The design of the mixer should minimize the possibility of frictional heating, compaction, and especially, confinement. Open mixers are preferable to enclosed mixers. Bearings and gears should be protected against the accumulation of ammonium nitrate dust. All surfaces should be accessible for cleaning. Mixing and packaging equipment should be constructed of materials compatible with the fuel-ammonium nitrate composition.
Cal. Code Regs. Tit. 19, § 1572.2