Fire performance of wood (Pinus radiata) treated with fire retardants and a wood preservative

FIRE AND MATERIALSFire Mater. 2008; 32:357–370Published online 10 April 2008 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/fam.973

Fire performance of wood (Pinus radiata) treated with fireretardants and a wood preservative

D. C. O. Marney1,∗,†, L. J. Russell1 and R. Mann2

1CSIRO Manufacturing and Materials Technology, Fire Science, P.O. Box 56, Highett, Vic. 3190, Australia2Ensis, Private Bag 10, Clayton South, Vic. 3169, Australia

SUMMARY

In this work, we co-formulated an oil-borne copper naphthenate/permethrin wood preservative system withsynthetic polymer-based fire-retardant additives prior to the impregnation of Pinus radiata sapwood. Weevaluated what effect, if any, the preservative had upon the fire performance properties of the fire retardantsand whether the fire retardants impacted on the fungicidal and termiticidal efficacy of the preservative.The fire retardants included halogenated and phosphorus-based systems. A mass loss calorimeter, inconjunction with a thermopile, was used to measure the time to ignition and the peak heat release rate(PHRR) from which the fire performance index (FPI) was determined. The preservative properties wereevaluated using termite and soil-block decay bioassays. In summary, we found that the rate of fire growthwas reduced when the fire retardants were used in combination with the wood preservative. We alsofound that the PHRR was a better determinant of fire performance than the FPI. The performance of thewood preservative was enhanced against fungal decay and termite attack when used in combination withthe fire retardants. The fire retardants also demonstrated some wood preservative properties of their own.Copyright q 2008 John Wiley & Sons, Ltd.

Received 11 January 2007; Revised 27 August 2007; Accepted 10 February 2008

KEY WORDS: Pinus radiata; fire retardants; bromine; chlorine; phosphorus; mass loss calorimeter; peakheat release rate; time to ignition; fire performance index; copper naphthenate/permethrin;termites; fungi

1. INTRODUCTION

Australia is one of the most bushfire (or wildfire)-prone countries in the world. Despite rigorousprecautions and total fire ban days, widespread seasonal grass and bushfires regularly occur.Bushfires impact greatly in terms of both property loss and loss of life and this problem is growingwith the continued expansion of urbanization as a result of lifestyle choices [1]. As such, there

∗Correspondence to: D. C. O. Marney, CSIRO Manufacturing and Materials Technology, Fire Science, P.O. Box 56,Highett, Vic. 3190, Australia.

†E-mail: [email protected]

Copyright q 2008 John Wiley & Sons, Ltd.

358 D. C. O. MARNEY, L. J. RUSSELL AND R. MANN

is a need for construction materials that will assist to minimize the impacts of bushfires at thesehigh-risk urban interfaces. Although there are currently a range of timber preservatives suitablefor these situations providing protection against biodegradation, they do not perform the functionof limiting the fire growth.

We have proposed to address this issue via a project funded by CSIRO, Ensis and the Forestand Wood Products Research and Development Corporation. This project was concerned with thedevelopment of a ‘proof of concept’ for a combined fire retardant–wood preservative treatmenttechnology for softwood species to satisfy both the Australian bushfire standard for fire performance(AS 3959) [2] and the Australian timber preservation standard for wood preservative performance(AS 1604.1) [3]. The development of such a treatment system would be both economically andsocially beneficial. The focus of the project was on products that found use in outdoor, above-groundapplications and as such it covered a range of fire retardants and preservatives.

Although single-step treatment systems do exist [4–6], they use preservatives that at this timestill require approval by the Australasian Wood Preservation Committee (AWPC) for use in outdoorabove-ground applications (i.e. hazard class H3 according to AS 1604.1), and as such would takea number of years to implement. Preservatives used in these treatment systems include borax,boric acid, didecyl dimethyl ammonium chloride (DDAC), 3-iodo-2-propynyl butyl carbamate withDDAC and urea, dicyandiamide, phosphoric acid and formaldehyde.

