Determination of dynamic air gap thickness and analysis of its relationship with firefighters' joint movement.

Objectives. The purpose of this study was to calculate the dynamic air gap thickness between the human body and the turnout gear. Relationships between the air gap thickness and joint range of motion (ROM) were also explored. Methods . The air gap thickness and joint ROM of 12 male firefighters walking in a control condition with no self-contained breathing apparatus (SCBA) and three varying-strapped SCBAs were measured using three-dimensional (3D) body scanning and 3D inertial motion capture. The interpolation technique was employed to predict the air gap thickness curve during walking. The dynamic air gap thickness was compared with the joint ROM to see how they relate to the location and percentage of movement restriction. Results . During the walking, the air gap fluctuated as a sine curve. Carrying SCBA reduced the air gap thickness at the trunk most ( F  = 11.17, p  < 0.001, η 2  = 0.63), and adjusting the shoulder strap length altered the air gap distribution at the trunk. The reduced air gap at the pelvis caused an incremental restriction on pelvis rotation. C onclusions. A compatibility design of the shoulder strap and hip belt in SCBA with the turnout jacket is suggested.