## 5 Conclusions  
To the authors' knowledge, this study is the first of its kind to investigate the impact of wearing an SCBA on garment fit, ease, and the subsequent reduction in air gaps. Therefore, this study only begins to quantify the realized impact of SCBA fit, weight, and design on firefighter performance. Although negligible differences were found for torso volume, air gap volume, and air gap distance when donning an SCBA, additional research is needed to expand the sample size and include a more representative group of body types and PPE (e.g., turnout suit manufacturers and SCBA models). Body scanning should also be conducted in dynamic postures to represent more realistic use scenarios. Further, correlation analysis of air gaps with heat loss and ergonomic mobility measures would better inform the design of both the SCBA and the turnout suit. This type of data would require the implementation of human wear trials, which were outside the scope of this study.  
As an understudied area of firefighting PPE, future research would benefit from the adoption of a full systems ensemble approach in which all elements of the ensemble are considered together, including the SCBA pack and mask. The impact on protection must also be considered as a reduction in air gaps may significantly decrease thermal protection in some areas; therefore, flash fire manikin testing with an SCBA pack should be performed to ensure minimum thermal protective performance is maintained.  
Ultimately, this study lays the foundation for full systems ensemble research to better understand how the design, weight, and fit of the SCBA impacts the thermal comfort, mobility, and protection of structural firefighters. Much more work is needed in this area to be able to provide SCBA manufacturers and PPE product developers with specific design improvements related to strap and pack design, material selection, and weight distribution to optimize SCBA fit. Limitations of this study include the small sample size, consideration of front torso measurements only, and scanning technology constraints when donning an SCBA. Further, as technology allows, the use of more dynamic postures should be considered.  
**Author Contributions:** Conceptualization, M.M.; methodology, M.M. and J.B.; software, J.B.; validation, J.B. and M.M.; formal nalysis, J.B. and M.M.; investigation, J.B.; resources, M.M.; data curation, J.B. and M.M.; writing--original draft preparation, J.B.; writing--review and editing, J.B. and M.M.; visualization, J.B. and M.M.; supervision, J.B. and M.M.; project administration, M.M.; funding acquisition, N/A. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Institutional Review Board Statement:** This study was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Board (or Ethics Committee) of Florida State University (protocol code #00000249; 22 August 2023).  
**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.  
**Data Availability Statement:** The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.  
**Acknowledgments:** The authors would like to acknowledge research assistants [PERSON], [PERSON], and [PERSON] for their data collection assistance, alongside our collaborators at the FSU Institute of Sports Sciences and Medicine (ISSM), including [PERSON].  
**Conflicts of Interest:** The authors declare no conflicts of interest.