## 3 Results and Discussion
### Zonal Heat Transfer Characteristics  
Frontal zone:Frontal-zone heat fluxes when wearing helmets were statistically different from values obtained for the same zone without a helmet except for Helmet A1 (\(p=1.0\)). From the plots (Figure 6), it was inferred that Helmets A1, A3, and A4 depicted similar frontal heat-transfer behavior due to design features. Results also showed that heat flux from the frontal zones decreased for closed helmets. _Occipital zones_: The superior occipital zone of the helmets when compared to the nude head showed that all helmets were significantly different (\(p<0.05\)). Helmets H1 and A4 showed the highest cooling efficiency for this zone. Helmet H1 had outlet vent openings at occipital zones resulting in unrestricted air flow. Moreover, there was no retention system interacting with the occipital region of the head during helmet H1 usage. Hence, resistance to heat transfer in this region was lower. The retention system of Helmet A4 was present but did not block air flow in the mentioned zone, as observed in other helmets. It is important to note that Helmet A1, with the highest overall cooling efficiency (slightly above 100%), transferred only 87%-93% of heat from the superior occipital region due to the retention system blocking air flow in that zone. When compared to the nude head, the inferior occipital zone of the helmets showed that all helmets were significantly different (\(p<0.05\)) except for A1. The cooling efficiency of Helmet A1 for the inferior occipital zone was the highest  
\begin{table} \begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{(a)} \\ \hline
**Helmet** & **Convective Heat Loss (W)** & \multicolumn{2}{c}{
\begin{tabular}{c} **Thermal Resistance** \\ **R\({}_{\text{ct}}\) (\({}^{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{ \text{\text{\text{\text{\text{\text{ \text{ \text{ }}}}}}}}}}}}}}}\)/W)** \\ \end{tabular}} } & **Cooling Efficiency (\%)** \\ \hline \multicolumn{4}{c}{Mean} & SD \\ \hline Nude & 21.9 & 0.30 & 0.052 & \\ \hline A1 & 22.1 & 0.42 & 0.051 & 100.9 \\ \hline A2 & 16.6 & 0.28 & 0.069 & 75.6 \\ \hline A3 & 19.8 & 0.48 & 0.057 & 90.5 \\ \hline A4 & 21.3 & 0.35 & 0.054 & 96.9 \\ \hline H1 & 19.5 & 0.12 & 0.058 & 89.0 \\ \hline \hline \end{tabular}  \end{tableamong the tested helmets. Helmet A4, which showed 97%-98% overall cooling efficiency for the tested velocities, dissipated 73%-82% of heat from the inferior occipital zone due to the presence of a retention system blocking air flow in that zone. Helmet A2 performed poorly between the tested helmets because of the helmet design that reduced air flow into the helmet. Ocular, Facial and Temporal zone characteristics: The ocular region of the helmets, when compared to the nude thermal manikin, showed no significant difference for Helmet H1 (\(p\) = 1.0). For this particular region, Helmet H1 also showed the highest heat loss among the tested helmets for both tested velocities. This is because the design of the helmet H1 favors the air flow in the ocular region. The gap between ocular region and the inner side of Helmet H1 was also found to be bigger when compared to the other helmets. It was also observed in all helmets that the gap between ocular region and helmet inner side was directly proportional to heat loss in the region, i.e., the higher the gap was, the higher the heat loss would be, and vice versa. The facial and temporal regions of the manikin with the helmets showed no significant difference when compared to the facial and temporal regions of the nude manikin for both velocities, which is logical since the helmets did not cover these regions of the head. However, the facial zone under helmet A1 recorded higher heat transfer from facial zone (Figure 6) than the nude head. This is due to the helmet front profile that directs more air flow onto the facial region as observed in this study [35], where some helmets showed more heat transfer from the facial zone than the mean value of the facial zone heat transfer from the nude head.