Rear Box : A mild steel box, open at the front and back, which is designed to be attached to the rear of the test sample to shield it from environmental influences
NFPA 290 Standard for Fire Testing of Passive Protection Materials for Use on LP-Gas Containers, 2003 ed. http://www.nfpa.org/assets/files/AboutTheCodes/290 /290-A2003-rop.PDF, (Std: Fr Tst of Passive Prot Mtrl for Use on LP-Gas Cont - Amer) {289 NFC}