To overcome the issues surrounding the introduction of a new chemical for AWPC approval, the‘proof of concept’ project involved addition of a fire retardant to an approved H3 preservative. Pinusradiata was subsequently treated and the fire and biodegradation performance assessed. During thisproject, an improvement in the termiticidal and fungicidal activity of one of the H3 preservatives(CuN/permethrin system) was observed when combined with halogenated fire-retardant chemicals,whereas phosphorus-based systems had the opposite effect.

The above observation is explored further in this paper, together with the fire performance of thecombined systems. Initial fire performance results for unweathered specimens are reported usingthe test criteria relevant to PHRR, (criterion b), of the Australian bushfire standard. Similarly, thepreservative performance in terms of termite [7] and soil-block decay [8] bioassays are reported.We use a mass loss calorimeter according to ASTM E2102-04a [9] instead of a cone calorimeter,since the former is considered to be adequate for screening purposes.

1.1. Australian bushfire and wood preservation standards environment

The Australian bushfire standard aims to reduce the risk of property damage occurring in the eventof a bushfire attack. It specifies that fire-retardant-treated timber is considered to be timber thatwhen tested in an oxygen consumption calorimeter using AS/NZS 3837 [10] (equivalent standardsare ISO 5660 [11] and ASTM E1354 [12]), meets the following parameters after having beensubjected to the weathering regime of the ASTM D2898 Method B [13]:

(a) ignition does not occur when the material is exposed to an irradiance level of 10kWm−2;(b) the peak heat release rate (PHRR) is not greater than 100kWm−2 and the average heat

release rate (HRR) for 10min following ignition is not greater than 60kWm−2 when thematerial is exposed to an irradiance level of 25kWm−2.

The Australian wood preservation standard aims to specify the requirements for preservative-treatedsawn and round timber for protection against decay, insect or marine borer attack. To meet thehazard class H3 specification, preservative-treated wood needs to have a mass loss of less than

Copyright q 2008 John Wiley & Sons, Ltd. Fire Mater. 2008; 32:357–370DOI: 10.1002/fam

FIRE PERFORMANCE OF WOOD TREATED WITH FIRE RETARDANTS 359

3% and 5% when exposed to fungi and termites, respectively. Although there are no equivalentInternational or American standards, ASTM D1413 [14] and CEN/TR 14839 [15] endeavour toassess the durability of wood with respect to (w.r.t.) decay by fungi and ASTM D3345 [16] andEN 118 [17] aim to evaluate the resistance of wood to termites.

1.2. Copper as a wood preservative

Copper carboxylate wood preservative systems have been studied for a number of years [18].Copper naphthenate is one of these systems, and a number of researchers [19, 20] have studiedits preservative efficacy. Its use as a biocide has been established by Freeman [21, 22] and ithas also shown some efficacy as a termiticide for pine in relation to Coptotermes formosanus, instudies by Grace et al. [23]. Copper naphthenate combined with the insecticide permethrin is awell-established system and is already used in a number of formulations designed to control bothfungi and termites [24, 25].

1.3. Common fire retardants for wood

In general, the types of compounds used for fire-retarding wood include phosphorus-basedcompounds (i.e. orthophosphorus acid, guanidine phosphate, guanylurea phosphate, melaminephosphate, ammonium (mono-, di- or poly-phosphate) and phosphonates). Boron-containingcompounds such as boric acid, boroxide, sodium tetraborate are also commonly used. Borax andboric acid already have the AWPC approval, but only for indoor, above-ground applications, i.e.hazard class H2 according to AS 1604.1.

1.4. Polymeric fire retardants used in this work

We chose established polymeric fire retardants for this work based on their chemical and physicalproperties and co-formulated them with the CuN/permethrin system. These polymeric fire retar-dants included tribromoneopentyl alcohol [26, 27], phosphoric acid 3-(diphenoxy-phosphoryloxy)-phenyl ester diphenyl ester [28–30], chlorinated paraffin with 65% chlorine content [31–34] andtetrabromobisphenol A bis (2,3-dibromopropyl ether) [35, 36], which is also known to possessbiocide functionality [37].

