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Article

Characterising the Chemical Composition of Bushfire Smoke and Implications for Firefighter Exposure in Western Australia

by
Kiam Padamsey
*,
Adelle Liebenberg
,
Ruth Wallace
and
Jacques Oosthuizen
School of Medical and Health Sciences, Edith Cowan University, Joondalup, Perth, WA 6027, Australia
*
Author to whom correspondence should be addressed.
Fire 2024, 7(11), 388; https://doi.org/10.3390/fire7110388
Submission received: 25 September 2024 / Revised: 22 October 2024 / Accepted: 24 October 2024 / Published: 28 October 2024
(This article belongs to the Special Issue Patterns, Drivers, and Multiscale Impacts of Wildland Fires)
Browse Figures
Figure 1
<p>Scenes at a typical burn.</p> "> Figure 2
<p>The principal researcher in full wildland PPE collecting data inside a smouldering area of Jarrah Forest.</p> "> Figure 3
<p>The dense vegetation of Blackwood Forest.</p> "> Figure 4
<p>Manjimup peat fire, pictured with the Gasmet Technology DX4040.</p> "> Figure 5
<p>The sandy soils and low-lying vegetation of Wilbinga, pictured with the DBCA commencing a prescribed burn.</p> "> Figure 6
<p>The laterite soils and kwongan heathland of Badgingarra.</p> "> Figure 7
<p>The tall, open canopies and sparse groundcover of the Julimar region.</p> "> Figure 8
<p>The ten most prevalent chemicals present in bushfire smoke, reported in parts per million (ppm).</p> "> Figure 9
<p>The tenth to nineteenth most prevalent gases in general bushfire smoke reported in ppm.</p> "> Figure 10
<p>The ten most prevalent chemicals present in peat fire smoke, reported in ppm.</p> "> Figure 11
<p>Mean concentration of chemicals present inside prescribed burn smoke across five unique ecoregions in WA expressed as parts per million (ppm). * Sulphur dioxide concentration at Manjimup was 9.5 ppm.</p> "> Figure 12
<p>Comparison of the mean chemical emissions across the flaming and smouldering phases of prescribed burns across four different prescribed burns (ppm).</p> ">
Versions Notes

Abstract

:
This study evaluates bushfire smoke as a workplace hazard for firefighters by characterising its chemical composition and potential health risks in Western Australia. Portable Fourier Transform Infrared (FTIR) spectrometry was used to measure airborne chemical concentrations at prescribed burns across five regions, including peat (acid sulphate) fire events. Samples were collected during both flaming and smouldering phases, as well as in perceived “clear” air resting zones. Results indicated that carbon monoxide (CO) was the dominant gas, reaching concentrations of 205 ppm at the fire front, followed by nitrogen monoxide (26 ppm) and methane (19 ppm). Peat fires produced distinct profiles, with ammonia (21.5 ppm) and sulphur dioxide (9.5 ppm) concentrations higher than those observed in typical bushfires. Smouldering phases emitted higher chemical concentrations than flaming phases 75% of the time. Even clear air zones contained measurable chemicals, with CO levels averaging 18 ppm, suggesting that firefighters are not free from exposure during rest periods. These findings highlight the need for fit-for-purpose respiratory protective equipment (RPE) and improved rest protocols to minimise exposure. The study underscores the importance of comprehensive health monitoring programs for firefighters to mitigate long-term health risks.

1. Introduction

1.1. Overview of Bushfires in Western Australia

Bushfires are a common occurrence in Australia. Due to the vastness of Western Australia (WA), this state sees bushfires burning throughout the year. In WA, the Mediterranean Souths’ bushfire season starts in the summer, compared to the tropical north where winter ushers in their bushfire season. During each region’s “off season”, prescribed burning events are scheduled. This all-year fire season places strain on the fire management agencies that have to respond to fire threats, often without respite. Human-caused ignitions are believed to be the leading cause of bushfires across the state, whether deliberately or accidentally lit [1]. The number of ignitions is highly dependent on factors such as fuel moisture content, previous rainfall, recent fire activity in the area, and localised weather [1]. The fire management agencies in WA comprise two divisions. The Department of Fire and Emergency Services (DFES) manages the state’s Volunteer Bushfire Service made up of 560 brigades and over 20,000 firefighters [2]. The Department of Biodiversity, Conservation and Attractions (DBCA) employs the state’s forestry firefighters, who are career land management employees, trained in both conservation and wildfire roles. The forestry department conducts the prescribed burning program annually, usually covering an area >20,000 hectares across the entire state [3]. Due to its large ‘burning calendar’, the state of WA was selected for this study across a wide array of regions.

