Dissipation of Oxygen from Outward Leak of Closed-Circuit Breathing Device Kathryn M. Butler and Rodney A. Bryant kathryn.butler@nist.gov , rodney.bryant@nist.gov Building and Fire Research Laboratory (BFRL) National Institute of Standards and Technology (NIST) Gaithersburg, MD 20899-8665, USA John G. Kovac jkk5@cdc.gov National Personal Protective Technology Laboratory (NPPTL) National Institute for Occupational Safety and Health (NIOSH) Pittsburgh, PA 15236 ABSTRACT 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. 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 progress on a computational fluid dynamics (CFD) study of oxygen dissipation into the environment surrounding a respirator facepiece. Actual heads and masks have been 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 will be determined for multiple leak geometries and for both normal and high stress breathing patterns. INTRODUCTION The National Institute for Occupational Safety and Health (NIOSH) is developing standards for the use of closed-circuit self-contained breathing apparatus (SCBA) by firefighters and other first responders after a terrorist attack (NIOSH/NPPTL 2004, NIOSH 2005). In addition to the respiratory protection of first responders against chemical, biological, radiological, and nuclear (CBRN) agents, the equipment must be usable under conditions of high heat and open flames. Although a leak is unlikely for a respirator with good fit, the possibility of outward leakage of oxygen in a fire environment is a concern. If the oxygen remains concentrated around the face in the presence of fuel gases and heat, ignition may occur. If the oxygen diffuses rapidly away from the face, however, the possibility of ignition is negligible.