2. MATERIALS AND METHODS

2.1. Timber, wood preservative and fire retardants

The timber used was P. radiata D. Don sapwood specimens with different dimensions for eachtype of test. The dimensions were as follows:

• fire testing: 10 (radial)×50 (tangential)×50 (longitudinal) mm;• termite bioassays: 15 (radial)×25 (tangential)×50 (longitudinal) mm;• soil-block bioassays: 20 (radial)×10 (tangential)×20 (longitudinal) mm.

The wood preservative used was an oil-soluble solution of copper naphthenate co-formulated withpermethrin (CuN). The original CuN solution contained 6% w/w copper and was obtained fromKoppers Arch Wood Protection Pty Ltd.



The fire retardants used included an aliphatic brominated fire retardant from Dead Sea Bromine,tribromoneopentyl alcohol (FR1), a triaryl phosphorus-based fire retardant from Great LakesChemical Corporation, phosphoric acid 3-(diphenoxy-phosphoryloxy)-phenyl ester diphenyl ester(FR2), an aliphatic chlorinated fire retardant from Orica (Australia), chlorinated paraffin with 65%chlorine content (FR3) and a combined aliphatic/aromatic brominated fire retardant from GreatLakes Chemical Corporation, tetrabromobisphenol A bis (2,3-dibromopropyl ether) (FR4). Theprimary solvent system for all the fire retardants was white spirit and toluene; FR2 also requireddichloromethane to assist with solubility; this allowed co-formulation with CuN for treatment ina single step.

2.2. Impregnation of wood

Co-formulations of CuN and fire retardants were prepared by diluting 7.66 g of the concentrate ofCuN plus the chosen fire retardant in the solvent system to a total of 400 g. Pinus radiata was thentreated with this solution using a full-cell impregnation process to give hazard class H3 retentionlevels of 0.1% copper active as specified in AS 1604.1 Section 4. Two controls (or blanks) werealso included in this work; one was untreated P. radiata and the second was P. radiata treated withthe solvent system used to impregnate the wood with the fire retardant and wood preservative.

The test specimens were weighted down in a vacuum desiccator and a vacuum of −90kPa wasapplied for 30min. The treatment solution was admitted to the desiccator under vacuum, afterwhich the vacuum was released and the specimens left to adsorb solution at atmospheric pressurefor 60min. Each specimen was weighed before and after the treatment to determine the uptakeand the retentions were calculated by multiplying the weight difference by the percentage of activetreatment solution. The levels for FR1, FR2 and FR4 were based on the maximum amount ofadditive that was soluble in the solvent system. The amount of FR3 used was based on the optimalfire performance ascertained after conducting fire tests at three different concentrations. Treatmentretention levels for both preservative and fire retardants are detailed in Table I.

After treatment, the specimens were wrapped in plastic bags and left for 1 week, then slowlyair dried. The specimens were then vacuum oven dried at −90kPa and 40◦C for five days, afterwhich they were reconditioned to an equilibrium moisture content of approximately 10%.

2.3. Fire performance evaluation methodology

The treated P. radiata specimens (including controls) were screened for fire properties such asthe time to ignition (TTI) and HRR using a Fire Testing Technology Ltd mass loss calorimeter(with thermopile), in accordance with ASTM E2102-04a. The HRR of a burning specimen wasestimated as per Annex 2 of the standard. This estimation is obtained by measuring the output ofa thermopile located in a chimney situated above the burning specimen, which is subjected to aknown heat flux from a conical heater. The output (in mV) is converted into HRR per unit area(in kWm−2), by the use of a calibration graph (thermopile output as a function of heat input)obtained previously by burning methane gas at different flow rates (i.e. different calorific values)and various cone heater irradiance levels, in the same instrument.

The estimation of the HRR is not considered to be as accurate as the conventional oxygenconsumption calorimetry method used in the cone calorimeter [10–12]. However, it was used inthis work because of its relative simplicity and because of the favourable comparison (as shown inSection X4 in ASTM E2102-04a) with the conventional cone calorimetry method when burning



Table I. Mean retentions of additives (standard deviation) impregnated intoP. radiata on an oven dried basis.

