Size-resolved particulate matter inside selected fire stations and preliminary evaluation of the effectiveness of washing machines in reducing its concentrations

Abstract

The study aimed to determine and compare the mass concentration and size distribution of particulate matter (PM) at two Polish fire stations, one equipped with a washing machine intended for the decontamination of uniforms (FSN) and the other not equipped with this type of device (FSC), to assess the effectiveness of washing machines in reducing PM concentrations inside fire stations and estimate PM doses inhaled by firefighters while performing activities in truck bays and changing rooms during one work shift. The average PM concentrations at the FSN were 18.2–28.9 µg/m³ and 27.5–37.3 µg/m³, while at FSC they were 27.4–37.9 µg/m³ and 24.6–32.8 µg/m³ in the truck bays and changing rooms, respectively. At each measurement point, most of the PM mass (65–75%) was accumulated as fine particles. The dominance of fine particles in the total mass of PM results in high values of PM deposition coefficients (0.59–0.61) in three sections of the respiratory tract at each monitoring site. This study initially indicates the effectiveness of washing machines in reducing the concentration of fine particles and demonstrates the necessity, as well as directions for further research in this area.

Introduction

A major factor that causes occupational exposure as firefighter to be “carcinogenic to humans” (Group 1) is fire smoke. Fire smoke is a mixture of substances considered as toxic, irritating and/or carcinogenic^1,2,3. The most popular components of fire smoke are: carbon monoxide (CO), hydrogen cyanide (HCN), formaldehyde (CH₂O), hydrogen chloride (HCl), phosgene (COCl₂), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), volatile organic compounds (VOCs), including the BTEX group (benzene, toluene, ethylbenzene and xylene), polycyclic aromatic hydrocarbons (PAHs), particulate matter (PM) and many others^4,5,6. PM is particularly important in terms of the impact of fire smoke components on human health. In addition to the fact that both short- and long-term exposure to high concentrations of PM increases the risk of respiratory, circulatory, and nervous system diseases^7,8, this heterogeneous mixture of solid particles and liquid droplets suspended in the air also constitutes a medium for other hazardous pollutants released during combustion and pyrolysis. Various substances such as PAHs, VOCs, HCN, and several other organic and inorganic compounds can be absorbed on the surface of PM particles^2,9,10.

PM is characterized by a wide range of particle sizes, ranging from nanometers to millimeters¹¹. Particle sizes constitute the basis for the classification of PM into different fractions or phases, which is described in many works and standards^{11,12,13,14,15}.

The most important factors determining the impact of PM on human health include its physical (the size and shape of PM particles, hygroscopicity, surface type) and chemical properties (the content of metals, PAHs, elemental carbon, inorganic ions, organic compounds). PM particles that settle on the walls of the alveoli may cause difficulty in gas exchange¹⁶. Furthermore, exposure to coarse, submicron, or ultrafine particles may cause an inflammatory response within the respiratory system, allergic sensitization, impairment of cardiovascular function, and several other adverse health outcomes, such as enhanced bronchial responsiveness or coughing¹⁷. These local reactions can initiate systemic responses. Inflammatory changes in the body can even result from a short contact time with harmful compounds and low-intensity exposure¹⁶. These consequences may have lower clinical significance in young and healthy firefighters, but they are considerable in older persons or those with chronic cardiopulmonary diseases¹⁶.

Firefighters are exposed to PM during firefighting activities, fire investigations, and self-improvement exercises^6,18. As it turns out, firefighters’ exposure to PM also occurs in fire stations, where the main sources of PM are personal protective equipment (PPE) (helmets, boots, gloves, and special clothing) and specialized equipment used to extinguish fires. PM settles on these surfaces during firefighting operations, and then during removal, cleaning, maintenance, or storage, it can be transferred to fire station rooms (office rooms, common rooms, dining rooms, and rooms intended for rest while on duty) and settle on various surfaces^10,14,19. Additional sources of exposure to PM in fire stations are fire trucks and combustion equipment (saws, motor pumps, etc.) tested before and at the end of a work shift, which usually occurs in truck bays or in the internal yards of fire stations^20,21,22. These devices emit pollutants from diesel particulate matter (DPM). DPM is a solid component of diesel exhaust. It consists mainly of elemental carbon (approximately 80%), organic carbon, and trace amounts of various metals^20,23,24,25. The effects of DPM exposure include irritation of the eyes and nose, changes in lung function, airway inflammation, headaches, fatigue, and nausea. Moreover, DPM is classified by the International Agency for Research on Cancer as a Group 1 carcinogen²⁵.

The solutions recommended to reduce the concentration of air pollutants, including PM, inside fire stations are mainly based on the implementation or configuration of heating, ventilation, and air conditioning systems in a way that prevents the migration of pollutants to the rooms where firefighters stay, the use of engine exhaust filters, the use of diesel exhaust removal systems connected to fire vehicles, improving engine bay and PPE storage room ventilation using natural or mechanical means (e.g. dilution ventilation), separation of a dirty zone in fire stations in which PPE used during rescue and fire-fighting activities is left, installation of washing stations enabling systematic washing of uniforms and fire-fighting equipment, and, in the case of newly built fire stations, adapting the building design and layout through locating dispatch centers and sleeping quarters away from truck bays or changing rooms^26,27.

