Encyclopedia
21st class
Class 21 — zones located in rooms where flammable dusts or fibers that can form explosive mixtures with air at a concentration of 65 grams per cubic meter or less are released into the air during normal equipment operation1.
Federal Law No. 123-FZ dated 22.07.2008 "Technical Regulation on Fire Safety Requirements", as amended on 2008-07-22, Article 19, subpara. 5 // Official Gazette of the Russian Federation. 2008. No. 30. Art. 3579. ↩