1.2. Health Impacts of Bushfire Smoke Exposure

The public health impacts caused by bushfire smoke in Australia [4] and globally [5] are well documented. The main concerns from large bushfire smoke plumes affecting residential areas are exacerbations of respiratory diseases such as chronic obstructive pulmonary disease (COPD) and asthma [6]. However, less research has been conducted into the health impacts of volunteer and forestry firefighters, particularly in Australia.
Workplace exposure monitoring revealed that firefighters operating in bushfire environments may be exposed to a variety of potentially harmful concentrations of particulate matter such as PM1, PM2.5, PM4.25, and PM10, as well as carbon monoxide and various volatile organic compounds (VOCs). However, this cited research was limited in its ability to identify specific individual VOCs, such as benzene, toluene, ethylbenzene, and xylene (BTEX), within the smoke and the concentrations at which these chemicals exist.

1.3. Previous Research and Gaps in Knowledge

Research on the composition of bushfire smoke identified a range of organic and inorganic compounds, including formaldehyde, acrolein, and various organic constituents such as levoglucosan, methoxyphenols, and polycyclic aromatic hydrocarbons [7,8]. These compounds are known to cause significant adverse health impacts, namely, cancer [9,10,11]. In addition, respirable particles, formaldehyde, and acrolein were identified as major contributors to the toxicological loading of bushfire smoke [12].
Smith et al. (2014) found that vegetation classes are insignificant in the constitution of bushfire emissions and that much of the variation is explained by modified combustion efficiency (the ratio of CO2 to CO indicating complete combustion). For several decades, the use of infrared-spectrometry-based methods have been instrumental in analysing the composition of smoke from different types of biomass fires, providing valuable insights into the atmospheric chemistry of smoke that was typically generated under experimental conditions [13].
Studies such as Smith et al. [14], have characterised smoke emissions from different vegetation types in Australia using emission factors derived from fixed monitoring sites and satellite imaging. While these methods provide valuable insights into atmospheric smoke composition, they do not capture the real-time, workplace-specific exposures that firefighters experience at the fire front. To address this gap, our study employs a novel occupational hygiene approach by using a portable Gasmet Technologies DX4040 Fourier transform infrared spectrometer (FTIR), Vantaa, Finland to measure airborne chemical concentrations directly where firefighters operate. Although this method could not be classified as conventional personal monitoring where a sampling device is attached to the lapel of a worker, it allowed for the determination of concentrations of chemicals in parts per million (ppm), which aligns well with the metrics used in occupational hygiene. Much of the previous research concerning smoke exposure and factors that may affect its composition has been conducted on the east coast of Australia [15,16,17]. These studies have commonly sought to calculate and express findings according to emission factors used from an environmental science and public health viewpoint, but these are less useful for assessing personal exposures of firefighters and cannot be utilised to quantify personal exposures.

1.4. Rationale and Aims

Firefighting agencies in WA have identified research gaps relating to the potential hazards present in bushfire smoke, particularly in light of the carcinogenic classification of wildland firefighting [18]. This study aimed to characterise the composition of smoke experienced by firefighters across a wide range of regions in WA. Using an occupational hygiene lens, this research sought to identify the toxicological profile and potential harms of bushfire smoke to the health of firefighters. The findings of this study contribute to the collective understanding of bushfire smoke and may assist the development or refinement of effective strategies to mitigate any associated health risks.

2. Methods

2.1. Participants

This research was conducted in Western Australia alongside forestry firefighters from the DBCA. The demographics of these firefighters have been previously described [19,20]. In brief, the forestry firefighters of DBCA are traditionally considered conservation employees, focusing on the preservation and upkeep of the national forests of Western Australia. In practice, the vast majority of their work is spent in fire environments either combatting wildfires or conducting hazard reduction burns prescribed to reduce the fuel loading of specific localities, thereby lessening the intensity of future bushfires. Typically, these firefighters spend around six months of the year conducting prescribed burns (cooler months), and during the warmer months, they respond to bushfires across the state. Their work is arduous, and previous research has highlighted the inequities of these firefighters compared to other agencies in WA, particularly around their access to personal protective equipment (PPE) and decontamination [19]. Ethical approval was obtained from the Edith Cowan University Human Research Ethics Committee before the research commenced (Reference: 2022-03698-PADAMSEY, granted 12 September 2022).