Fire retardant∗ Fire retardant active†Treatment Cu (% w/w) (% w/w) (% w/w)

CuN‡ 0.11 (0.01) —FR1 (Br) — 1.1 (0.1) 0.81FR2 (P) — 5.5 (0.7) 0.58FR3 (Cl) — 22.7 (1.4) 14.8FR4 (Br) — 1.9 (0.1) 0.65§ & 0.65¶

CuN‡/FR1 0.11 (0.01) 0.9 (0.1) 0.66CuN‡/FR2 0.12 (0.01) 5.5 (0.4) 0.58CuN‡/FR3 0.12 (0.01) 21.6 (1.3) 14.0CuN‡/FR4 0.11 (0.01) 2.0 (0.1) 1.4

∗Fire-retardant retentions are for full formulations.†Fire-retardant active is either bromine, chlorine or phosphorus.‡Includes 0.02% w/w retention of permethrin.§Aliphatic bromine.¶Aromatic bromine.

poly(methyl methacrylate). Data generated from this work are to be used for comparative purposesonly and cannot alone provide any direct guidance on the behaviour of, or safety in fire.

The P. radiata specimens were exposed to a radiant heat flux of 25kWm−2 in the horizontalorientation. This irradiation is the level specified in the Australian bushfire standard, AS 3959-1999, and it is also low enough to enable sufficient fire property differentiation between specimentreatments. A minimum of three replicates of the treated timber specimens were tested subsequentto a minimum of 7 days conditioning at 23◦C and 50% relative humidity. The specimens wereplaced on a kaoboard backing material within a specimen holder and the height adjusted so thatthe distance between the bottom surface of the cone heater and the top surface of the specimenwas 25mm. Ignition was achieved with the assistance of an external spark igniter. In addition,data were recorded at 5-s intervals. The PHRR data reported in this work were the maxima ofthe initial (or first) peak. An indication of the fire performance of a material was subsequentlycalculated from the ratio between the TTI and the PHRR to give the fire performance index (FPI)[38].

2.4. Termite bioassay methodology

Termite bioassays were conducted in accordance with the AWPC protocols [7]. Wood test specimenswere subjected to two species of subterranean termites, Mastotermes darwiniensis (Froggatt) andCoptotermes acinaciformis (Froggatt). The duration of exposure to the termites was 6 weeks forM. darwiniensis and 8 weeks for C. acinaciformis.

Mastotermes darwiniensis is a tropical species, the southern limit of its distribution approximatesto the Tropic of Capricorn, in both coastal and inland localities. In this zone it is by far the mostdestructive termite [39]. Coptotermes acinaciformis is widely distributed throughout mainlandAustralia and is responsible for greater economic loss than all the other Australian species oftermites combined.



Only fresh, field-collected stocks of termites were used for the bioassay. Three colony sourcesof each termite species were incorporated into the experimental design to ensure that some ofthe variability in vigour and wood consumption exhibited by different colonies were taken intoaccount [40]. Two replicate specimens of each treatment and controls were exposed to the twotermite species from each of the three colonies (i.e. six replicates per treatment). The treatmentswere considered effective in controlling the attack of termites when the mean mass loss of thetreated specimen was 5% or less.

2.5. Soil-block decay (fungal) bioassay methodology

Soil-block decay bioassays were conducted in accordance with the AWPC protocols [8]. Thetest specimens were subjected to a soil-block bioassay against four brown rot fungi, Fomitopsislilacino-gilva (isolate DFP 1109), Gloeophyllum abietinum (isolate DFP 13851, boron tolerant),Serpula lacrymans (isolate DFP 16508, copper tolerant) and Coniphora olivacea (isolate DFP1779). Six replicate test specimens of each treatment and controls were inoculated with eachfungus. A preservative was considered to have controlled a fungus when the mean mass loss was3% or less.

