## 2 Materials and Methods  
The tests were conducted using two fans commonly used by firefighting units in Europe [11]. The first fan is a conventional unit, and it is powered by a Briggs & Stratton 750 engine. The maximum power of the engine is 4.4 kW and its displacement capacity is 163 cm\({}^{3}\). The manufacturer's declared volumetric flow rate is 30,000 m\({}^{3}\)/h. The second fan is a turbo unit and is powered by a Honda GX200 internal combustion engine with the maximum power of the engine being 4.1 kW. The displacement of the spark-ignition internal combustion engine of this device is 196 cm\({}^{3}\). For the turbo fan, the manufacturer indicated that it generates of 31,799 m\({}^{3}\)/h of flow rate. The tests on flow characteristics, for the indicated samples, were carried out on a 7-story building, from which 4 floors were selected for testing. For these 4 floors, the volume of the gas exchange track was 198 m\({}^{3}\). A test stand (FRC--flow resisting curtain) was installed on the 4 th floor inside a window opening (present in the southeast wall), allowing the measurement of airflow velocity profiles generated by mobile fans, with the possibility of changing the size of the measurement area. The specified test stand was designed and manufactured by Centrum Naukowo-Badavcze Ochrony Przeciwpozarowej--Parastwowy Instytut Badawczy (Scientific and Research Center for Fire Protection--National Research Institute). The stand is constructed of a metal body (frame), which is tightly fitted to the window frame. The device is equipped with a roller shutter made of plastic, which, depending on the setting, changes the area of the outlet opening. On the front part of the measuring plane, guides made of aluminium profiles are fixed, which are used to transport the measuring module. A thermo-resistive anemometer is embedded in this module, which moves in a synchronized manner taking into account the current size of the outlet opening (position of the shutter). The station is driven by a stepper motor and its control (the position of the roller shutter and the sensor transport path) is possible due to a computer application that works with a dedicated controller. The tests of flow characteristics--volumetric flow rate--were performed by measuring the air flow velocity at the surface of the outlet hole, the measuring plane. The measurement was carried out, based on the requirements of the ISO 5221 standard [21]. The evaluation of flow velocity was carried out for 5 positions of variable outlet area: P1 (0.24 m\({}^{2}\)); P2 (0.48 m\({}^{2}\)); P3 (0.72 m\({}^{2}\)); P4 (0.96 m\({}^{2}\)); P5 (1.2 m\({}^{2}\)). A diagram of the test stand, including the distribution of measurement points, is shown in Figure 1. Air jet velocity was measured using a measurement module, which was equipped with a TSI 8455 thermo-resistive anemometer (0.127-50 m/s and 1% accuracy). The volumetric air flow rate was calculated taking into account the dependence of the product (ratio) on the average flow velocities and the geometric surface of the outlet opening [8]. At the same time, along with flow velocity measurements, pressure values were recorded (using Setta 265 transducers with a measurement range of 0-100 Pa and an accuracy of 0.25%). For the implementation of the research, 4 transducers were used, 1 being distributed on each floor, and fixed inside the building in the center of the front wall (Figure 1.). This selection of the measurement point was intended to measure the pressure as closely as possible to the average static pressure on a given floor--an area away from places where air movement can produce local back pressure or negative pressure. During the tests, the fans were set up in the following configuration--fan 1 (conventional) was positioned at a distance of 1 m, and the impeller angle was 17\({}^{\circ}\). Meanwhile, the positioning distance for fan 2 was 5 m, and the angle of inclination was 6\({}^{\circ}\).