2.2. Sampling Method

Following the DBCA burning prescription for the 2022/23 season, planned burns for inclusion in the study were identified by DBCA fire management. The research team travelled to the prescribed burn sites (Figure 1) at the pre-determined times and locations and collected airborne (smoke) samples without interrupting the work of the firefighters.
To analyse the chemicals present in the bushfire smoke, the researcher, a trained and experienced firefighter, approached the fire front in full personal protective equipment (PPE) with a Gasmet DX4040 portable Fourier Transform Infrared (FTIR) spectrometer carried on their back (Figure 2). The researcher stood at a distance that best represented where a firefighter would stand to combat the fire and took representative airborne samples at each sample location. The researcher remained within the general area, whilst the FTIR recorded the concentration of 20 pre-selected chemicals every 10 s for the uninterrupted 15 min interval. These 20 chemicals were chosen based on their potential to be present in vegetation fires as identified in the literature [21] and expertise provided by Gasmet Technologies. The sampling data were recorded onto the memory of the DX4040 for download and analysis. Multiple measurements were conducted at each fire, to explore different phases of the fire and varying locations of the fire ground to obtain a representative sample of the exposures a firefighter may experience. This typically meant two flaming phase samples and two smouldering phase samples to ensure adequate coverage of the sample area. A single 15 min sample was used for analysis across each location and phase.

3. Results

3.1. Sampled Locations

The prescribed burns assessed in this study have been previously described [19,20]. In summary, the ecoregions of Western Australia that were accessible to the researcher were limited by the burning prescription of the DBCA, the approval to attend the fires, and the ability of the research team to travel to these fires on what was often short notice. The five regions of WA that were sampled were Manjimup, Blackwood, Wilbinga, Badgingarra, and Julimar. Each location was selected to capture a diverse set of data across a wide range of biodiversity.
Blackwood, located in the southwest of WA, is predominantly covered by jarrah and marri forests. The jarrah forests of Blackwood (Figure 3) are characterised by their tall, straight trunks and dense canopy cover [22]. Underneath the canopy, a diverse understory of species such as banksias, grass trees (Xanthorrhoea), and native ferns thrive. Jarrah forests are well adapted to periodic fires, which play a vital role in recycling nutrients and promoting the germination of seeds [23]. Marri forests in the Blackwood region are dominated by the marri tree, which has rough, tessellated bark and produces distinctive, creamy white flowers. Marri forests are often interspersed with areas of understory plants, including she-oaks (Allocasuarina spp.), kangaroo paws (Anigozanthos spp.), and various species of orchids [22]. The selection of Blackwood provides insight into the behaviour and composition of smoke in environments with dense forest cover and high humidity, which are characteristic of many regions in the southwest of WA.
Manjimup, adjacent to Blackwood, was selected for assessment as the prescribed burn escaped containment lines and ran into peat soils (acid sulphate), which have historically troubled firefighters in this region. Peatlands are waterlogged ecosystems characterised by the accumulation of organic matter, primarily from partially decomposed plant material [24]. Peat soils can be several metres thick and store large amounts of organic carbon accumulated over thousands of years. However, these soils are highly susceptible to drying out during periods of low rainfall or increased temperatures, making them vulnerable to ignition during bushfires [25]. Peat soils can produce persistent, smouldering fires that generate significant smoke emissions, posing additional challenges to firefighting efforts (Figure 4).
Wilbinga, located north of Perth, is characterised by sandy soils and diverse vegetation dominated by banksia heathlands (Figure 5). These areas are renowned for their rich biodiversity and comprise various banksia species along with understory plants such as grasses, shrubs, and low-growing ferns [26]. These woodlands are adapted to the sandy soils and often experience frequent, low-intensity fires that play a crucial role in their regeneration cycle [27]. The combination of banksia woodlands and heathlands in Wilbinga presents a diverse array of fuel types. The surrounding heathlands in Wilbinga are dominated by species such as Melaleuca and Allocasuarina, alongside a rich array of flowering plants like Grevillea, Hakea, and Leptospermum [26]. Fires in banksia woodlands are typically characterised by the combustion of woody materials and resins, while fires in heathlands often involve the burning of leaf litter and finer fuels.
Badgingarra, located north of Perth, is a biodiversity “hotspot” in Western Australia, characterised by diverse vegetation communities. The region is known for its kwongan heathlands, which are unique to the southwest of Western Australia. Kwongan is a type of shrubland dominated by low-growing plants adapted to the nutrient-poor, gravelly soils, and Mediterranean climate of the region (Figure 6) [28]. The kwongan heathlands of Badgingarra are home to a rich array of plant species, including banksias, grevilleas, hakeas, and numerous species of flowering shrubs and groundcovers [29]. These plants have evolved to survive in the harsh conditions of the kwongan, with adaptations such as sclerophyllous leaves and proteoid roots to access nutrients from the nutrient-poor soils [28]. Fires in kwongan heathlands are typically fast-moving and can spread rapidly through the low-lying vegetation.
Julimar, located to the east of Perth, is characterised by sparse wandoo woodlands interspersed with areas of shrubland and open grassy plains. Wandoo (Eucalyptus wandoo) woodlands are iconic to the region, known for their tall, slender trunks and open canopy structure (Figure 7) [30]. These woodlands provide habitats for a diverse range of flora and fauna adapted to the dry, Mediterranean climate of the region. The wandoo woodlands of Julimar are dominated by wandoo trees, along with occasional occurrences of marri, jarrah, and she-oaks [30]. Underneath the canopy, a diverse understory of shrubs, grasses, and wildflowers thrives, creating a mosaic of habitats that support a variety of wildlife. Fires in the wandoo woodlands of Julimar are typically characterised by their fast-moving nature and high-intensity flames [31]. The open canopy structure allows for the penetration of wind, which can fan the flames and spread the fire rapidly through the understory vegetation.

