Interbarrier Space : That space between a primary and secondary barrier, whether or not completely or partially occupied by insulation or other material
NFPA 306 Standard for the Control of Gas Hazards on Vessels, 2001 ed. https://www.nfpa.org/assets/files/AboutTheCodes/30 6/306-A2001-ROC.pdf, (Std: Contr of Gas Haz on Vssl - Amer) {294 NFC}