These portable Grade-D filtration systems are designed to provide breathing air for a specific number of workers. the system filters inlet air to provider respirator users with Grade-D quality air and monitors for CO and/or Oxygen. The first stage element filters bulk water and particulates and has an auto drain. the second stage coalescing filter eliminates atomized oils, mists, ultra-fine particulates and has an auto drain as well. The third stage filter removes organic vapors and odors and has a manual drain. Filter change indicators 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 upright and closed positions. The Breather Box comes with a standard carbon monoxide airline monitor operated on disposable 9-volt batteries, 12-volt DC line voltage, or 115 VAC for continuous air monitoring. an external alarm and light signals the workers of high CO content. Remote alarms are available for portable and fixed applications. APPROVED INTRINSICALLY SAFE BREATHER BOX MODELS AVAILABLE. All models can be outfitted with an approved intrinsically safe monitor (DC power only). Pneumatic remote CO alarms are available. Consult customer service for details. NOTE: INTRINSICALLY SAFE (IS) VERSIONS ARE CSA APPROVED FOR CLASS I, DIVISION 1, GROUPS C AND D ENVIRONMENTS. UNITS ARE “DC” (9-VOLT) OPERATION ONLY.