Despite the growing awareness of the presence of combustion and pyrolysis products in fire stations, a search of the literature on the subject indicated that there is little research on the concentrations and fractional distribution of PM inside fire stations. The authors found only sixteen publications in this field²⁸. Ten were concerned with PM concentrations, and six were concerned with DPM concentrations inside fire stations. These studies were conducted at fire stations in Portugal, Poland, Korea, the USA, and Australia^{4,10,14,19,20,21,22,24,26,29,30,31,32,33}. Considering regional differences, including the occurrence of the heating season in some countries, the use of different sampling and measurement methodologies (automatic measurements, the filtration-weighing method for determining concentrations, or sampling using vacuum cleaners) and short measurement times, the authors draw attention to the need to conduct further long-term research in this area^14,19,26. Moreover, the authors of this article found only one study that assessed the effectiveness of the solution (an exhaust reduction system) recommended for reducing air pollution concentrations in fire stations²⁶.

One of the easiest solutions to implement, and therefore the most frequently used, is the installation of specialized washing machines in fire stations. The main purpose of using washing machines is disinfection, proper maintenance of uniforms and their impregnation, so that the fabrics do not absorb contaminants, but constitute a barrier for them. Due to the above, it was assumed that, firstly, washing machines can contribute to the removal of dust settled on uniforms, and thus reduce the phenomenon of dust re-suspension at fire stations, and secondly, systematic impregnation of uniforms can reduce dust settling on uniforms, and therefore less dust will be "brought" to the fire station. To our knowledge, this is the first study to focus on a comparison of concentrations, fractional distribution, and daily doses of PM inhaled by firefighters at two selected fire stations, one equipped with a professional washing machine and the other where such equipment has not yet been implemented²⁸. More specifically, the objectives of this work were: i) to determine and compare the PM mass concentration and size composition in truck bays and changing rooms at a fire station equipped with a washing machine and in a fire station without a washing machine, ii) to assess the effectiveness of laundries in reducing PM concentrations in fire stations, and iii) to estimate and compare the daily doses of respirable fractions of PM (i.e., PM_2.5) inhaled by firefighters while performing activities in the truck bays and changing rooms during one work shift at these two fire stations.

Materials and methods

Measurement site

Two fire stations were selected for research, meeting the three criteria that, according to the authors, are most important for the assumed scope of research, i.e. room volume, ventilation solutions, and the number of stored uniforms. Both fire stations are located in Poland. The first fire station (FSN) is located in the northern part of the country in the Pomeranian Voivodeship in a city with approximately 60,000 inhabitants (54°06’N, 18°48’E), and the second one (FSC) is located in the central part of the country in the Masovian Voivodeship in a city with approximately 3,000,000 inhabitants (52°11′N, 21°00′E) (Fig. 1). Both locations are characterized by typical urban buildings, i.e. tenement houses, blocks of flats, public buildings (hospitals, offices, and schools), and streets with high traffic intensity. There are four main roads within a radius of 10 km from the FSN with a traffic density of 12,183–29,750 vehicles/24 h³⁴. The FSC is located approximately 5 km from the city center. The unit is located at an intersection of streets, where the traffic intensity is in the range of 7,200–43,200 vehicles/24 h³⁴. The air quality in the FSN environment is determined by traffic emissions, emissions from energy production, the inflow of pollution, and air movement from the south of the country and along the sea^35,36,37. In the FSC environment main sources of pollution are traffic and combustion of various fuels used for heat and power generation³⁸.

Figure 1

Measurement site.

Both fire stations belong to the State Fire Service and are staffed by firefighters. In 2021, FSN firefighters intervened in 918 incidents, of which 209 were fires, whereas FSC firefighters intervened in 1,425 incidents, of which 232 were fires^39,40.

Both the FSN and FSC are located in a two-story building which were built in the 1960s. On the ground floor of both buildings are emergency rooms, a truck bay with a workshop area, and a dirty changing room. The first floor consists of sanitary, residential (kitchen, common room, canteen, and bedrooms), utility, and office rooms. None of the tested rooms were equipped with air conditioning. Therefore, natural ventilation is responsible for the exchange of air in the both fire stations which is provided by ventilation grilles and opening windows (when needed). Truck bays doors are controlled by a mechanical system that opens doors on departure/arrival. Additionally, truck bays of both fire stations are equipped with separate mechanical exhaust gas extraction systems for each parking space. Measurements were performed at both the FSN and FSC in the truck bays and changing rooms. Generally, each changing room of selected fire stations has an area of approximately 25 m² and each truck bay is 300 m². The height was approximately 3.5 m for the changing and 6.5 m for the truck bays. In the changing rooms of both fire stations, 25 to 30 sets of uniforms are stored at the same time. There are 3 fire trucks and 1 passenger car stationed in the truck bay at FSN, and 5 fire trucks and 2 passenger vehicles at FSC. At both the FSN and FSC, there are 12 firefighters on shift duty during the day, and an additional 2 and 3 firefighters work at FSC and FSN, respectively, on a daily basis. Moreover, during working days at 8.00 a.m.—4.00 p.m., both fire stations employ approximately 15 office workers. Each firefighter participating in fire-fighting operations has special clothing, gloves, balaclava and helmet. After a 24-h shift, the firefighter stores his/her clothes in lockers located in the changing room⁴¹. Due to the relatively high cost of these clothes, firefighters usually have only one or two sets of clothes.

