Spatial Analysis of the Impact of Motor Vehicle Fires on the Urban Environment using the Example of Warsaw

Globally, Europe constitutes a significant market in the automotive industry, with a 23.7% share of newly registered vehicles worldwide in 2022 [9]. Therefore, any manufacturer seeking to sell vehicles within the European Union must comply with prevailing regulations and obtain approvals for systems related, among other things, to road safety. This adherence to stringent requirements designed for the European market also ensures the safety of the same vehicles sold in other parts of the world. The implementation of flammability standards for materials used in vehicles is thus a crucial aspect of safety engineering, with the United Nations ECE regulations serving as vital tools in minimizing health risks associated with collisions and vehicle fires.

For instance, Regulation No. 34 of the UNECE deals with vehicle approval for fire protection in the event of a collision, as well as requirements regarding liquid fuel tanks. The regulation outlines methods for conducting impact resistance tests on tanks and the placement of fuel-related components within the vehicle. Moreover, the materials used for fuel tanks must be corrosion-resistant and fire-resistant. The regulation also specifies the pressure values at which each tank must maintain its integrity. Tanks meeting the stipulations of Regulation No. 34 must bear an international approval mark containing the letter “E” and the approval country's number [10].

European regulations also mandate equipping certain vehicles with fire suppression systems located in the engine compartment and other areas housing exhaust heaters. Regulation No. 107 applies to category M2 and M3 vehicles (buses designed to carry more than 8 passengers excluding the driver) and outlines general construction requirements. Information about fire suppression systems in the engine compartment and their operation constitutes only a brief portion of the entire regulation [11].

Another regulation related to fire safety is Regulation No. 118 of the UNECE. Regulation No. 118 focuses on regulating the flammability of materials used inside motor vehicles. This is crucial for safety, as vehicle fires can lead to hazardous situations. The regulation specifies requirements regarding material behaviour under burning conditions, introducing standards for flame resistance, flame propagation, and emission of smoke and toxic gases. By defining flammability criteria, the regulation aims to reduce the risk of rapid fire spread and limit the emission of toxic substances in case of an interior vehicle fire. These standards contribute to improving evacuation conditions, safeguarding drivers, passengers, and those providing assistance during emergencies. However, it's worth noting that Regulation No. 118 only applies to category M3 vehicles – those designed to carry passengers, with more than eight seats besides the driver's seat and a maximum mass exceeding 5 tons [12].

European Union regulations focus on ensuring overall passenger safety in the event of a road incident and ensuring the durability of fuel tanks. However, they do not address the harmfulness of vehicle fires themselves and the quantity of emitted toxic substances into the atmosphere. Legal regulations also do not govern the type and amount of combustible materials used in the production of passenger and commercial vehicles.

Vehicle fires pose a direct threat to the health and lives of residents. Emissions of toxic chemicals and gases can lead to severe respiratory and skin diseases in people exposed to fire smoke. Analyzing the health effects is crucial for assessing the severity of the issue and developing appropriate prevention strategies and crisis management plans. Moreover, vehicle fires release substantial amounts of greenhouse gases and other air pollutants, negatively impacting the air quality in cities. This, in turn, can lead to a reduced quality of life for residents and disrupt the balance of urban ecosystems. Analyzing these effects is essential for understanding the long-term ecological consequences. Vehicle fires also contribute to the generation of hazardous waste, such as burnt plastics and metals. Managing this waste presents a challenge for municipal authorities and waste management institutions. Effective strategies for processing fire-related waste are of utmost importance for minimizing environmental impact [13, 14, 15].

In automotive vehicles, various types of plastics are used, each with specific characteristics and applications. The most significant polymers include polypropylene (PP), polyamide (PA), polyurethane (PUR), polyethylene (PE), acrylonitrile-butadienestyrene (ABS), polyvinyl chloride (PVC), polycarbonate (PC), polyester resins (UP), polyester (PEST), polymethyl methacrylate (PMMA), polybutylene terephthalate (PBT) and rubber, which is a mixture of various elastomers, mainly of polybutadiene (PBD) and polyisoprene (PI) [16, 17, 18]. Table 1 provides examples of vehicle components made from different types of plastics.

