# Evaluation of Snowboarding Helmets in Mitigation of the Biomechanical Responses of Head Surrogate
## 2 Materials and Methods
### Test Setup and Test Procedure  
In this work, blunt impact with the snowfield hazards (e.g., tree stump, rock, pole) were simulated in a laboratory setting using a linear impactor system. The linear impactor system (Figure 3a) comprised a ram, pneumatic actuator, impactor head, and sliding table. The ram (made of mild steel) and the impactor head (made of Teflon) had a mass of 8.89 kg and 1.33 kg, respectively. Prior to the experiments, the compressed air tank was connected to the pneumatic actuator. With the help of the actuator, the ram was accelerated to a desired velocity using the compressed air and was allowed to hit the target (i.e., the head surrogate). The impact velocity of the ram was measured using a dual-beam light gate system. To prevent post-impact ram movement, a pneumatic ram braking chamber was utilized. In this work, an impactor velocity of 4.6 \(\pm\) 0.2 m/s was used. As per the snowboarding helmet testing standard ASTM F2040 [18], the impact velocities of 4.5-4.8 m/s are recommended for snowboarding impact recreation. Hence, an impact velocity of 4.6 \(\pm\) 0.2 m/s was used in this work. The generated head kinematics using this setup is consistent with the literature [23; 24] simulating snowboarding impact scenarios in a laboratory; these details have been discussed in the Discussion section.  
Prior to the experiments, the helmets were mounted on the head surrogate and secured properly by tightening the chin strap (Supplementary Figure S1). The helmet fit on the head surrogate was verified manually by ensuring that there was no relative motion between the helmet and head surrogate. The head-neck-helmet assembly was mounted on an adjustable sliding table and subjected to blunt impact (Figure 3a, Supplementary Figure S1). The adjustable sliding table facilitates the positioning of the head surrogate with respect to the impactor to accommodate a variety of impact conditions. The helmet condition was inspected after each impact and discarded if any deterioration was observed. The front and side (right side) orientations were considered in this work. The experiments were repeated five times (N = 5) for each test configuration (Table 3).  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{3}{*}{**Sr. No.**} & \multirow{3}{*}{**Orientation**} & \multicolumn{8}{c}{**Test Configurations**} \\ \cline{3-13}  & & \multicolumn{4}{c}{**Helmets with Comfort Liner *} & \multicolumn{4}{c}{**Helmets Without Comfort Liner *} & \\ \cline{3-13}  & & \multicolumn{2}{c}{**No**} & \multicolumn{2}{c}{**No**} & \multicolumn{2}{c}{**Conventional**} & \multicolumn{2}{c}{**MIPS**} & \multicolumn{2}{c}{**WaveCel**} & \multicolumn{2}{c}{**Silica**} & \multicolumn{2}{c}{**Pod**} & \multicolumn{2}{c}{**Helmet**} & \multicolumn{2}{c}{**Conventional**} & \multicolumn{2}{c}{**MIPS**} & \multicolumn{2}{c}{**WaveCel**} & \multicolumn{2}{c}{**Silica**} \\ \cline{2-13}  & & Front & ✓ & ✓ & ✓ & ✓ & ✓ & - & ✓ & ✓ & ✓ & - \\ \hline
2 & Side & ✓ & ✓ & ✓ & ✓ & ✓ & - & ✓ & ✓ & ✓ & - \\ \hline \hline \end{tabular}  
* N = 5 for each configuration and orientation, a total of 80 experiments were conducted.  
\end{table}
Table 3: Test configurations used in this work using the impact velocity of 4.6 \(\pm\) 0.2 m/s.