In 2020, the FSN was equipped with a professional industrial washing machine (model IY105, Alliance Laundry Systems LLC, USA), a high-speed dryer with spinning (model I190, Alliance Laundry Systems LLC, USA), and detergents for washing uniforms (Tenso S-1, Sallo, Spain; Wash Booster UN 1719, Eco Club, Poland; Septonit, Clovin, Poland). The above devices are used to clean, disinfect and impregnate 4 sets (uniform + gloves) simultaneously using automatically dosed detergents. At the FSC, it is not possible to wash uniforms; thus, they are sent to neighboring fire stations for cleaning. The uniforms (5–7 sets) are packed tightly in plastic bags and transported by vehicle to the laundry. A passenger vehicle is used for this purpose and it also collects clean uniforms. Both at FSN and FSC, uniforms are washed each time after incidents in which firefighters come into contact with biological material and petroleum-derived substances. In addition, uniforms are also washed after storms and long-lasting fires. Based on observations conducted during the research, interviews with firefighters and the consumption of detergents, it can be determined that at FSN washing is done on average 20 times a month, while at FSC it is washed on average 5 times a month.

Measurement method

The study involved automatic measurement of mass concentrations of five PM fractions (i.e., PM₁, PM_2.5, PM₄, PM₁₀, and PM₁₀₀ alternatively referred to as TSP), in the truck bays and changing rooms of two described above fire stations (FSN and FSC). The measurements were performed using an optical method with a DustTrak 8534 DRX dust meter (TSI, Minnesota, USA). The device allows for simultaneous real-time mass concentration measurements of PM with aerodynamic diameters of 0.1–100 μm in the range of 0.001–150 mg/m³. Quality control was guaranteed by a calibration of the device before measurements (October 2020) using a standardized dust sample (Arizona Dust; TSI). Zero calibration was performed before each measurement. The accuracy of the sampler is 5%. Every day, 8-h measurements were performed at a 1 s time resolution, averaging the results every 3 min. The average 8-h concentration was the arithmetic mean of the 160 3-min results. Additionally, at the beginning and end of each measurement day, in the same place where the dust meter was placed, indoor relative humidity (RH) and temperature (temp) were monitored with a portable device (AZ Instrument, SERIE 77,597; Taiwan) (FSN—mean RH: 43%, st. deviation: 5; mean temp.: 24°C, st. deviation: 2; FSC—mean RH: 47%, st. deviation: 5; mean temp.: 20 °C, st. deviation: 2).

At the FSC, measurements were performed in March–May 2021, while at the FSN, they were performed in June 2021. In order to identify phenomena influencing changes in PM concentrations, measurements were carried out between 8:00 a.m. and 4:00 p.m., i.e. during the period of greatest activity at fire stations. Measurements were performed in each room independently for seven days. In each of the rooms studied, the measuring devices were placed approximately in the middle of the wall opposite the garage door (truck bay) and door (changing room) at a height of approximately 1.5 m from the floor level and at a distance of at least 1.5 m from the wall. This arrangement of devices did not interfere with the daily functioning of the fire stations. In addition, the device was shielded from drafts that could affect the recorded concentrations.

Result analysis

Descriptive statistics were calculated using Excel (v. 2404. Microsoft Corporation, USA) while the statistical tests were done using Jamovi (version 2.3.28, 2024). Concentrations of five PM fractions are presented as means, median and ranges since normal distribution was not demonstrated by Shapiro–Wilk’s test. The non-parametric Mann–Whitney U test was used to compare the concentrations of five PM fractions found within the two fire stations (FSN, equipped with a washing machine, vs. FSC, not equipped with a washing machine). For each measurement point and for each PM fraction, aggregated data from seven 8-h measurements with a 3-min recording of the results were used for the analyses. The statistical significance was defined as p < 0.05. Additionally, the mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD) were determined using regression lines from the log-probability graph of PM size versus cumulative mass distribution^42,43. MMAD and GSD are two parameters that characterize particle size distributions (PSDs)⁴². Moreover, these two parameters constituted the basis to determine the PM deposition factors (DFs) in three different regions of the respiratory tract (RT), i.e. the upper respiratory tract (H), trachea and bronchi (TB), and alveoli (P) for individual locations. The DFs were calculated using the multiple-path particle dosimetry (MPPD v. 3.04, Ara Inc.) model developed by the Chemical Industry Institute of Chemical Toxicology and the Dutch National Institute of Public Health and the Environment. An age-specific symmetric lung model was adopted for modelling purposes⁴⁴. One age group was considered in the calculations: adults aged over 21 years. The deposition factor (DF), including inspiration (without expiration), was calculated for one breathing cycle. Moreover, the following assumptions were considered: an upright body orientation and nasal breathing under normal physiological activity. The specific physiological parameters used in the calculations were taken from⁴⁵. Using methodology developed by the U.S. Environmental Protection Agency (US EPA) and based on the estimated PM DFs, the average doses of respirable PM particles inhaled by firefighters while performing activities in the truck bays and cleaning rooms during a work shift (D_i) were calculated^46,47. It was assumed that while on duty, firefighters spent 6 h and 2 h per shift in the truck bays and changing rooms, respectively.

