The Breather Box™ is a portable Grade-D filtration system designed to provide breathing air for a specific number of workers. The system filters incoming air from a compressor to provide respirator users with Grade-D quality air and monitors for CO and/or Oxygen. Filter chang indictors are standard on all three stages of filtration. Filtration efficiency is 99.99% @ .01 micron. All Breather Boxes are designed to be used in the uright and closed position to prevent internal contamination. Model BB50-CO Specification: 50 cfm Breather Box, CO monitor (79 cfm flow cpacity), 4 couplings.