Codes and standards published by NFPA are displayed as read-only under license from NFPA solely for use within this system. NFPA material may not be downloaded, printed, reproduced, or transferred.NFPA 490 applies to the storage of ammonium nitrate in the form of crystals, flakes, grains, or prills including fertilizer grade as defined by Definitions and Test Procedures for Ammonium Nitrate Fertilizer, dynamite grade, nitrous oxide grade as defined by Standard for Ammonium Nitrate (Nitrous Oxide Grade), technical grade, and other mixtures containing 60 percent or more by weight of ammonium nitrate.