The following formula was used for calculations:

$$ {\text{D}}_{{\text{i}}} = {\text{ DF}}_{{\text{i}}} \times {\text{C}}_{{\text{i}}} \times {\text{t}}_{{\text{i}}} \times {\text{InhR}}, $$

(1)

where D_i is the average dose of inhaled PM during a stay at the i-th measurement point (truck bay and changing room) [µg], DF_i is the deposition factor at the i-th measuring site, C_i is the average concentration of respirable fraction PM (PM_2.5) at the i-th measurement site [µg/m³], t_i is the average time of stay at the i-th measurement site [day]. InhR is inhalation rate [m³/day]⁴⁵.

Results and discussion

Distribution of particulate matter concentrations in fire stations

The statistical parameters of the five PM fractions in the truck bays and changing rooms at two selected fire stations in Poland (FSN in North Poland and FSC in Central Poland) are summarized in Tables 1, 2 and Fig. 2. The lowest average concentrations of the five PM fractions were recorded in the truck bay at the FSN (PM₁, 18.2 µg/m³; PM₁₀₀, 28.9 µg/m³), while the highest were recorded in the truck bay at FSC (PM_2.5, 28.1 µg/m³; PM₁₀₀, 37.9 µg/m³) except for that of PM₁, which was recorded in the changing room at the FSN (27.5 µg/m³). At the FSN, higher PM concentrations were recorded in the changing room, and at FSC, they were recorded in the truck bay. In general, the average total concentrations for both rooms were higher at the FSC than at the FSN (Table 1). The Mann–Whitney U tests results for the truck bay and changing room, indicate that the differences between PM concentrations in these rooms in the two fire stations under study are statistically significant (p < 0.001) (Table 2). When the results of statistical tests and mean and median PM concentrations are taken into account, it seems to be that in the truck bay at the FSN the washing machine could have contributed to reducing PM concentrations. However, in the changing room, where mean and median concentrations were higher at the fire station with a washing machine, it was not possible to confirm the effectiveness of this device. It should be noted that the recorded result is not straightforward, because it was expected that differences in PM concentrations would indicate the effectiveness of the washing machines in the changing room, where the uniforms are stored. It is important to note that the changing rooms at both fire stations are in close proximity to the truck bay. The doors between these rooms are often open, which could facilitate air exchange between the two zones. To confirm of this, further research is required, including analysis of ventilation solutions and internal airflows, as well as measurements of PM concentration outdoors.

Table 1 Descriptive statistics of a series of 8-h concentrations of PM₁, PM_2.5, PM₄, PM_10, and PM₁₀₀ (μg/m³) in the truck bays and changing rooms at two fire stations (FSN in North Poland, equipped with a washing machine; FCS in Central Poland, not equipped with a washing machine) and at the Regional Environmental Protection Inspectorate (REPI) stations closest to the measurement sites.

Table 2 Mann–Whitney U test results.

Figure 2

Ranges and 8-h average concentrations of PM₁, PM_2.5, PM₄, PM₁₀, and PM₁₀₀ (μg/m³) in the truck bays and changing rooms at two fire stations (FSN in North Poland, equipped with a washing machine; FCS in Central Poland, not equipped with a washing machine). Boxes show the range between the 25th and 75th percentiles. The whiskers extend from the edge of the box to the 5th and 95th percentiles of data. Dots indicate outliers. The horizontal line inside indicates the median value.

Although the Mann–Whitney U tests showed statistical significance, it should be noted that, taking into account the values of standard deviations, the differences between the mean and median PM concentrations in the fire stations with and without the washing machine are relatively small. This may probably be due to the similar characteristics of both buildings (room layout, number of floors, ventilation solutions, and number of people working in a given fire station) and their surroundings.

Based on the obtained results, it can be concluded that the mean and median concentrations differed at all measurement points. In general, the means were overestimated by the maximum concentrations recorded, for example, at the moment of dynamic movement or when the activity was performed in close proximity to the devices. Therefore, the median was a better representation of the automatic measurements.

