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.