## 5 Conclusions  
The current work concerns the problem of the critical wind speed determination, which can cause the tip-over of the scissor lift. The analysis is performed for the device MEC 4191 RT. The estimation of the critical value of the wind speed is based on results obtained from the CFD analysis of the scaled model (assumed approximate scale of the model 1:14) of the scissor lift. The computations are performed with the use of ANSYS Fluent R22. Three different configurations of the scissor list at analyzed, namely: (a) The work platform raised to the maximum height with an additional bridge extended, (b) the work platform raised to the maximum height, and (c) the work platform half raised. The numerical model is verified by the experimental test in the wind tunnel. To verify the CFD results, the values of the \(F_{x}\) and \(F_{y}\) components of the aerodynamic forces are compared, which are obtained from numerical simulations and experimental tests. A relatively good agreement is observed. In the case of the force coefficient \(C_{x}\), the value of the average error does not exceed 9% for all investigated configurations. It is established that the most dangerous wind direction is the one that makes an angle of 30\({}^{\circ}\) with the \(X\)-axis of the global coordinate system, Figure 3, for all studied configurations of the scissor lift. The lowest critical wind speed is obtained for configuration 1 st and is equal to \(V^{1}{}_{CRT}\) = 22.315 m/s. For other configurations, the critical wind speed is higher and equal to \(V^{2}{}_{CRT}\) = 22.75 m/s, and \(V^{3}{}_{CRT}\) = 33.534 m/s, respectively. The impact of the workers on the platform of the scissor lift on the critical wind speed is estimated based on the values of the drag force of the human body, which are available in the literature. The presence of the workers decreases the critical wind speed and, in the case, when the four persons are on the platform, the critical wind speed is equal to \(V^{1}{}_{CRT}\) = 21.513 m/s, \(V^{2}{}_{CRT}\) = 21.874 m/s, and \(V^{3}{}_{CRT}\) = 32.459 m/s for the configurations 1 st, 2 nd, and 3 rd, respectively. The obtained results are in good agreement with these, which are obtained based on code EN 280-1:2022. The maximum wind speed that the standard and the manufacturer specify of 12.5 m/s gives a large safety margin, as shown in Figure 14. In this case, the capsizing moment values obtained from experimental and CFD studies do not differ significantly from the values calculated from the standard (the graph is flattened). The standard gives moment values regardless of wind direction. However, it should be borne in mind that the wind during a sudden change in weather very quickly increases in strength and the terrain and buildings cause turbulence or gust conditions. Currently, every summer in our climatic conditions, there are weather anomalies, where the determination of the wind speed is impossible, much less the direction from which it will hit this supporting structure, which is the scissor lift. It is worth referring to charts in Figures 14-16, which describe for which ranges of wind angle of attack the highest values of capsizing moment occur. The proposed system is unable to determine the timing of the speed increase from 12.5 m/s to higher speeds, such as 21.95 m/s. This is the speed that, for an angle of 15\({}^{\circ}\), can add a corresponding moment to the sum of overturning moments, causing a loss of stability in the structure. The time given by the manufacturer that the operator needs to lower the platform from the maximum height is 50 s. The open question is if a structure of this type (operating outdoors in the open air) should not be equipped with a system for continuous measurement of wind speed and wind direction. In the future, it is planned to study the dynamic response of this structure to strong gusts of wind. Moreover, it will take into consideration the so-called interference effect, which is connected with the existence of other objects (buildings, other crane devices, trees, etc.)