Considering the hourly concentration distribution in the individual rooms of the selected fire stations, the differences were much more pronounced (Figs. 2 and 3). At the FSN, throughout the measurement period (8 h), the concentrations of PM₁, PM_2.5, PM₄, PM₁₀, and PM₁₀₀ ranged from to 7–244 µg/m³ in the truck bay and 8–233 µg/m³ in the changing room. At the FSC, the maximum PM concentrations were more than three times higher than those at the FSN. In the truck bay, PM concentrations ranged from 4 to 735 µg/m³, while those in the changing room were 6–890 µg/m³. At both fire stations, the momentary jumps in PM concentrations and their reaching maximum values were probably caused by the phenomenon of resuspension, i.e., picking up dust settled on various types of surfaces (e.g., firefighting equipment, vehicles, and PPE) when opening windows and garage doors, taking uniforms out of the wardrobe, conducting cleaning works, testing equipment, and during departures/returning to/from rescue and firefighting operations⁴⁸. It can be assumed that the lower ranges of PM concentrations at the FSN may have resulted from the systematic use of washing machines at this fire station, and thus from the systematic decontamination of firefighters’ special clothing. The systematic washing of clothes removes contaminants that settle on uniforms during rescue and firefighting operations, which probably limited the resuspension phenomenon at the FSN⁴⁸. Although FSC firefighters use laundry facilities outside their fire stations (approx. 5 times per month), they are not as systematic as FSN firefighters (approx. 20 times per month). In addition, pollutants may be released when uniforms are packed into bags for transportation to laundries. The higher concentrations of PM at the FSC could also be due to the fact that more vehicles are stationed in the garage of this unit (5 fire trucks and 2 passenger cars) than at the FSN (3 fire trucks and 1 passenger car). uIn addition, it cannot be ignored that the measurements at both fire stations were carried out in different seasons, i.e., at the FSN in the summer (June 2021; non-heating season) and at the FSC at the end of the heating season (March–May 2021). In the vicinity of the FSC, in addition to typical urban buildings heated by the municipal network, there are residential buildings with individual coal and wood fireplaces, which are the sources of so-called low-stack emissions. Therefore, it cannot be ruled out that the PM concentrations at the FSC could have been determined by poor ambient air quality and the inflow of air from the outside, for example when opening garage doors for departures. However, to assess the impact of the surroundings, and therefore atmospheric air, on PM concentrations inside fire stations, broader research is needed, including simultaneous measurement of PM concentrations inside and outside the fire station and determination of the indoor/outdoor (I/O) coefficients.

Figure 3

Average hourly distribution of PM concentrations (μg/m³) in the truck bays and changing rooms at two fire stations (FSN in North Poland, equipped with a washing machine; FCS in Central Poland not, equipped with a washing machine).

As the authors did not perform measurements outdoors, the obtained results were compared with the measurement results provided by the Regional Environmental Protection Inspectorate (REPI; Table 1). To compare the results, urban background stations closest to the measurement sites that simultaneously conducted automatic measurements of PM_2.5 and PM₁₀ concentrations were selected. The first station, REPI Gdańsk-Leczkowa, is located on a straight line 32 km from the FSN, and the other station, REPI Warszawa-Wokalna, is located 3 km from the FSC. At both the FSN and FSC, the average concentrations of PM_2.5 and PM₁₀ were higher inside the fire stations than in atmospheric air. For PM_2.5, these differences were approximately twofold, which may indicate the existence of an internal source of fine PM at both fire stations, for example fuel combustion by fire vehicles and combustion equipment^10,24,26. In the case of FSN, this comparison should be approached with caution due to the long (32 km) distance to the nearest REPI station.

In Fig. 3, the distributions of the concentrations of the five PM fractions during the day at 8.00–16.00 at the FSN and FSC are presented. For each measurement point, the results were averaged over seven measurement days. The graphs show that the hourly variability in the concentrations of the five PM fractions was greater in the truck bays of both fire stations than in the changing rooms. Peaks were recorded at various times in truck bays. Analyzing the list of activities carried out at the FSN and FSC in the considered measurement periods, it can be noticed that jumps in PM concentrations at individual hours occurred during departures and returns from operations, equipment testing, exercises aimed at self-improvement of firefighters etc. (Appendix). In the changing rooms, momentary jumps in concentration were recorded mainly during the morning hours between 8.00 and 10.00 a.m. This was probably due to the removal of uniforms from wardrobes before the start of the work shift. Moreover, it cannot also be ruled out that before 8.00 a.m. PM concentrations may be determined by infiltration of pollutants related to traffic emissions. After 10.00 a.m., a decrease in PM concentrations was observed in the changing rooms, which may mean that over time, PM particles fell and settled on surfaces such as wardrobes and windowsills. The standard deviation values show that, at all measurement points, the highest variability of concentrations within the 8-h measuring period concerned the PM₁₀ and PM₁₀₀ fractions (Figs. 2 and 3). This may indicate the presence of an internal source of coarse PM (the fraction of particles larger than 10 μm), e.g., firefighting equipment and PPE contaminated with combustion products. It should be noted that coarse particles float in the air for a shorter time than fine PM and settle on surfaces faster; however, they are also subject to faster resuspension⁴⁸. This does not imply that the concentration of fine PM was constant. When there were jumps in the PM₁₀ and PM₁₀₀ concentrations, there were simultaneous jumps in the PM₁, PM_2.5, and PM₄ concentrations. This may indicate a common source of the five PM fractions analyzed, which should be considered to be combustion and pyrolysis products, especially since PM released during fires is known by various particle sizes, from nano particles to fly ashes, whose sizes range from 0.3 to 250 µm with a major fraction in the range of 20–25 µm^4,5,6.