2.6. Statistical analysis

A brief one-way analysis of variance (ANOVA) [41] was carried out on the termite and fungi massloss data to determine whether there was a statistically significant difference between the meanmass losses of the samples treated with copper napthenate and those treated with both coppernaphthenate and different fire retardants. This statistically significant difference was indicated byF statistic (Fcrit), which is generated by the ANOVA analysis. For this work (two sample setsof 6 points each) the Fcrit value at a 5% level of significance (�=0.05) was 4.964. This meansthat calculated Fcrit values less than 4.964 for the ANOVAs imply that there is no statisticallysignificant difference between the means, and values greater than 4.964 imply that there is.

3. RESULTS AND DISCUSSION

3.1. Fire performance

HRR is one of the most important parameters for characterizing material fire behaviour. It isan indicator of the rate of fire growth and intensity of the fire [42–44]. Typically, wood burnsaccording to the HRR curve as shown in Figure 1. An explanation of this curve is provided below.

After an initial heating induction period, a sufficient amount of pyrolysis volatile gases areevolved to allow ignition by an external spark igniter. This is the commencement of combustion(i.e. reaction between oxygen and volatile gases under the influence of heating). The heat gener-ated by these exothermic (combustion) reactions along with the externally applied heat sustainsthe pyrolysis of the wood, thus releasing more volatiles for ongoing sustenance of the flamingcombustion process. This corresponds with the first peak in the HRR curve.

After the initial release of volatiles, an insulating char layer forms, which makes heat transfermore difficult, thus slowing the pyrolysis process. This corresponds with the dip in the HRR curveand as the wood is sufficiently thick, the HRR reaches a more or less steady state.



Figure 1. Typical heat release rate curve for wood.

Table II. Fire parameters (standard deviation) of treated P. radiata determined using the mass losscalorimeter at a heat flux of 25kWm−2 (Results based on a minimum of three replicates).

Fire parameters

Treatment TTI (s) PHRR∗ (kWm−2) FPI (m2skW−1)

Untreated (control) 98 (1) 182 (7) 0.54 (0.02)Solvent (control) 127 (6) 180 (9) 0.71 (0.04)CuN 115 (10) 149 (8) 0.77 (0.05)FR1 101 (2) 121 (4) 0.83 (0.05)FR2 127 (16) 144 (3) 0.88 (0.09)FR3 81 (2) 103 (11) 0.82 (0.06)FR4 120 (25) 107 (5) 1.04 (0.28)CuN/FR1 70 (5) 107 (9) 0.66 (0.1)CuN/FR2 68 (7) 137 (6) 0.50 (0.05)CuN/FR3 55 (7) 97 (6) 0.57 (0.05)CuN/FR4 72 (16) 78 (4) 0.92 (0.15)

∗Maxima of initial peak heat release.

According to Spearpoint and Quintiere the second peak in the HRR curve results from the charlayer breaking down and contracting, thus producing small cracks on the surface [45]. These cracksfacilitate the escape of volatiles that combust and result in the observed increase in HRR. After thevolatiles have been exhausted, flaming combustion ends, leaving a solid char residue and reducedHRR [46]. Alternatively, according to pyrolysis modelling and cone calorimetry studies by Haggeet al., the shape, timing and presence of the second peak in the HRR profile is dependant on theconditions on the unexposed side of the timber [47].

The mass loss calorimeter data are presented in Table II. These data represent the initial screeningof unweathered specimens for fire properties that were subsequently considered for comparisonwith each other and the solvent control (or blank).



Wood treated with the fire retardants FR1 or FR3 demonstrated a reduction in the ignition timew.r.t. the blank. This could be attributed to (i) the oil-based nature of these compounds; FR1 isa waxy solid with a melting point of 62–67◦C and FR3 is a paraffinic-based material that is aviscous liquid at room temperature or (ii) low-temperature reactions between the fire retardants andvarious wood components resulting in earlier decomposition. The ignition times for wood treatedwith FR2 and FR4 were relatively similar to the blank. Although the CuN treatment showed somereduction in ignition time, this was not significant when the spread of results was considered (referstandard deviation in Table II). All combinations of fire retardants and CuN resulted in a reducedignition time of the treated wood w.r.t. the blank. This may be due to these additive combinationsreacting with wood components (degradation reactions) at lower temperatures.

