These portable Grade-D filtration systems are designed to provide breathing air for a specific number of workers. The system filters inlet air to provide respirator users Grade-D quality air. The first stage filters bulk water and particulate, second stage coalescing filter eliminates atomized oils, mists, and ultra-fine particulates, third stage removes organic vapors and odors. Filter change indicators are standard on all three stages. Filter efficiency is 99.99% @ .01 microns. A built-in carbon monoxide monitor operates on 9-volt DC, dual 8 - 16 volt DC or 115 VAC for continuous detection. An external alarm and light signals the worker of high CO content. Point-of-Attachment (POA) boxes can extend respirator usage beyond 300 feet. All Breather Box models are designed to be used in the closed position to prevent internal contamination. All portable and fixed breathing air filtration systems meet or exceed U.S. and Canadian breathing air standards.