Figure 4 presents the average over the entire measurement period (7 days) with respect to the aerodynamic diameter of the particles in the total mass of PM at individual sampling sites. On average, at each of the considered locations, most of the PM mass was accumulated in particles with an aerodynamic diameter in the range of 0.1–2.5 µm (65–75%). The highest average share of fine particles in the total mass of PM was recorded in the changing rooms (75% at both FSN and FSC), whereas the lowest was recorded in the truck bay at FSN (65%). Throughout the entirety of the measurement period, the percentages of particles with diameters below 2.5 µm in the total mass of PM were in the ranges of 42–78% in the truck bay at FSN, 52–88% in changing room at FSN, 45–89% in truck bay at FSC and 41–89% in changing room at FSC. Generally, the dominance of fine particles in the total mass of PM was relatively constant, with small decreases accompanying the increase in coarse particles at the times mentioned earlier, i.e., departures and returns from action, taking uniforms out of the closet, carrying out cleaning works, testing equipment, etc. These activities probably contributed to the accumulation of fine PM particles and the formation of large PM agglomerates in the truck bays and changing rooms at both fire stations⁴⁸.

Figure 4

Average percentage shares of individual particulate matter fractions in the total mass of particulate matter in the truck bays and changing rooms at two fire stations (FSN in North Poland, equipped with a washing machine; FCS in Central Poland, not equipped with a washing machine).

The high contribution of fine PM to the total PM mass was also evidenced by the low MMAD values (Table 3). The average MMAD values calculated for the entire measurement period at each sampling site ranged from 1.77 to 2.76 µm. This means that, in the truck bay at FSC, 50% of the PM mass was concentrated in particles with diameters below 1.77 µm, while in the truck bay at FSN, it was concentrated in particles with diameters below 2.76 µm (Table 3). The PM mass size distributions in all of the considered locations were similar—they were bimodal and their grater modes were between 0.1 and 1 µm while the smaller ones were between 4 and 10 µm (Fig. 4). At all sampling sites, the lowest share of particles with diameters ranging from 1–2.5 µm was recorded.

Table 3 Mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD) of particle mass size distributions (PSDs) in the truck bays and changing rooms at two fire stations (FSN in North Poland, equipped with a washing machine; FCS in Central Poland, not equipped with a washing machine).

Based on the average concentrations and medians (Table 1), statistical tests (Table 2), PM mass size distribution (Fig. 4) and values of MMAD (Table 3) it seems to be that washing machines are probably the most effective in reducing fine PM. This may be due to the fact that in fire stations there are numerous sources of coarse PM that cannot be eliminated by systematic washing of uniforms (e.g. dust settled on firefighting equipment, furniture, etc.).

Table 4 presents the results of the literature review on the measurement of PM concentrations inside fire stations. A comparison between the results obtained and the results of similar studies conducted worldwide showed that the average concentrations of PM₁, PM_2.5, PM₄, PM₁₀, and PM₁₀₀ in the truck bays and changing rooms at the fire stations under study are approximately 10 times lower than those of analogous PM fractions measured in truck bays, PPE storage rooms, bars, and common areas of Portuguese fire stations¹⁴. Moreover, the recorded PM concentrations were several times lower than the average monthly PM concentrations measured by Rakowska and her team in a truck bay at a fire station in southwestern Poland³². In studies described by Rogula-Kozłowska and her team, who also conducted studies on truck bays and changing rooms at two selected fire stations in Poland located in the south and north of the country, the average PM₄ concentrations were also several times higher than the average PM₄ concentrations in the fire stations under study¹⁰. The PM concentrations at the FSN and FSC were comparable to PM concentrations measured in the apparatus and truck bays of American fire stations^4,19,21, as well as in the truck bay of a fire station in Warsaw, Poland³³. The average PM concentrations at the FSN and FSS were also similar to those recorded at fire stations in Seoul, Republic of Korea, after the installation of an exhaust reduction system²⁶. In the studies^4,14,26, similar to the results of this study, it was observed that fine and ultrafine particles were dominant inside fire stations and accounted for approximately 80% of total PM mass. Moreover, similar to the research described in³², an increase in PM concentration was related to increased firefighter activity.

Table 4 Review of research on PM concentrations inside fire stations.

Owing to the different measurement methodologies, i.e., measurement methods used (reference and non-reference), sampling periods, and sampling accuracy, the above comparisons are indicative only and should be applied with caution.

