NFPA 91 Standard for Exhaust Systems for Air Conveying of Vapors, Gases, Mists, and Noncombustible Particulate Solids, 2004 ed. http://iepi.neu.edu.cn/Download/Standards/NFPA/NFP A%2091-2010%20Standard%20for%20Exhaust%20Systems%2 0for%20Air%20Conveying%20of%20Vapors,%20Gases,%20M ists,%20and%20Noncombustible%20Particulate%20Solid s.pdf, (Std: Exhaust Sys for Air Conveying of Vapors, Gas, Mists, and Noncomb Particulate Solids - Amer) {237 NFC}