3.2. Overview of Smoke Sample Characteristics

Data collected from smoke samples revealed the concentration of the chemicals present. Figure 8 presents the top ten most prevalent chemicals found in a smoke sample collected from the Blackwood region. These were used as a reference to the concentrations of chemicals found in bushfire smoke. The dominant chemical in the smoke sample was carbon monoxide (CO), which accounted for over three-quarters of the concentration (205 ppm) of the ten most prevalent chemicals. Nitrogen monoxide (NO) and methane (CH4) also contributed to the smoke composition, while other chemicals exhibited lower concentrations.
Figure 9 depicts the same smoke sample taken from the Blackwood prescribed burn. However, it explores the next nine most prevalent chemicals in bushfire smoke, following styrene, also shown in Figure 8. In this portion of the smoke sample, we observe more BTEX (benzene, toluene, ethylbenzene, and xylene) compounds and possible carcinogens, indicating their presence in natural bushfire smoke.

3.3. The Special Case of Peat Fires

Figure 10 presents the unique case of acid sulphate (peat) fires, exemplified by a fire in the southwest region where a prescribed burn escaped into an area previously mined for nutrient-rich soils. This graph highlights the distinctive concentrations of chemicals not observed in any other sampled bushfire. Notably, the levels of ammonia (NH3) are almost three times higher than those found in regular bushfires, while sulphur dioxide (SO2) levels are approximately 14 times higher compared to a typical fire, depicted in Figure 9. Additionally, ethylene (C2H4) and hydrogen cyanide (HCN) are among the top 10 most prevalent chemicals in this smoke sample. Obtaining representative samples during this fire was challenging, and even with respiratory protective equipment (RPE), the research team quickly experienced symptoms of fatigue and headaches.

3.4. “Clear” Air Is Potentially a Problem Too

Table 1 presents sampling data obtained from three separately sampled locations in “clear” air (no visible smoke present), where firefighters were resting and eating. The measurements were taken at least 50 m away from any fire activity, in “clear” airspaces where vehicles were parked. Although the concentrations are low, it is evident that the air assumed to be “clear” at these fires still contains low concentrations of chemicals emitted from the prescribed burn, at levels that could be of concern from a public health perspective. These findings suggest that even when trying to minimise their exposure, firefighters cannot entirely avoid contaminants in the air due to their need to remain in proximity to the fire for quick action if necessary.

3.5. Do Vegetation Patterns Matter?

Figure 11 displays the average concentration of ten chemicals sampled across five unique prescribed burns to investigate whether the ecoregion or plant types at the fires may influence the concentration of chemicals released. From the graph, it is evident that the Wilbinga fire (blue dots) consistently showed lower concentrations of chemicals compared to the other fires, with either the lowest or second lowest concentrations in 9 of the 10 gases measured. On the other hand, the Julimar fire (yellow dots) displayed higher concentrations compared to other fires in many categories. Overall, there is no clear trend evident, as chemicals varied widely between each fire.

3.6. Does Phase of the Fire Change the Emissions?

Figure 12 presents the average concentration of six prominent gases found at four prescribed burns, where samples were obtained at both the flaming and smouldering stages of the fire. Manjimup was excluded because the flaming phase expired by the time the research team arrived on site. Overall, of the 24 readings, the concentration of chemicals was higher in the smouldering phase compared to the flaming phase: 18 out of 24 times (75%). This difference varied, ranging from large margins to very small ones, and the relationship was not consistent across gases, except for sulphur dioxide and xylene, where every flaming concentration was lower than the smouldering concentration sampled.

4. Discussion

This research aimed to characterise the composition of wildfire smoke experienced by firefighters across a wide range of regions in WA, using an occupational hygiene lens. The benefit of conducting field work as opposed to assessing smoke generated under experimental conditions means we were better able to assess the occupational work environment of these firefighter cohorts. To the best knowledge of the research team, this is the first time this sampling methodology was followed in Australia, utilising a portable FTIR within the fire front to assess the workplace exposures of firefighters, with the aim of quantifying the risk of exposure to hazardous substances from an occupational hygiene point of view. Due to the novel nature of this research, there is limited research to compare directly with our findings. Studies that have used similar methodologies, however, can be used to compare to previous research that has used grab samples and laboratory analysis as well as satellite imaging to estimate emissions.