Particulate matter deposition and dose of PM inhaled

The total and regional PM depositions for firefighters at each test site are shown in Table 5. Overall, the total DFs for each measurement site ranged from 0.59 to 0.61. This means that when performing activities in the truck bays and changing rooms of the two selected fire stations (FSN and FSC), 59 to 61% of the inhaled PM is deposited in the respiratory tract during one respiratory cycle. The highest DF value was estimated for the truck bay at FSN (0.61), while the lowest value was estimated for the changing rooms at both FSN and FSC (0.59) (Table 5). By analyzing the regional DF (Table 5), it is clear that, in each of the analyzed measurement sites, the greatest mass of PM was deposited in the upper respiratory tract (41–46%), and 11 to 14% of the mass of PM penetrates the pulmonary region, where gaseous exchange between inhaled air and blood occurs⁴⁹.

Table 5 Particulate matter deposition factors (DFs) in the three regions of respiratory tract: (H—upper respiratory tract, TB—trachea and bronchi, P—alveoli) for firefighters during activities in the truck bays and changing rooms at two fire stations (FSN in North Poland, equipped with a washing machine; FCS in Central Poland, not equipped with a washing machine).

In addition to the DFs, Table 6 shows the average daily doses of PM inhaled by firefighters while performing activities in the truck bays and changing rooms at the FSN and FSC during one 24-h work shift. Unlike the DFs, owing to different PM concentrations in individual rooms and the assumed stay times in each room, the daily doses differed from each other. The data presented in the Table 6 indicate that firefighters staying in the truck bay at FSC are exposed to the highest dose of PM (64.1 µg) during a work shift. Also, the total PM dose aggregated for the truck bays and changing rooms was higher for firefighters working at FSC (82.9 µg) than for those working at FSN (65.0 µg). Considering these results and the DF calculated for the alveolar area (P) (Table 5), it can be concluded that FSC firefighters are more exposed to the adverse effects of PM than FSN firefighters. However, it should be noted that the results refer only to a part of the day, approximately 8 h, which is 1/3 of the work shift. If we also considered PM doses inhaled during fires and stays in other rooms of fire stations, these values would probably be several times higher. The literature search showed that few studies have assessed the daily doses of PM inhaled by firefighters while staying at fire stations; therefore, it is difficult to compare the results obtained with other studies. The authors of this article found only two studies on similar topics. One study estimated the lifetime daily dose of PM₄ inhaled by wildland firefighters in the USA depending on the duration of their professional careers⁵⁰. This study estimated that firefighters who worked 49 days per year are exposed to a daily dose of PM₄ that ranges from 150 to 740 µg for a 5- and 25-year career, respectively. The daily dose of PM₄ for firefighters working 98 days per year ranged from 300 to 1490 µg. Thus, these doses are several times higher than the daily doses estimated in the present study (Table 6). However, it should be noted that the modeling carried out by Navarro et al. considered longer exposure times (13.6 h per shift)⁴⁹, and the concentrations measured during the extinguishment of wildland fires were included in the calculations and did not consider PM DFs in the respiratory tract. The daily doses of PM estimated in this study are also lower than the PM doses estimated for firefighters from a fire station in Poland in a previous study⁵¹, where they were approximately 59 µg and 95 µg. However, in this study, the daily doses of PM inhaled only during firefighting were estimated. Owing to the different sampling and concentration measurement methodologies, as well as the assumptions used for modeling, the above comparisons are rough.

Table 6 Average daily doses of respirable particulate matter (PM_2.5) for firefighters during activities performed in the truck bay and changing room at two fire stations (FSN in North Poland, equipped with a washing machine and FCS in Central Poland, not equipped with a washing machine).

Strengths and limitations

To the best of the authors knowledge, this is the first study to validate the effect of the washing machines in reducing PM concentrations in fire stations. To date, in terms of assessing the effectiveness of solutions aimed at improving the air quality of fire stations, only the exhaust reduction system has been subject of assessment²⁶. Although the study was conducted on a small scale, the obtained results offer valuable insights for firefighters and policymakers. Firstly, the use of an instrument that provided continuous and real-time results enabled the identification of factors influencing momentary PM concentration jumps, thus facilitating the identification of PM sources and factors determining their concentrations in fire stations under study. Furthermore, a multi-channel particle counting device that measured PM mass in various size fractions generated a substantial quantity of data, which were used for a multitude of analyses, including health exposure assessment. The strength of the analyses lies also in the fact that the same measurements were performed in two rooms of two fire stations, allowing for a direct comparison of the results. Moreover, the use of the same meter throughout the research process eliminates potential errors resulting from the use of measuring devices based on different operational principles.

