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A Computational Model of an Outward Leak from a Closed-Ciucuit Breathing Device



Kathryn M. Butler


Closed-circuit breathing devices recycle exhaled air after scrubbing carbon dioxide and adding make-up oxygen from a tank of pure oxygen. This equipment provides up to four hours of use before oxygen cylinders and CO2-absorbent canisters need to be swapped out. Firefighting situations in which these devices would be useful include tunnels, mines, ships, high-rise buildings, and environments contaminated with biological or chemical toxins. Since firefighters may encounter environments containing open flame and high radiant heat, there is concern that a higher concentration of oxygen within the respirator may result in an enhanced possibility of fire ignition in the case of outward leakage around the facepiece. This study uses computational fluid dynamics (CFD) to investigate the flammability of the environment near a respirator leak from a closed-circuit self-contained breathing apparatus (CC-SCBA) during the breathing cycle. The physical boundary for the computational problem is defined by the combination of headform and respirator geometries obtained from 3D laser scanning. Velocity boundary conditions are defined along a narrow band representing a leak through the gap between respirator seal and head. Oxygen concentration fields and flow streamlines are presented for multiple combinations of fuel and air in the surrounding environment, for pure oxygen and air expelled from the leak, and for both normal and high stress breathing patterns. The flammability diagram for propane is used to estimate the flammable regions as a function of time.
Journal of the International Society for Respiratory Protection


closed-circuit SCBA, computational model, respirator leak, flammability, flammability diagram


Butler, K. (2008), A Computational Model of an Outward Leak from a Closed-Ciucuit Breathing Device, Journal of the International Society for Respiratory Protection, [online], (Accessed July 19, 2024)


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Created July 3, 2008, Updated February 19, 2017