4.1. General Smoke Composition

Our findings present a unique dataset that captures the smoke composition of various prescribed burns at the source of the fire, where firefighters are potentially exposed to health hazards. Significant levels of anthropogenic volatile organic compounds (VOCs) were found, which differ from previous research. Simmons et al. (2022), in a study conducted in New South Wales, found mean concentrations of the BTEXS family (benzene, toluene, ethylbenzene, and xylene) to be less than 0.5 parts per billion (ppb), with reported concentrations of NOx around 3.6 ppb and carbon monoxide at 181 ppb in smoky air. In contrast, our findings across multiple prescribed burns showed concentrations of these gasses to be orders of magnitude higher (Figure 8) than those reported by Simmons, Paton-Walsh, Mouat, Kaiser, Humphries, Keywood, Griffith, Sutresna, Naylor and Ramirez-Gamboa [12]. A possible reason for these findings is that those obtained by Simmons, Paton-Walsh, Mouat, Kaiser, Humphries, Keywood, Griffith, Sutresna, Naylor and Ramirez-Gamboa [12] were static readings from a fixed position continuously reading the FTIR spectrometer, confirming that the concentration of gases diminishes greatly as the distance from the fire front increases.
Laboratory-based studies by Dong, Hinwood, Callan and Stock [21] found that inorganic gases such as carbon monoxide (CO), sulphur dioxide (SO2), nitrogen oxides (NOx), as well as several VOCs such as formaldehyde, acetaldehyde, and benzaldehyde, are prevalent in a variety of burning plant species in Western Australia. Our findings reinforce these lab-based studies. The ability to report each chemical concentration in parts per million (ppm) provides more useful information to end-users, particularly in occupational health and hygiene when assessing health risks in the workplace.
The higher concentrations of VOCs observed in our study compared to previous research [21] may be attributed to several factors. Firstly, the use of FTIR-based methods allowed for real-time measurements at the fire front, providing a more accurate representation of the immediate environment firefighters are exposed to. Additionally, the diversity of vegetation types and burning conditions across our sampling locations may have contributed to variations in smoke composition. For example, the presence of peat soils in the Manjimup region and the diverse flora of the Blackwood and Julimar regions likely influence the types and quantities of VOCs emitted during combustion. Some examples of floral elements that may have influenced the findings may be the ratio of hardwood trees to leafy ferns in the area and the presence of Gastrolobium, a natural poison native to the southwest region [32].
Furthermore, the combustion efficiency of fires, influenced by factors such as fuel moisture content, temperature, and wind speed, can significantly affect the composition of smoke. Fires burning in dense vegetation with high fuel loads, such as those in Blackwood and Julimar, may produce more intense heat and combustion, leading to differing emissions of VOCs and other gases [33]. In contrast, peat fires in Manjimup, characterised by slow, smouldering combustion, may release different types of VOCs and particulate matter compared to fires in other vegetation types.

4.2. Smouldering Versus Flaming Chemical Emissions

Essentially, the flaming phase is defined as when the bushfire burns predominately with visible flames (typically a process lasting 15 min from time of ignition). Once all flames are self-extinguished, this period is defined as the smouldering phase. Often, smouldering continued for 12 or more hours across the burns sampled, and no water was used to transition the fire to the smouldering phase as they were all intentional mitigation burns. None of the fire events investigated started in the smouldering phase (which may occur at a bushfire from a travelling ember). Flames were introduced by a flamethrower, match-throwing or drip-torch method. Previous research conducted in Victoria, Australia, has shown that emission factors for PM2.5 are higher in the smouldering phase compared to the flaming phase [17]. This study also explored carbon monoxide and methane emission factors across the two stages of combustion using grab samples, consistently showing an increase in emission factors from flaming to smouldering phases for the two gases. Across 75% of the findings presented in our study (Figure 12), the concentration of relevant chemicals in the smoke was higher in smouldering compared to fires in the flaming phase. Although this trend was observed in the majority of cases, we could not identify any clear trend of all chemical concentrations being higher in the smouldering phase compared to the flaming phase in the same fire (Figure 12).
The variability in chemical emissions observed between flaming and smouldering phases may be attributed to several factors. Firstly, differences in combustion conditions between the two phases, such as temperature, fuel availability, and oxygen levels, can influence the types and quantities of chemicals released. During the flaming phase, combustion is typically more intense and efficient, leading to the production of certain gases and particles in higher concentrations. In contrast, the smouldering phase is characterised by lower temperatures and incomplete combustion, resulting in the release of different chemical compounds, including those associated with smouldering organic matter [34,35]. Furthermore, the composition of fuel and the presence of certain vegetation types can also impact chemical emissions during different combustion phases. For example, the combustion of organic-rich materials such as peat or wetland vegetation during the smouldering phase may release higher levels of VOCs and other gases compared to fires burning in dry forested areas during the flaming phase.