The large variation in some ignition times was not surprising as we used a relatively low radiantheat flux of 25kWm−2. This has also been noted by Grexa et al. [48] who found that a majorproblem with the evaluation of experimentally observed ignition data for Douglas fir plywood wasthe uncertainty of the time to sustained ignition. These researchers reduced the uncertainty bysetting the lower radiation exposure limit for the determination of ignition time at 30kWm−2.

When exposed to a constant radiant heat flux of 25kWm−2, all the treatments considered withinthis work acted to decrease the rate of fire growth of the wood w.r.t. the blank (i.e. a reducedPHRR). The measured PHRR value for the blank of 180kWm−2 was within the range of otherresearchers’ results for similar materials exposed to this radiation [44, 49]. Of interest was therelatively large reduction in the rate of fire growth w.r.t. the blank when the wood was treated withthe various combinations of fire retardant and wood preservative; i.e. there was a 40+% reductionof PHRR in some cases. It should be noted that, even though the treatment with CuN/FR4 resultedin a PHRR of less than 100kWm−2, it was not considered to meet the criteria for fire-retardant-treated timber as per the Australian Bushfire Standard because the treated specimens were notexposed to the ASTM D2898 method B weathering regime.

The reduction in PHRR of FR1 or FR4 w.r.t. the blank when combined with CuN appeared tobe additive; however, this additivity was not evident when FR2 or FR3 were combined with CuN.Both FR1 and FR4 incorporate bromine as the active fire retardant. Thus, in terms of the PHRRdata, this suggests that these two fire retardants acted independently of the wood preservative.However, FR2 (phosphorus-based) and FR3 (chlorine-based) had some level of interaction with thewood preservative, which resulted in a slightly higher rate of fire growth than would be expectedif they acted independently.

The FPI, calculated from the ratio of TTI to PHRR, confirmed the relatively good fire perfor-mance of the P. radiata treated with the fire retardants w.r.t. the blank. However, in general theFPI of the combination of FRs and CuN was lower than either the fire retardant or the woodpreservative, indicating a reduced fire performance w.r.t. the blank. This may be a function of thedecomposition of the fire retardant and its ability to degrade the wood at lower temperatures.

3.2. Bioassays

We were interested in determining if the termiticide and fungicide activity of the wood preservativesystem was altered by the addition of a fire retardant. A summary of the bioassay results togetherwith the ANOVA results is presented in Table III (soil-block bioassay) and Table IV (termitebioassay).

The results for the soil-block bioassays presented in Table III indicate that both controls wereheavily decayed by three of the brown rot fungi, F. lilacino-gilva, G. abietinum and S. lacrymans.



Table III. Mean mass loss (MML) data (standard deviation) of treated P. radiataafter completion of the soil-block decay test.

C. olivacea F. lilacino-gilva G. abietinum S. lacrymans

Treatment MML (%) SSD∗ MML (%) SSD MML (%) SSD MML (%) SSD

Untreated control 12.3 (3.4) 47.7 (0.7) 37.4 (1.3) 27.1 (1.7)Solvent control 13.8 (4.0) 52.4 (0.9) 31.2 (1.1) 25.0 (1.9)CuN† 9.6 (5.1) 40.0 (2.4) 0.8 (0.3) 16.5 (1.6)FR1‡ 11.8 (1.5) N 44.1 (2.2) N 26.7 (0.8) Y 21.3 (0.9) YFR2§ 5.4 (0.9) N 31.2 (0.9) Y 33.5 (2.8) Y 22.1 (2.2) NFR3¶ 6.6 (2.3) N 38.2 (0.9) N 22.1 (0.4) Y 13.6 (2.2) NFR4‖ 10.0 (2.0) N 47.7 (1.0) Y 28.4 (1.3) Y 23.5 (0.9) YCuN/FR1 5.2 (2.0) N 22.7 (5.1) Y 2.4 (1.0) N 6.4 (1.7) YCuN/FR2 0.5 (0.3) N 27.8 (1.4) Y 0.3 (0.2) N 15.6 (2.3) NCuN/FR3 0.2 (0.1) N 23.8 (2.3) Y 0.6 (0.1) N 7.0 (0.9) YCuN/FR4 8.7 (4.1) N 42.6 (2.3) N 1.3 (0.8) N 22.8 (1.9) Y

∗Statistically significant difference (SSD) at �=0.05 with respect to the CuN-treated wood; N, no; Y, yes.†Copper naphthenate/permethrin system.‡Aliphatic brominated fire retardant.§Triaryl phosphate fire retardant.¶Aliphatic chlorinated fire retardant.‖Combination of aliphatic/aromatic brominated fire retardant.

