A solid barrier in the horizontal position covering the entire rack, including all flue spaces at certain height increments, to prevent vertical fire spread
NFPA 30B Code for the Manufacture and Storage of Aerosol Products, 2002 ed. http://www.nfpa.org/assets/files/AboutTheCodes/30B /30B-A2002-rop.pdf, (Code: Code for the Mfg and Storage of Aerosol Prod for the Mfg and Storage of Aerosol Prod - Amer) {194 NFC}