4.3. Peat Fires

Peat fires present unique challenges due to their distinct chemical makeup and combustion characteristics compared to conventional bushfires [36]. Laboratory and satellite studies have shown that the chemical composition of peat fires differs from that of conventional bushfires [37,38], identifying carbon dioxide, carbon monoxide, methane, and ammonia as the most prominent chemicals in peat fire smoke using emission factors, a commonly used metric in atmospheric modelling. The utilisation of on-the-ground FTIR analysis supports these findings, demonstrating that carbon dioxide, ammonia, methane, and carbon monoxide are indeed prevalent in the smoke from peat fires. We found that nitrogen monoxide (NO) was the third most prevalent chemical in the smoke, alongside high concentrations of sulphur dioxide (SO2). The peat fire exposure profiles differ from regular bushfire exposure profiles assessed in this current study, suggesting that peat fires require special consideration for exposure risk.
The combustion of peat, with its high organic content, can produce smouldering fires that release large quantities of toxic gases and particulate matter (Figure 3). Additionally, the slow-burning nature of peat fires can result in prolonged exposure to harmful pollutants, increasing the risk of respiratory and cardiovascular diseases among exposed populations [36].The high levels of nitrogen monoxide and sulphur dioxide observed in peat fire smoke collected are concerning due to their potential health impacts. Nitrogen monoxide is a toxic gas that can cause respiratory irritation and exacerbate existing respiratory conditions, while sulphur dioxide is known to irritate the respiratory tract and can exacerbate asthma symptoms [39]. These elevated concentrations of NO and SO2 highlight the need for increased awareness and protective measures for firefighters and nearby communities during peat fire events.
Anecdotal evidence from our study further supports the potential health risks associated with peat fires. During sampling of a peat fire, firefighters reported experiencing headaches and feelings of sickness while working to prevent the fire from spreading. The research team members also experienced negative health symptoms despite wearing P3 respiratory protection. These outcomes indicate that the current RPE potentially does not provide protection from these gasses and may provide a false sense of security to the wearers. Prolonged exposure to smoke from peat fires, which can persist for weeks, may pose both acute and chronic health risks to firefighters and nearby communities.

4.4. Vegetation and Smoke Emissions

The chemical concentrations emitted from each prescribed burn varied widely from region to region. Fires in the Wilbinga region emitted chemicals in lower concentrations compared to the other fires. In contrast, fires in the Julimar and Badgingarra regions, as well as the peat fire in Manjimup, consistently exhibited high concentrations of chemicals.
Several factors may contribute to these variations in chemical emissions such as soil moisture content, weather patterns, and fuel loading [40]. The content of moisture in the soil, for example, has some evidence to suggest that higher fuel moisture content leads to a decrease in CO2 emission factors and an increase in CO and volatile organic compounds emissions [41]. In our study, the Wilbinga region, characterised by sandy soils and banksia heath vegetation, may have lower overall fuel loads and different combustion characteristics compared to other regions, resulting in the observed lower chemical emissions. In contrast, the Julimar and Badgingarra regions, with their diverse vegetation and higher fuel loads, may have produced higher concentrations of chemicals during combustion for these reasons. Further investigation of how these factors affect emissions from wildland fires is required as this presents a gap in our current knowledge.

4.5. Clear Air

As demonstrated in Table 1, our findings indicate that the clear air where firefighters eat and rest whilst on duty is consistently contaminated with small concentrations of chemicals present in bushfire smoke. This observation raises concerns, as it suggests that firefighters may be continuously exposed to smoke particles and pollutants even during their periods of rest. The presence of smoke particles in clear air zones may be an occupational health concern, as it indicates that firefighters are not afforded complete respite from smoke exposure during their shifts.
Forestry firefighters at the prescribed burns often work shifts of more than 12 h, which increases the potential for health impacts associated with smoke exposure. Prolonged exposure to smoke particles and pollutants, even at relatively low concentrations, can have adverse effects on respiratory health, cardiovascular function, and overall well-being [42]. The chemicals present in smoke, such as particulate matter, volatile organic compounds (VOCs), and gases like carbon monoxide and nitrogen oxides, have been linked to various health problems, including respiratory irritation, exacerbation of existing respiratory conditions [43] (such as asthma and chronic obstructive pulmonary disease), cardiovascular effects [44], and even cancer in the long term [45,46].
The continuous exposure to smoke, both during active firefighting and during rest periods in areas with clear air, highlights the need for improved measures to protect the health and safety of firefighters. This may include implementing measures to reduce smoke infiltration in rest areas and ensuring adequate rest periods to minimise cumulative shift exposure. Measures like these are seen already in other professions in which a mandated time of rest is required to allow for the excretion of toxins and recovery of the body [47,48].

