## 4 Discussion
At the deepest sampling points of the apparatus, where the snow density reached 304 kg\(\cdot\)m\({}^{-2}\), the measured DC for O\({}_{2}\) was approximately 5.7-9.5 mm\({}^{2}\cdot\)s\({}^{-1}\). At shallower depths, the measured O\({}_{2}\) DCs were up to 10 mm\({}^{2}\cdot\)s\({}^{-1}\) (1.6 times) higher than they should theoretically be. The measured DCs for CO\({}_{2}\) were consistent with the theoretical calculations. However, there is a possibility that the CO\({}_{2}\) absorption in water has compensated for the decreasing snow density and any potential faster diffusion. [PERSON] et al. [27] measured the distribution of CO\({}_{2}\) from soil to air through snow and determined that the measured DC of CO\({}_{2}\) in snow ranged from 2.6 to 10 mm\({}^{2}\cdot\)s\({}^{-1}\). However, it is important to note that the measurement was conducted mainly in snow with a higher density compared to this study. The measurement done by [PERSON] et al. [14] was performed in firm with a porosity between 0.13 and 0.5. The measured DCs were 0-10 mm\({}^{2}\cdot\)s\({}^{-1}\) for O\({}_{2}\) and 0-8 mm\({}^{2}\cdot\)s\({}^{-1}\) for CO\({}_{2}\), respectively. In the present study, the snow porosity ranged from 0.66 to 0.84. The measured DCs for both respiratory gases corresponded to those measured in the study by [PERSON] et al. [14]. The convective process of respiratory gas exchange in a closed environment between the lungs of a victim buried in avalanche snow and the surrounding avalanche snow, with increasing concentrations of CO\({}_{2}\) and decreasing concentrations of O\({}_{2}\), occurs so rapidly that only 30% of victims survive for 35 min under the snow [28]. The diffusion of respiratory gases during breathing experiments into the simulated avalanche snow has been considered in various experiments [4; 18; 29]. [PERSON] et al. [23] conducted an experimental study which indicates a negative correlation between CO\({}_{2}\) diffusion and snow density. The higher the snow density, the slower the diffusion of CO\({}_{2}\) from the subject. Based on research conducted by [PERSON] et al. [4; 29], higher snow porosity surrounding the air pocket may facilitate O\({}_{2}\) diffusion. Low and medium snow densities allow enhanced diffusion of O\({}_{2}\) into the air pocket and of CO\({}_{2}\) out of the air pocket, prolonging the duration of the breathing experiments. The results of the present study are consistent with the findings of the above studies that O\({}_{2}\) propagates faster than CO\({}_{2}\) and that the solubility or absorption of CO\({}_{2}\) could affect the rate of diffusion. It should be acknowledged, however, that the diffusion rate in snow is relatively slow compared to the rate of gas exchange (caused by the high cyclic tidal volumes and flows) in a subject breathing under avalanche snow, so the increase in survival time is limited. The similar diffusion properties of respiratory gases in snow and perlite, as well as the similar trends of gas exchange during breathing in snow and in dry and wet perlite [17], suggest the possibility of perlite being utilized as a suitable material for testing technical and new avalanche safety equipment prior to field experiments in mountain environments or for the preparation of breathing experiments and their protocols [30; 31; 32]. Perlite can also be used for studies on different population groups (i.e., with different physical conditions, ages, etc.) and for training subjects in the laboratory environment for outdoor experiments, if this training is a part of the protocol. The study has several limitations. As the measurements were carried out at temperatures around 0 \({}^{\circ}\)C, the snow may have melted along the cylinder wall, thus allowing respiratory gases to pass along the wall. Nonetheless, any gas flow along the cylinder wall was prevented by twelve airtight O-rings. Secondly, the amount of water contained in the snow could have varied throughout the experiment.