I am bidding a job and they require grade d air for the blast hood. What is that?
Grade D is a classification of breathing air developed in ANSI/Compressed Gas Association (CGA) G-7.1 – 1989. It has been adopted by OSHA in their respiratory standards in 29 CFR, 1910.134. For the technical specifications, please see the OSHA website at this link.
Grade D air can be achieved using a 3 stage filter and inline Carbon Monoxide (CO) monitor*.
*There are a few more specifications to achieve Grade D air, but a 3 stage air filter and CO monitor are the main two that makes most air systems compliant. See this pdf for a full list of specifications.