CuN was also unable to control the brown rot fungi, C. olivacea, F. lilacino-gilva, and S. lacrymansto a level sufficient to meet the requirements of the AWPC protocols (i.e. mass loss less than 3%).

With the addition of either FR2 or FR3 (to CuN) the results in Table III show that resistanceagainst C. olivacea was achieved (i.e. the 3% mass loss target was reached). However, the statisticalanalyses indicate that, for this fungi, the efficacy of the FRs individually or in combination withthe CuN was no different from that of CuN on its own. This anomaly in the statistical analyses isprobably due to the relatively large standard deviation for the mean mass loss for CuN.

With regard to the brown rot F. lilacino-gilva, all the FRs in combination with CuN, except FR4enhanced the preservative performance by reducing the mean mass loss, but not to the required 3%level specified in the AWPC protocols. The statistical analyses validate these results by showingthat the mean mass losses for FR1, FR2 and FR3 in combination with CuN were different.

Gloeophyllum abietinum was the only brown rot fungi that CuN was able to control to thespecified requirements within the AWPC protocols. None of the fire retardants affected the goodcontrol of CuN against this fungi. This was supported by the statistical analyses.

The fire retardants FR1 and FR3 were able to enhance the wood preservative performanceagainst S. lacrymans; however, this enhancement was not enough to meet the AWPC protocolrequirements of 3% mean mass loss. FR2 had no effect on the preservative performance whereasFR4 impacted negatively. These results were supported by the statistical analyses.

The results for the termite bioassays presented in Table IV indicate that both controls wereheavily attacked by the two termite species and CuN-treated wood was unable to sufficientlylimit the decay caused by the M. darwiniensis termite species to meet the AWPC protocols meanmass loss performance requirement of a maximum of 5% (after 6 weeks exposure). However, thisrequirement was achievable when the wood preservative was combined with the fire retardants,



Table IV. Mean mass loss (MML) data (standard deviation) of treated P. radiataafter completion of the termite bioassays.

M. darwiniensis C. acinaciformis

Treatment MML (%) SSD∗ MML (%) SSD

Untreated control 97.9 (4.3) 84.5 (8.8)Solvent control 99.1 (1.3) 78.9 (13.5)CuN† 20.8 (10.4) 1.3 (0.3)FR1‡ 33.3 (16.9) N 29.6 (11.8) YFR2§ 32.2 (4.4) Y 11.4 (1.9) YFR3¶ 2.8 (1.0) Y 3.0 (1.0) YFR4‖ 91.8 (7.0) Y 60.1 (10.7) YCuN/FR1 3.9 (1.6) Y 1.2 (0.1) NCuN/FR2 4.3 (0.9) Y 1.8 (0.3) YCuN/FR3 1.4 (0.4) Y 1.9 (0.8) NCuN/FR4 10.1 (2.9) Y 1.1 (0.3) N

∗Statistically significant difference (SSD) at �=0.05 with respect to the CuN-treated wood;N, no; Y, yes.†Copper naphthenate/permethrin system.‡Aliphatic brominated fire retardant.§Triaryl phosphate fire retardant.¶Aliphatic chlorinated fire retardant.‖Combination of aliphatic/aromatic brominated fire retardant.

FR1, FR2 or FR3. In addition, wood treated with FR3 in the absence of CuN, was able to achievethe mean mass loss requirement of 5%. Although wood treated with FR4 in combination with CuNdid not achieve the 5% mass loss limit, it did result in an improvement in the performance of CuNwith a reduction of ca. 50% in mean mass loss. These results were supported by the statisticalanalyses as every result was significantly different from that of CuN except for the mean massloss due to the FR1 treatment.

