Computational Model of Dissipation of Oxygen From an Outward Leak of a Closed-Circuit Breathing Device.
Computational Model of Dissipation of Oxygen From an
Outward Leak of a Closed-Circuit Breathing Device.
Butler, K. M.
NIST TN 1484; NIST Technical Note 1484; 47 p. June
Sponsor:Centers for Disease Control and Prevention, Atlanta, GA
breathing apparatus; self contained breathing apparatus;
dissipation; oxygen; leakage; first responders; carbon
dioxide; fire fighting; risks; fire fighters;
respirators; dissipation; computational fluid dynamics;
ignition; face masks; seals; face protection; geometry;
oxygen concentration; fuels; air; flammability; propane;
turbulence; respiratory systems
Closed-circuit breathing devices recycle exhaled air
after scrubbing carbon dioxide and adding make-up oxygen
from a tank of pure oxygen. Use of this equipment allows
first responders to work for up to four hours without
swapping out cylinders and scrubbing canisters.
Firefighting situations in which these devices would be
useful include tunnels, mines, ships, high-rise
buildings, and environments contaminated with biological
or chemical toxins. A risk perceived by firefighters
entering environments containing open flame and high
radiant heat is the possibility of fire ignition in the
vicinity of the respirator caused by the outward leakage
of oxygen around the facepiece. This paper presents the
results of a computational fluid dynamics (CFD) study of
oxygen dissipation into the environment surrounding a
respirator facepiece. Actual heads and masks are scanned
into a 3D data set for entry into the CFD software,
providing a physical boundary for the problem to be
solved. Leak geometries representing an imperfect seal
are defined. 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 during two
breathing cycles for each case.