4.6. Occupational Health Considerations

From an occupational health perspective, it is concerning that none of the forestry firefighters wore breathing protection during the prescribed burning operations described above. Essentially, all of the exposures reported were experienced by firefighters who had no protection for their respiratory health. Earlier research identified this issue and highlighted a concerning personal exposure profile of these firefighters [19]. However, this study provides a detailed breakdown of the exact harmful contaminants, some of which are carcinogenic, that these firefighters are being exposed to. Fortunately, we can report that the firefighters from this study will have access to P3 respiratory protective equipment (RPE) for the first time in their organisation’s history as they enter the 2024/25 bushfire season in Western Australia [19]. However, P3 protection may be insufficient as well, particularly in areas of high chemical exposure and another area of required further investigation.
Potential strategies should be investigated to minimise the workplace exposures of these firefighters. One approach could be organising rest breaks at a distance from the burn deemed safe. Future research needs to investigate where such safe zones are located and what measures can be implemented to ensure firefighters have access to air free of contaminants during breaks. From a public and occupational health perspective, it would be valuable to implement a health monitoring program for firefighters who work in wildland management in Australia. Despite their significant numbers (over 200,000), wildland firefighters have not been subject to research at the same level as their career counterparts. A cross-sectional investigation of exposure to firefighting and disease prevalence could be the starting point, but eventually, a long-term cohort study may be beneficial in understanding the long-term health effects of smoke exposure on wildland firefighters.
We understand that limiting smoke exposure to those working in the wildland space is a difficult task. However, implementing measures to protect the health and safety of firefighters, such as providing adequate respiratory protection, improving rest break procedures, and conducting regular health monitoring, are crucial steps in mitigating the risks associated with bushfire smoke exposure. These efforts are essential to safeguard the well-being of firefighters who play a critical role in protecting communities and the environment from the impacts of bushfires.

4.7. Strengths and Limitations

The major strength of our study is to provide this breakdown of wildland fire smoke across a diverse sample of locations. Firefighting bodies have been asking for these kinds of data to guide their PPE and firefighting procedures for decades. Additionally, being able to take the FTIR directly to the fire front increases the generalisability of these findings to what the firefighter may actually experience when attempting to extinguish these fires.
Our study also has several limitations that should be considered and addressed in future research. One major limitation is that we were not able to revisit locations and build a larger dataset in the same ecoregion across multiple burns. Future research should aim to address this limitation by conducting repeated sampling in the same ecoregions to capture variations over time and between burns. Another limitation of our study is the lack of particulate matter information from the different fires. Particulate matter is a key component of smoke and can have significant health impacts on firefighters and nearby communities. Including particulate matter data would provide a more comprehensive understanding of the health risks associated with bushfire smoke exposure.

5. Conclusions

This research provides an initial dataset on bushfire smoke profiles from a diverse set of wildland fires across WA. By identifying the specific chemical composition of bushfire smoke, including higher emissions during smouldering phases and persistent exposure in presumed “clear” air, this research highlights the need for improved respiratory protection measures. Fire management agencies must continue to focus on and enforce RPE policies tailored to varying fire conditions and chemical exposures. The provision of P3 respiratory protective equipment (RPE) for firefighters, while a positive step, may still be inadequate in certain high-exposure scenarios, such as peat fires. Beyond operational policies, this research emphasises the importance of firefighter well-being. Agencies should consider establishing regular health surveillance programs to detect and manage long-term health risks associated with chronic exposure.
Overall, these findings advocate for a shift towards more proactive occupational health strategies, prioritising both safety and systemic support for those working in hazardous fire environments.

Author Contributions

Conceptualisation, K.P. and J.O.; methodology, K.P. and J.O.; formal analysis, K.P.; investigation, K.P.; writing—original draft preparation, K.P.; writing—review and editing, K.P., A.L., R.W. and J.O.; supervision, A.L., R.W. and J.O. All authors have read and agreed to the published version of the manuscript.

Funding

We acknowledge and appreciate the support of Natural Hazards Research Australia who have provided a scholarship and support to the primary author for this important research. This research was supported by an Australian Government Research Training Program (RTP) scholarship.

Institutional Review Board Statement

The study was conducted in accordance with the Declaration of Helsinki, and approved by the Ethics Committee of EDITH COWAN UNIVERSITY (2022-03698-PADAMSEY) for studies involving humans.

Informed Consent Statement

Written informed consent was obtained from all subjects involved in the study.

Data Availability Statement

The data that support this study cannot be publicly shared due to ethical or privacy reasons. The raw data from this study, including detailed chemical concentration measurements by location, phase, and fire type, will be made available upon reasonable request to the corresponding author.

