0-0.5

H

J

LN

1

4

7 00.511.52

2.5

lm-2

Grassland 0.3% Foam

2-2.51.5-2

1-1.5

0.5-10-0.5

O

Q

S

U

1

4

7 00.51

1.5

2

2.5

lm-2

Grassland 0.5% Foam

2-2.5

1.5-21-1.50.5-10-0.5

38

Woodland plots.

1

4

7

10

A B C D E F G0

0.5

1

1.5

2

2.5

lm-2

Woodland Water

2-2.5

1.5-2

1-1.5

0.5-1

0-0.5

1

5

9

O Q S U

00.51

1.5

2

2.5

lm-2

Woodland 0.5% Foam

2-2.51.5-2

1-1.5

0.5-1

0-0.5

1

4

7

10

H I J K L M N0

0.5

1

1.5

2

2.5

lm-2

Woodland 0.3% Foam

2-2.51.5-2

1-1.5

0.5-1

0-0.5

39

Pine plots.

1

4

7

10

H I J K L M N0

0.4

0.8

1.2

1.6

lm-2

Pine Water

1.2-1.6

0.8-1.2

0.4-0.8

0-0.4

1

4

7

10

O P Q R S T U0

0.4

0.8

1.2

1.6

lm -2

Pine 0.3% Foam

1.2-1.6

0.8-1.2

0.4-0.8

0-0.4

1

4

7

10

A B C D E F G0

0.4

0.8

1.2

1.6

lm-2

Pine 0.5% Foam

1.2-1.6

0.8-1.2

0.4-0.8

0-0.4

40

Appendix 5. Fuel moisture samples.

These graphs present data from a single sample from each grid square along the transect

across each plot considered to have received the largest volume of suppressant. Due to the

variation of drop volume (Appendix 3), some of these grid squares received little or no

suppressant and are therefore little different to the control. The grid square that

demonstrated the highest FMC has been used to represent that transect in Section 3.8.

41

Grassland - Water Drop

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

0:00 0:20 0:40 1:00 1:20


FM

C %

A

B

C

D

E

F

Ref.

Expon. (F)

Expon. (E)

Expon. (C)

Expon. (A)

Expon. (B)

Expon. (D)

Expon. (Ref.)

Grassland - 0.3% Foam

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

0:00 0:20 0:40 1:00 1:20


FMC

%

H

I

J

K

L

M

Ref.

Expon. (I)

Expon. (J)

Expon. (H)

Expon. (K)

Expon. (M)

Expon. (L)

Expon. (Ref.)

Grassland - 0.5% Foam

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

0:00 0:20 0:40 1:00 1:20

Time since drops (hours:minutes)

FM

C (

%)

O

P

Q

R

S

T

Ref.

Expon. (Q)

Expon. (T)

Expon. (P)

Expon. (O)

Expon. (Ref.)

Expon. (R)

Expon. (S)

42

Eucalypt Woodland - Water

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:00 0:20 0:40 1:00 1:20 1:40 2:00 2:21 2:41 3:01 3:21


FM

C%

A

BC

D

EF

Ref.

Expon. (B)Expon. (A)

Expon. (E)

Expon. (F)Expon. (C)

Expon. (D)Expon. (Ref.)

Eucalypt Woodland - 0.3% Foam

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:00 0:20 0:40 1:00 1:20 1:40 2:00 2:21 2:41 3:01 3:21


FM

C%

H

I

J

K

L

M

Ref

Expon. (I)

Expon. (J)

Expon. (H)

Expon. (L)

Expon. (M)

Expon. (K)

Expon. (Ref)

Woodland 0.5% Foam - Durability

0%

10%

20%

30%

40%

50%

60%

70%

80%

0:00 0:20 0:40 1:00 1:20 1:40 2:00 2:21 2:41 3:01 3:21


FM

C%

O

P

Q

R

S

T

Ref

Expon. (Q)

Expon. (R)

Expon. (T)

Expon. (P)

Expon. (O)

Expon. (Ref)

Expon. (S)

43

Pine Plantation - Water

0%

20%

40%

60%

80%

100%

120%

140%

0:00 0:28 0:57 1:26 1:55


FM

C %

H

I

J

KL

M

REF

Expon. (H)

Expon. (I)Expon. (M)

Expon. (L)

Expon. (J)

Expon. (K)

Expon. (REF)

Pine Plantation - 0.3% Foam

0%

20%

40%

60%

80%

100%

120%

140%

0:00 0:28 0:57 1:26 1:55


FM

C %

O

PQ

R

S

T

REFExpon. (S)

Expon. (Q)

Expon. (T)

Expon. (O)

Expon. (P)Expon. (R)

Expon. (REF)

Pine Plantation - 0.5% Foam

0%

20%

40%

60%

80%

100%

120%

140%

0:00 0:28 0:57 1:26 1:55Time since drop (hours:minutes)

FM

C %

A

B

C

DE

F

REF

Expon. (E)

Expon. (F)Expon. (B)

Expon. (C)

Expon. (D)

Expon. (A)

Expon. (REF)

44

Appendix 6. Within-site canopy density and penetration

correlations.

Eucalypt woodland. Canopy density - Penetration correlation.

0

10

20

30

40

50

60

0 10 20 30 40 50

Canopy density (%)

Con

tain

er v

olum

e (m

ls)

Water

0.5% Foam

0.3% Foam

Linear (Water)

Linear (0.3% Foam)

Linear (0.5% Foam)

Pine plantation.Canopy density - Penetration Correlation

0

5

10

15

20

25

30

0 20 40 60 80

Canopy density (%)

Co

nta

iner

vo

lum

e (m

l)

0.5% Foam0.3% FoamWaterLinear (0.5% Foam)Linear (0.3% Foam)Linear (Water)

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