Importantly, the M. darwiniensis bioassay results indicated a strong positive interaction betweenthe preservative and the two fire retardants used at relatively low concentrations (FR1 and FR2),which resulted in an enhanced wood preservation performance. This is shown in Table IV by thesignificant reduction (ca. 80%) in the amount of material consumed by this termite species whenthe wood was treated with both of the preservative/fire-retardant co-formulations. The individualcomponents of the co-formulation yielded a mean mass loss of between 20 and 30%; however, onco-formulating, this figure fell to less than 5%.

After 8 weeks of exposure of the treated specimens to the C. acinaformis termite species, theCuN system was effective in controlling termite activity with a mean mass loss of only 1.3%.The interaction observed between fire retardant and preservative when exposed to M. darwiniensiswas not apparent after exposure to the C. acinaciformis as any anti-termite activity shown by thefire retardant was overshadowed by the good performance (low specimen mass loss) of CuN. Aninteresting result was that of the FR3 treatment in the absence of CuN, which was able to achievethe mean mass loss requirement of 5% or less as specified within the AWPC protocols. In addition,none of the fire retardants detracted from the CuN performance when used in combination withthe preservative.



The efficacy of these fire retardants as fungicides and insecticides is not surprising since organo-halogen compounds such as pentachloro phenol, [50–52], DDT [53, 54], dieldrin and lindane [24]are well-known insecticides as are organo-phosphorus compounds such as chlorpyrifos and pyri-daphention [55–58]. Both chlorine- and phosphorus-based compounds were shown to be efficaciousas fungicides in a study by Greaves et al. [59] and the organic halogen fire-retardant compound,tetrabromobisphenol A, is known to impact upon biota [37]. A surprising result was the apparentsynergy or additivity between some of the fire-retardant chemicals and the preservative system,where after co-formulation, there was an improvement in the fungicide and termiticide functionality(i.e., reduction in the mean mass loss).

4. CONCLUSIONS

Fire tests performed in line with the Australian bushfire standard of a commonly used externalconstruction timber, P. radiata, which was treated with synthetic polymer-based fire retardants viaan impregnation process, showed that the rate of fire growth was reduced by up to 40% whencompared with the untreated specimens. The halogen-based fire retardants had a more significantimpact on the rate of fire growth than the phosphorus-based compound. When the fire-retardanttreatments were combined with a wood preservative system, the rate of fire growth was reducedby a further 15% in some cases. It was found that the PHRR was a more appropriate indicator offire-retardant performance than the FPI because of some ambiguities in the TTI data. With respectto the Australian bushfire standard, it should be noted that specimens treated with the coppernaphthenate–permethrin wood preservative system in combination with tetrabromobisphenol A bis(2,3-dibromopropyl ether) were the only ones able to achieve a PHRR of less than 100kWm−2;however, this result was not considered to satisfy the definition of fire-retardant-treated timber, asthe treated specimens were not exposed to the ASTM D2898 method B weathering regime as perthe Australian bushfire standard.

Bioassay results indicated that the performance of copper naphthenate/permethrin (in wood),could be enhanced against fungal decay and termite attack by co-formulating with syntheticpolymer-based fire retardants. In general, these fire retardants did not detract from the performanceof the wood preservative against both the brown rot fungi and the termite species included in thisstudy. The fire-retardant treatments (in the absence of the wood preservative) also imparted somelevel of decay resistance and termite control to the wood.

ACKNOWLEDGEMENTS

The authors would like to thank Ms A. Hunt, Mr M. Muruganathan and Ms A Pereira (Ensis) forpreparation and treatment of wood specimens; Mr K. McCarthy, Ms J. Carr and Ms N. Chew (Ensis)for the bioassays and data collation; Dr L. Cookson (Ensis) and Mr V. Dowling (CSIRO-MMT) fortheir continued leadership and collaboration throughout this project and Dr D. Humphrey (formerly ofCSIRO-FFP) for his contribution towards the establishment of this project.

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Fire performance of wood (Pinus radiata) treated with fire retardants and a wood preservative