Acknowledgments

We graciously acknowledge the contributions of The Department of Biodiversity, Conservations and Attractions for their support and collaboration.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Scenes at a typical burn.
Figure 1. Scenes at a typical burn.
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Figure 2. The principal researcher in full wildland PPE collecting data inside a smouldering area of Jarrah Forest.
Figure 2. The principal researcher in full wildland PPE collecting data inside a smouldering area of Jarrah Forest.
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Figure 3. The dense vegetation of Blackwood Forest.
Figure 3. The dense vegetation of Blackwood Forest.
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Figure 4. Manjimup peat fire, pictured with the Gasmet Technology DX4040.
Figure 4. Manjimup peat fire, pictured with the Gasmet Technology DX4040.
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Figure 5. The sandy soils and low-lying vegetation of Wilbinga, pictured with the DBCA commencing a prescribed burn.
Figure 5. The sandy soils and low-lying vegetation of Wilbinga, pictured with the DBCA commencing a prescribed burn.
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Figure 6. The laterite soils and kwongan heathland of Badgingarra.
Figure 6. The laterite soils and kwongan heathland of Badgingarra.
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Figure 7. The tall, open canopies and sparse groundcover of the Julimar region.
Figure 7. The tall, open canopies and sparse groundcover of the Julimar region.
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Figure 8. The ten most prevalent chemicals present in bushfire smoke, reported in parts per million (ppm).
Figure 8. The ten most prevalent chemicals present in bushfire smoke, reported in parts per million (ppm).
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Figure 9. The tenth to nineteenth most prevalent gases in general bushfire smoke reported in ppm.
Figure 9. The tenth to nineteenth most prevalent gases in general bushfire smoke reported in ppm.
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Figure 10. The ten most prevalent chemicals present in peat fire smoke, reported in ppm.
Figure 10. The ten most prevalent chemicals present in peat fire smoke, reported in ppm.
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Figure 11. Mean concentration of chemicals present inside prescribed burn smoke across five unique ecoregions in WA expressed as parts per million (ppm). * Sulphur dioxide concentration at Manjimup was 9.5 ppm.
Figure 11. Mean concentration of chemicals present inside prescribed burn smoke across five unique ecoregions in WA expressed as parts per million (ppm). * Sulphur dioxide concentration at Manjimup was 9.5 ppm.
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Figure 12. Comparison of the mean chemical emissions across the flaming and smouldering phases of prescribed burns across four different prescribed burns (ppm).
Figure 12. Comparison of the mean chemical emissions across the flaming and smouldering phases of prescribed burns across four different prescribed burns (ppm).
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Table 1. Concentration of chemicals in clear air measured at prescribed burns and average of all three locations reported as parts per million (ppm).
Table 1. Concentration of chemicals in clear air measured at prescribed burns and average of all three locations reported as parts per million (ppm).
ChemicalLocation
WilbingaJulimarBadgingarraAverage
Carbon monoxide CO (ppm)25.558.4719.7617.93
Nitrogen monoxide NO (ppm)12.550.6610.337.84
Sulphur dioxide SO2 (ppm)0.050.000.020.02
Acrolein C3H4O (ppm)0.020.110.500.21
Formaldehyde CHOH (ppm)0.380.140.580.36
Benzene C6H6 (ppm)0.590.670.560.61
Toluene C7H8 (ppm)0.050.050.070.06
Ethyl benzene C8H10 (ppm)0.100.320.030.15
o-Xylene C8H10 (ppm)0.010.050.020.02
Styrene C8H8 (ppm)1.350.060.800.73
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Padamsey, K.; Liebenberg, A.; Wallace, R.; Oosthuizen, J. Characterising the Chemical Composition of Bushfire Smoke and Implications for Firefighter Exposure in Western Australia. Fire 2024, 7, 388. https://doi.org/10.3390/fire7110388

AMA Style

Padamsey K, Liebenberg A, Wallace R, Oosthuizen J. Characterising the Chemical Composition of Bushfire Smoke and Implications for Firefighter Exposure in Western Australia. Fire. 2024; 7(11):388. https://doi.org/10.3390/fire7110388

Chicago/Turabian Style

Padamsey, Kiam, Adelle Liebenberg, Ruth Wallace, and Jacques Oosthuizen. 2024. "Characterising the Chemical Composition of Bushfire Smoke and Implications for Firefighter Exposure in Western Australia" Fire 7, no. 11: 388. https://doi.org/10.3390/fire7110388

APA Style

Padamsey, K., Liebenberg, A., Wallace, R., & Oosthuizen, J. (2024). Characterising the Chemical Composition of Bushfire Smoke and Implications for Firefighter Exposure in Western Australia. Fire, 7(11), 388. https://doi.org/10.3390/fire7110388

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