It is estimated that for an average passenger vehicle in the United States with a mass of 1950 kg, approximately 186 kg are comprised of elements made from plastics and polymer composites. This accounts for 9.6% of the vehicle's own mass, primarily consisting of 44 kg of polypropylene (PP), 38.1 kg of polyurethane foam (PUR), 18.6 kg of nylon (PA), 15.4 kg of high-density polyethylene (HDPE), and 14.1 kg of polyvinyl chloride (PVC) [19]. The aforementioned general mass of plastics also includes rubber, which is the basic component of tires (approx. 80%) [20]. The average mass of a tire with a diameter between 16 and 17 inches is about 10 kg [21], so the share of rubber in the tires of an average four-wheeled vehicle may amount to 36 kg.

Assuming that the average mass of a European passenger vehicle is 1385 kg [22], a truck is 12,250 kg [23], a bus is 10,400 kg [24], and an average motor-powered two-wheeler is 180 kg [25], it is possible to roughly estimate the amounts of plastics in other types of vehicles using proportions. The quoted values are masses of different types of representative vehicles in Europe adopted for further calculations. Table 2 presents an overview of calculated and approximate masses of selected plastics used in the construction of various types of transportation.

As mentioned in the previous section of the article, plastics are a significant material in various industries, including the automotive sector. However, their flammability can pose certain hazards. In case of accidents or incidents leading to a fire, the presence of combustible plastics inside a vehicle can accelerate the spread of fire and generate toxic gases. Highly flammable plastics, such as polyurethane foams or certain types of polypropylenes, can release toxic substances during combustion, endangering the health of individuals inside the vehicle as well as rescue personnel. Additionally, the process of plastic combustion can rapidly weaken the vehicle's structure, hindering evacuation and rescue efforts.

The amount of substances generated during combustion depends on various factors, primarily combustion temperature and the amount of available oxygen. Real-world fires, not only in vehicles but also in buildings, are unpredictable, thus precise determination of combustion products is not possible. True fires are not conducted under repeatable laboratory conditions, which is why approximations of combustion product quantities are used in the article. Given the complexity of the combustion process, laboratory-perfect pollution levels are unattainable. Combustion products of selected polymers along with their approximate masses of selected pollutants are presented in Table 3.

Warsaw is the largest city and the capital of Poland, with a population of 1,863,056 people residing in an area of 517.2 km², resulting in a population density of approximately 3,602 people/km² according to 2022 data [30]. Warsaw serves as a significant financial and business hub in Central and Eastern Europe, experiencing a growing population year by year. Under the current administrative division, Warsaw is divided into 18 districts. Table 4 provides information about the area, population, and population density of each district in Warsaw.

Through Warsaw flows the Vistula River, the longest river in Poland, dividing the city into two sides – the northeastern and the southwestern. Figure 1 illustrates the administrative division of Warsaw, taking into account the population density of individual districts, along with the Vistula River flowing through the city.

Figure 1.

Thanks to the cooperation of the management of the Municipal Headquarters of the State Fire Service, data concerning vehicle fires in the capital city of Warsaw has been made available. The data, obtained from the Municipal Headquarters of the State Fire Service in Warsaw, includes the number of interventions by the State Fire Service due to vehicle fires in the period from January 1, 2010, to April 30, 2021, within the city of Warsaw.

The data was provided in the form of spreadsheets with filled cells. Vehicle fires were categorized into four groups: buses and trolleybuses, motorcycles and mopeds, trucks, and passenger vehicles. Each intervention, in addition to the date and time of the incident, includes a brief description of the burning vehicle, the street of the incident, and the geographic coordinates of the fire. Based on these coordinates, it was possible to conduct an analysis of city areas exposed to harmful substances resulting from vehicle fires.

The data was analyzed for accuracy. All errors were identified during spatial analysis and corrected accordingly. Most mistakes involved incorrectly determined fire locations, which were detected through repeated coordinates associated with different addresses.

Based on the number and locations of fires, it was possible to calculate the amount of emitted substances in specific districts of Warsaw. Furthermore, by dividing the emissions of pollutants by the population of each district, it was possible to estimate how much approximately toxic substances were emitted per resident due to vehicle fires.