## 5 Study Results and Discussion  
The results for the three (3) fall situations considered in the study present similarities between them. The most important concerns the system that dampens the shock effects, with large reductions in the accelerations suffered by the human body, when compared with those of the shelter structure. The damper device is more effective in the vertical direction (YY) and in the initial moments of the shelter impact (when the velocities are higher), while the neoprene springs and the bumpers are more effective in the horizontal direction (XX), even when the falls are tilted. These bumpers are also needed to keep the chair inside the shelter, despite that parts of the chair, and parts of the human body (only the feet), may theoretically pass beyond the shelter external limits due to the distortion of the lower and intermediate neoprene springs.  
Figure 10 shows the positions of the chair and the human body at different instants of the shelter vertical fall (situation 1). Since the results for all the considered situations are similar regarding the movement of the chair and body, those images are also representative of the other fall situations.  
The movement is, in an initial phase (about half a tenth of a second), essentially vertical, accompanied by clashes between the occupant's chest and the cushions that surround it. As the damper device reduces the speed of the chair structure and the body adapts to the seat cushion, the damper is much more effective in the vertical direction, by reducing the velocity in this direction, but not in the horizontal one. The chair then shows a tendency to move horizontally outwards the shelter at its lower end, being restrained by the bumpers of the lower UPN100 profile (Figure 2). With these clashes, as mentioned, the body is then projected backwards--the back against its cushions in the first place, followed immediately by the head against its back cushion.  
Figure 9: Chair solution and its fitness for child anatomy (1.40 m tall).  
Subsequently, already in the ascending phase of the movement of both the chair and the human body, the latter tends to take off from the seat and to hit the chest cushion, especially in the tilted falls (situations 2 and 3), right after a new impact of the chair columns against the bumpers of the UPN 100 profiles (around 150 milliseconds), with higher severity than the first ones (Figure 11). This severity is mainly due to the almost simultaneous impact of the columns against the top and the bottom bumpers of the UPN 100 profiles, which occurs only for tilted downfalls.  
Afterwards, there is a series of bounces against the pillows that surround the human body, repeating and decreasing in intensity as they occur. This upwards movement ends with the impact of the shoulders on the upper part of the back cushions (Figure 10, Time = 0.230 s), followed by a new impact of the head against its back, in a much higher position than in the first impact. Since the initial instant, about four (4) tenths of a second have passed, and velocities as well as accelerations in the chair and in the human body have decreased, reaching much lower values. The vertical downwards movement resumes, not necessarily in the same way, but with the generic features of the first cycle and with less intensity.  
The stresses on the chair's steel elements are always below its yielding limit (fy = 1.250 MPa), therefore not exceeding the elastic regime, and ensuring safety during free fall, which is consistent with the situation of several impacts along the fall.  
Figure 10: Vertical fall (situation 1) critical instants (t = 0, 40, 70, 90, 170, 230, 245, 330, 440 milliseconds).