MSA offers Duo-Flo respirators in both Constant-Flow and Pressure-Demand versions. Constant-Flow respirators are normally used where an ample air supply is available, such as that provided by an air compressor. Pressure-Demand respirators are generally used where only compressed-air cylinders are available. Duo-Flo respirators feature air-purifying canisters to protect against a wide variety of contaminants. Duo-Flo respirators are popular in the pharmaceutical, chemical, petrochemical and nuclear industries. The unique D/PD switchable exhalation valve, standard on Pressure-Demand respirators, also makes these units especially well-suited for abatement work. This MSA respirator should not be used in atmospheres containing less than 19.5% oxygen.