## 1 Introduction  
Positive-pressure ventilators are an important tool used in rescue and firefighting operations. [PERSON] et al. [1] pointed out in 2021 that due to the conditions of use of these devices (operation in a fire environment), they should be characterized by proper efficiency and reliability of operation. Tests related to the use and performance evaluation of mobile fans are being carried out by researchers from around the world. [PERSON] et al. (2017) performed tests related to the evaluation of the size of the inlet opening on the effectiveness of PPV (positive-pressure ventilation) [2]. During the tests, an increase in the effectiveness of positive pressure ventilation was noted, with the opening area being reduced by installing a smoke curtain. [PERSON] et al. (2022) [3] investigated the effect of the placement distance of a turbo-type fan on the amount of airflow through the exhaust vent. In his tests, he showed that ventilation efficiency (for a turbo unit) increases with increasing positioning distance, but only up to 5 m. In contrast, another research team, which used a conventional fan, showed a relationship in which the closer the fan is positioned, the higher the flow rate is [4]. [PERSON] et al. [5] showed in 2022 that the tested fan achieved the highest output, measured at the surface of the door opening for 4 m (42,269.3 m\({}^{3}\)/h). The team proved that if a fan is placed at a distance of 1 m the volumetric flow rate will decrease by 38%. With regard to the recommendations being developed on positioning parameters, among other things, it is suggested that some of the research results may already be outdated. This is due to the ongoing development of design elements for fans, in the form of flow direction systems. We are referring to the specially shaped rotor blades and their housing, which is also the flow guide of the generated air stream [6; 7]. This evolution is also related to the widespread availability of CFD tools to evaluate the product already at the design stage [8; 9]. There are about 60 models of fans on the European market that are used for rescue operations [10]. Half of these units are units powered by an internal combustion engine, and the other half are electric. Fan units have different power ranges. A total of 74% of electric fans are in the 1.1-2.2 kW power range, while fans with combustion engines are in a much larger range from 0.7 to 92 kW. With regard to positive-pressure ventilators, the division of these units into conventional and turbo types is also present in the market [11]. This division is related to the profile and velocity vector of the air stream (i.e., the area of effective distribution versus distance). Analyzing the issues of procedures for assessing the conformity of technical and user parameters, depending on the requirements of the country, these devices may be subject to special requirements [11]. It should also be pointed out that various methods are used in Europe to assess the volumetric flow rate [1; 5; 12; 13]. Nevertheless, as pointed out by [PERSON] et al. in 2022 [11], volumetric airflow tests should be carried out under conditions that reflect real aspects of the operation of this type of equipment--free-flow operation. The use of tactical mechanical ventilation is a very important measure used by fire protection units. The indicated action allows, among other things, the removal of hot and toxic fire gases [14; 15], which accumulate in the spaces covered by the fire [16; 17]. Over the past years, a number of techniques have been developed to move smoke in building spaces, and these include [18] positive-pressure ventilation, negative-pressure ventilation and positive-pressure attack.