This research is a first stage of a broader research project aimed at identifying and ultimately limiting health exposure to harmful substances, including combustion products, in places where firefighters are stationed, as well as in the workplace of office workers of the state fire service. The authors have identified several limitations and contextual factors that must be taken into account when analysing the results and planning future research. Primarily, the research conducted focused on a small sample, specifically two fire stations. This was due to the fact that at the time of the research (2021), it was challenging to find fire stations equipped and/or not equipped with a washing machine with comparable ventilation solutions, number of calls and type of incidents, similar room volumes, ventilation solutions and the number of firefighters per shift (number of uniform clothes used/stored). At the time, the solution in the form of washing machines was still in its infancy, with only a few units in operation due to the need for renovation works to designate a special room. It would therefore be valuable to conduct similar research now with a larger number of fire stations. Despite the advantages demonstrated above, continuous measurements also have some limitations. The average PM concentration is frequently overestimated by the dynamic states (e.g. departures to events, returns, cleaning, exercises, etc.), that are prevalent in the case of fire stations. Future research could benefit from the isolation of static states as background and dynamic states, with a thorough analysis of activities performed at the measurement site and comparison of PM concentrations at different fire stations. Additionally, our studies did not consider the impact of ventilation solutions and air changes on the recorded PM concentrations. This is due to the frequent opening of garage doors, which makes it challenging to assess the amount of incoming and outgoing air. Additionally, there is a lack of technical documentation regarding natural ventilation and no mechanical ventilation in the analysed buildings. Due to technical difficulties, measurements of outdoor PM concentrations were also not carried out.

Despite the limitations presented, pilot studies such as those described herein are useful because they allow us to collect preliminary data, test the suitability of the methodology used, identify problems in conducting the research, and develop solutions for future research.

Conclusions

A comparison of the concentrations and mass size distribution of five PM fractions (PM₁, PM_2.5, PM₄, PM₁₀, PM₁₀₀) at a fire station equipped with specialized washing equipment (FSN) and at a fire station not equipped with this type of device (FSC) was carried out for the first time. Despite the more frequent washing of uniforms at FSN (FSN—approx. 20 times a month vs. FSC—approx. 5 times a month), overall the average concentrations of PM₁, PM_2.5, PM₄, PM₁₀, and PM₁₀₀ in truck bays and changing rooms both fire stations were similar and ranged from 18 to 29 µg/m³ at FSN, and 27–38 µg/m³ at FSC. At all sampling sites, the vast majority of the PM mass (65–75%) was accumulated in fine particles with aerodynamic diameters smaller than 2.5 µm. In the truck bays, increases in PM concentrations were recorded during firefighters’ activities, i.e., departures to events, when returning from events, testing equipment before and after the start of work a shift, putting on and taking off uniforms, and activities related to storing and preparing PPE for operations. In the changing rooms, momentary jumps in PM concentrations were recorded in the morning during the shifts of duty, i.e., when the receiving shift took the uniforms out of the wardrobes and the returning shift put them on. Although the average PM concentrations at both fire stations were similar, the studies showed clear differences in daily concentration distributions. Temporary peaks in PM concentrations (i.e. maximum concentrations) were more than 3 times higher at the FSC than at FSN, which allowed us to assume that the presence of washing machines probably limited the scale of the resuspension of dust at the fire station equipped with a washing machine. Increases in PM concentrations during activities related to the use of firefighting uniforms and equipment indicate that one of the main sources of pollution in fire stations is the combustion and pyrolysis products generated during fires and deposited on uniforms and firefighting equipment. Due to the high share of fine particles in the total mass of PM (65–75%), the PM deposition coefficients in three sections of the respiratory tract estimated for each measurement site assumed similar, relatively high values (0.59–0.61). High depositions factors, domination of fine PM, and penetration of the lung alveoli, which, according to the modeling, reach approximately 10% of the inhaled PM, require the introduction of solutions aimed at limiting PM concentrations at fire stations.

In light of the analyses presented in this paper (statistical tests, mass size distributions, hourly PM concentration distributions, deposition coefficients, average daily doses of PM), it can be assumed that washing machines contribute to a reduction in the share of fine particles in the total mass of PM in fire stations, especially in the truck bay. Consequently, the dose of inhaled PM, and thus the health exposure of firefighters in a unit with a washing machine, is lower than in a unit without a washing machine. Obtained results indicate that washing machines should not be the only solution introduced in fire stations to improve air quality, and the introduction of new solutions requires research to check their effectiveness. Nevertheless, these are preliminary analyses conducted on a limited sample, therefore further and broader studies in a greater number of fire stations are needed. Additionally, further research in this area should also include the analysis of the concentrations of other pollutants, such as PM-bound metals, PAHs and gaseous pollutants, as well as a more extensive analysis of the impact of atmospheric air and ventilation solutions.

The present study may constitute an introduction to further studies on PM concentrations inside fire stations and the assessment of the contribution of PM exposure at fire stations to firefighters’ occupational health risks. The authors believe that the present studyλ makes an important contribution to the limited knowledge on the exposure of firefighters to PM not only during fires, but also during their stay at fire stations, which, in addition to being a place for self-improvement exercises and preparation of firefighters and equipment for action, it is also a place for office work of administrative employees, as well as a place for firefighters to rest and regenerate between incidents.

Appendix

See Table

Table 7 List of departures and returns from events and activities carried out at fire stations during the measurements.

7.